The reconstruct of the stick-slip and creep histories is essential for understanding fault activities and seismic hazard assessment. Distinguishing stick-slip and creep using geodetic technology has become a hot research area in recent years, but distinguishing and estimating seismic slip and creep on geological timescales(e.g., over hundreds of years)is challenging due to the lack of historical, geodetic and remote sensing data extending back more than a few hundred years. This study uses a newly developed dating technique(rock surface optically-stimulated-luminescence(OSL)dating)combined with the OSL decay parameters of granite samples from the Langshan fault in Inner Mongolia to simulate optically stimulated OSL-depth curves and depths of half saturation of luminescence signal under various scenarios such as fault seismic slipping, creeping, and erosion of colluvial wedge. The study compares these OSL-depth profiles, especially the depths of the half saturation, under different slipping modes, and summarizes their features.

During fault seismic slip, samples at different heights along the fault scarp display a “step-like” distribution pattern at their depths of half saturation. While during creep, however, they exhibit a “slope-like” pattern. Such differences may lie in that the slope during accelerating creeping is steeper than the slope during constant-speed creeping. Correspondingly, the resolution of residual luminescence-depth profile and depth of half saturation is also higher during accelerating creeping. During intra-earthquake creep events between seismic slip occurrences on the bedrock fault scarp, the distribution of half-saturation depth in the samples includes segments resembling both “steps” and “slopes”, which indicate the seismic slip and creep activities of the fault respectively. If the samples at the base of the colluvial wedge have had a sufficiently long last exposure time, the luminescence-depth profile and half-saturation depth distribution due to the erosion of the colluvial wedge would be approximately the same as in the three-phase seismic slip scenario. This indicates that samples previously buried by the colluvial wedge may be considered within the seismic displacement. Conversely, if the last exposure time of the base samples at the base of the colluvial wedge is short, the bleaching depth of the luminescence signal of these base samples will be noticeably shallower than that of the other samples within the seismic displacement, indicating the observed erosion of the colluvial wedge in this case. Furthermore, the seismic displacement ideally should include the buried location of the colluvial wedge. Therefore, when the luminescence curves and half-saturation depth distributions fail to identify the presence of the colluvial wedge, it is acceptable to include the buried location of the colluvial wedge in the seismic displacement calculation. Conversely, the luminescence-depth curves and half-saturation depth distributions document the erosion caused by the colluvial wedge. The simulation results demonstrate that this method can effectively distinguish between fault slipping and creeping, obtain corresponding displacements, and potentially record the erosion of colluvial wedge.

This study also analyzes the temporal resolution of the method for distinguishing fault activity times and the spatial resolution for quantifying displacements. The specific situation is as follows. When exposure age of the bedrock fault scarp is within a thousand years, the rock surface OSL dating method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval of hundreds of years. When exposure age of the bedrock fault scarp is in the range of 10⁰-10¹ka, the method can easily distinguish types of active slips and seismic displacements for the earthquakes with a recurrence interval exceeding a thousand years. When exposure age of the bedrock fault scarp is over ten-thousand years, the resolution of this method may be significantly reduced. The spatial resolution of seismic displacements using this method depends on interval between sampling and testing samples, typically in 10~30cm.

The M_S7.1 earthquake in Wushi, Xinjiang on January 23, 2024, represents the largest earthquake in the Tianshan seismic belt since the 1992 Suusamyr M_S7.3 earthquake in Kyrgyzstan. Preliminary precise aftershock localization and initial field investigations indicate an NE-trending aftershock zone with a length of 62km that is concentrated at the mountain-basin transition area. This event produced geological hazards, including slope instability, rockfalls, rolling stones, and ground fissures, primarily within a 30-kilometer radius around the epicenter. The epicenter, located approximately 7 kilometers north of the precise positioning in this study, witnessed a rapid decrease in geological hazards such as collapses, with no discernible fresh activity observed on the steep fault scarp along the mountainfront. Consequently, it is inferred that the causative fault for this main shock may be an NW-dipping reverse fault, with potential rupture not reaching the surface.

Moreover, a surface rupture zone with a general trend of N60°E, extending approximately 2 kilometers, and displaying a maximum vertical offset of 1m, was identified on the western side of the micro-epicenter at the Qialemati River. This rupture zone predominantly follows the pre-existing fault scarp on higher geomorphic surfaces, indicating that it is not new. Its characteristics are mainly controlled by a southeast-dipping reverse fault, opposite in dip to the causative fault of the main shock. The scale of this 2-kilometer-long surface rupture zone is notably smaller than the aftershock zone of the Wushi M_S7.1 earthquake. Further investigation is warranted to elucidate whether or not the M_S5.7 aftershock and the relationship between the SE-dipping reverse fault responsible for the surface rupture and the NW-dipping causative fault of the main shock produced it.

Fold scarps, a type of geomorphic scarp developed near the active hinge of active folds due to the local compressive stress, are formed by folding mechanisms of hinge migration or limb rotation. At present, there are several proven methods, which are only based on the fold scarp geometry combined with the occurrences of underlying beds and do not use the subsurface geometry of thrust fault and fold to obtain the folding history. The use of these methods is of great significance to illuminate the seismic hazards and tectonic processes associated with blind thrust systems.
The Sansuchang fold-thrust belt is a fault-propagation anticline controlled by the Sansuchang blind thrust fault located in the southern Longmen Shan foreland area. Previous study used the area-depth method to calculate the shortening history of the Sansuchang anticline since the late Pleistocene(73~93ka)based on the terrace deformation of Qingyijiang River. However, due to the serious erosion damage to the terrace after its formation, the shortening history obtained by incomplete terrace deformation needs to be further verified.
A~9km long scarp was found on the Dansi paleo-alluvial fan on the eastern limb of the Sansuchang fold-thrust belt. According to the detailed field investigation and the fold geometry built by the seismic profile, we found the scarp is near the synclinal hinge, which separates beds dipping 10°~17° and 43°~57° east and parallels with the Sansuchang fold hinge. Therefore, we determined the scarp is a fold scarp formed by the forelimb hinge migration of the fault-propagation fold.
The maximum height of the scarp, extracted by the swath topographic profile across the scarp, is about 28~35m. According to the parameters of the fold scarp height, the underlying beds dip angle near the fold scarp, and the quantitative geometric relationship between shortening and the blind Sansuchang thrust fault, it can be estimated that, after the deposition of the Dansi paleo-pluvial fan((185±19)ka), the anticline forelimb horizontal shortening rate is~0.1mm/a, the fault tip propagation rate of the Sansuchang blind fault is(0.5+0.3/-0.1)mm/a, and the total shortening rate of the Sansuchang anticline is(0.3+0.2/-0.1)mm/a.
The folding rates of the Sansuchang fold-thrust belt since the late middle Pleistocene has been obtained by the local deformation characteristics of the fold scarp in this study. The result is basically consistent with the shortening rate since late Pleistocene obtained by complete terrace deformation across the anticline, which proves that the shortening rate of the Sansuchang anticline is relatively stable at~0.3mm/a. It provides a new idea for studying the activity characteristics of fold-thrust belts in the southern Longmen Shan foreland thrust belt area with a fast denudation rate and discontinuous geomorphic surface.

The Altyn Tagh Fault(ATF)is one of the most prominent active strike-slip faults in the India-Eurasia collision. Fresh features of surface ruptures, which are attributed to seismic events taking place in the last millennium, are identified at several sites along the Che'erchen River to Qingshui River section on the central part of ATF. Accurate chronology of these earthquake events would help understand the spatial-temporal relationship of the recent earthquakes. However, great difficulties are encountered. The central ATF is located in the arid area, and the vegetation cover is so limited that rare organic materials appropriate for radiocarbon dating can be found in the sediments. Luminescence dating technique may serve as an alternative to directly determine the burial ages of the earthquake related sediments. The optically stimulated luminescence(OSL)signal of quartz, which has been widely employed for luminescence dating, displays unwanted charateristics for accurate dating. Firstly, the quartz OSL signal is not sensitive to irradiation, which leads to low signal-to-noise ratio or even no measurable quartz OSL signal. Secondly, the targeted samples of the last millennium are very young, and the radiation dose received during the burial is expected to be less than 3~4Gy, which futher deteriorates the signal-to-noise ratio of the quartz OSL signal. Therefore, quartz OSL signal is not appropriate for dating the sediments relevant to the recent earthquakes on ATF.
The infrared stimulated luminescence(IRSL)signal of potassium feldspar is an alternative, and it is in usual an order of maginitude more sensitive to raidation than the quartz OSL signal. The enhanced signal-to-noise ratio makes it applicable to young samples. The post-IR IRSL signal has been successfully applied to date the sediments beyond the Holocene, however, the relatively slow bleaching of the post-IR IRSL signal poses challenges on applying it to young sediments, especially for the sediments deposited during the last millennium. In this study, we investigated the feasibility of using post-IR IRSL signal from potassium feldspar to date the earthquake events of the last millennium by employing modern sag pond deposits with different sorting and expected equivalent dose(D_e)of 0Gy. Choosing an appropriate measurement procedure and identifying the well bleached pottassium feldspar grains are essential for post-IR IRSL dating of young sediments. The non-fading characteristic of the post-IR IRSL₁₇₀ signal measured at 170℃ following a prior IR stimulation at 110℃ was verified by employing the D_e plateau test with respect to the signal integration interval and IR stimulation temperature together. Reducing the amount of potassium feldspar grains mounted on an aliquot would help reveal the among grains variation of bleaching level of post-IR IRSL₁₇₀ signal before depostion and identify the most sufficiently bleached grains. Therefore, the post-IR IRSL₁₇₀ D_e values of 2mm aliquots were measured for three samples with different sedimentary textures. The median of D_e distribution of well sorted and stratified sag pond deposits is consistent with the minimum D_e value inferred from the minimum age model(MAM-3) and finite mixture model(FMM), while for the poorly sorted deposits, the median is significantly overestimated compared with the minimum D_e values from the MAM-3 and the FMM. The minimum D_e values of 0.6~0.8Gy of all three samples are consistent with the unbleachable residual dose previously reported for post-IR IRSL signals measured at similar temperature for well bleached samples. It implies that by combined use of small aliquot and statistical age models, the well-bleached potassium feldspar grains could be identified. Such an intrinsic unbleachable component needs to be properly corrected when earthquake events of last millennium are to be dated in this area. Otherwise, the post-IR IRSL₁₇₀ age would be overestimated by 200~300a.
The post-IR IRSL₁₇₀ procedure investigated in this study is not only applicable for dating the paleoearthquake events along the Altyn Tagh Fault, but also with great potential to be applied to other tectonically active area. With consideration of the potential variability in post-IR IRSL signal characteristics of potassium feldspar grains from different origins, the signal stability needs to be routinely inspected. The modern analog sample would also be informative for justifying the measurement procedure and analytical method employed.

Tianshan is one of the longest and most active intracontinental orogenic belts in the world. Due to the collision between Indian and Eurasian plates since Cenozoic, the Tianshan has been suffering from intense compression, shortening and uplifting. With the continuous extension of deformation to the foreland direction, a series of active reverse fault fold belts have been formed. The Xihu anticline is the fourth row of active fold reverse fault zone on the leading edge of the north Tianshan foreland basin. For the north Tianshan Mountains, predecessors have carried out a lot of research on the activity of the second and third rows of the active fold-reverse faults, and achieved fruitful results. But there is no systematic study on the Quaternary activities of the Xihu anticline zone. How is the structural belt distributed in space?What are the geometric and kinematic characteristics?What are the fold types and growth mechanism?How does the deformation amount and characteristics of anticline change?In view of these problems, we chose Xihu anticline as the research object. Through the analysis of surface geology, topography and geomorphology and the interpretation of seismic reflection profile across the anticline, we studied the geometry, kinematic characteristics, fold type and growth mechanism of the structural belt, and calculated the shortening, uplift and interlayer strain of the anticline by area depth strain analysis.
In this paper, by interpreting the five seismic reflection profiles across the anticline belt, and combining the characteristics of surface geology and geomorphology, we studied the types, growth mechanism, geometry and kinematics characteristics, and deformation amount of the fold. The deformation length of Xihu anticline is more than 47km from west to east, in which the hidden length is more than 14km. The maximum deformation width of the exposed area is 8.5km. The Xihu anticline is characterized by small surface deformation, simple structural style and symmetrical occurrence. The interpretation of seismic reflection profile shows that the deep structural style of the anticline is relatively complex. In addition to the continuous development of a series of secondary faults in the interior of Xihu anticline, an anticline with small deformation amplitude(Xihubei anticline)is continuously developed in the north of Xihu anticline. The terrain high point of Xihu anticline is located about 12km west of Kuitun River. The deformation amplitude decreases rapidly to the east and decreases slowly to the west, which is consistent with the interpretation results of seismic reflection profile and the calculation results of shortening. The Xihu anticline is a detachment fold with the growth type of limb rotation. The deformation of Xihu anticline is calculated by area depth strain analysis method. The shortening of five seismic reflection sections A, B, C, D and E is(650±70) m, (1 070±70) m, (780±50) m, (200±40) m and(130±30) m, respectively. The shortening amount is the largest near the seismic reflection profile B of the anticline, and decreases gradually along the strike to the east and west ends of the anticline, with a more rapidly decrease to the east, which indicates that the topographic high point is also a structural high point. The excess area caused by the inflow of external material or outflow of internal matter is between -0.34km² to 0.56km². The average shortening of the Xihubei anticline is between(60±10) m and(130±40) m, and the excess area caused by the inflow of external material is between 0.50km² and 0.74km². The initial locations of the growth strata at the east part is about 1.9~2.0km underground, and the initial location of the growth strata at the west part is about 3.7km underground. We can see the strata overlying the Xihu anticline at 3.3km under ground, the strata above are basically not deformed, indicating that this section of the anticline is no longer active.

In the realm of the numerical simulation, finite difference method and finite element method are more intuitive and effective than other simulation methods. In the process of simulating seismic wave propagation, the finite differences method is widely used because of its high computational efficiency and the advantage of the algorithm is more efficient. With the demand of precision, more and more researchers have proposed more effective methods of finite differences, such as the high-order staggered-grid finite differences method, which can restore the actual process of wave propagation on the premise of ensuring accuracy and improving the efficiency of operation. In the past numerical simulation of seismic wave field, different models of isotropic medium are mostly used, but it is difficult to reflect the true layer situation. With the research demand of natural seismology and seismic exploration, the research on anisotropic media is more and more extensive. Transversely isotropic(TI)media can well simulate the seismic wave propagation in the formation medium, such as gas-bearing sandstone, mudstone, shale et al., the character of TI media is reflected by introducing the Thomsen parameters to reflect its weak anisotropy of vertical direction by using Thomson parameter. Therefore, studying the process of seismic wave propagation in TI media can restore the true information of the formation to the greatest extent, and provide a more reliable simulation basis for the numerical simulation of seismic wave propagation. In the geodynamic simulation and the numerical simulation of the seismic wave field, under the limited influence of the calculation area, if no boundary conditions are added, a strong artificial boundary reflection will be generated, which greatly reduces the validity of the simulation. In order to minimize the influence of model boundaries on the reflection of seismic waves, it is often necessary to introduce absorbing boundary conditions. At present, there are three types of absorption boundary conditions: one-way wave absorption boundary, attenuation absorption boundary, and perfectly matched layer(PML)absorption boundary. In terms of numerical simulation of seismic waves, the boundary absorption effect of PML is stronger than the first two, which is currently the most commonly used method, and it also represents the cutting-edge development direction of absorption boundary technology. The perfectly matched layer absorbing boundary is effectively applied to eliminating the reflective waves from model boundaries, but for transversely isotropic medium, the effect of the absorbing is not very well. For this reason, the elastic dynamic wave equations in transversely isotropic media are derived, and we describe a second-order accurate time, tenth-order accurate space, formulation of the Madariaga-Virieux staggered-grid finite difference methods with the perfectly matched layer(PML)are given. In addition, we have established vertical transversely isotropic(VTI)media and arbitrary inclined tilted transversely isotropic(TTI)media models, using a uniform half-space velocity model and a two-layer velocity model, respectively. By combining the actual geoscience background, we set the corresponding parameters and simulation conditions in order to make our model more research-oriented. When setting model parameters, different PML thickness, incident angle, source frequency and velocity layer models were transformed to verify the inhibition of boundary reflection effect by PML absorption boundary layer. The implementations of this simulation show that the formula is correct and for the transversely isotropic(TI)media of any angular symmetry axis, when the thickness of the PML layer reaches a certain value, the seismic wave reflection effect generated by the artificial boundary can be well suppressed, and the absorption effect of PML is not subject to changes in incident angle and wave frequency. Therefore, the results of our study indicate that our research method can be used to simulate the propagation process of seismic waves in the transversely isotropic(TI)media without being affected by the reflected waves at the model boundary to restore the actual formation information and more valuable geological research.

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.

The M_W6.6 Arketao earthquake occurred on November 25, 2016 in Muji Basin of the Kongur extensional system in the eastern Pamir. The region is the Pamir tectonic knot, one of the two structural knots where the India plate collides with the Eurasian plate. This region is one of the most active areas in mainland China. The seismogenic structure of the earthquake is preliminarily determined as the Muji dextral-slip fault which locates in the north of Kongur extensional system. Based on field surveys of seismic geological hazard, and combined with the characteristics of high altitude area and the focal mechanism solution, this paper summarizes the associated distribution and development characteristics of sandy soil liquefaction, ground fissures, collapse, and landslide. There are 2 macroscopic epicenters of the earthquake, that is, Weirima village and Bulake village. There are a lot of geological hazards distributed in the macroscopic epicenters. Sand liquefaction is mainly distributed in the south of Kalaarte River, and area of sand liquefaction is 1 000m². The liquefaction material gushed along the mouth of springs and ground fissures, because of the frozen soil below the surface. More than 60% of soil liquefactions are formed in the mouth of springs. According to the trenching, these liquefactions occurred in 1.8 meters underground in the gray green silty clay and silty sand layers. The ground fissures are mainly caused by brittle failure, and the deformation of upper frozen soil layer is caused by the deformation of lower soil layer. The ground fissures at Weirima village are distributed in a chessboard-like pattern in the flood plain of Kalaarte River. In the Bulake village, the main movement features of the ground fissure are tension and sinistral slip, and the directions of ground fissures are 90°~135°. The collapse and landslide are one of the important geological disasters in the disaster area. The rolling stones falling in landslide blocked the roads and smashed the wire rods, and the biggest rolling stone is 4 meters in length. We only found a small landslide in the earthquake area, but there are a large number of unstable slopes and potential landslides in the surroundings. The ground fissures associated with sand liquefaction are an important cause of serious damage to the buildings.

By dating detrital zircon U-Pb ages of deposition sequence in foreland basins, we can analyze the provenance of these zircons and further infer the tectonic history of the mountain belts. This is a new direction of the zircon U-Pb chronology. The precondition of using this method is that we have to have all-around understanding to the U-Pb ages of the rocks of the orogenic belts, while the varied topography, high altitude of the zircon U-Pb ages of the orogenic belts are very rare and uneven. This restricts the application of this method. Modern river deposits contain abundant geologic information of their provenances, so we can probe the zircon U-Pb ages of the geological bodies in the provenances by dating the detrital zircon U-Pb ages of modern rivers' deposits. We collected modern river deposits of 14 main rivers draining from Pamir, South Tian Shan and their convergence zone and conducted detrital zircon U-Pb dating. Combining with the massive bed rock zircon U-Pb ages of the magmatic rocks and the detrital zircon U-Pb ages of the modern fluvial deposit of other authors, we obtained the distribution characteristics of zircon U-Pb ages of different tectonic blocks of Pamir and South Tian Shan. Overlaying on the regional geological map, we pointed out the specific provenance geological bodies of different U-Pb age populations and speculated the existence of some new geological bodies. The results show that different tectonic blocks have different age peaks. The main age peaks of South Tian Shan are 270~289Ma and 428~449Ma, that of North Pamir are 205~224Ma and 448~477Ma, Central Pamir 36~40Ma, and South Pamir 80~82Ma and 102~106Ma. The Pamir syntaxis locates at the west end of the India-Eurasia collision zone. The northern boundary of the Pamir is the Main Pamir Thrust(MPT)and the Pamir Front Thrust(PFT). In the Cenozoic, because of the squeezing action of the India Plate, the Pamir thrust a lot toward the north and the internal terranes of the Pamir strongly uplifted. For the far-field effect of the India-Eurasia collision, the Tian Shan on the north margin of the Tarim Basin also uplifted intensely during this period. Extensive exhumation went along with these upliftings. The material of the exhumation was transported to the foreland basin by rivers, which formed the very thick Cenozoic deposition sequence. These age peaks can be used as characteristic ages to recognize these tectonic blocks. These results lay a solid foundation for tracing the convergence process of Pamir and South Tian Shan in Cenozoic with the help of detrital zircon U-Pb ages of sediments in the foreland basin.

There are many examples of exposed or buried rock surfaces whose age is of interest to geologists and archaeologists. Luminescence dating is a well-established method of absolute chronology which has been successfully applied to a wide range of fine-grained sediments from hundreds of years to several hundred thousand years. Optical stimulated luminescence (OSL) has been recently proposed as a new method to date these rock surfaces (Laskariset al., 2011; Sohbatiet al., 2012a; Chapotet al., 2012; Pedersonet al., 2014; Sohbatiet al., 2015; Freieslebenet al., 2015). The basic principle is that luminescence signal of rock surface will soon decay when the rock is exposed to sunlight. When the rock surface is turned to be buried side, the OSL signal begins to accumulate again. With the variation of residual luminescence with depth, it is possible to estimate exposure and burial history of the rock. This article describes briefly the different luminescence dating methods for rock surfaces, its progress, application examples and present problems. For instance, Sohbatiet al. (2011) studied the depth dependence of the bleaching of the IRSL signal from granitic rocks, Laskaris and Liritzis (2011) proposed a mathematical function to describe the attenuation of daylight into rock surfaces, Sohbatiet al. (2012a) developed their model to include the environmental dose rate, Sohbatiet al. (2012b) overcame the problem of parameter estimation by using a known-age road-cut sample for calibration, Sohbatiet al. (2012c) further developed the OSL surface exposure dating model by including the simultaneous effect of daylight bleaching and environmental dose rate, and so on. These studies indicate that OSL dating method for rock surface can be applied widely to studies of geological and geomorphological evolution, archeology and Quaternary tectonic activity.

The M_W6.6 Arketao earthquake,which occurred at 14:24:30 UTC 25 November 2016 was the largest earthquake to strike the sparsely inhabited Muji Basin of the Kongur extension system in the eastern Pamir since the M 7 1895 Tashkurgan earthquake.The preliminary field work,sentinel-1A radar interferometry,and relocated hypocenters of earthquake sequences show that the earthquake consists of at least two sub-events and ruptured at least 77km long of the active Muji dextral-slip fault,and the rupture from this right-lateral earthquake propagated mostly unilaterally to the east and up-dip.Tectonic surface rupture with dextral slip of up to 20cm was observed on two tens-meter long segments near the CENC epicenter and 32.6km to the east along the Muji Fault,the later was along a previously existing strand of the Holocene Muji fault scarps.Focal mechanisms are consistent with right-lateral motion along a plane striking 107°,dipping 76° to the south,with a rake of 174°.This plane is compatible with the observed tectonic surface rupture.More than 388 aftershocks were detected and located using a double-difference technique.The mainshock is relocated at the Muji Fault with a depth of 9.3km.The relocated hypocenters of the 2016 Arketao earthquake sequence showed a more than 85km long,less than 8km wide,and 5~13km deep,NWW trending streak of seismicity to the south of the Muji Fault.The focal mechanism and mapping of the surface rupture helped to document the south-dipping fault plane of the mainshock.The listric Muji Fault is outlined by the well-resolved south-dipping streak of seismicity.The 2016 Arketao M_W6.6 and 2015 Murghob M_W7.2 earthquakes highlight the importance role of strike-slip faulting in accommodating both east-west extensional and north-south compressional forces in the Pamir interior,and demonstrate that the present-day stress and deformation patterns in the northern Pamir plateau are dominant by east-west extension in the shallow upper crust.

The fold scarp, a type of geomorphic scarp on the land surface formed by folding without fault offsets on the surface, can be used to constrain folding and slip rates and kinematics and to reconstruct a folding history despite a lack of full constraints on the subsurface structure. Recently, the conceptual, geometric, and kinematic models of fold scarps formed by fault-bend folding(fault-bend fold scarp)were developed. But for other types of fold scarp, there are few detailed investigations till now.
Located at southern foreland of Chinese Tianshan, the Mingyaole anticline is interpreted to be a detachment fold. On the Kezilesu river terraces in the south limb, a series of detachment fold scarps occur. The height, width, and slope of fold scarps on the T₂ and T₃b terraces are ～16m/～40m/～25° and ～20m/～50m/～26° respectively. The scarp locations are correlated with an underlying synclinal hinge separating a 50° dip and a 15°dip domain and the strike of the scarp is parallel with the hinge. Detailed geologic and geomorphic mapping and dGPS survey data reveal important characteristics of detachment fold scarp. 1)The fold scarps are formed by synclinal hinge migration. 2)During initial growth, the height, width and slope of the fold scarp increase gradually. When the fold scarp's horizontal width increases to be at least twice that of the hinge, the slope will approach a maximum, and will subsequently remain constant even as the height and width continue to increase gradually. 3)The scarp height and underlying bedding dips on either side of the hinge can be used to calculate incremental shortening absorbed by the fold scarp. Based on the height ～16m of the fold scarp on the T₂ and its exposure age ～8.0ka, the shortening rate absorbed by south limb of the Mingyaole fold is estimated to be ～1.3mm/a. Despite similarities with fault-bend fold scarps, detachment-fold scarps have some pronounced differences, which suggest that the type of fold scarp should be defined prior to calculating folding rates.

The foreland basin of contractional orogen commonly occurs in thrust related fold. Quantitative constraint on fold's growing process is important to understand the spatial and temporal evolution of orogens, and for seismic hazard assessment and hydrocarbon resource prospect evaluation. Fluvial terrace, as a kind of widely distributed, easy dating and passively deformed geomorphic marker, is more and more applied to defining the growth mechanism and rates of active folds. Combining deformed fluvial terrace with pre-growth and growth strata, we can acquire the total shortening and the initiation age, and retrieve the whole evolving history of a fold.Based on geometry and kinematical characteristics, thrust related fold can be classified into fault bend fold, fault propagation fold and detachment fold. As occurred on the tip of a fault, the fault propagation fold and detachment fold are generally named fault tip fold. According to different stress situation, folding deformation includes no shear, simple shear and pure shear, and displays as two end-member models: kink band migration and limb rotation. In different models, the fluvial terrace shows different deformation characteristics, which can be used to distinguish the models.We summarized and discussed how to use deformed terraces to constrain the shortening rates and uplift rates of the sinusoidal and chevron flexural-slip fold, classical fault bend fold, as well as pure shear fault tip fold, and briefly introduced the conception of fold scarp. However, the natural fold is usually formed by combination of different mechanisms, which is much more complicated than the models mentioned. Therefore, the future study should be concentrated on modeling the fold produced by different mechanisms, rather than only one mechanism. In addition, we mentioned three different types of fold scarps: fold scarp occurring in classical fault bend fold and fold scarp formed by kink band migration and limb rotation in detachment fold.

In recent times, some moderate-large earthquakes occurred in active folds and thrusts, which seem not directly related with known active faults on the surface and did not form surface ruptures. Although such individual earthquakes might correspond to a known surface active fault, most of them occurred under active folds, formed by displacement of burial thrusts which are located at depth of tens kilometers beneath the folds. Stein named such earthquake as "folding earthquake". It is quite a challenging issue to study and assess the seismic hazards of folding earthquakes occurring in compressive tectonic regions with active folds and burial thrusts. Derived from active folding secondary faults such as flexural-slip faults, bend-moment faults, it is easier to identify that the fold itself. These secondary faults have coseismic slip at the surface and record the active history of seismogenic thrusts which provide an effective way to study the seismic activity of blind thrusts. Many flexural-slip fault scarps are developed on several terrace surfaces at the two limbs of Mingyaole anticline, located along the western margin of the Tarim Basin. These scarps mainly form on the limb of steep beds closest to active axial surfaces(dips of 74°～89°, 18°～20° and 45°～60°, separately), within a range of 50～1 200m from active axial surface, and most are 90～1 000m wide. Overall, the height of the flexural-slip fault scarps gradually deceases away from the active axial surface. These scarps occur at nearly equidistant or multiple distance spacing on the same terrace surface. The strike of the flexural-slip fault scarp is consistent with the strike of underlying bedrock, which is dominated by interbedded medium-thick layered sandstone or fine-grain sandstone with similar rock mechanical properties. Since the abandonment of terrace T3 at the south limb of the Mingyaole anticline, the shortening rate and uplift rate absorbed by flexural-slip faults are at least (1.0±0.2)mm/a, (1.2±0.1)mm/a, respectively. Movement of the flexural-slip faults is characterized by repeatability and neo-activity.

Folding growth in three dimensions involves shortening in transversal direction,uplift in vertical direction and lateral propagation in longitudinal direction. The impact of these three components changes along the fold's strike: the middle part is dominated by shortening and uplift,and deformation neighboring the fold tip involves not only shortening and uplift,but also strong lateral propagation. Previous studies are focused on the middle part,and the fold tip,a relatively special part,however,is poorly investigated. Thereby,how does the fold tip grow,what is the deformation difference between fold tip and the middle part,and how do terraces deform in response to folding growth？Our study to the southwestern tip of the Mingyaole anticline,located at the Pamir-Tianshan convergent zone,indicates terrace surfaces are strongly back-tilted,and display increasing dips with age,implying a limb rotation mechanism. According to the OSL ages of the T_2b,T_3b and T_4a,as well as a magnetostratigraphy age of underlying bedrock,rotation angle increments of the dip domain 46° display a parabola tendency with the age of<～0.35Ma,(93.9±18.7)ka,(82.6±16.5)ka and(19.4±2.9)ka,and the average rotation rate is>(0.13±0.01)°/ka,(0.08±0.02)°/ka,(0.05±0.01)°/ka and(0.04±0.01)°/ka,which display an obviously decreasing tendency too. However,the shortening rate absorbed by this dip domain keeps constant.The fluvial terraces display not only tilted and uplifted in response to the shortening and uplift of the fold,but deformed in response to lateral propagation. Toward west,density,width and depth of gullies on the terraces decrease,and elevation to the riverbed of the terrace surface,height of the terrace riser as well as rotation angles of terrace surfaces display a decreasing tendency too,both of which are consistent with the fold's western-ward propagation. Based on the magnetostratigraphy age of～1.6Ma at the Kapake valley section,the average western-ward lengthening rate is about 16～16.8mm/a.

Terrestrial in situ cosmogenic nuclides burial dating has a promising application in dating of late Cenozoic detrital sediments,for example,cave sediments,fluvial sediments and moraine.This method relies on a pair of cosmic-ray-produced nuclides that are produced in the same rock or mineral target at a fixed ratio,but have different half-lives.For example, ²⁶ Al and ¹⁰ Be are produced in quartz at ²⁶ Al :¹⁰ Be=6.75 :1.The ratio is not affected by latitude and altitude.After sediments are buried,the ratio would become less as time goes.Therefore, ²⁶ Al/¹⁰ Be ratio can be used as a geological clock.The dating range can be from several hundreds of thousand years to five million years.In this article,we introduce four methods and their applications: exposure-burial diagram method,depth profile method,isochron method, ²⁶ Al-²¹ Ne and ¹⁰ Be-²¹ Ne method.Exposure-burial diagram method is often applied to cave sediments dating, for exposure-burial history of cave deposits is easy.Depth profile method is applied to fluvial sediments dating.There is a good application for isochron approach in till-paleosol sequences in North America. ²⁶ Al-²¹ Ne and ¹⁰ Be-²¹ Ne method has a great potential applicaton in future for its larger dating time and less uncertainty than other methods.The dating method still has many problems.Firstly,there are no exact half-lives.For example,there is still controversy for ¹⁰ Be half-life.Its estimate is 1.51±0.06Ma or 1.36±0.07Ma.Secondly,it is also a debate how to determine nuclides' production rates.In addition,post-burial or preburial erosion rate,inheritance nuclides concentration,post-burial nuclide production,effect of post-burial or preburial muonic production,sediment rework,complicated exposure-burial history of sediments all bring great challenges to cosmogenic nuclides dating.

To carry out the project "Study on paleo-tsunami in east and southeast seashore area of China" supported by China Ministry of Science and Technology,we made a study tour to Japan in April,2007.In this visit,we investigated roughly the tsunami deposits in Ishinomaki Plain,Miyaki County,Japan,where a huge earthquake of M_W 9.0 occurred at March 11,2011.This earthquake caused a great tsunami along the northeast coast of Honsyu Island,Japan,bringing lots of death and huge economic loss.To understand the tsunami history in this area and the methods of investigating tsunami deposits,it is necessary to introduce briefly our investigation in Ishinomaki Plain,Miyaki County,Japan.Our investigation results demonstrated three tsunami events occurred in this area. The latest one occurred before 915 AD,when the Towada volcano erupted and the tephra from this eruption covered almost all of the Northeast Japan,corresponding to the 869 AD Jogan earthquake tsunami.

The Tashkurgan-Yarkant River,which is the upper reach of the Tarim River,originates from the Karakoram Mountains in the west syntaxis of the Tibetan Plateau.Thick terrace sediments are widespread along the Tashkurgan-Yarkant River.These deposits contain geologic fingerprints that allow identification of the environmental changes and geologic hazards.However,few geochronological data was available on these sedimentations to allow us to build an irreproachable age model.4 samples of fine grains from one terrace profile were dated by optically stimulated luminescence(OSL)dating method.In darkroom,fractions of fine grains(4～11μm)were extracted from the bulk samples.OSL signal measurements were performed on an automated Daybreak system.Identical D_e plateau in the thermal treat was observed in preheat plateau test.Tests of luminescence characteristics confirm the suitability of the material for OSL dating.Our results indicate the deposition age for these sediments is between 4.3～7.3ka.After the river terrace deposited,the river has deeply incised for 27±5m,with the incision rate 6.3±1.2mm/a.The thermochronologic data show that the magnitude of exhumation decreases from upstream(west)to downstream(east)along the Tashkurgan-Yarkand River.These data may reflect the the active uplift process of Mustagh Ata antiform.

The research of optical dating about modern strong earthquake sediments will be useful for understanding geological significance of paleoearthquake related sediments,improving dating precision and accuracy,and better understanding the law of earthquake occurrence.This article chooses some typical sediments related with 2008 Wenchuan earthquake, such as dammed lake deposits,floodwater deposits and ejected sands, to do optical dating of fine-grained quartz.Preliminary results from optical dating of fine-grained quartz extracted from 11 samples suggest that fine-grained quartz is sensitive and D_e values obtained from the three sections indicate residual D_e up to 10Gy. Caution should be taken for optical dating of sediments related to paleoearthquake with a recurrence interval of hundreds or thousands of years,but the effect can be neglected for the paleoearthquake with a recurrence interval of ten thousands or hundred thousands of years.Residual D_e values less than 0.2Gy are observed in two samples collected from pre-earthquake surface.Therefore,we should collect samples on pre-earthquake surface to limit the event time.

In historical records,no earthquake of magnitude comparable with that of the Wenchuan M_S 8.0 earthquake has ever been reported in Chengdu and Longmenshan regions.The penultimate event similar to the 12 May 2008 M_S 8.0 was revealed by the surface ruptures in the vicinity of Xiaoyudong.It is important,therefore,to date accurately when the prior large earthquake happened.This paper presents 7 optically stimulated luminescence(OSL)ages from Xiaoyudong trench.We investigate the use of simplified multiple aliquot regenerative-dose(SMAR)protocol and single aliquot regenerative-dose(SAR)protocol from fine-grain quartz to date deposits associated with earthquake.The results of SMAR and SAR protocols are consistent.The behavior of quartz to different internal consistency checks of SAR protocol(preheat plateau,thermal transfer,recycling ratio,recuperation and growth curves)and of SMAR protocol(dose recovery)used for the dose estimation method was satisfactory.Various internal consistency tests of the measurement protocols indicate that the dose estimates from the fine grain quartz are accurate and the optical ages are reliable.The preliminary OSL ages indicate that the last large earthquake happened between 1.7～2.2ka and the slip rate of Xiaoyudong Fault was 1.0±0.08mm/a at least in Holocene.

The fluvial terrace has plenty of paleoclimate and paleoenviromental information which play an important role in paleoclimate and paleoenviromental researches.In this paper,we drilled a 42.85m-long core(N06S2)in 2007,which was located in the south bank of Yangtze River at Shifuqiao in Qixia district of Nanjing City.Firstly,fine quartz grains(4～11μm)were extracted from bulk samples in dark room,and the quartz purity tests were conducted.The results show that purity can satisfy the experiment.All measurements were performed on an automated Daybreak 2200 TL/OSL system with blue(470±5nm)light stimulation and U-340 luminescence detection filters.Thick source alpha counting(TSAC)was used to measure the uranium and thorium concentrations.The potassium content was determined using flame spectrophotometer.Secondly,the preheat plateau test and dose recovery test were performed on one sample using the SAR protocol.The results indicate that the fast component dominates the OSL signals.In preheat plateau test,identical D_e in the thermal treat from 160～260℃ was observed,thus we use the preheat temperature of 220℃ for 10 seconds.The recuperation ratios of zero point are below 2％and the recycling ratios lie between 0.9 and 1.1.In dose recovery test,OSL signal sensitivity changes are well corrected.Tests of luminescence characteristics confirm the suitability of the material for OSL dating.At last,samples from this drilling core were systematically dated by optically stimulated luminescence(OSL)dating method,and samples which contain organic matters were dated by AMS¹⁴ C.The results show that the D_e values from the two methods accord with each other very well.However,OSL dating results show that there is a hiatus in this core,and the hiatus,which ranges from 1.9ka to 7.9ka,may be the result of change of Yangtze River's channel or the erosion of the river.The ages of the fluvial deposition mainly range from 0.26ka to 1.9ka and 7.9ka to 9.1ka,it could be attributed to the results of paleoclimate and sea levels change.Meanwhile,study results on pollen and spores show that the paleoclimate has changed from warm wet to temperate wet during the stage of hiatus.

This paper presents a comparison of the calendar range of individual paleoearthquake calculated by conventional calibration,Bayesian analysis of series of peat samples as well as depth-age wiggle matching.The results suggest that: (1)The Bayesian analysis provides an excellent means to enhance chronological resolution when applied to a series of radiocarbon dates from sections with clear stratigraphic relationships.Such application can assess systematic errors when combined with independent chronological information,and determine the optimum chronological information for specific events and contexts.(2)The calendar ranges of series of samples collected from the same peat but different sampling thickness were compared with that of depth-age wiggle matching.The result shows that the chronological resolution by depth-age wiggle matching for the peat sample with thickness less than 2cm could achieve less than 100a.Therefore,the condition to obtain a high resolution calendar age is to have 5～6 samples with 0.5～2cm sampling thickness each and the interval of samples is 0.5～1cm.(3)The calendar range of paleoearthquakes constrained by the Markov chain Monte Carlo(MCMC)Bayesian analysis model,which constructs the order of samples according to their position in the strata with series of radiocarbon dates,was compared with calendar range by the conventional method.The results show that Bayesian analysis could obtain high-precision calendar dates for closely spaced samples.(4)Therefore,the calendar interval of the paleoearthquake event on the middle segment of Huaiyuan Fault was inferred as 1340～1114cal a BP(2σ)by the above systematical comparsion.

Locating at eastern end of the Pamir Front Thrust(PFT),the Mushi anticline grows initiating from early-Pleistocene till now.The anticline,with a gentle south limb and steep north limb,outcrops Pliocene Atushi formation and lower-Pleistocene Xiyu formation.Topographic profiles and drainage pattern indicate the lateral growth of the anticline from west to east.Combining mapping data and seismic profiles from the neighboring area,we find the Mushi anticline is a detachment fold,with a total shortening of ～0.7km and a total uplift up to～1.5km.Northern part of the anticline is dominated by a series of wide,flat terraces.According to OSL samples,the age of the terrace T2a,T3and T4 is 15.8±2.4ka,55.1±10.3ka and 131.4±23.9ka respectively.Correlating with Marine Isotopic stages(MIS),the formation of terraces has some relationship with global climate change.As growing of the anticline,terrace surfaces deformed obviously,which is characterized by fault scarps,surface tilting or back-tilting,folding scarps and lateral tilting.Deforming patterns of the terrace surfaces indicate the Mushi anticline grows by limb rotation in late-Pleistocene.Using calculating models,we can confine the minimum shortening rate is 1.6±0.3mm/a and the minimum uplift rate is 1.9±0.3mm/a. Longitudinal profiles of terraces indicate the Mushi anticline grows laterally through limb rotation.According to relationship between uplift and lateral propagation,we can acquire a faster eastward lateral propagation rate of the anticline during the period of 131～16ka,with a rate about 14.6±3.6mm/a; however,since 16ka,the rate reduced to 1.7±0.3mm/a,implying the anticline tip stopped propagating to the east,and growing of the anticline was mainly dominated by lateral limb rotation in late Quaternary.

The Mushi anticline locates at the frontier Pamir arcuate nappe tectonics belt(PFT),which is a detachment fold with a gentle south limb and steep north limb,and its earth crust minimum shortening is ～0.7km with uplift up to 1.5km.The north limb fault of Mushi anticline is composed of a series of obsequent slope fault scarps,and the distribution of vertical displacements among different fault scarps presents a pattern of one increasing and the other decreasing.No matter of the entire western segment of the northern limb faults or a single fault,the displacement distribution is asymmetric,that is,high in the east and low in the west,and the same to displacement gradient.This may reflect the late Quaternary folding of Mushi anticline as being intensive in the east and feeble in the west.The fault may be a shallow,rootless secondary fault formed during the growth process of the anticline in order to accommodate the constantly decreased space of anticline nucleus as the fold tightened gradually.The late Quaternary shortening rate of the fault is 0.8mm/a,absorbing only one fifth of the nowadays crustal shortening rate of the region.The growth of Mushi anticline and the north limb fault of Mushi anticline both are in accordance with global fault dataset scaling relationship,that is,fault length is over 100m.The power-law regression scaling exponent of west segment of the northern limb fault of Mushi anticline is n=1.37(R²=0.88),and its specific value(k)of maximum fault displacement and fault length is far less than that of the Mushi anticline,which is ～4.3％,but 1～2 orders of magnitude larger than that of global fault dataset(10^-4～10^-5). This may show that the northern limb fault of Mushi anticline is the offshoot of several moderate strong earthquakes,and it is still in initial stages.

The western Tarim Basin is a convergent zone of the Southwestern Tianshan and the Pamir,and there have been big debates about its exact boundary.However,in the Mayikake Basin,the boundaries of two tectonic systems are very clear: the north-vergent Pamir Front Thrust is the leading edge of the Pamir,and south-vergent thrust at south limb of the Wulagen anticline,which was discovered in recent field study,is the south margin of the Southwestern Tianshan.The thrust created 7.5～17.6m high scarps on the Tk3(the high terrace of the Kezilesu river)and Tb3(the high terrace of the Bieertuokuoyi river),with an occurrence of 6°∠15°.To the west,the thrust cuts all terraces of the Bieertuokuoyi river and the underlying youngest alluvial fans ultimately.The total length of thrust trace is about 12km.As activity of the thrust,lots of subparallel flexural-slip scarps are formed on terrace surfaces,which make terrace surfaces obviously differential back-tilted(tilted to south),and the locations of tilted degrees changed are corresponding to locations of flexural-slip faults.Shortening at south limb of the Wulagen anticline is absorbed by the thrust and flexural-slip faults,which is about ～71.4m since abandonment of the high terrace.Regional correlation indicates the high terrace is the same surface as the T2 located at north limb of the Mushi anticline with the age of～16ka,which indicates the average shortening rate of south limb of the anticline in late Quaternary is～4.5mm/a.

Based on the interpretation of satellite images,combined with field geomorphic and tectonic investigations and surveys,we get the parameters of surface rupture zones of the 1895 Tashkorgan earthquake,such as the geometry,the types of rupture,the displacements and their distribution and so on.And on these grounds,we estimate the possible magnitude,the epicenter and seismogenic fault of this earthquake.The south segment of Muztag Fault and the whole Taheman Fault were ruptured by the Tashkorgan earthquake.The length of the surface rupture zone is 27km.The rupture zone strikes NNE,and it changes from N25°W in the north to N25°E in the south segment.The surface rupture zone is composed of consequent or obsequent normal fault scarps,represented by horst,graben,and step-like structure on the profile,and distributed in patterns as en echelon,parallel,convergent and parallel cross shaped and so on in the plane.The surface ruptures are dominated by pure dip-slip,with little lateral displacement.The general width of these overlapping surficial fault rupture strands is ca.30～60m, and the largest may come to 825m.The largest co-seismic displacement of a single scarp is 4.2±0.2m. The surface ruptures are composed of three independent secondary segments.The seismogenic fault of this earthquake is Taheman Fault.The south segment of Muztag Fault was also ruptured.Moreover,we find a younger fault scarp which may be induced by the 1895 earthquake in the small basin between the two above-mentioned faults.

The northern margin of the Pamir salient indented northward by ～300km during the late Cenozoic,however,the spatiotemporal evolution of this process is still poorly constrained.Regional deformation within the Pamir salient is asymmetric.Previous work has shown that deformation along the western flank of the Pamir was accommodated by northwest-directed radial thrusting and associated anticlockwise vertical axis rotation of the Pamir over the eastern margin of the Tajik Basin,along with a component of left-slip faulting along the Darvaz Fault.In contrast,subduction of the Tajik-Tarim Basin beneath the Pamir along the MPT was absorbed along the eastern margin of the salient by dextral-slip along the Kashgar-Yecheng transfer system,accompanied with Oligocene-Miocene northward underthrusting, thickening and widespread melting of the middle and lower crust beneath the Pamir,eventually led to east-west extension along the Kongur Shan extensional system at ～7～8Ma.The slip rate of the KYTS decreased substantially from 11～15mm/a to 1.7～5.3mm/a since at least 3～5Ma,termination of slip along the northern segment of the Karakorum Fault occurred almost at the same time.Late Quaternary and present active deformation in the Pamir is dominated by east-west extension along the Kongur Shan extensional system and north-south contraction along the PFT and the Atux-Kashi fold belts in the southern margin of Tianshan.

Paleoseismic studies conducted along the surface rupture of the Wenchuan earthquake(M_S 8.0)of 12th May 2008 provide important information regarding earthquake reoccurrence intervals and slip rates of the Longmen Shan Fault zone.The Leigu trench was excavated along the middle segment of the surface rupture of the Yingxiu-Beichuan Fault zone.Based on the syntectonic sedimentary structure,two earthquake events,including the Wenchuan event,were identified at this site.This study utilizes Optically Stimulated Luminescence(OSL)dating of samples collected from the Leigu trench section,using SMAR(Sensitivity-corrected Multiple Aliquot Regenerative-dose)protocols.AMS¹⁴C dating was also carried out on charcoal from the same sediments.OSL ages are generally consistent with the calibrated AMS¹⁴C ages(cal a BP)for the same units.The penultimate earthquake event similar to Wenchuan earthquake scale in this region occurred(2.1?0.2)ka to(1.1?0.2)ka.

Surface ruptures of the M_S 8.0 Wenchuan earthquake are distributed mainly on the Longmenshan central fault and front-range fault,extending 235km and 72km,respectively.The ruptures exhibit complicated characters in geometry and kinematics.On the riverbed of Baisha river,a backthrust scarp was formed in the southwest of the major fault that comprises four right-step sub-faults,and precise topographical measurement shows a kinematic character of fault block and surface tilting in the rupture process;In Shiyan village,the master fault and the secondary fault formed an imbricate structure,and show as flexures and earthquake swells on ground surface.We analyzed the ruptures at Tongmakan village and Shiyan village,both locating on the central fault,by geometry and kinematics,and the results indicate that the earthquake rupturing along the central fault is mainly characterized by thrusting associated with right-lateral strike-slipping.This result is consistent with the focal-mechanism solutions which are promulgated by U.S.Geological Survey,Harvard University and China Earthquake Networks Center.In addition,the profiles of Tongmakan and Shiyan display different tilting directions,and the reason is that the former locates at the trailing edge of the fault,while the latter in the leading edge of fault.

With the occurrence of the 12May 2008 Wenchuan,Sichuan,China earthquake,two high-relief surface ruptures were formed on the Yingxiu-Shikan segment of the range-front fault and the Bailu-Hanwang segment of central fault along the Longmenshan Fault zone,and around the faults almost all buildings were razed.Furthermore,surface ruptures on the central fault broke through the accustomed activity segmentation boundary and extended to the northern segment by about 60km.Aftershocks also have a trend of migrating to the northern segment from the middle segment of Longmenshan Fault zone.It would be interesting to know as what kinds of effects this giant earthquake has on the earth's surface along the northern segment of Longmenshan Fault zone,and whether there have been earthquakes occurring since late Quaternary? In order to accumulate more reliable and detailed data and have a primary understanding to solve these questions and for post-quake reconstruction,we made a detailed geological and geomorphologic survey of the co-seismic earth's surface transformation and the late Quaternary Fault activity along the northern segment of the range-front fault on the basis of researches by predecessors.And then we excavated trenches at two relatively heavily-damaged and suspicious sites with legible linear shadows on image to investigate whether there exists active fault or fold.Our observation suggests that the northern segment is quite distinct in geology and geomorphology,and the coseismic earth's surface transformation is different from that in the middle segment of front-range fault and there is no clear trace to indicate that it is a late Quaternary active fault.So the late Quaternary active segment of range-front fault may terminate nearby the south of the Yong'an town.Our observation also suggests that the so-called active fault scarp as argued by some researchers near the Yong'an village is in fact an eroded river bank.