Weak overburden layers at shallow surfaces would substantially affect the ground motion characteristic parameters of ground motion, such as spectral accelerations, and these influences regularly showed obvious nonlinearity with the increase of ground motion strength. Despite the differences between motions down the borehole and ground motions on bedrock, the surface/borehole spectral ratios could reflect the seismic site effect to some extent and overcome the shortcomings of the lack of reference bedrock stations in the standard spectral ratio method and the assumption of seismic point source in the generalized inversion method. In recent years, more and more scholars have studied the nonlinear dynamic characteristics of the soil body and its change trend based on the strong motion data by comparing the surface/borehole spectral acceleration ratios under different motion strengths. However, the research conclusions, especially the quantitative characterization of the nonlinear characteristics, still need to be improved due to the insufficient statistical sample size.

It was found that the surface/borehole spectral acceleration ratio curves at the same station exhibited high similarity under different motion strengths. However, these spectral acceleration ratios significantly decreased as motion strength increased and shifted towards longer periods at certain period ranges. The surface/borehole spectral acceleration ratios at different motion strengths corresponding to the same period point cannot adequately reflect their nonlinear characteristics. It is more reasonable to characterize these features by the corresponding relationships between the points on the surface/borehole spectral acceleration ratio curve shapes at different motion intensities. Although some scholars have proposed methods for correcting the dominant frequency offset, there remains a lack of effective methods for fixing the period shift of the surface/borehole spectral acceleration ratio across the wholeentire period range, as well as for the quantitative characterization of nonlinear characteristic parameters throughout the wholeentire period range. Dynamic Time Warping(DTW)algorithm is a nonlinear alignment method that combines time alignment and measurement matching. The core idea of the Dynamic Time Warping(DTW)algorithm is to find the optimal mapping between two-time series by calculating the distance between their respective discrete points and identifying the best path connecting them. This process enables point-to-point matching between the two-time series, and the DTW distance(sum of distances along the best path)can be utilized to assess their similarity.

In this study, we selected 166 700 strong-motion records from 180 stations in Japan's KiK-net network them. We grouped them by ground motion intensity to obtain the surface/borehole spectral acceleration ratios and their average values for each station under different intensity levels. A dynamic time warping algorithm was employed to effectively correct long-period shifts in the spectral acceleration ratio curves, which allowed for the precise extraction of both the period shift and amplitude attenuation values at various period points for each seismic station. Subsequently, a detailed statistical analysis was conducted to assess how these values varied about different levels of ground motion intensity. In addition, nonlinear characteristic parameter curves, dependent on both the period and seismic intensity changes, were derived for different site categories, accompanied by the establishment of corresponding empirical relationships. Furthermore, a novel method was proposed to predict the surface-to-borehole spectral ratio under conditions of strong seismic motion, utilizing the spectral acceleration ratio data obtained from weaker ground motion intensity scenarios. This approach is intended to offer more precise and detailed data support for adjusting nonlinear site effects in China's seismic design codes and seismic hazard zoning maps. Ultimately, the goal is to provide a more refined and comprehensive basis for enhancing the nonlinear site response adjustments in China's seismic design specifications and seismic motion parameter zoning maps.

The quantitative analysis of period offset characteristics of the surface/borehole spectral acceleration ratios indicated that the period offsets were more significant under larger motion strength. Meanwhile the period offsets at different periods were not consistent, and the relative period offsets at the same period exhibited linear relationships with motion strength under the double-logarithmic coordinates. The relative period offsets could be reliably expressed by the period offset coefficient defined empirically. The period offset coefficients obtained at each station and on each site class (Ⅰ, Ⅱ, Ⅲ, and Ⅳ) of Chinese standards were all related to the period, which showed a trend of initially increasing and subsequently decreasing with the increase of the period. Furthermore, the period offset coefficients increased with the thickness and softness of the overburden layers, which indicated more significant period offsets on sites of thick and soft overburden layers. The quantitative analysis of the amplitude decay characteristics of the surface/borehole spectral acceleration ratios indicated that the spectral ratio amplitude was lower under more considerable motion strength. Meanwhile, the amplitude rates at different periods were not consistent, and the spectral ratio amplitude at the same period exhibited fine linear relationships with motion strength under the semi-logarithmic coordinates. The amplitude decay rate could be reliably expressed by the amplitude decay coefficient defined empirically. The amplitude decay coefficients obtained at each station and on each site class (Ⅰ, Ⅱ, Ⅲ, and Ⅳ) of Chinese standards were all related to the period. They approximately conformed to a Gaussian function under the semi-logarithmic coordinates, indicating that the amplitude decay rates were lower in the middle period range(the platform segment of spectral accelerations)compared to the shorter or longer period ranges. Moreover, the amplitude decay coefficients (<0) decreased with the thickness and softness of the overburden layers, which indicated faster amplitude decay rates on sites of thick and soft overburden layers. Despite the differences between surface/borehole spectral acceleration ratios and soil surface/bedrock surface spectral acceleration ratios, the period offset coefficients and amplitude decay coefficients derived statistically could reflect the nonlinear characteristics of seismic site effects to some extent. According to the empirical relationships for relative period offsets and amplitude decay rates of surface/borehole spectral acceleration ratios on different site classes (Ⅰ, Ⅱ, Ⅲ and Ⅳ) of Chinese standards, the surface/borehole spectral acceleration ratios under stronger motions could be predicted reliably by surface/borehole spectral acceleration ratios under weaker motion.

Understanding the mechanism of earthquake sequence in the mining area is important for the time-dependent hazard assessment. An earthquake of M_L4.1 occurred in Gujiao, Taiyuan, Shanxi on February 20th, 2022, which caused strong ground motion in Gujiao and surrounding counties. The epicenter of this earthquake is located in the area of Lvliang uplift, where historical earthquakes are relatively rare. In addition, the coal resources are well developed in the earthquake source area which has attracted much attention from society and local governments.

To investigate the mechanism and the seismogenic fault of Gujiao M_L4.1 earthquake, we first apply the double-difference location method to retrieve highly accurate hypocenter locations. The results show that the earthquakes mainly occur at a depth range of 3~5km, and display a dominant distribution direction nearly EW-trending, which differs significantly from the NE-trending fault distribution pattern in this region. We further collect the broad-band seismic waveforms from the regional network of Shanxi province to perform focal mechanism inversion. The inversion results show that the Gujiao earthquake is a left-slip seismic event with a moment magnitude of M_W3.96. The optimal double-couple solution is characterized by a strike of 90°, dip of 80°, and a rake angle of -21° for fault plane Ⅰ, while for the fault plane Ⅱ, the strike is 184°, dip is 69°, and rake angle is -169°. The best centroid depth is estimated to be at 3km. This earthquake shows an extremely shallow focal depth. Moreover, By using cluster analysis method, we obtained the central solution for the seismogenic fault plane of the GuJiao earthquake, with a fault strike of 91°and a dip angle of 70°. The focal solutions show that the earthquake exhibit a strike-slip type, and the orientations of earthquake sequence coincide well with the focal mechanisms.

In addition, to discuss the effect of Gujiao M_L4.1 earthquake on regional stress, we calculate the stress drop of this seismic sequence. The results show that the stress drop is significantly smaller than that of the regional earthquakes, exhibiting at least one order of magnitude lower than that of the background earthquakes in the same region. This phenomenon reflects that the stress level in the focal area of the GuJiao earthquake is not high, suggesting that the background stress enhancement in the focal area is not obvious.

Based on regional geological structure, we found that the known faults in the region are all high-angle normal faults, and the strike of these faults are inconsistent with the focal mechanism solution of Gujiao earthquake sequence, which suggests that the existing faults are not the seismogenic fault. Taking the regional mining activities into account, we speculated that mining may cause strong disturbance to the stress field, and lead to stress redistribution within the rock mass. Such coal mining activity may generate a high stress disturbance on the hidden fault plane, and then the fault become the carrier of stress transfer. So we conclude that the seismogenic mechanism of the Gujiao-seismic sequence may be related to coal mining activities near the focal area, which leads to local stress changes, thus resulting in the activation of preexisting hidden faults and triggering the occurrence of the Gujiao earthquake.

The Weinan Tableland Piedmont fault is an important near-EW-trending Holocene active fault in the southeastern margin of the Weihe Basin, which is closely related to the occurrence of the 1556 Huaxian M8 earthquake. The northern branch of the fault, the northern branch fault in front of the Weinan tableland, passes through the urban area of Weinan. Therefore, finding out the distribution, shallow structure, late Quaternary activity, and seismic capacities of the northern branch fault are of great significance for local earthquake prevention and reduction. The Weihua fault zone, which is composed of F₁ and F₂ faults, generally strikes near east-west and has a gentle wave shape on the plane. It is a group of active normal faults rising in the south and descending in the north belt one. The Wei-Hua fault zone can be divided into two segments, east and west, and according to its spatial location and geometric distribution, strike change and the difference in geology and landforms on both sides. The eastern section is distributed in front of Huashan Mountain and is called Huashan Piedmont Fault(F₂); the western section is distributed in Piedmont of Weinan tableland and is called Weinan Piedmont Fault(F₁). There is a large sub-parallel branch fault about 2km to the north of the Piedmont Weinan tableland fault(F₁)in the west section, which is called the branch fault on the north side of the Piedmont Weinan tableland. It is also the boundary fault between the Weinan tabland and the Gushi Sag. The Weinan tableland Piedmont Fault(F₁)starts from the Weinan Xihekou in the west and extends eastwards through the Fenghe River to Mayukou, Huaxian County, with a length of about 54km; it strikes NWW from the Mayukou to Chishui River, and nearly EW from the Chishui River to the Fenghe River, the west of the Minhe River is NE to NEE, and it is mostly distributed in the form of broken lines or oblique rows. The fault plane dips northward with a dip angle of 60°~70°. The latest activity of the fault is manifested in the latest terraces and alluvial-pluvial fans faulting the Holocene strata, river valleys, and gullies; along the main fault, and a series of stepped normal faults on the north and south sides, a Holocene steep ridge belt with a width of between tens of meters and hundreds of meters, the Holocene strata are vertically faulted by 6~7m, and the vertical slip rate since the Late Pleistocene is about 0.29mm/a. In this paper, the shallow location and structural characteristics of the branch fault on the north side of the front of the Weinan tableland are determined through the combined profile detection of shallow seismic exploration and drilling, and evidence of the new activity of the fault is provided. The shallow seismic exploration results of the four survey lines all reveal the existence of a branch fault on the northern side of the front of the Weinan tableland, as well as the distribution location and cross-sectional structural characteristics of the fault new understanding. The results show that the branch fault on the north side of the Weinan Tableland Piedmont fault is a parallel branch of the main fault in front of the Weinan tabland. The branch fault on the north side of the front of the Weinan tableland is located at the front edge of the second-level terrace of the Weihe River in front of the Weinan tableland. The south end of the road, the mouth of the river, Zhangbaozi, and the outside of the north gate, have a length of at least 22km. The main section of the fault is inclined to the north, with a dip angle of about 70°~80° and a break distance of 6~20m at the upper breaking point, so it is a normal fault. Mainly concealed active faults, which have at least faulted the strata from the Middle Pleistocene to the late Pleistocene in the upward direction. In the four seismic sections, it appears as a normal fault zone with a width of 200~1 800m, including the main and secondary normal faults. Stepped structures and small grabens; secondary faults also fault up at least the Late Pleistocene strata. The combined geological profile of the Chongye Road borehole revealed that the main fault on the north side of the Weinan tableland had been faulted with many landmark strata of the Late Quaternary, and the latest fault occurred after 19ka; the average vertical activity rate since the middle of the Late Pleistocene between 0.07~0.26mm/a. Combined with phenomena such as fault ridges developed along the surface of the fault, it is judged that the fault was active in the Holocene. The branch fault on the north side of the front of the Weinan tableland has had strong activity since the late Quaternary, which means that the fault, as one of the branches of the southeastern boundary zone of the Weihe fault basin-the Weihua fault zone-obviously bears part of the deformation of the belt At the same time, the fault is located in the historically strong earthquake-prone area of the southeastern boundary of the Weihe fault basin, and it cannot be ruled out that it once participated in the rupture of the 1556 Huaxian M8 earthquake. Considering that the branch fault on the north side of the Weinan tableland passes through the urban area of Weinan, its potential seismic hazard and hazard are urgent research topics.

The northern Qinling fault zone is an important active structure in the southern margin of the Weihe Graben Basin, containing many branch faults, of which the near EW striking Taochuan-Huxian Fault is located on the northern side of the fault zone, and the eastern segment is buried in the Weihe Graben Basin. Shallow seismic exploration has been carried out on the middle part of the buried segment of this fault, and the fault inferred to be a late Pleistocene fault with normal strike-slip movement, but the age and rate of the latest activity have not been determined. By conducting new shallow seismic and drilling joint exploration, we further study the shallow structure, the geometric distribution, the latest activity era and the slip rate in the Quaternary in the two segments of the Taochuan-Huxian Fault. The profile of shallow seismic exploration line TB1 reveals that the west segment of the Taochuan-Huxian Fault with NEE trend can extend at least 20km westward from Taochuan Town. The main fault plane dips to N, and the normal-slip movement has faulted the Quaternary bottom boundary and the underlying crystalline basement in the Taibai Basin. The vertical offset of the Quaternary bottom boundary is about 300m, and the remnants of the old thrust structure are still preserved in the fault zone. The shallow seismic reflection lines ZZ1 and YX1-2 reveal the location of the eastern Taochuan-Huxian Fault with the EW striking buried in the Quaternary of the Weihe Graben Basin in Zhouzhi and Huxian. The main fault plane dips to N, and the fault zone is represented by a fault depression zone of about 6km wide and a stepped structure of about 4km wide respectively. The fault up-breakpoints on both profiles offset the bottom boundary of the Holocene in the Weihe Graben Basin. The drilling joint profile exploration applied at Tanjiazhai in Zhouzhi County and Xiashimasi in Meixian County show that the Taochuan-Huxian Fault is distributed in the junction of the southern Weihe Granben Basin and the Qinling Mountains, where the Holocene marker layer S₀ has been vertically offset by 4~5m, yielding an average vertical slip rate of 0.4~1.3mm/a. Combined with the results of shallow seismic surveys, it is well demonstrated that the eastern segment of the Taochuan-Huxian Fault(buried in the Weihe Graben Basin)shows Holocene activity, and it is significantly more active than the western segment(the Taibai Basin segment). This may be due to the fact that the eastern segment has been incorporated into the Weihe Graben Basin and has become part of the primary active tectonic zone on the block boundary, while the western segment has not been incorporated. Spatially, the eastern segment of the Taochuan-Huixian Fault is subparallel to the middle-eastern segment of the North Qinling Fault, which is capable of generating strong earthquakes of magnitude 7 or higher. As an important branch of the North Qinling Fault, the Taochuan-Huixian Fault may also be under the same strong seismic background. These two faults probably jointly control the important active boundary of the southern margin of the Weihe Graben Basin. Future research in seismology and geology of these two faults should be strengthened, including their interrelationships at depth, their roles in vertical and horizontal movement distribution, and their seismogenic capacity and potential seismic hazard. In particular, the activity of the Taochuan-Huoxian Fault since the late Quaternary has only recently received attention, and the level of seismo-geological research on the fault is generally low. In this paper, we conducted preliminary studies on the location, shallow tectonic structure, activity segmentation, latest activity and Holocene vertical slip rate of this fault. Future research on the seismogenic structure of the Taochuan-Huoxian Fault needs to be strengthened in order to deepen and improve the understanding of the fault activity and to provide a basis for analyzing the seismic hazard of this fault.

The reliability of anomaly extracting methods is crucial for pre-seismic thermal anomalies research. However, there is a lack of relevant researches. We compared two commonly used anomaly extracting methods, Z-score(ZS)and Robust satellite technology(RST)method, taking the 2014 Yutian earthquake as a typical example and the 2008 Wenchuan earthquake as a validation. The four aspects of extracted results are compared qualitatively and quantitatively, including the extraction effect, sensitivity to slight change, suppression of background information and indication of seismic information in the actual earthquake case. Moreover, the extracted results of validation case are used to validate the reliability of typical case results. Many intermittent anomalies in surface temperature and outgoing longwave radiation appeared before Yutian earthquake. The frequency of anomalies increases with the proximity of earthquake. The spatial distribution of surface temperature and outgoing longwave radiation anomalies gradually concentrated around the fault zone at the same time. The largest surface temperature and outgoing longwave radiation anomalies occurred one month before Yutian earthquake. The difference between the extraction results of ZS and RST method is mainly manifested in the frequency and amplitude of anomaly changes. The frequency and amplitude of anomaly changes obtained by RST method are higher than those obtained by ZS method. To further explore the reason for these differences, we further evaluate the two methods quantitatively by combining the data of two non-seismic years before and after Yutian earthquake respectively. The sensitivity of anomaly extraction method represents its ability to identify the slight changes of thermal parameters caused by the seismogenic process. The two methods are sensitive to slight changes, but the RST method is better than ZS method. The background information represents normal variation in surface temperature and outgoing longwave radiation caused by non-seismic factors. Suppression of background information determines the accuracy of extraction results. The comparison results show that both methods have certain suppression effect to background information, but the ZS method is better. The spatial distribution of pre-seismic thermal anomalies is an important index for predicting earthquake information(e.g. time of occurrence and location of epicenter). The results of quantitative comparison through normalized distance index show that for surface temperature data, ZS method is slightly better than RST method in indicating the location of epicenter. However, RST method is better for outgoing longwave radiation data. The maximum value of normalized distance index of ZS method occurred closer to the origin time of earthquake. We used the same quantitative evaluation method for the validation earthquake case. The verification results show that in addition to the sensitivity to anomaly changes, the comparison results of the two earthquake examples are similar in terms of the ability to suppress background information and indicate earthquake information. The difference is that ZS method has a better ability to suppress background information and RST method is better in indicating earthquake epicenter in the verification earthquake example. The main reason for the difference in extraction effect between the two methods is that the RST method averages the ground feature classification, and the difference between the observed value and the average value of the classification makes the RST method have a certain amplification effect on the weak signal. The difference between the typical earthquake case and the verification earthquake case is mainly due to the different complexity of the object types in the regions. Based on the above research results, we believe that ZS method and RST method have certain ability to extract pre-seismic anomalies. However, comparatively speaking, the RST method also has a good effect on the extraction of anomalies caused by other factors, and there is uncertainty in the ground feature classification. We believe that ZS method is a more appropriate and simple anomaly extraction method in the general seismic anomaly change extraction.

At 01:45 on January 8, 2022, Beijing Time, an M_S6.9 earthquake occurred in Menyuan County, Haibei Prefecture, Qinghai Province, with a focal depth of 10km. The microscopic(instrument)epicenter is located at 37.77°N latitude and 101.26°E longitude in the intersection between the Toleshan fault zone and the Lenglongling fault zone in the northern Qilian-Qaidam block. The epicenter is 54km away from Menyuan County in Qinghai, 99km away from Qilian County, 100km away from Haiyan County, 83km away from Minle County in Gansu Province, 83km away from Yongchang County, and 141km away from Xining City. When the earthquake occurred, Menyuan County and Xining City, the capital of Qinghai Province, were strongly felt, and Yinchuan, Lanzhou, Xi'an and many other places were felt. At the same time, affected by the earthquake, the Lanxin high-speed rail line, an important railway transportation hub of the Belt and Road, was suspended. This earthquake is the largest earthquake in the world since 2022. It is also another earthquake of magnitude 6.0 or above in Qinghai Province following the Maduo M_S7.4 earthquake on May 22, 2021. Besides, this earthquake is the event with the highest magnitude and the longest surface rupture in the region after the two M6.4 Menyuan earthquakes of August 26, 1986 and January 21, 2016. Therefore, this earthquake has attracted much attention from the society. The coseismic surface rupture distribution, combination characteristics, development properties and coseismic displacement of this earthquake were identified in time to help to have a correct understanding of the earthquake seismogenic structure, rupture process, and assessment of short-term earthquake hazards. It is also of great significance for major project route selection, earthquake fortification and rescue and disaster relief. On the basis of the on-site seismic geological investigation, based on the interpretation and analysis of high-resolution satellite remote sensing images, and combined with the low-altitude photogrammetry of unmanned aerial vehicles(DJI PHANTOM 4RTK), the author obtained the coseismic rupture data of five typical sites along the surface rupture zone generated by the earthquake. Using Agisoft Metashape Professional software to process the aerial photos of each section indoors, a high-resolution orthophoto map(DOM)was generated. At the same time, the five typical earthquake surface rupture sections were described in detail in ArcGIS Pro software based on the orthophoto map. Preliminary research shows that the surface rupture zone of the Menyuan M_S6.9 earthquake is more than 22km long and consists of the main rupture of the northern branch and the secondary rupture of the southern branch. The north branch main rupture zone is distributed in the middle-western segment of the Lenglongling Fault of central Haiyuan fault zone, with a length of more than 18km and an overall strike of 295°. The maximum co-seismic horizontal displacement is located in the middle of the rupture zone at Liuhuangou(37.799°N, 101.2607°E), which is about 3.1m and gradually decays towards both ends. The secondary rupture of the southern branch is distributed on the local segments of the eastern Toleshan Fault in the central-western Haiyuan fault zone, with a length of about 4km and a strike of 275°, constituting a secondary branch rupture zone arranged in a left-stepped en-echelon pattern to the western segment of the main rupture zone. There are en-echelon extensional stepovers between the two rupture zones of the north and south branches. The whole surface rupture zone is mainly composed of linear shear cracks, oblique tension cracks, tension-shear cracks, compressional bulges and other structural types. The coseismic surface rupture has the characteristic of typical left-lateral strike-slip motion with a thrust component, and the maximum vertical dislocation is 0.8m.

The M_S6.4 earthquake occurred in Yangbi County, Dali Prefecture, Yunnan Province on May 21, 2021, the epicenter is located at the southwest boundary of Sichuan-Yunnan rhomboid block, where Weixi-Qiaohou-Weishan Fault meets Honghe Fault. According to data released by the China Earthquake Networks Center, the Yangbi M_S6.4 earthquake is the only earthquake in recent years with M_S>6.0 in the epicentral region. The National Strong-Motion Observation Network System(NSMONS)of China has built strong motion stations with relatively large density in Yunnan and Sichuan Provinces, NSMONS has obtained a large number of high quality strong ground motion acceleration recordings during this earthquake. In the process of earthquake, the different characteristics of strong ground motion often lead to the different characteristics of building structure damage in the epicentral region. In-depth analysis of ground motion observation characteristics is helpful to deepen the understanding of earthquake damage.
In this study, the NGA-West 2 data processing flow and reasonable and reliable high-pass filtering frequency selection criteria were used to process 29 sets of strong ground motion acceleration recordings of the earthquake, we obtained reliable peak ground acceleration(PGA), peak ground velocity(PGV), and 5%damped acceleration response spectra(SA). We drew the spatial distribution maps of PGA and PGV in the E-W, N-S, and U-D directions, compared the observed ground motion PGA, SA with the calculated values of the ground motion attenuation relationships commonly used in western China and Sichuan-Tibet region, and analyzed the amplitude and time-frequency characteristics of the observed ground motions, and a comparative analysis was performed between the spectral acceleration recorded by the near-field stations with the design spectra of the code for seismic design of buildings in China. Combined with the on-site earthquake damage investigation, the main reasons for the lighter structural damage in the meizoseismal area were analyzed.
The results show that the maximum horizontal PGA and PGV of the Yangbi M_S6.4 earthquake recorded by the station both locate near the epicenter and the horizontal ground motion attenuates the slowest along the north-northwestern direction, which is basically the same as the long axis direction of isoseismals of seismic intensity map released by Yunnan Earthquake Agency. However, the vertical ground motion attenuates the slowest along the near north-south direction. The actual observation values on the soil site in the Yangbi earthquake are in good agreement with the calculated values of the horizontal ground motion attenuation relationships commonly used in western China and Sichuan-Tibet region, while the observation values on the bedrock site are smaller than the calculated values of the horizontal ground motion attenuation relationships commonly used in western China and Sichuan-Tibet region, which indicates the horizontal ground motion attenuation relationships commonly used in western China and Sichuan-Tibet region derived from the transfer method may over-predict the observation values on the bedrock site. According to the time-frequency diagram obtained by using the wavelet transform, the energy recorded in the EW and NS directions of the station 53YBX, which is the nearest station to the epicenter, is mainly concentrated in 8~15Hz, and the corresponding period range is 0.07~0.13s, while the energy recorded in the UD direction is mainly concentrated in 20Hz, and the corresponding period range is about 0.05s. When the period is smaller than 0.14s, the spectral accelerations in the EW and NS directions of the station 53YBX is significantly higher than the basic ground motion design spectra and rare ground motion design spectra of the code for seismic design of buildings in China; the remarkable period of the acceleration response spectra is 0.1s, the reaction spectrum decreases rapidly when the period is greater than 0.1s, the spectral acceleration corresponding to the superior period in the N-S direction of station 53YBX is 3.87 times the value of the rare ground motion design spectra platform. Most buildings near the epicenter are the one-story old timber frame structures which were built in the 1980s and 1990s, with a natural period of 0.1s, and the 2~3-story brick and concrete frame structures which were built in recent years. According to the analysis of above ground motion characteristics of the Yangbi M_S6.4 earthquake, the most serious damage of this earthquake is the one-story old timber frame structure, while the 2~3-story brick and concrete frame structure has little damage or very light damage. This phenomenon should be related to the characteristics of the structure itself and the disrepair of the structure, the extremely rich ground motion component with a period of 0.1s, and the relatively less ground motion component with a period of more than 0.14s.

At 02:04, May 22, 2021, an earthquake with M_S7.4 occurred in Maduo County, Guoluo Tibetan Autonomous Prefecture, Qinghai Province. The epicenter of the earthquake is about 70km(34.59°N, 98.34°E)south of the east Kunlun fault zone on the northern boundary of the Bayan Har block, with a focal depth of 17km. The Maduo M_S7.4 earthquake is the largest in China after the 2008 Wenchuan M_S8.0 earthquake. As of 07:00 on June 12, 2021, 58 aftershocks of M≥3.0 had been recorded, including 0 earthquakes of M7.0~7.9, 0 earthquakes of M6.0~6.9, 1 earthquake of M5.0~5.9, 17 earthquakes of M4.0~4.9 and 40 earthquakes of M3.0~3.9.
Field geological surveys after the earthquake showed that the earthquake occurred in the Yematan area, which is more than 30 kilometers south of the county seat of Machali Town. The seismic surface rupture shows obvious segmentation, which can be initially divided into 3~4 segments. The rupture spreads from east to west in a left step, gradually approaching the middle of the Yematan Basin. The nature of the fault is mainly left-lateral strike-slip.
The earthquake produced a large-scale continuous surface rupture in the area from the west of National Highway 214 to the south of Eling Lake, with a length of about 45km and a strike of N95°~105°E. The surface rupture zone is composed of a series of compressional bulges and right-hand echelon fractures, forming large-scale seismic bulges(ridges), seismic fissures, left-lateral displacement and other geomorphic features, and producing the seismic geological disasters such as sand and water gushing, soft soil seismic subsidence and so on. From the east of National Highway 214 to the east of Xueluodong, the fracture zone strikes N100°E, which is composed of discontinuous, small-scale tension shear cracks and small-scale bulge(ridge). In the vicinity of Xuema village, Changmahe Township, a section of about 10km long, N75°E striking, large-scale tension shear fracture and seismic bulge(ridge) with good continuity is developed.
The earthquake caused left-handed displacement of geological bodies, water system gullies, roads, etc. and formed strike-slip scratches in the strata. Through measurement, the horizontal displacement of this rupture is 1.5m in the Langmajiaheri area, 1.3m in the area of Yematanshangtou, and 1.1m west of Xuema Village. There is an obvious vertical displacement of 1.4~0.8m near Yematanshangtou, and the vertical displacement of other sections is not obvious. Generally speaking, the horizontal displacement is greater than the vertical displacement, and the rupture is dominated by strike-slip.Based on the field geological survey results, it is considered that the seismic rupture of this earthquake is large in scale and has a good continuity at its both ends, while the rupture scale is small and the continuity is poor in the middle. The preliminary inversion results of seismic rupture process, InSAR processing results and small earthquake precise positioning results show that the Maduo earthquake is a bilateral rupture with a rupture length of about 170km. The field geological investigation results are basically consistent with the geophysical inversion results.
The Maduo M_S7.4 earthquake(the instrument epicenter is located at 34.59°N, 98.34°E)occurred inside the Bayan Har block on the south side of the main Arak Lake-Tosuo Lake section of the east Kunlun fault zone. Existing data show that a number of nearly parallel NW-trending strike-slip faults are developed around the earthquake sequence. According to previous studies and this geological survey, the seismogenic structure of this earthquake is determined to be the Jiangcuo Fault. According to a comprehensive survey of the scale and length of the earthquake surface rupture and the damage to the buildings, it is believed that surface rupture zone in the Langmajiaheri area is large in scale with good continuity and multi types of surface ruptures. The area can be preliminarily determined as the macro-epicenter. The geographic coordinates of the macro-epicenter are 34.736°N, 97.794°E, which is nearly 50km away from the micro-epicenter. The difference is mainly due to the sparse seismic stations and weak monitoring capability in the area.
The fact that the Maduo earthquake occurred inside the Bayan Har block on the south side of the east Kunlun main fault demonstrates the possibility of generating earthquakes with magnitude 7 or greater in the interior of this block. Therefore, the seismogenic conditions and mechanism of strong earthquake activity inside the Bayan Har block should be a scientific issue that needs more attention in the future.

At 02:04 a.m. on May 22, 2021, a M_S7.4 earthquake occurred in the Maduo County, Qinghai Province, China. Its epicenter is located within the Bayan Har block in the north-central Tibetan plateau, approximately 70km south of the eastern Kunlun fault system that defines the northern boundary of the block. In order to constrain the seismogenic fault and characterize the co-seismic surface ruptures of this earthquake, field investigations were conducted immediately after the earthquake, combined with analyses of the focal parameters, aftershock distribution, and InSAR inversion of this earthquake.
This preliminary study finds that the seismogenic fault of the Maduo M_S7.4 earthquake is the Jiangcuo segment of the Kunlunshankou-Jiangcuo Fault, which is an active NW-striking and left-lateral strike-slip fault. The total length of the co-seismic surface ruptures is approximately 160km. Multiple rupture patterns exist, mainly including linear shear fractures, obliquely distributed tensional and tensional-shear fractures, pressure ridges, and pull-apart basins. The earthquake also induced a large number of liquefaction structures and landslides in valleys and marshlands.
Based on strike variation and along-strike discontinuity due to the development of step-overs, the coseismic surface rupture zone can be subdivided into four segments, namely the Elinghu South, Huanghexiang, Dongcaoarlong, and Changmahexiang segments. The surface ruptures are quite continuous and prominent along the Elinghu south segment, western portion of the Huanghexiang segment, central portion of the Dongcaoarlong segment, and the Huanghexiang segment. Comparatively, coseismic surface ruptures of other portions are discontinuous. The coseismic strike-slip displacement is roughly determined to be 1~2m based on the displaced gullies, trails, and the width of cracks at releasing step-overs.

In the process of intense compression and shortening of the orogenic belt, a series of thrust faults and folds related to reverse faults developed in the piedmont. Determining the kinematic characteristics of these reverse faults and folds is of great significance for understanding the deformation mode of the orogenic belt. The Qilian Shan is located on the northeastern margin of the Tibetan plateau and is the front edge of the plateau expansion. The area has undergone strong tectonic activity since the Late Quaternary, with developed active structures and frequent earthquakes. There are a series of piedmont thrust faults and thrust related folds in the northern and southern margins of Qilian Shan. Compared with a large number of research results of active folds in Tian Shan area, the study of active folds in Qilian Shan is relatively weak. In the northern margin of the Qilian Shan, in addition to the study of individual active folds, most previous studies focused on the thrust faults in the northern margin of the Qilian Shan and the Hexi Corridor, and obtained the active characteristics of these faults. In the southern margin of Qilian Shan, that is, the northern margin of the Qaidam Basin, some studies have been carried out on paleoearthquakes and slip rate of the fault in the southern margin of Zongwulong Shan. However, the study on the late Quaternary folds in this area is relatively weak and there are only some sporadic works.
Shidiquan anticline is located in the intermountain basin surrounded by Zongwulong Shan and Hongshan in the northern margin of Qaidam Basin. It forms the first row fold structure in front of Zongwulong Shan with Huaitoutala and Delingha anticline. Constraining the tectonic geomorphic features of the Shidiquan anticline is of great significance for studying the crustal shortening in the northern margin of the Qaidam Basin and the expansion of the Qilian Shan to the Qaidam Basin. In this paper, the tectonic and geomorphic characteristics of Shidiquan anticline are obtained by means of geological mapping, high-precision differential GPS topographic profile survey, geological profile survey and cosmogenic nuclide dating. Field investigation shows that Shidiquan anticline is an asymmetric fold with steep south limb and gentle north limb, and is controlled by a blind reverse fault dipping northward. The age of the alluvial fan3 obtained from cosmogenic nuclide dating is(158.32±15.54)ka. This age coincides with the Gonghe Movement, indicating that the formation of Shidiquan anticline responds to the Gonghe Movement in the northeast margin of Tibetan plateau. The uplift rate of Shidiquan anticline since 158ka is(0.06±0.01)mm/a, and the shortening rate is(0.05±0.01)mm/a. The folding effect of Shidiquan anticline indicates that the folding of the intermountain basin in the northern margin of the Qaidam Basin, similar to the thrust shortening of the piedmont fault, plays an important role in regulating the shortening of the foreland crust.

The Kouzhen-Guanshan Fault trends in near E-W direction and obliquely cuts the active NEE-striking northern boundary fault zone of the Weihe Graben Basin, a fault zone that constitutes the boundary between Weihe Graben Basin and the Ordos block. Medium to small earthquakes occur frequently along the fault. Since the 1980s, a series of researches have been carried out on this fault, and certain cognition has been gained on its geometry, kinematics, tectonic evolution, recent activity and seismogenic capacity. However, most of the eastern segment of the fault is concealed in the Quaternary sediments of Weihe Graben Basin, and the corresponding research and attention are less. By conducting new field geological surveys and combining data from fault-crossing leveling and creepmeter observation, we studied the activities of the Kouzhen-Guanshan Fault during the late Quaternary and in the recent decades, supplemented the geological evidence of fault activity in the late Quaternary, and analyzed the characteristics and differences of tectonic activities on the western and eastern segments of the fault. Our research provides new insights as follows: 1)For the Kouzhen-Guanshan Fault, previous geological surveys were mainly carried out in the western segment with a focus on studying the vertical movement. It is considered that the fault activity has been stronger in the western segment and weaker in the eastern segment since the late Pleistocene. Our field investigation of three geologic cross-sections on the eastern bank of the Shichuan River in the eastern segment provides the understanding of the geological activity on the eastern segment. It reveals that the eastern segment of the Kouzhen-Guanshan Fault has a vertical motion component since the late Pleistocene, where the late Pleistocene stratum has been vertically offset by 8.8m, yielding a vertical slip rate of >0.13mm/a. At places between the central and western segments of the fault, the offset gullies were gradually cut down after the accumulation of loess layer L₁, and the age of S₁ at the bottom of L₁ can represent the lower limit of the left-lateral dislocation age of these gullies. The horizontally-faulted geomorphic features produced in the late Pleistocene have an average left-lateral displacement of 34m, which yields a left-lateral strike-slip rate of >0.49mm/a. These suggest that the Kouzhen-Guanshan Fault is a normal-sinistral oblique-slip one dipping steeply to the south; it would also be a growing transfer fault to adjust the non-uniform horizontal extension between segments of the Weihe Basin by obliquely cutting the northern boundary fault zone of the Basin. 2)Creeping movement is found to occur continuously on two connecting segments of the Kouzhen-Guanshan Fault at least in the last more than 30 years. Fault-crossing leveling observation for more than 30 years has been carried out on the Kouzhen and Jingyang sites on the western segment of the fault, respectively, and fault-crossing creepmeter observation has been carried out for nearly 7 years at Jingyang site, both of which have detected the present activity characteristics of the western segment of the fault. Among them, the two fault-crossing leveling observation time series show that the trends of vertical creep movement are basically the same since 1986. The creepmeter observation at Jingyang site shows that the fault has experienced continuously normal-sinistral creeping, and the horizontal-transverse stretching alternates with sinistral creeping since 2012. At Kangcun site on the western segment of the fault, fault-crossing leveling observation has been carried out for nearly 20 years. For the western segment, the fault creep is relatively stable with time and shows normal-sinistral oblique-creep faulting with the rates of 0.16~0.76mm/a for the vertical component, 0.42~0.78mm/a for the sinistral-creep component, and 0.15~0.26mm/a for the horizontal-transverse stretching component, respectively. Although technical means to observe or detect horizontal deformation are absent on the eastern segment of the fault, the campaign leveling surveys suggest that the fault creep on this segment has an average rate of 1.59mm/a for the vertical component(relative decline in the southern part of the fault)and shows a time series pattern of “step-like” or “episodic” creep, and the fault creep here with a rate as high as 13mm/a during the “step-like” period(2011 to 2014)may represent one slow slip event. 3)The present vertical creeping velocity of the eastern and western segments of the fault is different. The creep rate of the eastern segment is higher than that in the west, which may reflect the eastern segment of the fault is closer to the core of Weihe Graben Basin in space. This inference can be derived from the evidence that the new activity of the fault zone in the northern margin of Weihe Graben Basin, the development of ground fissures belt and seismicity along the Kouzhen-Guanshan Fault are all stronger in the eastern segment. 4)Both the seismicity and the cause of ground fissures belt along the Kouzhen-Guanshan Fault are closely related to the motion of normal-sinistral oblique-creep on this fault, which is controlled by the fault activity and should be the reflection of the surface macroscopic deformation of creeping. 5)The observed creeping movement on the Kouzhen-Guanshan Fault, especially, the phenomenon of “episodic” creep(rarely reported in China)in the vertical motion component on the eastern segment of the fault, proves that slow slip or creep may also occur on faults in tectonically active tensional environments of mainland China. There is obvious difference of normal creep faulting in the eastern and western segments of the fault. It is further necessary to study the differences in the friction properties of the fault segments reflected by the differences in the creep characteristics of these two segments, as well as seismic tectonic and seismic precursory implications of creeping with different characteristics. We therefore suggest strengthening the monitoring of the fault motion and the study of potential seismic hazards. 6)Regarding the “step-like” or “episodic” creep of the fault, the existing research mainly comes from the strike-slip fault. It is found that the present vertical motion component of the Kouzhen-Guanshan Fault shows obvious “step-like” or “episodic” creep characteristics. Therefore, it is necessary to study the relationship between the creeping effect and the phenomenon of seismicity and ground fissures alone the fault. In the future, we intend to combine the microseismic activity and fault friction theory to study the possible mechanism of the “episodic” creep, as well as the tectonic and seismic precursory implications of slow slip events similar to those observed at Kangcun site during 2012—2014.

The large-volume airgun system was introduced to excite highly repetitive seismic signal for medium change monitoring. Using dense seismic array to record the seismic wavefield will be helpful to high spatial resolution time-lapse tomography. However, most dense arrays employ the nodal short-period geophone with built-in battery that is not suitable for permanent monitoring. The novel distributed acoustic sensing(DAS)technology uses fiber-optic itself as sensor that providing small station spacing. The incident seismic wavefiled induces tiny strain of the fiber-optic that leads to phase change of the Rayleigh backscattered optical signal. Therefore, measuring the phase difference between two signals scattered at two nearby scatterers can be used to recover seismic signal. Since the scatter is randomly distributed in the fiber-optic, it is possible to record seismic wavefield with spacing down to sub-meters. Each optical signal is processed in the interrogator. Therefore, the DAS array is easily maintained as a permanent dense array for seismic monitoring. We conducted a pilot experiment to test feasibility of using DAS array to record airgun signal in Binchuan, Yunnan Province.
The Binchuan Fixed Airgun Signal Transmission Station built in 2011 is the first inland large-volume airgun in China. The airgun system consists of four Bolt LL 1500 airguns and fires at 10m depth in a reservoir. The seismic energy released by one airgun shot is close to the one of M_L0.7 earthquake. During this pilot experiment, the airgun was continuously shot after midnight with an interval of 15 minute. The DAS array is a micro-structured fiber-optic buried in an “L-shape” trench, which is about 9.8km away from the airgun. To enhance SNR of the optical signal used for recover seismic signal, a series of ultra-weak fiber Bragg gratings were built in the fiber with 2m spacing. The 180m fiber-optic is buried at about 20cm depth and the trench is backfilled with sand. The channel spacing is 4m and the interrogator continuously records at 1 000Hz.
The signal is barely visible on the record of single shot due to strong ambient seismic noise and optical noise. Since the seismic signal excited by the airgun is highly repetitive, we used the time-frequency phase weighted stacking method to stack records of multiple shots. The signals clearly emerge on the stack traces and the arrival time agrees well with the records of a co-located seismometer. Compared with the seismometer's record, the DAS records concentrate in a higher frequency band(5~8Hz). Since the DAS and seismometer record the seismic wavefield in dynamic strain and particle velocity, respectively, the frequency-wavenumber scaling algorithm was used to convert DAS's strain record to particle velocity record that shows clear phase difference from seismometer's record. The difference between records of DAS and seismometer was analyzed in time-frequency domain. The largest difference occurs between 3 and 6Hz in the airgun signal wave train, which may due to lower sensitivity in lower frequency band of DAS.
The bootstrapping resample method was used to evaluate the stacking converge rate of two datasets. Comparing to the reference trace that is stacked with 24 shots, the cross-correlation coefficient reaches 0.9 with only four shots for the seismometer dataset. At the meantime, the cross-correlation coefficient is only 0.8 with 20 shots for the DAS dataset. To improve the stacking efficiency, we also tried the array stacking method. The records of 26 channels on the X lag of the array were stacked. The one-shot stacking suppressed the traffic noise from a nearby street and the airgun signal clearly emerges on the one-shot stacking trace. The airgun signals on the stacking traces of multiple shots and multiple channels are comparable, which suggest the multiple channels stacking can be used to improve time resolution for time-lapse tomography/monitoring.
In summary, the airgun signal is successfully recorded by a DAS array with an engineered fiber-optic cable. Comparing with the seismometer, DAS dataset is strongly affected by the traffic noise and lower sensitive to lower frequency band. The dense spacing also provides opportunity to stack multiple channels’ records that improves SNR of airgun signal. Since the lack of reliable vertical component records, the phase identification cannot be done via particle motion analysis. The aperture of our DAS array is too small to estimate the apparent velocity to identify seismic phase too. In the future, it is worth to use telecom fiber-optic cables as sensor for time-lapse tomography, which have been widely deployed in urban area and significantly reduced deployment cost.
The clear variation of waveforms across one lag arising from un-uniform coupling was also observed. To comprehensively evaluate the monitor capability, it is important to deploy large aperture DAS array for seismic signal attenuation analysis. Our result suggests that the stronger lower frequency system noise of the DAS integrator reduces the sensitivity to seismic signal. More attention should be paid to approaches such as environmental vibration isolation and optical noise reduction. Another issue is accurate response function. Calibration with co-located seismometers and numerical modeling are helpful to provide accurate sensitivity and response function, which is important in seismology studies.

On March 3, 2017, an earthquake swarm of M_L 4.5 occurred near Dazhushan Island in Miaodao archipelago, Shandong Province, as of December 31, 2017, 2 453 aftershocks were recorded, including 46 earthquakes of M_L3 and above and 4 earthquakes of M_L4 and above. It is the most active and frequent earthquake swarm activity in Miaodao Islands area in the regional network records. On September 2, 2017, another earthquake swarm of M_L3.0 occurred near Beichangshan Island, about 15km away from the south of Dazhushan Island. More than 300 earthquakes were recorded, including one earthquake of M_L3 or above. According to the seismic data, two earthquake swarms were also recorded near Daheishan Island and Tuoji Island in Miaodao archipelago from February to March 1976. It is believed that these two swarms may be the “precursory earthquake swarms” of Tangshan strong earthquake with M=7.8 in 1976. The differences in spatial location, energy release and focal depth between the two swarm events are very similar to those in 2017. Therefore, in this paper, the three-dimensional velocity structure of P-wave in Miaodao archipelago area and the results of seismic precise relocation are obtained by using the double-difference tomography method, and the deep structural environment factors of the preparation of the earthquake swarms and the differences in the characteristics of the earthquake swarms are analyzed in combination with the fault activity and medium characteristics.
The velocity structure provides important information related to earthquake location and focal medium, and provides important basis for understanding the background of earthquake preparation and the mechanism of earthquake occurrence. Based on the observation report data of Shandong and Liaoning seismic networks, this paper selects 4 766 seismic events recorded clearly from January 2008 to December 2017 in Miaodao archipelago and nearby areas, and excludes the data with the difference of P-wave and S-wave travel time and time distance curve larger than 5s. After the difference grouping of earthquake events, 4 555 events recorded by 65 stations are finally selected for double-difference tomography inversion, and there are 26 430 P-wave absolute arrival data, 513 299 difference arrival data, 26 356 S-wave absolute arrival data and 508 482 difference arrival data. Limited by geographical conditions, the ray density is dense in the south and sparse in the north. After repeated test and selection of inversion parameters and model recovery test, high-resolution P-wave three-dimensional velocity structure image and high-precision earthquake positioning results are obtained in Miaodao archipelago, Shandong Province, and the following conclusions are obtained:
(1)The results of seismic precise relocation show that the convergence of seismic distribution near Miaodao islands is good, the NW direction zonal distribution of earthquake swarm activity is obvious, and the focal depth is mainly concentrated in the middle and upper crust. The characteristics of swarm activity show group occurrence in a short period of time, and there are obvious differences in the form of expression: the swarm near Tuoji Island has deep focal point, high frequency, large release energy, and wide distribution of focal area; the swarm activity characteristics near Daheishan Island and Beichangshan Island are just the opposite.
(2)The horizontal velocity structure shows that the lateral heterogeneity of velocity structure exists in every depth layer, which reflects the unbalanced uplift of crystalline basement and the zone filling of igneous rock. The velocity structure of the shallow crust is in good agreement with the known geological structure; the middle and shallow layers clearly reveal the basement uplifting area and the subsidence zone on both sides of Miaodao Islands; the velocity structure of the middle and lower layers is obviously affected by the deep faults and magmatic activities, and near the Dazhushan Island-Weihai North Fault, it shows obvious low-velocity characteristics, while the northern sea area of Jiaodong Peninsula is characterized by independent high-velocty abnormal blocks.
(3)The velocity structure profile shows that there is a certain correlation between the activities of faults and earthquake swarm and the velocity structure of P wave. There is an obvious low velocity region in the middle and upper crust in the profile passing through the Dazhushan Island earthquake swarm, and the earthquake swarm is nearly vertical and layered scattered in the relatively high velocity medium between the upper and lower low velocity bodies or near the velocity conversion zone, which is consistent with the characteristics of the Dazhushan Island-Weihai North Fault. The profile across the Beichangshan Island earthquake swarm reveals that there are small high-speed bodies in the middle and upper layers of the crust, and the earthquake swarm occurs at the edge of the high-velocity body.
(4)Earthquake swarm often occurs in places with dense fracture distribution, relatively weak medium and low strength. Based on the analysis of the characteristics of earthquake swarm and the three-dimensional velocity structure of P-wave in Miaodao archipelago area, it is considered that the two significant earthquake swarm activities in 1976 and 2017 are the energy release caused by the inhomogeneity of local medium and the low stress friction of regional fault during the process of regional background stress enhancement(adjustment).

As documented in history, an M6¼ earthquake occurred between Qianjiang, Chongqing and Xianfeng, Hubei(also named the Daluba event)in 1856. This earthquake caused serious geological hazards, including a lot of landslides at Xiaonanhai, Wangdahai, Zhangshangjie and other places. Among them, the Xiaonanhai landslide is a gigantic one, which buried a village and blocked the river, creating a quake lake that has been preserved to this day. As the Xiaonanhai landslide is a historical earthquake-induced landslide, it is impossible to obtain the remote sensing image and DEM data before the earthquake, which brings certain difficulties to the estimation of landslide volume and the establishment of numerical simulation model. In this paper, the original topography before the earthquake is inferred by the methods of geomorphic analogy in adjacent areas and numerical simulation, and the volume of the Xiaonanhai landslide body is calculated. Firstly, the principle and application of UAV aerial photography are introduced. We employed an unmanned airplane to take pictures of the Xiaonanhai landslide and adjacent areas, yielding high-precision DOM images(digital orthophoto graph)and DEM data which permit generating terrain contours with a 25m interval. We also used the method of intensive manual depth measurement in waters to obtain the DEM data of bottom topography of Xiaonanhai quake lake. Based on field investigations, and combining terrain contours and DOM images, we described the sizes and forms of each slump mass in detail. Secondly, considering that the internal and external dynamic geological processes of shaping landforms in the same place are basically the same, the landforms such as ridges and valleys are also basically similar. Therefore, combining with the surrounding topography and landform of the Xiaonanhai area, we used MATLAB software to reconstruct two possible original landform models before the landslide. The original topography presented by model A is a relatively gentle slope, with a slope of 40°~50°, and the original topography presented by model B is a very high and steep slope, with a slope of 70°~80°. Thirdly, Geostudio software is used to conduct numerical simulation analysis on the slope stability. The safety factor of slope stability and the scale of landslide are analyzed under the conditions of static stability, seismic dynamic response and seismic dynamic response considering topographic amplification effect. The results show that large landslide is more likely to occur in model B, which is more consistent with the reality. In order to verify the credibility of recovered DEM data of valley bottom topography, we visited the government of Qianjiang District, collected the drilling data of 11 boreholes in two survey lines of Xiaonanhai weir dam. It is verified that the recovered valley bottom elevation is basically consistent with that revealed by the borehole data. Finally, according to the two kinds of topographic data before and after the landslide, the volume of the landslide is calculated by using the filling and excavation analysis function of ArcGIS software. There is a gap between the calculation results of filling and excavation, the filling data is 3×10⁶m³ larger than the excavation data. The reasons are mainly as follows: 1)Due to the disorderly accumulation of collapse blocks, the porosity of the accumulation body became larger, causing the volume of the fill to expand; 2)It has been more than 150a since the Xiaonanhai earthquake, and the landslide accumulation has been seriously reconstructed, therefore, there are some errors in the filling data; 3)The accumulation body in Xiaonanhai quake lake might be subject to erosion and siltation, this may affect the accuracy of the filling data. In conclusion, it is considered that the calculated results of the excavation are relatively reliable, with a volume of 4.3×10⁷m³.

The Shanxi Graben System is one of the intracontinental graben systems developed around the Ordos Block in North China since the Cenozoic, and it provides a unique natural laboratory for studying the long-term tectonic history of active intracontinental normal faults in an extensional environment. Comparing with the dense strong earthquakes in its central part, no strong earthquakes with magnitudes over 7 have been recorded historically in the Jin-Ji-Meng Basin-and-Range Province of the northern Shanxi Graben System. However, this area is located at the conjunction area of several active-tectonic blocks(e.g. the Ordos, Yan Shan and North China Plain blocks), thus it has the tectonic conditions for strong earthquakes. Studying the active tectonics in the northern Shanxi Graben System will thus be of great significance to the seismic hazard assessment. Based on high-resolution remote sensing image interpretations and field investigations, combined with the UAV photogrammetry and OSL dating, we studied the late Quaternary activity and slip rate of the relatively poorly-researched Yanggao-Tianzhen Fault(YTF)in the Jin-Ji-Meng Basin-and-Range Province and got the followings: 1)The YTF extends for more than 75km from Dashagou, Fengzhen, Inner Mongolia in the west to Yiqingpo, Tianzhen, Shanxi Province in the east. In most cases, the YTF lies in the contact zone between the bedrock mountain and the sediments in the basin, but the fault grows into the basin where the fault geometry is irregular. At the vicinity of the Erdun Village, Shijiudun Village, and Yulinkou Village, the faults are not only distributed at the basin-mountain boundary, we have also found evidence of late Quaternary fault activity in the alluvial fans that is far away from the basin-mountain boundary. The overall strike of the fault is N78°E, but the strike gradually changes from ENE to NE, then to NWW from the west to the east, with dips ranging from 30° to 80°. 2)Based on field surveys of tectonic landforms and analysis of fault kinematics in outcrops, we have found that the sense of motion of the YTF changes along its strikes: the NEE and NE-striking segments are mainly normal dip-slip faults, while the left-laterally displaced gullies on the NWW segment and the occurrence characteristics of striations in the fault outcrop indicate that the NWW-striking segment is normal fault with minor sinistral strike-slip component. The sense of motion of the YTF determined by geologic and geomorphic evidences is consistent with the relationship between the regional NNW-SSE extension regime and the fault geometry. 3)By measuring and dating the displaced geologic markers and geomorphic surfaces, such as terraces and alluvial fans at three sites along the western segment of the YTF, we estimated that the fault slip rates are 0.12~0.20mm/a over the late Pleistocene. In order to compare the slip rate determined by geological method with extension rate constrained by geodetic measurement, the vertical slip rates were converted into horizontal slip rate using the dip angles of the fault planes measured in the field. At Zhuanlou Village, the T₂ terrace was vertically displaced for(2.5±0.4)m, the abandonment age of the T₂ was constrained to be(12.5±1.6)ka, so we determined a vertical slip rate of(0.2±0.04)mm/a using the deformed T₂ terrace and its OSL age. For a 50°dipping fault, it corresponds to extension rate of(0.17±0.03)mm/a. At Pingshan Village, the vertical displacement of the late Pleistocene alluvial fan is measured to be(5.38±0.83)m, the abandonment age of the alluvial fan is(29.7±2.5)ka, thus we estimated the vertical slip rate of the YTF to(0.18±0.02)mm/a. For a 65° dipping fault, it corresponds to an extension rate of(0.09±0.01)mm/a. Ultimately, the corresponding extensional rates were determined to be between 0.09mm/a and 0.17mm/a. Geological and geodetic researches have shown that the northern Shanxi Graben System are extending in NNW-SSE direction with slip rates of 1~2mm/a. Our data suggests that the YTF accounts for about 10% of the crustal extension rate in the northern Shanxi Graben System.

Studies on the effect of near-surface overburden soil layers on seismic motion have shown that the overburden soil layers have a significant impact on the seismic effect of the site due to the formation age, genetic type, thickness difference, structure, and dynamic characteristics of the soil layers. In this paper, the one-dimensional seismic response analysis of a nuclear power plant site containing a thick hard interlayer was conducted to discuss the influence of the hard interlayer thickness on the site seismic response, so as to provide a basis for determining the seismic motion parameters for seismic design of similar sites. Based on the engineering geological data of a nuclear power plant site, five models of one-dimensional soil-layer seismic response analysis were built, and the equivalent linear method of the one-dimensional site seismic response was applied to analyze the effect of the interlayer thickness on the peak acceleration and the acceleration response spectra of the site seismic response. The seismic response characteristics of the site and influence rules of the hard interlayer thickness are summarized as follows:1)Under different input seismic motion levels, the peak acceleration at the top of the hard interlayer was less than the input peak acceleration, and the peak acceleration at the ground surface of site was greater than the input peak acceleration. 2)Under the same input seismic motion, the ratios of the peak accelerations at the top of hard interlayer to the input peak accelerations were smaller than the ratios of the peak accelerations at the ground surface to the input peak acceleration, and these ratios first decreased and then increased gradually with the increase of the hard interlayer thickness; while for the same hard interlayer thickness, these ratios gradually decreased as the input peak acceleration increasing. 3)For the same input seismic motion, the ratios of the peak accelerations at the ground surface of site to those at the top of the hard interlayer increased gradually as the hard interlayer thickness increased; however, corresponding to different hard interlayer thicknesses, the variation characteristics of ratios which are the peak accelerations at the ground surface of site to those at the top of the hard interlayer were inconsistent with the increase of the input peak acceleration. 4)The hard interlayer had a significant influence on the short-period acceleration response spectrum and the thicker the hard interlayer was, the wider the influence frequency band would be; while for a special hard interlayer thickness, the influence frequency band is certain, and the hard interlayer had little effect on the acceleration response spectrum coordinates outside this frequency band, the longer the period is, the less the influence of the hard interlayer on the acceleration response spectrum coordinates. The seismic response characteristics of the site and influence rules of the hard interlayer thickness indicate that the hard interlayer thickness has a significant impact on the peak acceleration and the acceleration response spectra of the site seismic response, and the hard interlayer has obvious isolation effect at the seismic motion, and the increase of its thickness reduces the nonlinear effect of the site and leads to the wider influence frequency band. Meanwhile, the higher the input peak acceleration is, the stronger the nonlinear effect of the site, and it's remarkable that the soft layer overlying the hard interlayer has a significant amplification effect on the seismic motion.

It is important to detect the fine velocity structures of the crust and uppermost mantle to understand the regional tectonic evolution, earthquake generation processes, and to conduct earthquake risk assessment. The inversion of uppermost mantle velocity and Moho depth are strongly influenced by crustal velocity heterogeneity. In this study, we collected first arrivals of Pg and Pn and secondary arrivals of Pg wave from the seismograms recorded at Fujian provincial seismic network stations. New 3-D P-wave velocities were inverted by multi-phase joint inversion method in Fujian Province. Our results show that the fault zones in Fujian Province have various velocity patterns. The shallow crust is characterized by high velocity that represents mountains, while the mid-lower crust shows low velocities. The anomalous velocities are correlated closely with tectonic faults in Fujian Province. Velocity anomalies mainly show NE-trending distribution, especially in the mid-lower crust and uppermost mantle, which is consistent with the NE-trending of the regional main fault zones. Meanwhile, a part of velocity patterns show NW trending, which is related to the secondary NW-oriented faults. Such velocity distribution also shows a geological structural pattern of "zoning in east-west direction and blocking in north-south direction" in Fujian area.
In the crust, a low velocity zone is found along Zhenghe-Dapu fault zone as mentioned by previous study, however our result shows the low velocity exists at depth of 20~30km in mid-lower crust. Compared with previous study, this low velocity zone is larger and deeper both in range and depth.
The crustal thickness of 28~35km from our joint inversion is similar to the results from the receiver functions of previous studies. The thinnest crust(28km)is observed at offshore in the north of Quanzhou; while the thickest crust(35km)is located west of Zhangzhou near the Zhenghe-Dapu fault zone. Generally, thinner crustal thickness is found in offshore of Fujian Province, and thicker crustal thickness is in the mainland. However, we also found that crustal thickness becomes thinner along the east side of Yongan-Jinjiang Fault.
The values of Pn velocities in the region vary from 7.71 to 8.26km/s. The velocity distribution of the uppermost mantle presents a large inhomogeneity, which is correlated with the distribution of the fault zone. High Pn velocity anomalies are found mainly along the west side of the Zhenghe-Dapu fault zone(F₂), and the east side of the Shaowu-Heyuan fault zone(F₁), which is strip-shaped throughout the central part of Fujian. Low Pn velocity anomalies are observed along the coast and Taiwan Straits, including the Changle-Zhaoan fault zone, the coastal fault zone, and the Fuzhou Basin. We also found a low Pn velocity anomaly zone, which extends to the coast, in the Shaowu-Heyuan fault zone at the junction of the Fujian, Guangdong and Jiangxi Provinces. In the west of Taiwan Straits, both high and low Pn velocity anomalies are observed.
Our results show that the historical strong earthquakes(larger than magnitude 6.0) are mainly distributed between positive and negative anomaly zones at different depth profiles of the crust, and similar anomalies distribution also exists at the uppermost mantle, suggesting that the occurrence of strong earthquakes in the region is not only related to the anomalous crustal velocity structure, but also affected by the velocity anomaly structure from the uppermost mantle.

Influenced by the far-field effect of India-Eurasia collision, Tianshan Mountains is one of the most intensely deformed and seismically active intracontinental orogenic belts in Cenozoic. The deformation of Tianshan is not only concentrated on its south and north margins, but also on the interior of the orogen. The deformation of the interior of Tianshan is dominated by NW-trending right-lateral strike-slip faults and ENE-trending left-lateral strike-slip faults. Compared with numerous studies on the south and north margins of Tianshan, little work has been done to quantify the slip rates of faults within the Tianshan Mountains. Therefore, it is a significant approach for geologists to understand the current tectonic deformation style of Tianshan Mountains by studying the late Quaternary deformation characteristics of large fault and fold zones extending through the interior of Tianshan. In this paper, we focus on a large near EW trending fault, the Baoertu Fault (BETF) in the interior of Tianshan, which is a large fault in the eastern Tianshan area with apparent features of deformation, and a boundary fault between the central and southern Tianshan. An M_S5.0 earthquake event occurred on BETF, which indicates that this fault is still active. In order to understand the kinematics and obtain the late Quaternary slip rate of BETF, we made a detailed research on its late Quaternary kinematic features based on remote sensing interpretation, drone photography, and field geological and geomorphologic survey, the results show that the BETF is of left-lateral strike-slip with thrust component in late Quaternary. In the northwestern Kumishi basin, BETF sinistrally offsets the late Pleistocene piedmont alluvial fans, forming fault scarps and generating sinistral displacement of gullies and geomorphic surfaces. In the bedrock region west of Benbutu village, BETF cuts through the bedrock and forms the trough valley. Besides, a series of drainages or rivers which cross the fault zone and date from late Pleistocene have been left-laterally offset systematically, resulting in a sinistral displacement ranging 0.93~4.53km. By constructing the digital elevation model (DEM) for the three sites of typical deformed morphologic units, we measured the heights of fault scarps and left-lateral displacements of different gullies forming in different times, and the result shows that BEFT is dominated by left-lateral strike-slip with thrust component. We realign the bended channels across the fault at BET01 site and obtain the largest displacement of 67m. And we propose that the abandon age of the deformed fan is about 120ka according to the features of the fan. Based on the offsets of channels at BET01 and the abandon age of deformed fan, we estimate the slip rate of 0.56mm/a since late Quaternary. The Tianshan Mountains is divided into several sub-blocks by large faults within the orogen. The deformation in the interior of Tianshan can be accommodated or absorbed by relative movement or rotation. The relative movement of the two sub-blocks surrounded by Boa Fault, Kaiduhe Fault and BETF is the dominant cause for the left-lateral movement of BETF. The left-lateral strike-slip with reverse component of BETF in late Quaternary not only accommodates the horizontal stain within eastern Tianshan but also absorbs some SN shortening of the crust.

The eastern Himalaya syntaxis is located at the southeastern end of the Qinghai-Tibet Plateau and is the area where the Eurasian plate collides and converges with the Indian plate. The Namjabawa is the highest peak in the eastern section of the Himalayas, and the Yarlung Zangbo River gorge is around the Namjabawa Peak. The NE-striking Aniqiao Fault with right-lateral strike-slip is the eastern boundary fault of the Namjabawa syntaxis. Motuo Fault is in the east of and parallel to the Aniqiao Fault, distributing along the valley of the Yarlung Zangbo River. The section of Yarlung Zangbo River valley at the eastern side of the Namjabawa area is located in the southern foothills of the Himalayas and belongs to the subtropical humid climate zone with dense tropical rainforest vegetation. Dense vegetation, large terrain elevation difference, strong endogenetic and exogenic forces, and abundant valley deposition bring enormous difficulty to the research on active faults in this area.
Since 1990s, surface morphology can be quantitatively expressed by digital elevation models as the rapid development of remote sensing technology. Geomorphic types and their characteristics can be quantified by geomorphological parameters which are extracted from DEM data, describing geomorphologic evolution and tectonic activity. But to date, researches based on quantitative geomorphic parameters are mainly focus on the differential uplift of regional blocks. In the study and mapping of active faults, surface traces of active faults are acquired by visual interpretation of remote sensing images. It has not been reported to identify the location of active faults via the change of quantitative geomorphic parameters. The distribution map of topographic elevation variation coefficient is suitable to reflect the regional erosion cutting and topographic relief, and the places with higher topographic elevation variation coefficient are more strongly eroded. In this paper, we attempt to identify the active faults and explore their distribution in the Yarlung Zangbo Gorge in the east of the Namjabawa Peak based on the application of two quantitative geomorphic parameters, namely, the topographic slope and the elevation variation coefficient.
Using the DEM data of 30m resolution, two quantitative geomorphic parameters of topographic slope and elevation variation coefficient in Namjabawa and its surrounding areas were obtained on the ArcGIS software platform. On the topographic slope distribution map, the slope of the eastern and western banks of the Yarlung Zangbo River near Motuo is steep with a slope angle of more than 30°. Under the background of steep terrain, there are gentle slope belts of 5°~25° distributing intermittently and NE-striking. On the distribution map of topographic elevation variation coefficient, the elevation variation coefficient of the Yarlung Zangbo River near Motuo is greater than 0.9. On the background of the high topographic fluctuation area, it develops gently topographic undulating belts with elevation variation coefficient of 0.2~0.9. The belts are intermittently distributed and northeastern trending. Through the field geological and geomorphological investigation and trench excavation, it is found that the abnormal strips of the above-mentioned geomorphological parameters are the locations where the active faults pass. The above results show that the quantitative analysis of the topographic slope and the coefficient of variation of elevation can help us find active faults in areas with large terrain slope, serious vegetation coverage and high denudation intensity.

With the continuous collision of the India and Eurasia plate in Cenozoic, the Qilian Shan began to uplift strongly from 12Ma to 10Ma. Nowadays, Qilian Shan is still uplifting and expanding. In the northern part of Qilian Shan, tectonic activity extends to Hexi Corridor Basin, and has affected Alashan area. In the southern part of Qilian Shan, tectonic activity extends to Qaidam Basin, forming a series of thrust faults in the northern margin of Qaidam Basin and a series of fold deformations in the basin. The southern Zongwulong Shan Fault is located in the northeastern margin of Qaidam Basin, it is the boundary thrust fault between the southern margin of Qilian Shan and Qaidam Basin. GPS studies show that the total crustal shortening rate across the Qilian Shan is 5~8mm/a, which absorbs 20% of the convergence rate of the Indian-Eurasian plate. Concerning how the strain is distributed on individual fault in the Qilian Shan, previous studies mainly focused on the northern margin of the Qilian Shan and the Hexi Corridor Basin, while the study on the southern margin of the Qilian Shan was relatively weak. Therefore, the study of late Quaternary activity of southern Zongwulong Shan Fault in southern margin of Qilian Shan is of great significance to understand the strain distribution pattern in Qilian Shan and the propagation of the fault to the interior of Qaidam Basin. At the same time, because of the strong tectonic activity, the northern margin of Qaidam Basin is also a seismic-prone area. Determining the fault slip rate is also helpful to better understand the movement behaviors of faults and seismic risk assessment.Through remote sensing image interpretation and field geological survey, combined with GPS topographic profiling, cosmogenic nuclides and optically stimulated luminescence dating, we carried out a detailed study at Baijingtu site and Xujixiang site on the southern Zongwulong Shan Fault. The results show that the southern Zongwulong Shan Fault is a Holocene reverse fault, which faulted a series of piedmont alluvial fans and formed a series of fault scarps.The 43ka, 20ka and 11ka ages of the alluvial fan surfaces in this area can be well compared with the ages of terraces and alluvial fan surfaces in the northeastern margin of Tibetan Plateau, and its formation is mainly controlled by climatic factors. Based on the vertical dislocations of the alluvial fans in different periods in Baijingtu and Xujixiang areas, the average vertical slip rate of the southern Zongwulong Shan Fault since late Quaternary is(0.41±0.05)mm/a, and the average horizontal shortening rate is 0.47~0.80mm/a, accounting for about 10% of the crustal shortening in Qilian Shan. These results are helpful to further understand the strain distribution model in Qilian Shan and the tectonic deformation mechanism in the northern margin of Qaidam Basin. The deformation mechanism of the northern Qaidam Basin fault zone, which is composed of the southern Zongwulong Shan Fault, is rather complicated, and it is not a simple piggy-back thrusting style. These faults jointly control the tectonic activity characteristics of the northern Qaidam Basin.

Study of historical earthquake is one of the important methods to understand the seismic activities and analyze the seismogenic faults. On the May 25^th, 1568 AD, a destructive earthquake occurred to the northeast of the present-day city of Xi'an, Shaanxi Province. Because this earthquake happened shortly after the 1556 M8 earthquake and was regarded as an aftershock, it has received little attention in previous studies. Previous earthquake catalogue agreed in assigning a magnitude 6 3/4 to this earthquake but had different epicentral locations and seismic intensity, and the seismogenic structure remains ambiguous.
Based on textual research of historical earthquake and field investigation, the Jingyang County, Gaoling County, and Xianning County, were the worst hit area by the earthquake, and the areas, including Yongle Town, Gaozhuang Town at southeastern Jingyang County to Gaoling County and its southeastern present-day Jijia and Zhangbu, should be the mesoseismal area of this earthquake. The epicenter intensity of this earthquake is Ⅸ⁺(9~10 degrees), and the magnitude is estimated to be 7. The isoseismal lines were drawn to exhibit the various intensities of the areas damaged during the event, with its major axis directed NWW. Intensities reached Ⅸ⁺ in the zone extending west-northwest parallel to the Weinan-Jingyang Fault. This fault, characterized by a normal fault that developed during the Cenozoic extensional history of the Weihe Basin, dipping to the north at an angle of 60°~80°, is one part of the southern boundary faults in Weihe graben. There are geomorphological and geological evidences of recent activity of the fault during (180±30)a BP to (1 600±30)a BP. At T₁-T₂ fluvial terraces on the north bank of Weihe River, the scarps were faulted during Ming Dynasty, and sandy soil liquefaction, dense structural tensional fissures and faulted strata are noted in stratigraphic profiles and trenches. Thus, we suggest that this fault can reliably be regarded as being active during Holocene, and re-name the earthquake as the Shaanxi Gaoling earthquake.

Since the earthquake of M_L3.8 occurring on October 1, 2013 in Ruishan, Weihai City, Shandong Province, the sequence has lasted for about 4 years(Aug. 31, 2017). Seismicity is enhanced or weakened and fluctuated continuously. More than 13250 aftershocks have been recorded in Shandong Seismic Network. During this period, the significant earthquake events were magnitude 4.2(M_L4.7)on January 7, 4.0(M_L4.5)on April 4, M3.6(M_L 4.1)on September 16 in 2014 and M4.6(M_L5.0)on May 22, 2015. The earthquake of M_L5.0 was the largest one in the Rushan sequence so far. In order to strengthen the monitoring of aftershocks, 18 temporary stations were set up near the epicenter at the end of April, 2014(official recording began on May 7)by Shandong Earthquake Agency, which constitutes an intensified network in Rushan that surrounds the four quadrants of the small earthquake concentration area together with 12 fixed stations nearby, and provides an effective data foundation for the refinement of Rushan earthquake sequence.
The velocity structure offers important information related to earthquake location and the focal medium, providing an important basis for understanding the background and mechanism of the earthquake. In this paper, double-difference tomography method is used to relocate the seismic events recorded by more than six stations of Rushan array from May 7, 2014 to December 31, 2016, and the inversion on the P-wave velocity structure of the focal area is conducted. The Hyposat positioning method is used to relocate the absolute position. Only the stations with the first wave arrival time less than 0.1 second are involved in the location. A total of 14165 seismic records are obtained, which is much larger than that recorded by Shandong Seismic Network during the same period with 7708 earthquakes and 2048 localizable ones. A total of 1410 earthquakes with M_L ≥ 1.0 were selected to participate in the inversion. Precise relocation of 1376 earthquakes is obtained by using double-difference tomography, in which, there are 14318 absolute traveltime P waves and 63162 relative travel time P waves. The epicenters are located in distribution along NWW-SEE toward SEE and tend to WS, forming a seismic belt with the length about 3km and width about 1km. The focal depths are mainly concentrated between 4km and 9km, occurring mainly at the edge of the high velocity body, and gradually dispersing with time. It has obvious temporal and spatial cluster characteristics. Compared with the precise relocation of Shandong network, the accuracy of the positioning of Rushan array is higher. The main reason is that the epicenter of Rushan earthquake swarm is near the seaside, and the fixed stations of Shandong Seismic Network are located on the one side of the epicenter. The nearest three stations(RSH, HAY, WED)from the epicenter are Rushan station with epicentral distance about 13km, the Haiyang station with epicentral distance about 33km, and Wendeng station with epicentral distance about 42km. The epicentral distance of the rest stations are more than 75km. In addition, the magnitude of most earthquakes in Rushan sequence is small. The accuracy of phase identification is relatively limited due to the slightly larger epicentral distance of the station HAY and station WED in Shandong Seismic Network. Furthermore, the one-dimensional velocity model used in network location is simple with only the depth and velocity of Moho surface and Conrad surface. The epicentral distances of the 18 temporary stations in Rushan are less than 10km, and the initial phase is clear. The island station set up on the southeast side and the Haiyangsuo station on the southwest side form a comprehensive package for the epicenter. Compared with the double-difference algorithm method, the double-difference tomography method used in this paper is more accurate for the velocity structure, thus can obtain the optimal relocation result and velocity structure.
the velocity structure shows that there are three distinct regions with different velocities in the vicinity of the focal area. The earthquakes mainly occur in the intersection of the three regions and on the side of the high velocity body. With the increase of depth, P wave velocity increases gradually and there are two distinct velocity changes. The aftershock activities basically occur near the dividing line to the high velocity side. The south side is low velocity abnormal body and the north side is high velocity abnormal body. High velocity body becomes shallower from south to north, which coincides with the tectonic conditions of Rushan. Considering the spatial relationships between the epicenter distribution and the high-low velocity body and different lithology of geological structure, and other factors, it is inferred that the location of the epicenter should be the boundary of two different rock bodies, and there may be a hidden fault in the transition zone between high velocity abnormal body and low velocity abnormal body. The interface position of the high-low velocity body, the concentrating area of the aftershocks, is often the stress concentration zone, the medium is relatively weak, and the intensity is low. There is almost no earthquake in the high velocity abnormal body, and the energy accumulated in the high velocity body is released at the peripheral positions. It can be seen that the existence of the high-low velocity body has a certain control effect on the distribution of the aftershocks.

The Xiaojiang fault zone is located in the southeastern margin of the Tibetan plateau, the boundary faults of Sichuan-Yunnan block and South China block. The largest historical earthquake in Yunnan Province, with magnitude 8 occurred on the western branch of the Xiaojiang Fault in Songming County, 1833. Research on the Late Quaternary surface deformation and strong earthquake rupture behavior on the Xiaojiang Fault is crucial to understand the future seismic risk of the fault zone and the Sichuan-Yunnan region, even crucial for the study of tectonic evolution of the southeastern margin of Tibetan plateau. We have some new understanding through several large trenches excavated on the western branch of the Xiaojiang fault zone. We excavated a large trench at Caohaizi and identified six paleoseismic events, named U through Z from the oldest to the youngest. Ages of these six events are constrained at 40000-36300BC, 35400-24800BC, 9500BC-500AD, 390-720AD, 1120-1620AD and 1750AD-present. The Ganhaizi trench revealed three paleoearthquakes, named GHZ-E1 to GHZ-E3 from the oldest to the youngest. Ages of the three events are constrained at 3300BC-400AD, 770-1120AD, 1460AD-present. The Dafendi trench revealed three paleoearthquakes, named E1 to E3 from the oldest to the youngest, and their ages are constrained at 22300-19600BC, 18820-18400BC, and 18250-present. Caohaizi and Ganhaizi trenches are excavated on the western branch of the Xiaojiang Fault, the distance between them is 400m. We constrained four late Holocene paleoearthquakes with progressive constraining method, which are respectively at 500-720AD, 770-1120AD, AD 1460-1620 and 1833AD, with an average recurrence interval of 370~440a. Large earthquake recurrence in the late Holocene is less than the recurrence interval of~900a as proposed in the previous studies. Thus, the seismic hazard on the Xiaojiang Fault should be reevaluated. We excavated a large trench at Dafendi, about 30km away south of Caohaizi trench. Combining with previous paleoseismological research, it is found that the western branch of Xiaojiang Fault was likely to be dominated by segmented rupturing in the period from late of Late Pleistocene to early and middle Holocene, while it was characterized by large earthquakes clustering and whole segment rupturing since late Holocene.

In order to complete the field investigation to the 25 November 2016 Arketao M_W6.6 earthquake, ultra-low altitude remote-sensing data were obtained from miniature unmanned aerial vehicle. The surface rupture surveying has important significance for earthquake research. This paper selects the macro-epicenter of Arketao as the study area. The pictures were obtained with DJI Phantom 3 professional input into the software, the Digital Elevation Model (DEM), Digital Orthophoto Map (DOM) were acquired based on photogrammetry method using the overlapped optical remote-sensing images of UAV. Using these data, we can identify surface ruptures that have vertical dislocation.
We selected six feature points and drew the elevation profile. In the elevation profile map, we chose smooth part of the surface rupture sides and obtained the trend line. A stable point in the surface rupture was selected and the abscissa of the point was taken into the equation of two straight lines. Then subtracting the results of the two equations, we can get the vertical dislocation of the surface rupture. On this basis, we chose six feature points and determined their vertical dislocation, which are between 4.4cm and 10.4cm. What's more, taking Bulungkou Xiang in Xinjiang Uygur Autonomous Region for example, we speculated some surface ruptures that have vertical dislocation. It can provide a new method for identifying surface rupture in the field.
In addition, we get DEM data of the Bulunkou area where ambient conditions are very poor, by using miniature unmanned aerial vehicle and taking 255 photos. Putting those photos into the EasyUAV software, we got the area digital elevation of 2cm resolution. Comparing these data with RTK data, we summarized some practical problems and solutions in the practical operation and evaluated the accuracy of miniature unmanned aerial vehicle data. The Pearson Correlation Coefficient is 0.996 6. In terms of absolute elevation, the average result of UAV and RTK differs by 156.96m. In terms of relative elevation, the average result of UAV and RTK differs by 9.74m. Compared with the previous test of Pishan County, there is a notable divergence in the results. It shows that the data accuracy will be affected to some extent in the cold weather in high elevations. The specific impact needs further exploration.

Based on the rupture models of the 2015 Pishan M_W6.4 earthquake and half space homogeneous elastic model, the Coulomb stress changes generated by the earthquake are calculated on the active faults near the earthquake region. The horizontal stress changes and the displacement field are estimated on the area around the epicenter. Results show that:(1)The Coulomb stress is decreased in the west of the western Kunlun frontal thrust fault(9.5×10³Pa), and increased in the east of the western Kunlun frontal thrust fault and the middle of the Kangxiwa faults. More attention should be taken to the seismic rick of the east of the western Kunlun frontal thrust fault; (2)Based on the analysis on the location of the aftershocks, it is found that most of the aftershocks are triggered by the earthquake. In the region of increased Coulomb attraction, the aftershock distribution is more intensive, and in the area of the Coulomb stress reduction, the distribution of aftershocks is relatively sparse; (3)The horizontal area stress increases in the north and south of the earthquake(most part of the Qaidam Basin and the northwest of the Qinghai-Tibet plateau), and decreases in the east and west of the earthquake(northern part of the Qinghai-Tibet plateau and eastern part of the Pamir Mountains). In the epicenter area, the principal compressive stress presents nearly NS direction and the principal extensional stress presents nearly EW direction. The principal compressive stress shows an outward radiation pattern centered on the epicenter with the principal extensional stress along the direction of concentric circles. The principal compressive stress presents NW direction to the west of the epicenter, and NE to the east of the epicenter. With the increase of radius, the stress level gradually decays with 10⁷Pa in the epicenter and hundreds Pa in the Maidan Fault which is in the north of the Qaidam Basin.

On April 1, 1936, an M6&frac34; earthquake occurred on the Fangcheng-lingshan Fault. So far, the Lingshan M6&frac34; earthquake is the biggest one in South China. There are some reports about the Lingshan earthquake fissures, but its surface rupture hasn't been systemically studied. Based on the geological mapping and measurement of the right-lateral displacement and vertical offset, the surface rupture zone caused by the Lingshan M6&frac34; earthquake was found, which contains two secondary surface rupture zones in the east and west respectively, its strike varies from N55°E to N60°E with en echelon-like distribution along the north section of Lingshan Fault, and its total length is about 12.5km. The western surface rupture zone locates intermittently along Gaotang-Xiatang-Liumeng, about 9.4km in length, with a right-lateral displacement of 0.54~2.9m and a vertical offset of 0.23~1.02m; the other one appears between Jiaogenping and Hekou, about 3.1km in length, with a right-lateral displacement of 0.36~1.3m and a vertical offset of 0.15~0.57m. The maximum right-lateral displacement and vertical offset are 2.9m and 1.02m, appearing at the east of Xiatang reservoir. The types of surface rupture mainly contain earthquake fault, earthquake scarp, earthquake fissure, earthquake colluvial wedge, earthquake caused landslide and liquefaction of sand and so on. The earthquake fault develops at the east of Xiatang and Jiaogenping, earthquake scarp appears at Xiaoyilu and Xiatang, earthquake fissure locates at Xiatang, there are multiple earthquake landslides along the surface rupture zone, and the trench LSTC03 exposes the earthquake colluvial wedge. In order to further investigate the Lingshan earthquake surface rupture zones, the author compares the parameters of Lingshan M6&frac34; earthquake with the similar typical earthquakes in western China, the results show that the parameters of Lingshan earthquake are similar to the typical earthquakes in western China. The length of Lingshan earthquake surface rupture is shorter, but the dislocation is bigger. The author considers that this is mainly related with the parameters of Lingshan earthquake, site condition and structural environment of surface rupture zone, the symbols of dislocation measuring, human activity and weather condition and so on. The research of surface rupture zone features and analysis of Lingshan M6&frac34; earthquake provides important and basic data for exploring the seismogenic structure of Lingshan M6&frac34; earthquake, and it has important scientific significance.

Based on the rupture models of the 2015 Nepal earthquake sequence and half space homogeneous elastic model, the displacement field near the epicenters is estimated. The horizontal components converge to the epicenters from north and south with maximum value of 871~962mm. The farther the epicenter distance is, the smaller of the horizontal displacement occurred. The displacement on the south side of the epicenters decreases more rapidly than that on the north side as the distance from the epicenter increased. Significant settlement occurred on the north side of the epicenters with maximum of 376~474mm, while large uplift occurred on the epicenters and its south side with maximum value of 626~677mm. Then, the displacement of the peaks of the Himalaya near the epicenters is estimated. The largest displacement occurred at the peak of Shishapangma with 393mm horizontal component and 36mm settlement. Mt. Everest, the world's highest peak, moves 36mm in nearly southward direction with 9mm settlement. The displacements of other peaks of the Himalaya are different with the epicentral distance and azimuth of the 2015 Nepal earthquake sequence.

On April 1, 1936, an M6(3/4) earthquake occurred on the Fangcheng-lingshan Fault. This event is the biggest historical earthquake on the coastal seismic zone, South China ever. But so far, no any findings about the surface rupture of this event have been reported. This paper is the first to find several intact surface rupture zones associated with the 1936 Lingshan seismic event, in the areas of Gaotang, Jiaogengping etc. on the northeast segment of the Fangcheng-Lingshan Fault. According to the field work, the surface rupture stretches to 10km and distributes along NE direction in front of Luoyang Mountain, represented by earthquake scarp, extensional fracture, dextrally faulted gully and river system etc. The characteristics of surface ruptures and faulted landforms indicate that the surface rupture is of normal-dextral strike slip faulting. The trenching on this fault exposed that at least three seismic events have been recorded, including two historical earthquake events and the latest one is the 1936 Lingshan M6(3/4) earthquake. These surface rupture zones are the key to the detection of seismogenic structure and the re-estimate of magnitude of this event. The new finding of these surface rupture zones would be particularly significant for the detection of the seismogenic structure of Lingshan M6(3/4) earthquake.

The Xiangshan-Tianjingshan fault zone is an important part of the arc tectonic zone in northeastern Tibet, whose eastern segment is characterized by primarily left-lateral slip along with thrust component. In contrast, the fault movement property on the western segment of the Xiangshan-Tianjingshan fault zone is more complicated. According to the offset geomorphic features and cross sections revealed by the trenches and outcrops, the western segment is mainly a left-lateral strike-slip fault with normal component, and only accompanied with reverse component at specific positions. To determine the genetic mechanism of fault movement property on the western segment, we obtained three main factors based on the integrated analysis of fault geometry:(1)Step-overs:the left-stepping parallel faults in a sinistral shear zone create extensional step-overs and control the nearby and internal fault movement property; (2)terminal structures:they are conductive to stop rupture propagation and produce compressive deformation at the end of the fault trace; and(3)double bends:strike-slip faults have trace that bends such that slip between two adjacent blocks creates a compressive stress and thrust fault. Additionally, the Tianjingshan sub-block moves to SEE and creates an extensional stress at the end of the sub-block associated with normal faults. It shows that the Xiangshan-Tianjingshan fault zone has a complex evolution history, which is divided into two distinctive periods and characterized by laterally westward propagating.

Nine earthquakes with M≥6 have stricken the northern segment of the Red River fault zone since the historical records, including the 1652 Midu M7 earthquake and the 1925 Dali M7 earthquake. However, there have been no earthquake records of M≥6 on the middle and southern segments of the Red River Fault, since 886 AD. Is the Red River fault zone, as a boundary fault, a fault zone where there will be not big earthquake in the future or a seismogenic structure for large earthquake with long recurrence intervals?This problem puzzles the geologists for a long time. Through indoor careful interpretation of high resolution remote sensing images, and in combination with detailed field geological and geomorphic survey, we found a series of fault troughs along the section of Gasha-Yaojie on the southern segment of the Red River fault zone, the length of the Gasha-Yaojie section is over ten kilometers. At the same time, paleoseismic information and radiocarbon dating result analysis on the multiple trenches show that there exists geological evidence of seismic activity during the Holocene in the southern segment of the Red River fault zone.