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.

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 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.

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.

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.

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.

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.

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.

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.

The Yangjia Village-Yaodian segment of Weihe Fault, starting from Yangjia Village in the west, passing through Weijiaquan, Jinjiazhuang, Donger Village, Chenjiatai to Yaodian, occurs as a NE-striking fault dipping south with a total length of 33 kilometers. As a syn-depositional normal fault, it extends along the leading and trail edge of T₁, T₂ and T₃ terrace at the northern bank of Weihe River. Results of remote sensing interpretation, shallow seismic exploration, exploratory trench, and drilling show that the Yangjia Village-Yaodian section of Weihe Fault manifests as fault scarps, overlapping with the NE-extending terrace scarp at the northern bank of Weihe River. Weihe Fault broke the T₁ that can be distinguished on the shallow seismic profile and multiple profiles with broken signs from T₁ to the ground, which is the same with the cracks through the Han Tomb at the top of the exploratory trench in Yangjia Village. It shows that the fault may still be active from the late Pleistocene to Holocene. Through composite drilling section and the analysis of exploratory trench, there is no significant difference in activity between the Yangjia Village-Jinjiazhuang and Donger Village-Yaodian section. This segment has experienced a large displacement event since (46.0±3.3)ka BP, approximately 11.0~16.5m, with a vertical slip rate of 0.34~0.45mm/a. The most recent activity occurred approximately around 2.0ka BP. The left-step en echelon fracture zone at Jingjiazhuang separates this section into two minor ones, Yangjia Village-Jinjiazhuang section and Donger Villag-Yaodian section. Yangjia Village-Yaodian section in Weihe Fault and Yaodian-Zhangjiawan section which was found out in the Xi'an active fault detection and seismic risk assessment project can be combined into the Yangjia Village-Zhangjiawan section.

Coseismic displacement plays a role in earthquake surface rupture, which not only reflects the magnitude scale but also has effect on estimates of fault slip rate and earthquake recurrence intervals. A great historical earthquake occurred in Huaxian County on the 23^rd January 1556, however, there was lack of surface rupture records and precise coseismic vertical displacements. It's known that the 1556 Huaxian earthquake was caused by Huashan front fault and Weinan plateau front fault, which are large normal faults in the east part of the southern boundary faults in Weihe Basin controlling the development of the basin in Quaternary. Here, we made a study on three drilling sites in order to unveil the coseismic vertical displacements.
It is for the first time to get the accurate coseismic vertical displacements, which is 6m at Lijiapo site of Huashan front fault, 7m at Caiguocun site, and 6m at Guadicun site of Weinan plateau front fault. These coseismic displacements measured based on same layers of drilling profiles both at footwall and hanging wall are different from the results measured by former geomorphological fault scarps. It's estimated that some scarps are related with the nature reformation and the human beings' activities, for example, fluviation or terracing field, instead of earthquake acticity, which leads to some misjudgment on earthquake displacements. Moreover, the vertical displacements from the measurement of geomorphological scarps alone do not always agree with the virtual ones. Hence, we assume that the inconsistency between the results from drilling profiles and geomorphological scarps in this case demonstrates that the fault scarp surface may have been demolished and rebuilt by erosion or human activities.

The 2008 M_S8 Wenchuan earthquake occurs on a high angle listric thrust fault. It is the first time that the near and far field strong ground motion was observed for such special type thrust earthquake. This paper jointly interprets the distribution of peak acceleration of ground motion data with seismogenic structure and slip propagating process to investigate how high angle listric thrust fault controls the pattern of strong ground motion. We found that the distribution of peak acceleration of strong ground motion during the Wenchuan earthquake has four distinctive features: 1)The peak acceleration of ground motion inside the Longmenshan fault zone is large, that is, nearly twice as strong as that outside the fault zone; 2)This earthquake produces significant vertical ground motion, prevailing against horizontal components in the near field; 3)The far field records show that the peak acceleration is generally higher and attenuates slower versus station-fault distance in the hanging wall. It is doubtful that the attenuation of horizontal components also has the hanging wall effect since no evidence yet proving that the unexpected high value at long distance need be omitted; 4)As to the attenuation in directions parallel to the source fault(Yingxiu-Beichuan Fault), the far field records also exhibit azimuthal heterogeneity that the peak acceleration of horizontal components decreases slower in the north-northeastern direction in which the co-seismic slip propagates than that in the backward way. However, the attenuation of vertical component displays very weak heterogeneity of this kind. Synthetically considered with shallow dislocation, high dip angle, and prevailing vertical deformation during co-seismic process of the Wenchuan earthquake, our near and far field ground motion records reflect the truth that the magnitude of ground motion is principally determined by slip type of earthquake and actual distance between the slipping source patches and stations. As a further interpretation, the uniqueness of high angle listric thrust results in that the ground motion effects of the Wenchuan earthquake are similar to that due to a common thrust earthquake in some components while differ in the others.

In recent years, there have been few researches and analysis published on the seismic activity and stress state in Shandong segment of Tanlu fault zone using digital seismological methods such as seismic apparent stress, focal mechanism solution and so on. In this paper, source parameters such as focal mechanism solutions and apparent stress are calculated using the waveform data of M_L≥1 moderate-small earthquakes in Shandong segment of Tanlu fault zone recorded by Shandong digital seismic network since 2007. According to focal mechanism solutions, a statistical analysis is done on the focal dislocation types in the study area using triangle graphical method, and the results show that the faulting in this area is mainly of strike-slip mechanism, and there are less thrust and normal mechanism. Calculation with the mean stress tensor method illustrates that the direction of mean principle stress of Shandong segment of Tanlu fault zone is NEE-SWW, which is the result of the combined effect of the subduction of West Pacific plate and the extrusion of Indian plate to Eurasian plate; the small dip angle indicates that the mode of action of stress is nearly horizontal, and the direction of principal stress axis is nearly perpendicular to the Tanlu fault zone. Under the action of such compressive stress field, dislocation is not likely to occur and the stress accumulation is enhanced on both sides of the fault. The apparent stress is calculated using the source spectral parameters method. Apparent stress has positive correlation with the magnitude and increases with the increased magnitude. So we get apparent stress difference by subtracting the empirical fitting value from the apparent stress. By removing the impact of magnitude, and according to the temporal-spatial evolution image of apparent stress difference, we found that the apparent stress in Shandong segment of Tanlu fault zone generally has a trend of decrease starting from the Wenchuan earthquake in 2008, and the spatial distribution of apparent stress in the region is very uneven. Combined with the spatial distribution of b values, the result shows that high stress is mainly located in Anqiu segment and Tancheng-Juxian segment, especially in Anqiu segment where small magnitude earthquakes appeared accompanying with the high stress. Low b-value means high stress and low frequency means low stress release, which indicates that Anqiu segment might accumulate higher stress and is at the fault locking stage. The research will provide new data for better understanding the present active feature and stress state of the Shandong segment of the Tanlu fault zone.

On September 7, 2012 at 11: 19 and 12: 16(Beijing time), two catastrophic earthquakes with M_S5.7 and M_S5.6 struck the junction area of Yiliang County, Yunnan Province and Weining County, Guizhou Province, China. The research result indicates that the September 7, 2012 Yiliang earthquake triggered a mass of secondary geological disasters. The spatial distribution of the Yiliang earthquake triggered geological disasters is presented in this paper, by field check and using visual interpretation of remote sensing imageries. The statistical analyses results of their spatial distribution indicate that there are about 213 geological hazards throughout an area of about 0.67km², consisting of collapse, landslide, rolling stones and mud-rock flow etc. We analyzed five characteristic parameters of these geological disasters triggered by Yiliang earthquake using GIS spatial analyses, such as seismic intensity, the formation stratum, slope angle, distances to river system and distances to road, and investigated in depth the control effect of these influence factors on the earthquake-induced geological hazards. This study reveals that: 1)most of the earthquake-induced geological hazards occurred in the Carboniferous strata along the Luoze River; 2)seismic region with intensity Ⅷ within the study area is the high incidence area of geological disasters, and the geological hazards have positive correlation with seismic intensity; 3)the hazards are mostly distributed in the slope range between 20°~50°; 4)geological disasters are densely distributed in the distance of 500m to river system and road, and they have negative correlation with the distance.

In order to understand the role of underdeveloped immature small faults and conditions of the occurrence of medium-size earthquakes induced by fluid injection into deep reservoirs, we carry out an integrated study involving geological survey of small faults, seismological investigation of typical cases of injection-induced seismicity, and rock fracture test in laboratory. At first, we briefly summarize the general features of several important cases of injection-induced seismicity in gas/oil reservoirs in the Sichuan Basin, China. It is suggested that major induced earthquakes, especially those of a moderate size, result from the reactivation of pre-existing faults. We also present some pieces of field and petrologic evidence showing such small faults exist widely in reservoirs and are important channels for fluid migration. Then, we present experimental results with a focus on the formation and the after-slip of fault in typical sedimentary rocks under tri-axial compression. Finally, methodology for risk assessment and injection management is discussed based on insights gained from the integrated approaches.
Our results are helpful for understanding the question—why injection-induced seismicity is so significant in the Sichuan Basin. Major Pre-Triassic sedimentary rocks, including dolomite, shale, and dolomitic limestone are strong and demonstrating brittle fracturing behaviors. Such properties are necessary conditions for maintaining high level of reservoir stress and leading to seismic fracturing. Insights gained from this study may shed some lights to the general earthquake seismology and provide a better understanding of why damaging injection-induced earthquakes occur so that they can either be avoided or be mitigated. In general, existing of critically or sub-critically stressed faults of a dimension of a few kms is a necessary condition for M～5 level earthquakes. In addition, AE, or in other words, micro-seismicity monitoring is useful in risk assessment and injection management and should be fully utilized in injection applications.

The hazard grade assessment,which simply and clearly reveals how big the damage is,is an important part of emergency response and rescue work after disaster. Upon collection and sorting out of the data on Asian natural disasters occurring between 1900 and 2011,this paper studies the method of classifying those disasters. After discussing the definition of catastrophe and that of earthquake-affected population and exploring the basis on which catastrophe could be classified,this paper comes up with a formula,in which the logarithms of three factors,death toll,direct economic loss and quake-affected population,are summed up. Then,Asian catastrophes are classified by the formula. The calculation based on the formula shows that the results of 54 of all the disasters are above 10.0,102 above 9.0 and 178 above 8.0.After repeated comparison with data from several other disaster databases,it is concluded that the result achieved by the formula of the disaster which is generally considered as a catastrophe,is above 8.0.Therefore,a disaster with a result above 8.0 is defined as a catastrophe. The formula mentioned above in this paper is simple and convenient,and is suitable for making a comparison of the damage caused by the disasters of different types in different regions in Asia.

Shear wave splitting is a possible method for earthquake stress-forecasting.We applied shear wave splitting analysis to a seismic dataset generated by airguns in a reservoir.We found that the seismic data contains shear waves(Sg and SmS).The shear waves are converted at the water-solid interface from P-waves generated by the airgun source,and the energy of the converted shear wave is equivalent to the energy released by a M_L 1.6 earthquake.We analyzed the data recorded by a seismic line deployed over the Yanshan uplift.The results show that the predominant polarizations of the fast shear wave are in the directions of NWW and NEE,which are affected by the characteristics of the local fault system.Using an airgun as a repeatable seismic source and recording the data at a fixed point,the variation of shear wave splitting parameters can indicate the variation of local stress-strain fields,and hence provides a method for earthquake stress-forecasting.

Based on the survey and study of active faults at three sites,i.e.Yaodian,Shiheyang and Dujiapu on the north bank of Weihe River in Xianyang,Shaanxi,this paper probes into the methodology of survey of the loess-covered active faults coincident with terrace scarps,and presents the displacement amount of the Weihe Fault zone at Shiheyang in late Pleistocene.At Shiheyang,exploration of the Weihe Fault zone was carried out by means of shallow seismic prospecting,drilling,topographic analysis and age dating.The initial survey result showed a displacement of 17.94m of the stratum S1 on the Weihe Fault zone.The causes leading to this false result were mainly due to incorrect judgment on geomorphic unit,and followed by the so big spacing of drill holes that the subtle change of strata tilting due to erosion couldn't be seen.The drop of the same stratum at the profile detected at two drill holes far away from each other was mistaken for fault displacement.With the scarp caused by erosion added to the fault displacement,the fault throw was magnified.By densifying the drill holes to a spacing of 1.9m between holes,we get the displacement of the top of S₁ to be only about 1.2m.At Yaodian,data are available,including the 200m deep drilling section data,the densified mid-deep drilling data and shallow seismic prospecting data.Drilling data with borehole spacing of 30m revealed an offset of 4.8m on the top of S1 by the Weihe Fault.Since the two holes were located at scarp change zone,the 4.8m height difference of the top of S1 might be the elevation difference of tilted terrain superimposed possibly with certain amount of faulting.The 30m hole spacing is too large to affirm that S1 has been faulted.The drilling section at Dujiapu was implemented at last,in which deficiencies in dealing with the first two ones were avoided.At this site,the shallow seismic methods couldn't be performed,therefore the fault was located by combining the deep drilling with shallow drilling at a hole spacing as small as possible(2～3m).In spite of the small borehole spacing,it was difficult to identify the displacement amount of the fault according to the paleosol layer S1,which is probably due to too small fault throw.All the explorations of fault at the above three sites have a certain deficiency in methodology,mainly in the depth and spacing of drill holes.The common shortcoming is that no deep trenches were excavated.If allowable,it would be better to verify the fault location and activity by trenching.The above results show that the exploration of loess-covered active faults coincident with terrace scarps shall be carried out with comprehensive method combining topographic analysis,shallow seismic survey,drilling and trenching.Particularly for drilling exploration,deep,medium and shallow holes shall be combined in use with the medium and deep holes drilled to determine the location of faults at depth,and the shallow holes used to identify the location and activity of faults near surface.Due to river erosion,the fluvial deposition layer in terrace scarp zone is tilted.Aeolian paleosol layer draping over the tilted layer is tilted too.As a result,the spacing between holes must be small(2～3m preferable)when such strata are used to identify the location and movement of faults.Excessive spacing may lead to the addition of the height of erosion-formed scarp to the fault offset,thus greatly overstating the later.It is highly recommended to make verification by trenching in the end.The above exploration results show that the Weihe Fault zone coincides with the scarps of the third terrace at Yaodian,Shiheyang and Dujiapu.The displacements associated with faulting only have a small proportion of the terrace scarp and the 1～2m offset of the first late Pleistocene paleosol layer by faulting is much less than the difference in elevation of terrace surface.The previously thought 4.8m and 17.94m displacements are incorrect.

The M_S 8.0 Wenchuan earthquake on 12^th May 2008 caused heavy casualties and economic loss.According to the field investigations,the characteristics can be included as follows:The meizoseismal region with an intensity of XI,showing obviously zonal distribution,suffers serious destruction from the earthquake,and the destruction perpendicular to the rupture decreases sharply.At the same time,the intensity X and IX degree regions perpendicular to the rupture are narrow and therefore their coverage area is small.The intensity on both sides of the rupture attenuates rapidly,but the Ⅶ degree region and the VI degree region are wide,the latter region covering about 240,000 square kilometers.In the VI degree region,the damage area perpendicular to the rupture in the southern part is much larger than that of the northern part.Besides,many new understandings about the destruction types and destructive modes of all kinds of buildings,landform and terrain are gained in this paper.

The M_S8.0 Wenchuan earthquake is one of the most devastating earthquakes in recent 30 years in the world.Based on a number of on-the-spot investigations,preliminary research on the macro-epicenter and meizoseismal region has been done.The analysis reveals that the meizoseismal region,whose intensity is Ⅺ and shows obviously zonal distribution,is controlled by the rupture process and there exists a close relationship between the meizoseismal region and the rupture zone.What's more,the macro-epicenter of Wenchuan Earchquake is quite different from those of previous earthquakes,not just one point any more but a group of points.This group of points begins from the village of Caijiagang of Xuankou town of Wenchuan county,passes through Yingxiu town,Yinxing town of Wenchuan county,the north of Hongkou town of Dujiangyan city,the north of Xiaoyudong town and Longmenshan town of Pengzhou city,the north of Hongbai town of Shifang city,and ends at Qingping town of Mianzhu city.Skipping over Anxian county,it continues from Leigu town of Beichuan county to Xuanping town,Qushan town,Chenjiaba town,Pingtong town of Pingwu county,and ends at the north of Nanba town.The shape of the macro-epicenter area of the Wenchuan earthquake can be considered as a narrow belt or line,broken in the middle.This point of view will influence our overall understanding of quake-hit areas to a great extent.Besides,the realization that the macro-epicenter of a severe earthquake probably presents like a line is of great significance when we cope with severe earthquakes later,especially when determining key relief areas,planning the relief work,evaluating the earthquake situation,identifying key areas of scientific investigation and so on.

The late Pleistocene aeolian loess distributes widely in the loess tableland area.It has obvious features and is directly related with faulting.By the observation,measurement and dating to three typical sections at Xiaobaopo,Qiaogou and Zhongdicun,this paper obtained the activity parameters of the Lintong-Chang an Fault since the late Pleistocene and the age stratigraphic sequence of the tablelands of Bailuyuan,Shaolingyuan and Henglingyuan.Research results show that the Bailuyuan tableland has experienced

The Weihe Fault is an important blind fault in Weihe Basin and controls the formation,evolution and seismicity of Weihe Basin. The deep seismic reflection survey results show that the fault is not a deep crustal fault; it is located right below the C layer at about 15km depth and cuts through the crystalline basement and the C layer,causing a throw of about 4km between the two sides of crystalline basement. The dip angle at the shallow part of the fault(depth<5km)is big and flattens with depth,and the fault turns to be a listric fault.Shallow seismic survey results show that the dip angle of the Weihe Fault in the middle and deep parts is about 85°; the attitude is different on the two walls of the fault,the footwall is horizontal and the hanging wall is tilting to the south direction; and its dip angle increases quickly.Drilling survey results show that the fault at the shallow part is obviously manifested. The lithology,thickness and attitudes of strata are quite different between the two sides of fault. The attitude on the footwall is horizontal and that on the hanging wall tilts a bit to the fault side. The late Pleistocene displacement is about 4～6m.Trenching results show that the Weihe Fault near ground is still active. Since Holocene epoch it has undergone 3 paleoearthquakes and 1 history earthquake,so it is a Holocene active fault.

The Longmenshan Fault zone,trending in NE,lies between the Songpan-Ganzi orogenic belt and the Yangzi block.It consists of four major faults,such as the Houshan Fault,and related thrusting sheets.It is a nappe structure characterized by forward spreading.It formed during the Indo-China movement and was active many times since then.Since the Quaternary,this fault zone has been very active,and exhibits differential activity on its various sections.In this work,we make an integrated analysis of this fault zone based on data of geomorphology,geology,Bouguer gravity anomalies,and earthquakes.The results show that the near NS-striking Leidong Fault,located along Beichuan-Anxian,is the boundary between the middle and northeastern sections of the Longmenshan Fault zone.The two sections have high distinctive activity.The middle section is very active since late Pleistocene time with frequent medium-and small-sized earthquakes,while the northeastern section has weak activity since Quaternary with occasional small earthquakes.Due to the compression and uplift of the Tibetan Plateau and lateral sliding of blocks,the Sichuan-Qinghai block moves towards SEE,resulting in an active boundary of the block.This boundary includes the Mingshan uplift and the middle and southwestern sections of the Longmenshan Fault zone,both of which are truncated by the Mingshan uplift.And the northeastern section of the Longmenshan Fault zone has been abandoned.

Weihe Fault is an important buried fault in Weihe basin.The predecessors have investigated the location and activity of the fault from various points of view,but up to now,the level of researches on the precise location and activity for the fault is still very low.There are few strata profiles of late Pleistocene which are found to be offset by the fault zone.Especially,it is still unknown whether the Weihe Fault was active in Holocene and there were paleoseismic events occurring on it.It is indicated from exploratory trench excavated at Bili village in the west section of Weihe Fault that over the past 9110a,the Yaodian—Zhangjiawan segment of Weihe Fault zone has experienced a historical earthquake and 3 paleoearthquake events.The historical earthquake is manifested by soil liquefaction.According to the study on historical and cultural relics,stratigraphic chronology and seismogenic tectonics,we propose the occurrence time of the historical earthquake is between 1487 and 1568;the age of paleoseismic event I is(9110±90)a,but there is no answer for the age of event II and event Ⅲ.The coseismic vertical displacement of event I,II and Ⅲ is 0.5m,0.5m and 0.2m respectively.The exploratory trench excavation also indicates that the Yaodian-Zhangjiawan segment of the Weihe Fault is a Holocene active fault.

The Lintong-Chang'an Fault zone locates in the middle part of Cenozoic Weihe depression.It is the boundary fault controlling the Lishan diamond block and Xi'an sag.The landforms are obviously different between the sides of the fault,and the geomorphic forms are stepped fault scraps and loess scraps.In the paper,by field geological survey to the Zhongdi Village,Wangjiabian Village and Qiaogou profiles on the Lintong-Chang'an Fault,and in combination with the dating data of regional loess and paleosol profile(An Zhi-sheng and Sun Jian-zhong),the fault is studied in order to explore the times of its latest activity and the characteristic of its late Quaternary movement.The fault strikes NE as a whole and is characterized with tensile vertical movement.The fault obviously offset the first paleosol layer S₁ in loess stratum,indicating that it is still active since late Pleistocene epoch.But most fault displacements are less than 2m,the slip rate is low,and the activity level is higher in the northern and central segments than that in the southern segment of the fault.Regarding that the Lintong-Chang'an Fault consists of several secondary faults,its whole activity should be much higher than the local slip rate of the fault we have derived.The fault displacements show an increasing trend with depth and the slip rates calculated using the dating data of different strata are almost the same.So perhaps,the fault is mainly dominated by vertical creep-slip since the late of middle Pleistocene epoch.