At 2:04 on May 22, 2021, an earthquake of M7.4 occurred in Maduo County, Golog Prefecture, Qinghai Province, with the focal depth of 17 kilometers, the epicenter at 34.59°N and 98.34°E. This earthquake was the largest after the Wenchuan earthquake in China. The epicenter of the earthquake is 38km away from Maduo county seat and 385km from Xining, the provincial capital. The earthquake caused some houses to collapse and some damage to roads in the epicenter. But due to the sparse population in the epicenter area, the earthquake did not cause casualties.

Seismologist believe that the earthquake is the result of the continuous activity of the boundary fault of the Bayankala block, which is geographically located in the north of the Qinghai-Tibet Plateau and is the hub for the transformation of the direction of the crustal movement of the plateau. In recent years, many destructive earthquakes occurred inside the block. This earthquake is another strong earthquake after the M7.1 Yushu earthquake in Qinghai in 2010. According to the analysis of this earthquake briefing, the fault zone that induced this earthquake is speculated to be the Maduo-Gande fault zone or the Kunlun Mountains Pass-Jiangcuo fault zone.

In order to find out which fault is the seismogenic structure and the distribution of the seismogenic structure of this earthquake, we relocated the dense earthquakes by double-difference method based on the data of 1357 aftershocks in the Maduo M7.4 earthquake area recorded by 72 fixed stations of the digital seismic network of Gansu and its adjacent seismic network and 12 portable seismographic stations during the May 22 to May 27, and obtained the source parameters for 1289 earthquakes. The accurately located small earthquakes distribute along both sides of the Kunlun Mountains Pass-Jiangcuo Fault, which is NNW-trending obviously. It shows that the seismogenic structure of this earthquake is the Kunlun Mountains Pass-Jiangcuo Fault, rather than the Maduo Gande Fault as considered previously by some scholars. This is consistent with the research results of surface fracture zone, magnetotelluric detection, InSAR coseismic deformation and relocation of other aftershocks. Most earthquakes distribute at the depth range of 0~15km of the crust after the relocation, and the result shows that the focal depths are more concentrated. The relocation also shows that the east and west ends of the main fault have bifurcations. It may be that the complex stress distribution triggered two new branch faults during the occurrence of the great earthquake, and the overall fault shows a “tree-type” structure. The west branch trends 306°and intersects the main fault at 21°. The east branch is nearly EW trending and connected with the east section of the main fault.

Generally, the earthquakes are closely related to active tectonics, large earthquakes and its aftershocks usually occur on fault zones with obvious activity. The distribution of small earthquakes is related to the complex underground stress state and the complex structure of the fault zone. We can inverse the shapes and positions of the fault planes using spatial distribution of hypocenters of mainshock and the corresponding aftershocks, according to the principle that clustered earthquakes occur near the faults. Six rectangular regions are selected according to the distribution characteristics of relocated aftershocks and by reference to the distribution of geological faults and earthquake rupture zones. We obtained the detailed parameters of fault plane in each region by using the simulated annealing algorithm and the Gauss-Newton algorithm according to the source information after the relocation in 6 rectangular areas. On this condition, rake angle of the fault plane is further inferred from regional tectonic stress parameters. The results show that the main fault is a large, high dip angle, sinistral strike-slip fault with thrust component, striking 285°~290° and about 146km long. It extends from Tanggema Township of Maduo in the southeast(34.49°N, 98.91°E)to Gazejialong Township in the northwest(34.81°N, 97.54°E). The movement characteristics of the newly generated western segment 2 show dextral strike slip and thrust, which is diametrically opposite to that of the main fault. This shows the complexity of the earthquake rupture process, and further research is needed on the tectonic mechanics and deep structures that produce this special rupture.

Compared with the focal mechanism solutions obtained by domestic and foreign authorities, the fault plane parameters obtained in this paper are similar to them, indicating that our conclusions are reliable. Besides, the spatial distribution of inverted fault plane is basically identical to that of the rupture zone derived from post-earthquake investigation in the earthquake area.

Beijing plain is a strong earthquake tectonic area in China, where the Sanhe-Pinggu earthquake with M8 occurred in 1679.The seismogenic fault of this earthquake is the Xiadian Fault. An about 10km-long earthquake surface fault is developed, striking northeast. Deep seismic exploration reveals that this surface fault is a direct exposure of a deep fault cutting through the whole crust, and it is concealed in the Quaternary layers to both ends. Previous studies have not yet revealed how the deep fault with M8 earthquake extended to the southwest and northeast. In the study of Xiadian Fault, it is found that there is another fault with similar strike and opposite dip in the west of Xiadian Fault, which is called the West Xiadian Fault in this paper. In this study, six shallow seismic profiles data are used to determine the location of this fault in Sanhe city, and the late Quaternary activity of the fault is studied by using the method of combined drilling, magnetic susceptibility logging and luminescence dating.

The results of shallow seismic exploration profiles show that the fault is zigzag with a general strike of NE and dip NW. In vertical profile, it is generally of normal fault. It shows the flower structure in one profile, which indicates that the fault may have a certain strike-slip property. On two long seismic reflection profiles, it can be seen that the northwest side of the fault is a half graben structure. This half graben-like depression, which has not been introduced by predecessors, is called Yanjiao fault depression in this paper. The maximum Quaternary thickness of the graben is 300m. The West Xiadian Fault is the main controlling fault in the southern margin of the sag.

The Xiadian Fault, which is opposite to the West Xiadian Fault in dips, controls the Dachang depression, which is a large-scale depression with a Quaternary thickness of more than 600m. The West Xiadian Fault is opposite to the Xiadian Fault, and there is a horst between the West Xiadian Fault and the Xiadian Fault. The width of the horst varies greatly, and the narrowest part is less than 1km. The West Xiadian Fault may form an echelon structure with Xiadian Fault in plane, and they are closely related in depth.

According to the core histogram and logging curves of ten boreholes and eight effective dating data, the buried depth of the upper breakpoint of the concealed fault is about 12m, which dislocates the late Pleistocene strata. The effective dating result of this set of strata is(36.52±5.39)ka. There is no evidence of Holocene activity of the fault, but it is certain that the fault is an active fault in the late Pleistocene in Sanhe region. The vertical slip rate is about 0.075mm/a since late Pleistocene, and about 0.03mm/a since the late period of late Pleistocene. These slip rates are less than those of the Xiadian Fault in the same period. According to our study, the vertical slip rate of Xiadian Fault since late Pleistocene is about 0.25mm/a.

Although the latest active age, the total movement amplitude since Quaternary and the sliding rate since late Pleistocene of West Xiadian Fault are less than those of Xiadian Fault, its movement characteristics is very similar to that of Xiadian Fault, and the two faults are close to each other in space, and closely related in deep structure. It can be inferred that the fault is probably a part of the seismogenic structure of the 1679 Sanhe-Pinggu M8 earthquake. In a broad sense, the Xiadian fault zone is likely to extend to the southwest along the West Xiadian Fault.

Due to the ongoing collision between Indian and Eurasian plates, the internal blocks of the Tibet plateau are experiencing eastward extrusion. Resulting from the blocking of the Sichuan Basin along the eastern boundary of the Bayanhar block, the plateau begins to rotate clockwise around the eastern syntaxis, and continues to move toward the IndoChina Peninsula. Such process forms the Hengduan Mountains with thousands of gullies in the Sichuan-Yunnan region, and generates major earthquakes across the entire Red River Fault, where infrastructures and residents are seriously threatened by the frequent earthquakes. InSAR observations feature a high spatial resolution and short intervals, ranging from several days to over a month, depending on the satellite revisit period.
On May 21, 2021, an earthquake struck the Yangbi city. This event provides a rare opportunity to look at the local tectonic and seismic risk in the north of the Red River Fault. We processed the Sentinel-1 SAR data with D-InSAR technology and generated the surface deformation caused by the Yangbi M_S6.4 earthquake occurring on May 21, 2021. Due to the abundant vegetation and moisture in Yunnan, significant atmospheric noise needs to be corrected for the derived InSAR displacement field. The results show a maximum deformation of~0.07m in line-of-sight for ascending track and~0.08m for descending track. The quality of interferogram on the ascending track is low, and only one of the quadrans can be distinguished, the rest of the interferogram is regarded as phase noise. However, the descending interferogram contains two deformation regions, with its long axis roughly along the NW-SE direction. The northeast part of interferogram moves towards the satellite, while the southwest part moves away from the satellite. The InSAR interferograms pattern shows a right-lateral strike-slip movement. Then, we combined coseismic displacement data obtained from the Global Navigation Satellite System(GNSS)and InSAR(both the ascending and descending)to invert the coseismic slip model of the Yangbi earthquake. The inversion test shows that our data cannot give strong constraints for the dip orientations, and the two slip models with opposite dip orientation can explain the observations within the noise level. No matter what the dip orientation is, the slip models show that the coseismic slip concentrated at depth of 2~10km, with a maximum slip of~0.8m, which corresponds to a moment magnitude of M_S6.4, and is consistent with body-wave-based focal mechanism. But the relocated aftershocks in 3 hours immediately after the mainshock reveal a SW-dipping fault plane 10km away to the west of Weixi-Qiaohou-Weishan Fault, we therefore conclude that the Yangbi earthquake ruptured a SW-dipping dextral fault, which is previously unknown. To analyze the effects of the Yangbi earthquake on the seismic risk of the regional dextral faults, we estimated the Coulomb stress change caused by our preferred slip model. The Coulomb stress at 7.5km depth is negative, indicating stress unloading, while the Coulomb stress at 15km depth is positive, indicating slightly loading, but still less than the empirical triggering threshold. The results indicate that Yangbi earthquake partially relieved the strain accumulated on the nearby faults, thus restraining the seismic risk of these faults.

The Aketao M_S6.7 earthquake occurred on November 25, 2016, which was located at the intersection of Gongur extensional system and Pamir frontal thrust. This region is characterized by complex fault structure, high altitude, complex terrain conditions, sparsely populated and few observed data, so the conventional geodetic survey technology is difficult to obtain comprehensive surface deformation information, while InSAR can take advantage of its all-weather, all-day, large-area and high-density continuous monitoring of ground motion. Therefore, this study takes M_S6.7 earthquake as the research object to carry out the co-seismic deformation field extraction and fault static slip distribution inversion. Firstly, the co-seismic deformation field was obtained by using ascending and descending data of Sentinel-1A. The results indicate that the interferogram spatial decorrelation is more serious in the north side of fault, which is affected by the steep terrain. The fringes in the south side of fault were distributed as elliptical semi-petal shapes, and the fringes are smooth and clear. The northern and southern part of the fault was asymmetric: The interferogram fringes of the southern part were dense while fewer fringes were formed in the northern part, and the fringes were semi butterfly-shaped on the surface. The horizontal displacements dominated the co-seismic deformation in this event, with magnitude of 12cm in ascending and -21cm in descending. The deformation occurred mainly on the south wall of fault. Based on the right view imaging of Radar, the co-seismic deformation is consistent with the movement features of dextral strike-slip fault and the focal mechanism provided by USGS and GCMT. The cross section of aftershocks after precisely positioning showed that the dip angle of fault is larger above the depth of 15km, which is generally manifested as the shovel-like structure with the dominant tendency of southward dip. By conducting a comprehensive analysis of deformation feature and aftershocks profile, we proposed that the southwest-dipping Muji Fault is the seismogenic fault. Secondly, a large area of continuous deformation images obtained by InSAR technology contains millions of data points and there is a high correlation between them. In order to ensure the calculation efficiency and inversion feasibility in the inversion process, the quadtree sampling method was used to reduce the number of data points and the datasets were finally obtained that can be received by the inversion system on the basis of retaining the original details of the deformation field. The two tracks InSAR datasets which were down-sampled by quadtree method were used to constrain the inversion to retrieve the fault geometry parameters and slip distribution. The single-segment and two-segment static slip distribution on the fault plane based on uniform elastic half space model were constructed during inversion process. The F-test of fitting residuals based on single-segment and double-segment fault model show that the population variance of the two models was significantly different at the confidence level of 95%, and the variance of the double-fault model was smaller. Through the comprehensive analysis of predicted deformation field, residuals and F-test, it is considered that the simulated results of double fault model are better than that of the single, and the observation data can be better interpreted. The result shows that the simulated co-seismic deformation field and its corresponding observed values were consistent in morphology and magnitude, and the correlation between observed and modeled is up to 0.99. In addition, as can be seen from the spatial distribution and frequency histogram of residuals, the overall residual was not large, mainly concentrated in the range of -0.2~0.2cm with the characteristics of normal distribution. However, there were still some larger residuals on the near fault in ascending track, which may be related to the simplified model. There were two patches with significant slip distribution on each segment and the rupture basically reached the surface. The slip was mainly distributed along the downdip range of 0~20km and was about 50km along the fault strike. The rupture reached the surface and the peak slip of 0.7m was at the depth of 9km. The western segment is dominated by the right-lateral strike-slip and the eastern segment is dominated by the right-lateral strike-slip with slightly normal faulting. The seismic moment derived from inversion was 8.81×10¹⁸N·m, which is equivalent to M_W6.57. The average slip angle obtained by inversion is -175° in the west section and -160° in the east section. The synthetic analysis holds that the source characteristics of the M_S6.7 earthquake was characterized by dextral strike-slip with a slightly normal component, which was composed of two sub-seismic events. The western section was basically pure right-lateral strike-slip with a dip angle of 75°, while the eastern was characterized by dextral strike-slip with a small amount of normal component with a dip angle of 55°. The Aketao earthquake occurred on the northern Pamir salient and its tectonic deformation was mainly characterized by crustal shortening, strike-slip and internal extension of the frontal edge observed by GPS. Generally speaking, the Pamir salient was blocked by nearly east-west South Tian Shan in the process of strong northward pushing under the action of NE direction pushing of Indian plate, and “hard and hard collision” occurred between them. The eastern part of Pamir salient extruded eastward along the nearly NS trending Gongur extensional system, and at the same time rotated clockwise, which caused the nearly EW extension since the Late Quaternary. The Aketao earthquake is a tectonic event occurring at Gongur Shan extensional system, which shows that the pushing of the Indian plate in the NE direction is continuously strengthened, and also implies that the internal crustal deformation of the Pamir Plateau is still dominated by extension in EW direction, which is basically consistent with the present observation of GPS.

On November 18, 2017, a M_S6.9 earthquake struck Mainling County, Tibet, with a depth of 10km. The earthquake occurred at the eastern Himalaya syntaxis. The Namche Barwan moved northward relative to the Himalayan terrane and was subducted deeply beneath the Lhasa terrane, forming the eastern syntaxis after the collision of the Indian plate and Asian plates. Firstly, this paper uses the far and near field broadband seismic waveform for joint inversion (CAPJoint method)of the earthquake focal mechanism. Two groups of nodal planes are obtained after 1000 times Bootstrap test. The strike, dip and rake of the best solution are calculated to be 302°, 76° and 84° (the nodal plane Ⅰ)and 138°, 27° and 104° (the nodal plane Ⅱ), respectively. This event was captured by interferometric synthetic aperture radar (InSAR)measurements from the Sentinel-1A radar satellite, which provide the opportunity to determine the fault plane, as well as the co-seismic slip distribution, and assess the seismic hazards. The overall trend of the deformation field revealed by InSAR is consistent with the GPS displacement field released by the Gan Wei-Jun's team. Geodesy (InSAR and GPS)observation of the earthquake deformation field shows the northeastern side of the epicenter uplifting and the southwestern side sinking. According to geodetic measurements and the thrust characteristics of fault deformation field, we speculate that the nodal plane Ⅰ is the true rupture plane. Secondly, based on the focal mechanism, we use InSAR data as the constraint to invert for the fine slip distribution on the fault plane. Our best model suggests that the seismogenic fault is a NW-SE striking thrust fault with a high angle. Combined with the slip distribution and aftershocks, we suggest that the earthquake is a high-angle thrust event, which is caused by the NE-dipping thrust beneath the Namche Barwa syntaxis subducted deeply beneath the Lhasa terrane.

In this paper, we processed and analyzed the Sentinel-1A data by "two-pass" method and acquired the surface deformation fields of Menyuan earthquake. The results show the deformation occurred mainly in the south wall of fault, where uplift deformation is dominant. The uplift deformation is significantly larger than the subsidence and the maximum uplift of ascending and descending in the LOS is 6cm, 8cm respectively. Meanwhile, based on the Okada model, we use the ascending and descending passes data as constraints to invert jointly the fault distribution and source parameters through constructing fault model of different dip directions. The optimum fault parameters are:The dip is 43°, the strike is 128°with the mean rake of 85°. The maximum slip is about 0.27m. The inverted seismic moment M₀ is 1.13×10¹⁸N·m, and the moment magnitude M_W is 5.9. The SW-dipping Minyue-Damaying Fault is possibly the seismogenic fault, based on the comprehensive analysis of the focal mechanisms, aftershocks relocation results and the regional tectonic background. The focus property is dominated by thrust movement with a small amount of dextral strike-slip component. The earthquake is the result of local stress adjustment nearby the Lenglongling Fault under the background of northeastward push and growth of Tibet Plateau.

The Sanweishan fault is located in the northern margin of the Tibetan plateau. It is a branch of the Altyn Tagh fault zone which extends to the northwest. A detailed study on Late Quaternary activity characteristics of the Sanwei Shan Fault can help understanding the strain distribution of the Altyn Tagh fault zone and regional seismic activity and northward growth of the Tibetan plateau. Previous research on this fault is insufficient and its activity is a controversial issue. Based on satellite images interpretation, field investigations and geological mapping, this study attempts to characterize this feature, especially its activity during Late Quaternary. Trench excavation and sample dating permit to address this issue, including determination of paleoseismic events along this fault.
The results show that the Sanweishan fault is a large-scale active structure. It starts from the Shuangta reservoir in the east, extending southward by Shigongkouzi, Lucaogou, and Shugouzi, terminates south of Xishuigou, with a length of 175km. The fault trends in NEE, dipping SE at angles 50°~70°. It is characterized by left-lateral strike-slip with a component of thrust and local normal faulting. According to the geometry, the fault can be divided into three segments, i.e. Shuangta-Shigongkouzi, Shigongkouzi-Shugouzi and Shugouzi-Xishuigou from east to west, looking like a left-or right-step pattern. Plenty of offset fault landforms appear along the Sanweishan Fault, including ridges, left-lateral strike-slip gullies, fault scarps, and fault grooves. The trench study at the middle and eastern segments of the fault shows its activity during Late Pleistocene, evidenced by displaced strata of this epoch. Identification marks of the paleoearthquakes and sample dating reveal one paleoearthquake that occurred at(40.3±5.2)~(42.1±3.9) ka.

For analyzing the role that reservoir impounding plays in triggering earthquake, the process of diffusion of pore pressure and its mechanism of action should be understood firstly. The temporal distribution of seismicity, which occurred before the M_S8.0 Wenchuan earthquake, following the impoundment of Zipingpu reservoir is studied in this paper. Then the mechanisms of the occurrence and development of reservoir triggered seismicity are discussed. A comparative analysis of the temporal distribution of seismicity and the submerged area by reservoir impounding is carried out firstly. Then the influence of various factors on modeling is analyzed in detail. After calculating, the pore pressure change by the Zipingpu reservoir impoundment is obtained. The following observations are made:(1)Conspicuous swarms of earthquakes, of which the sources are located on the same fault of the M_S8.0 Wenchuan earthquake, occurred orderly with the impoundment of Zipingpu reservoir.(2)Because of the influences of the terrain and the medium, the range of effect of pore pressure change by the impoundmemt is limited and anisotropic. Hydraulic diffusivities(D)of 0.7 and 0.35m²/s along the fault strike and the fault dip are reached respectively by a semi-quantitative assessment. Of course, the qualitative pressure constraints on the surface are also applied for the modeling.(3)The calculation results show that the temporal distribution of seismicity near the Zipingpu reservoir is related with the pore pressure change. After the pore pressure reached the threshold of triggering earthquake, whether the pressure head change is high or not, the change rate of pressure head change plays a key role in the decrease or increase of seismicity. It means that the triggered seismicity by pore pressure is a dynamic triggering process.

According to the Region-Time-Length (RTL) algorithm,the analysis of seismicity changes prior to the 2014 Yunnan Jinggu M_S6.6 earthquake was conducted by using the earthquake catalogues about 6 and 15 years before this earthquake,respectively.When the studied period was nearly 6 years,an enhancement of seismic activity was detected around the epicenter since the beginning of 2013.The anomalies mainly distributed in the region of 22.5°~24.5°N and 99°~102°E.The range and degree of anomalies changed from small to large,and then to small chronologically.As the surface integral in respect to RTL,the physical parameter I_RTL,which could reflect the regional seismicity level,began to increase since August 2013,and then reduced after reaching the peak point.The time length from the peak point of I_RTL curve to the earthquake occurrence was 9 months.When the analyzed catalogue was nearly 15 years,the 2007 Ninger M_S6.4 occurred in the studied region.Seismicity quiescence was detected prior to the Ninger M_S6.4.Before the Jinggu M_S6.6,seismicity quiescence was detected firstly,and then enhanced activity was observed 1 year prior to the earthquake occurrence.The anomalies mainly distributed in the region of 22.5°~24.5°N and 99°~102°E.The time length from the peak point of I_RTL curve to the earthquake occurrence was 7 months.The above study showed that even the earthquakes location was near and the magnitude was close to each other,a big difference in seismic activity before the earthquakes may exist.Before the Jinggu M_S6.6,there was some difference in seismicity changes according to different beginning time of catalogues,but the distribution of anomalies and the time length from the peak point of I_RTL to the earthquake occurrence were uniform.So there was an important significance for exploring the relationship between the distribution of anomalies and the earthquake location,and the relationship between the time of the peak point of I_RTL and the earthquake occurrence time.

Although the kinematics and mechanics of the Yilan-Yitong fault zone (YYFZ) since the Mesozoic-early Cenozoic were studied very well in the past decades,few results about the average recurrence interval of great earthquakes in late Quaternary,which is the most important parameter for us to understand the active tectonics and potential seismic hazard of this crucial structure,were obtained because of its unfavorable work environments.Based on interpretations of high-resolution satellite images and detailed geologic and geomorphic mapping,we discovered that there exist linear fault scarp landforms and troughs in the Shangzhi part of YYFZ with a length of more than 25km.Synthesized results of trenches excavation and differential GPS measurements of terrace surfaces indicate two paleo-events EⅠ and EⅡ occurring in Shangzhi part during the late Holocene,which resulted in ca.(3.2±0.1) m accumulated vertical coseismic displacement with strike-slip motion accompanied by thrusting and shortening deformation.¹⁴C samples dating suggests that event EⅠ might occur at (440±30) and (180±30) a BP and event EⅡ might happen between (4 090±30) and (3 880±30) a BP,and the average recurrence interval of major earthquakes on the YYFZ is around (3 675±235) a.Historical written records discovered from Korea show that the event EⅠ may correspond to the earthquake occurring in AD 1810(Qing Dynasty in Chinese history) in Ningguta area with magnitude 7.0.

The Dengdengshan and Chijiaciwo faults situate in the northeast flank of Kuantanshan uplift at the eastern terminal of Altyn Tagh fault zone, striking northwest as a whole and extending 19 kilometers and 6.5 kilometers for the Dengdengshan and Chijiaciwo Fault, respectively. Based on satellite image interpretation, trenching, faulted geomorphology surveying and samples dating etc., we researched the new active characteristics of the faults. Three-levels of geomorphic surfaces, i.e. the erosion rock platform, terrace I and terrace Ⅱ, could be found in the northeast side of Kuantanshan Mountain. The Dengdengshan Fault dislocated all geomorphic surfaces except terrace I, and the general height of scarp is about 1.5 meters, with the maximum reaching 2.6 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 2.7 meters, the average vertical dislocation of each event changed from 0.5 to 1.2 meters. By collecting age samples and dating, the event Ⅰ occurred about 5ka BP, event Ⅱ occurred about 20ka BP, and event Ⅲ occurred about 35ka BP. The recurrence interval is about 15ka BP; and the vertical slip rate since the late Pleistocene is about 0.04mm/a.
The Chijiaciwo Fault, however, dislocated all three geomorphic surfaces, and the general scarp height is about 2.0 meters with the maximum up to 4.0 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 3.25 meters, the average vertical dislocation of each event changed from 0.75 to 1.5 meters, and the vertical slip rate since the late Pleistocene is about 0.06mm/a. Although the age constraint of paleoearthquakes on Chijiaciwo Fault is not as good as that of Dengdengshan Fault, the latest event on Chijiaciwo Fault is later than Dengdengshan Fault's. Furthermore, we infer that the recurrence interval of Chijiaciwo Fault is 15ka BP, which is close to that of Dengdengshan Fault.
The latest event on Chijiaciwo Fault is later than the Dengdengshan Fault's, and the vertical displacement and the slip rate of a single event in late Quaternary are both larger than that of Dengdengshan Fault. Additionally, a 5-kilometer-long discontinuity segment exists between these two faults and is covered by Quaternary alluvial sand gravel. All these indicate that the activity of the Chijiaciwo Fault and Dengdengshan Fault has obvious segmentation feature.
The size of Chijiaciwo Fault and Dengdengshan Fault are small, and the vertical slip rate of 0.04~0.06mm/a is far smaller than that of Qilianshan Fault and the NW-striking faults in Jiuxi Basin. All these indeicate that the tectonic deformation of this region is mainly concentrated on Hexi Corrider and the interior of Tibet Plateau, while the activties of Chijiaciwo and Dengdengshan faults are characterized by slow slip rate, long recurrence interval(more than 10ka)and slow tectonic deformation.

In the past few years, the improved InSAR technology based on time series analyses to many SAR images has been used for measurement of interseismic deformation along active fault. In the paper, we first made a summary and introduction to the basic principle and technical characteristics of existing Time Series InSAR methods(such as Stacking, PSInSAR, SBAS). Then we presented a case study on the central segment of Haiyuan Fault in west China. We attempt to use the PS-InSAR(Permanent Scatter InSAR)technique to estimate the motion rate fields of this fault. We processed and analyzed 17 scenes of ENVISAT/ASAR images in descending orbits from 2003-2010 using the PS-InSAR method. The results reveal the whole movement pattern around the Haiyuan Fault and a remarkable velocity gradient of about 5mm/a across the central segment of the fault. The motion scenes are consistent with left-lateral strike-slip. On this basis, we make a discussion on some issues about observation of fault activity using Time Series InSAR methods, such as the changes of LOS deformation rates with fault strike and region width observed across a fault, fault reciprocity and motion style indicated by Time Series InSAR rate map and the relationship between the InSAR LOS deformation and the ones from other methods. All these studies will benefit the promotion of InSAR application in detection of tectonic movement.

Vertical coseisimic deformation near seismogenic fault is one of the most important parameters for understanding the fault behavior, especially for thrust or normal fault, since near field vertical deformation provides meaningful information for understanding the rupture characteristics of the seismogenic fault and focal mechanism. Taking Wenchuan thrust earthquake for an example, we interpolate GPS horizontal observed deformation using Biharmonic spline interpolation and derive them into east-westward or north-southward deformation field. We first use reliable GPS observed value to correct InSAR reference point and unify both GPS and InSAR coordinate frame. We then make a profile using InSAR data and compare it to that from GPS data and we find GPS and InSAR observation reference point has a 9.93cm difference in the hanging wall side, and around -11.49cm in the footwall. After correction, we obtain a continuous vertical deformation field of the Wenchuan earthquake by combined calculation of GPS and InSAR LOS deformation field. The results show that the vertical deformation of both hanging wall and foot wall of the fault decreases rapidly, with deformation greater than 30cm within 50km across the fault zone. The uneven distribution of the vertical deformation has some peak values at near fault, mainly distributed at the southern section(the town of Yingxiu), the middle(Beichuan)and the northern end(Qingchuan)of the seismogenic fault. These three segments have their own characteristics. The southern section of the fault has an obvious asymmetric feature, which exhibits dramatic uplift reaching 550cm on the hanging wall, with the maximum uplift area located in Yingxiu town to Lianshanping. The middle section shows a strong anti-symmetric feature, with one side uplifting and the other subsiding. The largest uplifting of the southern segment reaches around 255cm, located at the east of Chaping, and the largest subsiding is in Yongqing, reaching around -215cm. The vertical deformation of the northern section is relatively small and distributed symmetrically mainly in the north of Qingchuan, with the maximum uplift to be 120cm, locating in the northernmost of the seismogenic fault.

Many NW-trending faults are developed in West Shandong. Cangshan-Nishan Fault,about 130km long,striking 310°～340°,dipping to SW and NE with dip angle 70°～80°,is the largest one among these faults. According to geomorphological characteristics and relationship between fault and Quaternary deposits,Cangshan-Nishan Fault can be divided into three segments: the western segment(Fangshan-Tianhuang segment),about 30km long,controlling the western margin of Qufu Basin; the middle segment in the bedrock area(Tianhuang-Ganlin segment),about 80km long,forming a valley and controlling evolution of Baiyan River; and the eastern segment(Ganlin-Cangshan segment),buried in the Quaternary basin,about 20km long.
The western segment(Fangshan-Tianhuang segment)appears as a linear scarp in the satellite images. Field investigation shows that the linear scarp is mainly composed of rock with 2～5m high in topography. On the northeast side of the scarp is mountains composed of Archaeozoic Taishan group gneiss,and on the south-west side is late Pleistocene alluvial fan. A lot of profiles reveal that the late-Pleistocene deposits(the thermoluminescence dating results)are dislocated by the fault. The fault cross sections near the Qufu city show it is a normal fault with high scarps. The highest scarp is 4.7m high and the normal vertical slip rate is 0.07mm/a. However,the fault cross sections near the Tianhuang Town show it is a reverse fault with high dip angle. The highest scarp is about 1.5m high, lower than that near the Qufu city. All these information indicate that the fault,from west to east,is changed gradually from normal feature to reverse feature,and the height of fault scarp is decreased gradually from west to east.
Based on reported results in this area,Cangshan-Nishan Fault is a left-lateral strike-slip hinge fault. The results presented in this paper suggest that the western segment is dominated by normal dip-slip with left-lateral strike-slip component,the middle segment is dominated by left-lateral strike-slip with reverse dip-slip component. As the axes of hinge fault,the middle segment is the most active segment of Cangshan-Nishan Fault. Besides Cangshan-Nishan Fault,a series of NW-trending faults are developed in West Shandong with weak activity since late-Pleistocene. Many moderate-strong earthquakes are related to these NW-trending faults. We thus think these NW-trending faults have capability of generating moderate-sized quakes.

Xiadian Fault zone is a NNE-trending lithospheric-scale regional deep fault in the eastern part of the capital,also an active fault zone with strong earthquake activities in the history. According to the results of gravity,shallow seismic and high-density electrical geophysical prospecting,by "relay stitching" vertically from the deep to the shallow,and in combination with the methods of drilling and other means,the Xiadian Fault zone is studied by dividing it into two parts: the bedrock fault zone and the Quaternary fault zone,and new insights are gained on the characteristics of deep structure and activity of the Xiadian Fault zone. The results show that: (1)the bedrock fault zone of Xiadian Fault consists of main faults and secondary faults. Its northern part,the Mafang-Xiji area,is composed of two major faults with a narrower width,and the southern part,the Xiji-Fengheying area,is composed of three major faults,with a wider width; (2)The Quaternary fault zone of Xiadian Fault is the upward extension of the bedrock fault zone,which is the visual representation of the latest activity of the fault zone and controlled by the bedrock fault zone. The Quaternary fault zone is also composed of main faults and secondary faults. The northern part(Mafang-Xiji area)consists of two major faults and secondary faults distributed in the northern end,corresponding well with the bedrock fault zone. Occurrence of the two major faults is quite different,and the latest movement of the faults is both in Holocene. While,the southern part of the fault zone(the Xiji-Fengheying area)is quite discontinuous and is difficult to distinguish between the major and secondary faults. The faults have poor correspondence to the bedrock ones and are inferred to be related with the segmentation of faulting of the bedrock faults. Both major and secondary faults are steep and the date of their latest movement is late Pleistocene-early Holocene; (3)The amount of vertical dislocation of the bottom boundary of the Holocene sediments in the hanging and foot walls of Xiadian Fault zone is 1.7～4.8m,and that of late,middle and early Pleistocene are 6～26m,26～167m and 44～330m,respectively. The vertical dislocation on the whole fault zone differs greatly,with the highest in the Xiadian area,and decreasing gradually to the south and north ends; (4)Considering the spatial distribution,structure,occurrence,activity and characteristics of seismic activity along of the fault zone,the Xiadian Fault zone is divided into the southern and northern segments with the Zhangjiawan Fault as the boundary. The northern part experienced intensive Quaternary activity,with frequent moderate and small earthquakes. Quaternary activity is weak along the southern part,where only small earthquakes occurred.

Within almost five years,the 2008 Wenchuan M_S 8.0 and 2013 Lushan M_S 7.0 earthquakes ruptured the Longmenshan Fault zone successively. The characteristics of earthquakes and their development tendency on this fault zone have been a focus of subject of research. This article attempts to explore some features of seismic preparation process of the 2008 Wenchuan event from temporal-spatial evolution of earthquakes along the Longmenshan Fault zone during more than 40 years.(1)The spatial range of the earthquake preparation,or seismic nucleation,is much smaller than that of co-seismic rupturing. It indicates that the seismic source,probably consisting of some small asperities or barriers,prepared on a finite fault segment can be connected and expand into a large-scale rupture section along the fault when the fast instability occurs at the source.(2)Prior to the 2008 Wenchuan giant shock,its preparation area had experienced a dense distribution of small earthquakes for eight years or more,while no conspicuous slip and deformation were observed on the surface. This implies that the seismogenic fault segment of the Wenchuan event on the Longmenshan Fault was undergoing probably compressive deformation,accompanied with cataclastic process. When the cataclastic deformation of the great-shock source reached a critical state,fault instability occurred along the fault with rapid rupturing. (3)To further study the variations of the main-shock area prior to the event,this article analyzes the temporal-spatial processes of small earthquakes around the main shock since 2004 recorded by a special seismic network in the Zipingpu reservoir. The results indicate that the scope of the seismicity expanding along the fault took place along the fault in October 2005 and October 2006,respectively,in accordance with the time when the reservoir reached its high water level. Among them,the second expanding from October 2006 covered a relatively large area and with relatively big magnitudes,implying great importance for the study of the final instability process of the 2008 Wenchuan huge earthquake. Besides,this paper discusses the correlation of the rupturing process of the 2008 Wenchuan giant event with the geometry of the fault and the reason why the 2013 Lushan earthquake occurred many years after the Wenchuan event rather than immediately following this giant shock like usual big aftershocks. The research results are helpful for understanding of seismogenic processes of major earthquakes of the thrust type.

The distribution and characteristic of ground deformation is a key issue in geodesy,which brings insight into the geometry of the ruptured fault and seismic hazard assessment in the future in the surrounding areas. It also provides better constraint conditions for geophysical inversion. Compared with field research,satellite imagery regularly provides detailed and spatially comprehensive images and is a most valuable alternative especially for the study in remote areas. So,observing seismic rupture is urgent after earthquake. InSAR is useful for measuring ground displacement,but the technique has severe limitations that are mainly due to data decorrelation and signal saturation,and it does not generally provide measurements in the near-fault area where large displacements occur. In this paper,the sub-pixel correlation method and SPOT image are used to map the Wenchuan earthquake rupture and to identify the faults activated by the earthquake. A computation is introduced of the inverse projection matrices for which a rigorous resampling is proposed. Image registration and correlation is achieved with an iterative unbiased processor that estimates the phase plane in the Fourier domain for subpixel shift detection,then the earthquake deformation field is derived.The results indicate that the Wenchuan earthquake produced at least surface ruptures on two faults along the Longmenshan Fault,the main rupture named Beichuan-Yinxiu rupture zone(Longmenshan town-Gaochuan in this map)and the secondary rupture named Hanwang rupture zone.The former is characterized by dextral-slip thrusting with a horizontal displacement of 4～6m in average and a dextral-slip displacement of 1～3m near Gaochuan town.The latter is characterized by pure thrusting,with horizontal displacement 1～2m in average. There is no obvious ground rupture along Wenchuan-Maoxian Fault.The research indicates that sub-pixel correlation using optical image can be a powerful complement to differential radar interferometry,which can measure ground displacement near the fault zone.The study also shows that earthquake displacement fields can be calculated by remote sensing technology.The surface rupture can be traced and the meizoseismal area can be located by this method. Compared with field research,satellite imagery regularly provides detailed and spatially comprehensive images and is a most valuable alternative especially for the study in remote areas.

The interferometric baseline is a vital parameter in the InSAR technique,which determines the correlation between two repeat-pass images and imposes direct effect on the accuracy and reliability of the mapping result. If the baseline is not accurately estimated,the residual phases from the orbit and topography will be left in the expected phase of deformation leading to errors of the final result. In this work,we analyze the influences of the baseline on the reference phase and simulated topography phase,and present several methods of interferometric baseline estimation. Then we study the mapping process of the coseismic and post-seismic deformation of the 1997 Mani,Tibet M7.7 earthquake based on the 8-sence ERS2-SAR data and InSAR.Our attention is focused on comparison of interferograms under varied conditions for baseline estimations,such as rough orbit data,precise orbit data,frequency of interferometric fringes and control points on the ground. The result shows that when the baseline is estimated by rough orbit data,the yielded differential interferograms contain considerable phases of orbit residuals which make fringes dense and deformation enlarged. Thus we must use the precise orbit data for baseline estimation. Sometimes,however,the influence of the orbit cannot be removed completely even if we employ precise orbit data. In this case we should make further corrections,including removing superfluous fringes based on interferometric fringes frequency and baseline correction using the control points on the ground. With these improvements,the resultant coseismic displacement along the fault of the Mani earthquake is 4.5m. The post-seismic deformation by this event is concentrated in a narrow 10～20km-long zone around the fault. The accumulated fault slip 508 days after the main shock reaches at least 5.6m,which continues to grow with time. These analysis results are consistent with the field observations,meaning the improvement method presented in this paper is effective.

Many NW-trending faults have been developed on the north of the eastern segment of Altyn Tagh Fault. The Tarwan Fault,about 10km long and striking NW on the whole,is the western segment of the largest Tarwan-Dengdengshan-Chijiaciwo Fault among these faults. The fault appears as a straight linear scarp in the satellite image and a geomorphic scarp of dozens of centimeters to 5 meters high,topographically. The scarp dips NE and is composed mainly of beds of early Pleistocene conglomerate and Holocene aeolian sandy soil. As revealed by a measured topographic profile,the scarp composed of Holocene aeolian sandy soil is about 5m high,and that of early Pleistoscene conglomerate is about 1m high. Field investigation and trenches excavated on the vertical scarp have revealed the Tarwan Fault is a thrust fault,striking NW and dipping SW.The Geogene mudstone is thrust over the early Pleistocene conglomerate,with a throw of 0.5m. The Holocene aeolian sand and late Pleistocene gravel layers overlying the fault are not dislocated. The hanging wall of the fault is Geogene mudstone with rich groundwater and well-developed vegetation. Due to the protection and control of sand movement with vegetation,aeolian sand was accumulated constantly and preserved,and as a result,the aeolian sand layer became higher gradually. The foot wall of the fault consists of a Gobi gravel layer of a few centimeters thick on the surface and hard cemented conglomerate of early Pleistocene under it,with groundwater and vegetation being undeveloped. Therefore,Holocene aeolian sand is only developed on the hanging wall of the fault,and there is no Holocene stratum developed in the footwall. The height of the scarp formed on the early Pleistocene conglomerate is far lower than that on the Holocene aeolian sand. These findings indicate that the topographic scarp composed of Holocene aeolian sand was produced by external dynamic process rather than faulting,and that the Tarwan Fault is an early-middle Pleistocene thrust fault.

So far,although many reservoirs have been built,few of them have triggered seismicity.In order to study the mechanism of triggered seismicity so as to provide useful reference data for site selection of dams,we analyze the effects of hydro-geological structures and gravity loads in reservoir areas,and draw some conclusions:1)Rapid-response type seismicity may occur when there are some abandoned mines or karst caves;2)Based on the results of numerical calculation,Coulomb stress on different faults changes differently when the gravity load of the reservoir increases or decreases.The calculation results change with the stress field,the fault parameters and the relative position of the fault and reservoir.When the reservoir is on the down-thrown block and the fault dip is large,the fault may be more unstable because of the gravity load.In this case,Coulomb stress may increase locally on normal dip-slip faults,but on whole reverse dip-slip fault.Under the same fault occurrences,the Coulomb stress change of a normal dip-slip fault is larger than that of the reverse dip-slip fault.When the coefficient of friction is 0.6,the quantity of Coulomb stress change induced by gravity load is about 1/4 as much as that induced by pore water pressure in the fracture of the saturated karst cave.So,more attention should be paid to pore water pressure in the fracture.

Based on teleseimic data for the period of 2007 to 2010 acquired from the Three Gorges reservoir(Chongqing section)seismic network and Chongqing regional seismic network,we obtained the crustal thickness and Possion's ratio of the area through receiver function method.The results show that the crustal thickness ranges from 38.9km to 50.9km.Station CHK in northeastern Chongqing has the largest thickness which is about 50.9km;the thinnest crust is 38.9km under the station ROC in the west of Chongqing,and Poisson's ratio is about 0.27.The results show that the maximum Posson's ratio is beneath station JIZ in the east of the Chongqing section of Three Gorges Reservoir area,and the minimum Possion's ratio is beneath the station WUL,which is 0.228.In comparison with the Poisson medium(0.25),its maximum deviates up to 20.8%,and the minimum deviates by-8.80%.The Bouguer gravity anomaly often reflects subsurface density and crustal thickness variation.In this paper,the two agree with each other.The largest negative Bouguer anomaly is between CHK(50.9km)and WUX(49.7km),where the crust is the thickest.The smallest negative Bouguer anomaly is between ROC(38.9km)and YUM(41km),where the crust is the thinnest.

Complex terrain causes great MT noise.This paper puts forward a modeling technique of FEM using adaptive topography and quadratic element based on studies of some scholars.This technique can model all kinds of complicated terrain and geoelectric bodies preferably.The numeric modeling,calculation of the auxiliary field and definition of resistivity are deduced by electromagnetic equations.Lastly,several examples show the method is rapid,effective and of high accuracy.

Songhuajiang-Liaohe Basin is surrounded by several folded mountains,with some major deep faults running across them.Among these faults,the Tanlu Fault is one of biggest active faults in the east China continent.This kind of geological environment makes Liaoning and its adjacent areas be capable of highly active tectonic movement and high seismicity.As crustal thickness and Poisson ratio are closely related to seismogenic structure,studying on these parameters will be very important for us to understand the seismogenic process of Liaoning and its neighboring regions.In this work,teleseismic P wave records from 15 permanent broadband seismic stations in Liaoning province are collected and processed by inverse convolution method in spectral domain to get the P wave receiver functions.The H-Kappa stacking method is further used to obtain the crustal thickness and Poisson ratio under each seismic station.The result shows that Poisson ratio in this region is between 0.25and 0.29,and crustal thickness ranges from 31km to 36km.Comparing with the Harbin Basin,the crustal thickness of the west and east fold belts in this region is about 2～4km thicker.The distribution pattern of crust thickness shows that the crust is getting thicker from east to west and from north to south,with an average crustal thickness about 31km in Songliao Basin.This pattern shows that the Songhuajiang-Liaohe Basin is a typical rift basin,its seismogenic process may mainly be controlled by the subsidence of the basin and the horizontal extension from the east and the west boundaries.

We used the radar data from the satellite ALOS/PALSAR of Japan and the differential interferometric synthetic aperture radar(D-InSAR)technology to derive the coseismic displacement field produced by the M_S 8.0 Wenchuan,Sichucan Province,China earthquake on 12 May 2008.Based on processing SAR data of 7 tracks and 112 scenes by the two-pass method,we obtained the interferometric map of 450km×450km covering the causative fault and determined the distribution range of incoherent zones.Proper phase unwrapping was performed to these tracks of continuous and discontinuous phases,yielding digital image of the interferometric displacement field,which is analyzed by displacement contours and the profile across the fault.The result shows that the Wenchuan M_S 8.0 earthquake has produced a vast area of surface deformation along the Yingxiu-Beichuan Fault,primarily concentrated in a near-field range of 100km wide on the both sides of the causative fault.In this field,the 250km-long and 15～35km wide incoherent zone nearby the fault has suffered the largest deformation with surface ruptures,of which the amount is too large to measure by InSAR.The secondary deformed areas are 70km wide on each side of the incoherent zone,where envelope-like fringes are clear,continuous and converging towards the fault,indicative of increasing gradient and amplitude of displacements which exhibit sunk north wall and uplifted south wall in sight line.With respect to the north and south edges of the data track,the maximum subsidence in the north wall is 110～120cm appearing northeast of Wenhcuan and Maoxian,and a big range of descents of 55～60cm occurred nearby the epicenter south of Lixian.The largest uplift 120～135cm in the south wall is present at the epicenter west of Yingxiu,north to Dujiangyan and around Beichuan.The maximum relative displacement between the north and south walls is up to 240cm that appears nearby the epicenter west of Yingxiu and north to Dujiangyan.In the far-field 70km away from the incoherent zones on the both sides of the causative fault,there are sparse fringes indicative of displacements less than 10cm.The profile across the fault indicates a highly variable gradient of deformation with profound heterogeneity near the fault and in its hanging wall,and a relatively uniform deformation in the foot wall.These differences of deformation can be attributed to complicated thrust faulting.Our analysis suggests that the fault rupture of the Wenchuan earthquake is a relative thrust between the two walls of the fault.

Using D-InSAR technology and by processing 7 track 56 scenes ALOS/PALSAR data,the surface deformation field of Wenchuan,Sichuan earthquake on May 12,2008 has been extracted.The deformation field covers a 500km?450km area and crosses Jinchuan-Shimian,Heishui-Leshan,Songpan-Pengshan,Nanping-Jianyang,and Kangxian-Chongqing regions,including the severely earthquake-hit areas,such as Lixian,Wenchuan,Maoxian,Beichuan,Qingchuan,and so on.The results show that the deformation field scope is large and the Sichuan basin has been deformed to different degrees.The incoherent belt near earthquake fault shows that the main earthquake surface rupture zone is on the Beichuan-Yingxiu Fault zone.The trackable surface rupture zone runs from the southwest of Yingxiu near the macroscopic epicenter to the north of Suhe in Qingchuan county,about 230km long.The southwest section of the seismogenic fault from Wenchuan to Maoxian shows an incoherent band width obviously larger than that of other incoherent parts,which is closely related to the surface rupture from Dujiangyan to Anxian on the Pengxian-Guanxian Fault(the Mountain Front Fault),and this surface rupture zone is about 70km long.Away from the seismic fault region,the northwest wall of the fault uplifted and the southeast wall subsided.However,both walls in the vicinity of the seismic fault uplifted locally,and along the fault the distribution is very uneven,showing strong segmentation,which indicates the fault is characterized by reverse thrust.The differences of epicentral positions and earthquake origin time given by Harvard,USGS,NEIC,CENC also show that the Wenchuan earthquake rupture process is a multi-point breakdown process.The largest relative deformation amounting to 260cm occurred in the epicentral region on the west of Yingxiu;if converted into vertical deformation,the relative vertical deformation of the two regions is up to 3.3m.In Ya'an and Emei mountain area,the settlement is about 35cm.In Chongqing and to its south,there is about 25cm small-scale uplift.

Field investigation on the surface ruptures of the M_S8.0 Wenchuan earthquake along the segment between Beichuan and Qingchuan shows that there is one surface rupture zone developed on this segment,which extends generally along the Beichuan-Qingchuan Fault zone.Observation at Huangjiaba Chenjiaba,Guixi,Pingtong,Nanba,and Shikan suggests that the surface ruptures on this segment spread continuously along the trend of the fault,with single structure and a length of 60～90km.The surface rupture has not reached Guanzhuang of Qingchuan county.The observable rupture zone is about 62km,between Beichuan and Shikan,trending 20°～55° in general,dipping NW with an angle of 70°,showing mainly thrusting with dextral strike-slipping.The most distinct feature of the surface ruptures of this earthquake is the vertical surface bending,which indicates the thrusting of the deep fault.Its horizontal motion on this segment displays as dextral strike slipping,without sinistral slipping component.The value of the vertical coseismic displacements decreases gradually from 3m at Huangjiaba to about 1.5m at Nanba and Shikan;The amount of the dextral displacements does not change evidently,generally between 1.5m and 2.0m.Features of the surface rupture show that the causative tectonics of this M_S8.0 Wenchuan earthquake is the Yingxiu-Beichuan-Qingchuan Fault,whose movement is characterized mainly by thrusting,with a dextral slipping component,and the thrusting direction is from west to east.

The Longmenshan Fault zone is an important thrust belt on the eastern margin of the Qinghai-Tibet Plateau,consisting of the back-range,the central and the front-range faults,which differ from each other in size and activity.The rupture zone of the Wenchuan earthquake of 12 May 2008 occurred over a length of～270km along the Yingxiu-Beichuan Fault(a segment of the Central Fault)and a length of～70km along the Guanxian-Anxian Fault(a segment of the Front-Range Fault).The northern end of the fracture zone is at the Nanba region in Central Fault.In this work,we make a detailed field investigation on the northeast segment of the Longmenshan Fault zone.Qingchuan Fault is the northeast segment of the Longmenshan Back-range Fault,and the Chaba-Lin'ansi Fault is the northeast segment of the Longmenshan Central Fault.Along the above two faults,we make geological and geomorphologic mapping of Tuguanpu,Da'an and Hujiaba regions,where the Qingchuan Fault runs through the Tuguanpu and Da'an area,and Chaba-Lin'ansi Fault runs through the Hujiaba area.Based on the field investigation,there are five terraces in the northeast Longmenshan area along the major rivers.The height above the river of T1 terrace is about 3～5m,and the formation time is Holocene.The heights of T2 and T3 terraces are 10m and 30～35m above the river,and the deposition time of alluvium and diluvium is Late Pleistocence.The remnant of T4 terrace's sediment covers on some hills,with the height above the river of about 60～70m.In the remnant,granite cobble and sandstone cobbles have been air slaked,these gravels have the shapes only.T5 terrace's height is about 90m,the sediment on it has been eroded.Qingchuan Fault and Chaba-Lin'ansi Fault were strongly active faults in the times before T3 and after T4 formed.Some fault grooves were formed on T4 or T5 terrace,they have 30～180m in width,and 8～20m in depth.The vertical displacement of T4 terrace's gravels is 10～15m.Fault groove didn't form on T3 terrace,or the terrace height on a fault wall is consistent with other fault wall.At some places,T3 terrace's gravels overlie the fault zone.

In the surveying of earthquake active fault,many methods in geology,geophysics,geochemistry,geodetic survey,and remote sensing,have been widely used,resulting in various formats of surveying data and interpretation data.In this paper,we use ESRI ArcGIS 3D Analyst as interactive 3D graphics environment and present a solution for visualizing,interactive perspective viewing,and analyzing of all active fault surveying data and explanation data.

Based on 44 ¹⁴C dates of humic acids and humins under different weather conditions,a statistics analysis was made to estimate their performance in paleosols.The following suggestions are reached:(1)A normal distribution analysis for HA/HM values deduced from 44 ¹⁴C dates results in average value of 0.98 with standard deviation of 0.20.This seems that the humin may be the oldest fraction of soil and its ¹⁴C age can represent the age of the paleosol.(2)The relationship between HA/HM value and the age of paleosol samples shows that the ages of humic acid and humin are indistinguishable for samples deposited in late Quaternary,but are obviously different from paleosol samples in Holocene.Their different behaviors in late Quaternary and Holocene may be related to the pollutant due to Holocene soil exposed to the surface and easily influenced by pollutant.Therefore it is suggested to use the different fractions for Holocene soil to obtain reliable radiocarbon ages for soil samples.(3)Assuming that the modern carbon pollutant entered into soil one-off,the amount of modern carbon into original carbon is estimated to be about 1.49% for late Quaternary soil sample,but this value increases to 21.37% in Holocene soil.Therefore,the amount of pollutant for Holocene soil is over 15 times than that for late Quaternary soil.If such pollutant continues to enter into soil with similar quantity during deposition,the impact percentages are 5.71% and 30.46% for late Quaternary and Holocene soil samples,respectively.The amount of modern carbon by continuously entering into soil is 2.6 times that of the one-off entering into soil for one sample in the same condition.It is further needed to state that which fractions could obtain more reliable ages for soil samples still depends on other factors such as geomorphic location,climatic zone,and soil type.

This paper introduces a simple and practical way to construct quenching calibration curve for tritium DPM measurements basing on efficiencies of a series of known activity standard sources and quenching parameter SQP(E)used to define the quench level in Quantulus 1220.Ten standard sources and two test samples were prepared with tritium-free water as quenching materials and progressively added to Hisafe 3 cocktail.A linear curve or polynomial function curve was fitted with each pair of quench parameter SQP(E)and efficiency of standard source.The test sample demonstrated that the error of linear curve was small within routine quenching range of 776 to 785.Therefore,the quenching calibration curve can be beneficial to improving accuracy and reliability of tritium counting.