The Sichuan-Yunnan region is located in the southeastern part of the Qinghai-Tibet Plateau. Because of the compression and collision dynamics of the Indian Plate and the Eurasian Plate, the tectonic deformation is strong and seismic activities occur frequently. There have been many earthquakes above magnitude 7.0 in history. A series of active fault zones have developed in the region, among which the Sichuan-Yunnan rhombus block bounded by multiple active faults has attracted great research interests in recent years. The Longpan-Qiaohou fault zone is a boundary fault of the Sichuan-Yunnan rhombus block. The fault zone starts from Longpan in the north, passes through Jiuhe, Jianchuan, and Shaxi in the south, and ends at Qiaohou. It is about 120km long and the fault trend is 15°~20°. This fault zone is large in scale and highly active, with frequent seismic activity, complex mechanical properties, and variable movement patterns. The Mesozoic movement was intense. In the early Cenozoic, compression-thrust movement was dominant, and in the late Cenozoic, tension-strike movement was dominant. Since the Holocene, the fault zone has been characterized by left-lateral strike-slip movement with normal faulting properties, and earthquakes of magnitude 5 or above have occurred many times. Therefore, studying the activity of this fault zone is of great significance for the prediction and evaluation of regional strong earthquake risk. Thick calcite veins are well developed on the Henancun Fault of the Jianchuan section of the Longpan-Qiaohou fault zone, providing very valuable materials for fault dating. Calcite veins are coseismic rapid precipitation formed during seismic activity or syntectonic precipitation that filled along fractures after seismic activity. Therefore, their ages represent the latest time at which seismic activity occurred. Previous studies have shown that tensional fissures formed during coseismic events can close in a short period of time(days to months), suggesting that the filling of calcite veins within fault fissures is a relatively rapid process. This paper uses the ESR method to conduct dating study on the calcite veins in the study area. The results show that the ages of the four calcite veins(HNC-ESR01, HNC-ESR02, HNC-ESR03 and HNC-ESR04) are: (7.1±0.8)ka, (7.1±0.9)ka, (7.3±1.7)ka and (6.9±1.5)ka, respectively. The age results are concentrated, and the average age is(7.1±1.3)ka, indicating that the fault was active no later than(7.1±1.3)ka. The age results are consistent within the error range with the second paleoseismic event time revealed by trenching work in the area(between(6 130±30)a BP and(6 320±40)a BP), indicating that the dating of ESR in the fault zone is an effective dating method for the study of active tectonics and paleo-earthquakes. It is an effective chronological method for research, but it can be seen that compared with ¹⁴C and luminescence dating, the error of ESR results is relatively large. For faults with short earthquake recurrence intervals, it is still very challenging to accurately judge their activity. In the follow-up work, it is necessary to further improve the experimental process and reduce experimental errors, including refinement of sample pretreatment, accurate monitoring of irradiation dose, and accurate calculation of dose rate. In addition, by using five fitting functions(LIN, SSE, DSE, EXP+LIN and D_gamma)to calculate the equivalent dose values of calcite vein samples in this study, we found that the SSE function is capable of providing the best fitting effect.

The research on the activity history of seismogenic faults is the basis for the research and prevention of natural disasters such as earthquakes and landslides. Dating has always been the focus and difficulty of the research on the activity history of fault. However, it is difficult to carry out geochronological surveys for faults and landslides evolution in the carbonated areas due to the lack of suitable dating materials, such as the region of south-eastern Tibet where the main lithology is carbonate bedrock. The exposure dating of cosmogenic nuclides is the main method to determine the activity history of fault. But the cosmic nuclides  36Cl and ¹⁴C dating methods still have some limitations, such as the complex generation mode of  36Cl being caused by fission under the action of cosmic rays, neutron capture and meson action, the yield of  36Cl being changed with chemical composition change of dating mineral(the range of 2-171atom/g·a), and so on. More importantly, the rapid rock weathering in the carbonate bedrock area is a big problem. Once exposed, the bedrock will start rapid weathering and erosion and dissolution. Therefore, it is necessary to find new dating materials or dating methods in carbonate bedrock areas, especially in areas with little or no quaternary sediments. When a large landslide moves on the sliding surface of carbonate bedrock, heat is often generated due to high-speed friction, and then the dynamic metamorphism can occur easily on the sliding surface to form recrystallized carbonate, which can be used to determine the active time of faults.

Carbonate is one of the main materials for ESR dating. As early as the 1970s, Ikeya made the first electron spin resonance(ESR)dating study of carbonates using stalactite calcite. After that, many researches on the ESR signal characteristics of carbonate(such as coral, shell, aragonite, stalagmite and etc)were carried out, and the carbonate ESR dating then became one of the main methods in Quaternary chronology and had been widely used. The recrystallized carbonate on the fault friction surface and the sliding surface of the landslide is a newly discovered dating material. Although its main component is calcium carbonate, its origin is different from the carbonate materials commonly used in ESR dating(such as stalagmite, stalactite, etc.), so it is necessary to study its characteristics of ESR dating.

The characteristics of recrystallized carbonate collected from the fault friction surface of Jianchuan section on Lijiang-Xiaojinhe Fault(Yin et al., 2021)and the sliding surface of Qiaojia landslide which is located at the intersection of Xiaojiang Fault and Zemuhe Fault(Liu et al., 2023)have been studied, including microstructure, thermal annealing characteristics, sunlight bleaching characteristics, and compared with the previous dating results of AMS ¹⁴C and OSL on sediments. Yin et al.(2021)and Liu et al.(2023)analyzed and demonstrated the feasibility and reliability of the recrystallized carbonate ESR dating method used in the analysis of bedrock fault and landslide activity in the carbonate bedrock area, and established the recrystallized carbonate ESR dating technology.

Therefore, the ESR dating of recrystallized carbonate is an effective dating technology and can be used widely for the studying of activity history of faults and landslides in carbonate bedrock areas. This paper introduced the latest research progress of recrystallized carbonate ESR dating in the Carbonate rock area of southwest China by Yin et al.(2021)and Liu et al.(2023). In this paper, the requirements for sample collection and the range of dating were proposed which provide technical support for dating of key geological samples for research on fault and landslide activity history, engineering exploration, active structure, and seismic risk assessment in Carbonate rock bedrock area.

On May 21, 2021, a strong earthquake of magnitude 6.4 occurred in Yangbi County, Dali Prefecture, Yunnan Province. The focal depth of this earthquake is 8km. The earthquake broke the calm of magnitude 6 earthquake that had lasted for more than 6 years in Yunnan, and is a significant strong earthquake in the northwestern Yunnan region. Before the M_S6.4 Yangbi earthquake, the foreshock activity near the epicenter was frequent, and the maximum magnitude of foreshock is 5.6. After the M_S6.4 earthquake, another M_S5.2 earthquake, and many aftershocks of magnitude 3 and 4 occurred. The earthquake sequence was very rich. In order to further study the spatio-temporal distribution, source characteristics and seismogenic structure of the magnitude 6.4 earthquake sequence in Yangbi, in this paper more than 2 800 seismic events of the Yangbi earthquake sequence were relocated using the double-difference relative positioning method based on the seismic phase data from the Seismic Cataloging System of China Earthquake Networks Center, and finally 2 116 precise location results were obtained. At the same time, based on the broadband digital waveform data provided by the China Earthquake Networks Center, focal mechanism solutions 31 earthquakes of the sequence were obtained by MTINV program.

The results of the moment tensor inversion show that the moment magnitude of the Yangbi M_S6.4 earthquake is M_W6.0, the centroid depth is 10km, and the optimal double-couple solution is strike 135°, dip 81° and rake 176° for nodal plane I, and strike 226°, dip 86° and rake 9° for nodal plane Ⅱ. It is a strike-slip earthquake. Combining the strike of the fault in the earthquake source area and the distribution of aftershocks, it is inferred that the seismogenic fault is the nodal plane Ⅰ which strikes NW. Focal mechanism solutions of other 30 earthquakes of the sequence are mainly strike-slip type, which are consistent with the main shock. There are also a few events with mixed types. The focal mechanisms of several earthquakes close to the occurrence time of the M_S6.4 main earthquake are in good agreement with the main earthquake. The relocation results show obvious linear distribution characteristics of the sequence. The overall strike is in the NW direction and the dip to the SW direction. The depth profile sequence is horizontally linear along the strike. The dip angles of the fault planes in the south and north sections are different. The dip angles of the northern section are approximately vertical, and that of the southern section is about 45° or so. However, the sequence of the northern section is more concentrated along the fault plane than southern section. The dominant strike of the Yangbi earthquake sequence is NW-SE, the dip angles are concentrated between 70° and 90°, and the rakes are distributed around 180°, indicating that the Yangbi earthquake sequence is mainly characterized by strike-slip faulting. The dominant azimuth of the P-axis is SN and that of the T-axis is EW. The plunge of P-axis and T-axis are near horizontal. This indicates that the activities of the Yangbi earthquake sequence are mainly controlled by the regional SN-direction horizontal compression stress field. The dominant directions of the sequence’s fault planes and P-axis parameters are single, indicating that it is less likely that complex fault activity and large-scale stress adjustment will occur in the source area of this earthquake.

Integrating the results of relocations and focal mechanisms, it suggests that the seismogenic fault of Yangbi earthquake is a right-handed strike-slip active fault, striking northwest and dipping to the southwest, and the dip distribution is segmented. The dip angle of the northern segment is nearly vertical, and the dip angle of the southern segment is lower than that of the northern segment. There may exist rupture segmentation in the fault in the earthquake source area, and the structure morphology of local small areas may be more complicated.

The 2014 Ludian, Yunnan M_S6.5 earthquake triggered an unusually large number of co-seismic landslides compared with other events of similar magnitudes in southwestern China. We use landslide-area ratios(LAR)based on a grid(cell size ≈1km²)to delineate the specific distribution of landslides rather than the averaging landslide density that is commonly employed. Results show that the distribution of co-seismic landslides triggered by the 2014 Ludian M_W6.5 earthquake contains LAR values ranging from less than 1.0% to 36.1% with the high values concentrating in river valleys of the study area. Then we examine the correlation between some topographic parameters and the co-seismic landslides in each grid cell and especially focus on the grids with larger LAR(>10%). In addition to examining the correlation between the elevation, local relief and average slope angle(S), we propose a notion of the expected slope degree(ES)to further analyze the correlation between these co-seismic landslides and local topographic features. The expected slope degree can be calculated by dividing the local relief(the difference between the maximum and minimum elevation)by cell length for each grid cell, which is a kind of smooth of the local terrain instead of the average slope. After this procedure, we make a regression analysis on the expected slope degrees and the average slope degrees for all grid cells. Finally, we choose those cells that deviate from the regression line as the unstable units and examine their relation with landslide distribution. Results show that the elevation has a negative relationship with both the average slope degrees and the local relief in the study area, which can be classified as a kind of negative topography implying strong river erosion on the landform. In general, there exists a good positive linear correlation between expected slope degrees and average slope degree for the study area. While larger LAR values(LAR≥10%)lie at the sites that deviate from the regression line, likely representing unstable slopes prone to landsliding. Moreover, it is found that most of these sites with high LAR are just located along river valleys, which permits to predict that mass wasting by future earthquakes or other factors will recur at these places. As a contrast, the analysis results of topographic parameters in the Jiuzhaigou earthquake affected area show different characteristics. Thus, the understanding of the relationship between the geomorphic features and the spatial distribution and scale of landslides is helpful to improve the accuracy of prediction on earthquake-induced landslides and to identify potential large-scale landslides in the early stage.landscape evolution, landslides, adaptive adjustment, expected slope, the Ludian earthquake

Uplift of Tibet Plateau and formation of Asian Monsoon greatly affect East Asian geomorphological evolution, climate change and environment systems. Thus, those phenomena also control the origin, size and direction of river systems. The Yangtze River, as the most important linkage between Tibet Plateau and the East Asian marginal seas, delivers large volumes of water, sediment, and associated chemicals from its headwater regions and tributaries to the East China Sea, significantly influencing sedimentary system evolution in its drainage basin. Therefore, the formation of the modern Yangtze River and its geological-time evolution history have been paid more and more attention to since the beginning of the last century. After debated for more than a century, the First Bend in Shigu area and the Three Gorges have been known as the key capture point of the Yangtze River’s evolution history. In particularly, the Three Gorges incision period remains greatly controversial, which mainly focuses on Cretaceous period-Neogene period, early Pleistocene period, and late Quaternary period.
The Yichang Gravel, just located downstream and outlet of the Three Gorges with an inverted triangle shape, is mainly distributed in western Jianghan Basin with over 1 000km². Because of its wide distribution and key geographical location, many typical profiles of Yichang Gravel have been the critical materials for studies on stratigraphic division, geomorphic evolution, and paleoenvironment change in middle Yangtze River Basin, especially on the Three Gorges incision history. Based on the previous field investigation, the Yichang gravel unconformably overlies the Cretaceous bedrocks and underlies the mid-Pleistocene vermicular red earth. In addition, studies on heavy mineral assemblages, Pb isotopic compositions of detrital K-feldspar grains, magnetic characteristics as well as pollen assemblage characteristics have showed that sediments in Yichang Gravel are mainly derived from upper Yangtze River Basin, such as Jinshangjiang drainage, Minjiang drainage, Jialingjiang drainage and Wujiang drainage. Based on the above comprehensive analysis, researchers demonstrated that the depositing time of Yichang Gravel can best constrain the Three Gorges incising time.
The absolute altitude of Yichang Gravel exceeds 110m, and many thick sand lens are developed from top to bottom of the profiles. In this study, we applied the quartz Ti-Li center ESR dating method in Yichang Gravel to determine its absolute formation age, and then to constrain the minimum cutting-through time of Three Gorges. Eight samples(SXY-1, SXY-2, YC-1—4, LJY-1, LJY-2)were collected from the sand lens at depths of 4m, 19m, 40m, 51m, 63m, 75m, 83m and 99m respectively from the top of the profile. At the same time, in order to evaluate the residual dose of Ti-Li center after sunlight bleaching, we also sampled four modern surface Yangtze River sediments near Yichang Gravel for ESR measurement.
The result shows that the quartz Ti-Li center ESR signal intensity of the 4 modern fluvial sediments samples are zero, which implies that the Ti-Li center ESR signal intensity of quartz in Yichang Gravel sand lens could be bleached to zero before the last burial. Thus, the above results indicate that the ESR dating results of this paper are reliable. The ESR absolute age from top to bottom of the profile is 0.73Ma BP,0.87Ma BP,0.98Ma BP,1.04Ma BP,1.05Ma BP,1.10Ma BP, 1.11Ma BP, 1.12Ma BP, respectively. The ESR dating results show that the Yichang Gravel began to deposit at about 1.12Ma BP until 0.73Ma BP, and the Ti-Li center ESR age indicates that the Yangtze River cut through Three Gorges area no later than 1.12Ma BP.

Tanlu fault zone is the largest strike-slip fault system in eastern China. Since it was discovered by aeromagnetics in 1960s, it has been widely concerned by scholars at home and abroad, and a lot of research has been done on its formation and evolution. At the same time, the Tanlu fault zone is also the main seismic structural zone in China, with an obvious characteristic of segmentation of seismicity. Major earthquakes are mostly concentrated in the Bohai section and Weifang-Jiashan section. For example, the largest earthquake occurring in the Bohai section is M7.4 earthquake, and the largest earthquake occurring in the Weifang-Jiashan section is M8.5 earthquake. Therefore, the research on the active structure of the Tanlu fault zone is mainly concentrated in these two sections. With the deepening of research, some scholars carried out a lot of research on the middle section of Tanlu fault zone, which is distributed in Shandong and northern Jiangsu Province, including five nearly parallel fault systems, i.e. Changyi-Dadian Fault(F₁), Baifenzi-Fulaishan Fault(F₂), Yishui-Tangtou Fault(F₃), Tangwu-Gegou Fault(F₄)and Anqiu-Juxian Fault(F₅). They find that the faults F₃ and F₅ are still active since the late Quaternary. In recent years, we have got a further understanding of the geometric distribution, active age and active nature of Fault F₅, and found that it is still active in Holocene. At the same time, the latest research on the extension of F₅ into Anhui suggests that there is a late Pleistocene-Holocene fault existing near the Huaihe River in Anhui Province.
The Tanlu fault zone extends into Anhui Province and the extension section is completely buried, especially in the Hefei Basin south of Dingyuan. At present, there is little research on the activity of this fault segment, and it is very difficult to study its geometric structure and active nature, and even whether the fault exists has not been clear. Precisely determining the distribution, active properties and the latest active time of the hidden faults under urban areas is of great significance not only for studying the rupture behavior and segmentation characteristics of the southern section of the Tanlu fault zone, but also for providing important basis for urban seismic fortification. By using the method of shallow seismic prospecting and the combined drilling geological section, this paper carries out a detailed exploration and research on the Wuyunshan-Hefei Fault, the west branch fault of Tanlu fault zone buried in Hefei Basin. Four shallow seismic prospecting lines and two rows of joint borehole profiles are laid across the fault in Hefei urban area from north to south. Using ¹⁴C, OSL and ESR dating methods, ages of 34 samples of borehole stratigraphic profiles are obtained. The results show that the youngest stratum dislocated by the Wuyunshan-Hefei Fault is the Mesopleistocene blue-gray clay layer, and its activity is characterized by reverse faulting, with a maximum vertical offset of 2.4m. The latest active age is late Mesopleistocene, and the depth of the shallowest upper breaking point is 17m. This study confirms that the west branch of Tanlu fault zone cuts through Hefei Basin and is still active since Quaternary. Its latest activity age in Hefei Basin is late of Middle Pleistocene, and the latest activity is characterized by thrusting. The research results enrich the understanding of the overall activity of Tanlu fault zone in the buried section of Hefei Basin and provide reliable basic data for earthquake monitoring, prediction and earthquake damage prevention in Anhui Province.

Strike-slip faults and normal faults are dominant active tectonics in the interior of Tibetan plateau and control a series of basins and lakes showing extension since the Late Cenozoic, by contrast with the thrust faulting along the orogenic belts bordering the plateau. The late Neotectonic movement of those faults is key information to understand the deformation mechanism for Tibetan plateau. The Gyaring Co Fault is a major active right-lateral strike-slip fault striking~300° for a distance of~240km in central Tibet, in south of Bangong-Nujiang suture zone. The Gyaring Co Fault merges with the north-trending Xainza-Dinggye rift near the southern shore of Gyaring Co. From NW to SE, Dongguo Co, Gemang Co-Zhangnai Co, Zigui Co-Gyaring Co form the Gyaring Co fault zonal drainage basin. Some scholars have noticed that the formation of lakes and basins may be related to strike-slip faults and rift, but there is no analysis on the Gyaring Co fault zonal drainage basin and its response to regional tectonics. In recent years, a variety of quantitative geomorphic parameters have been widely used in the neotectonic systems to analyze the characteristics of the basin and its response mechanism to the tectonic movement. In this paper, we applied ASTER GDEM data on the ArcGIS platform, extracted the Gyaring Co fault zonal drainage basin based on Google Earth images (Landsat and GeoEye) and field work. We acquired basic geomorphic parameters of 153 sub-basin (such as grade, relief, average slope, area) and Hypsometric Index (HI) value and curve. Statistical results have indicated significant differences in scale(area and river network grade)in north and south sides of the fault. Southern drainage basins' relief, slope, HI value are higher than the northern basins, and the overall shape of hypsometric curve of northern basins are convex compared with southern concavity. Along the strike of the Gyaring Co Fault, average slope, and HI value are showing generally increasing trending and hypsometric curve become convex from west to east. By comparing and analyzing the lithology and rainfall conditions, we found that they have little influence on the basic parameters and HI value of drainage basins. Therefore, the changes of basin topographic differences between northern and southern side of fault and profile reveal the Gyaring Co Fault has experienced differential uplift since the late Cenozoic, southern side has greater uplift compared to the north side, and the uplift increased from NW to SE, thus indicate that normal faulting of the Gyaring Co Fault may enhanced by the Xainza-Dinggye rift. The early uplift of the Gangdise-Nyainqentanglha Mountain in late Cenozoic might provide northward inclined pre-existing geomorphic surfaces and the later further rapid uplift on the Gangdise-Nyaingentanglha Mountain and Xainza-Dinggye rift might contribute to the asymmetrical development of the Gyaring Co fault zonal drainage basin.

This paper analyses the deformations of middle and southern segments of Xiaojiang Fault zone using the theory of phase shift and amplitude changes between tidal water level and earth tides caused by water exchange among the systems of well hole-fracture-micro fracture. Seismic waves and deformation caused by tectonic stress can lead to changes of phases shift and amplitudes of tide levels in fractured confined aquifer. Seismic waves can increase water exchange between the aquifer and the borehole. So the fluid pathways can be unclogged during the earthquake and permeability in the fractured rock system can be increased after the earthquake. Smaller phase shift lag implies the higher permeability in the system. Permeability will return to background value gradually because of reclogging of fluid pathways and phase shift decreases. The long-term trend of phase shift represents the information of aquifer deformation caused by tectonic stress. The middle and southern segments of Xiaojiang Fault zone deform differently. The middle segment of the fault zone shows both strike-slip and compression characteristics. Deformation of this section is accumulated continuously. Phase shift and amplitude of the monitoring wells located at the intersection of Xiaojiang Fault zone and Honghe Fault zone change in a small scope. This shows that deformation of this section is not obvious and the aquifer is not squeezed remarkably.

Xiangshan-Tianjingshan Fault is one of the major active faults of the arc fault zone on the northeastern margin of the Qinghai-Tibet Plateau. The Yellow River in the Shapotou area flows through the fault and forms a perfect "Ω-shape" bend. Shapotou not only is a tourist mecca,but also a hotspot for studying the geomorphology,neotectonics,the uplift of Qinghai-Tibet Plateau and other issues. Xiangshan-Tianjingshan Fault is mainly a left-lateral strike-slip fault with a minor thrust component. So to study the fault's offsets is of vital importance. This paper,based on the characteristic of the distribution of the Yellow River terraces in the Shapotou Big Bend area,analyzes the offsets of the Xiangshan-Tianjingshan Fault since the formation of the terraces. The results reveal that 3 river terraces are developed on the right of the Yellow River in the Shapotou area,while there is no terrace developed on the left of the river. The maximum left-lateral displacement of Xiangshan-Tianjingshan Fault is less than 880m,and the slip rate is less than 5.18mm/a since 170ka BP.

Because of lack of Quaternary volcano activity in China,Quaternary sediments become the main dating material in the study of geological structure, topographic feature and environment evolution,etc.ESR is a potential dating method for the sediments older than 200ka.After sunlight bleaching or heating,the quartz ESR signals,including E'-,Ge-,Al-,Ti-center,can attenuate or be reset.The sediments deposited during Quaternary period only have the effect of sunlight bleaching before the last burial time.Therefore,the sunlight bleaching characteristics of ESR signal centers is one of the most important factors in ESR dating.In this study,the paper firstly makes a simple introduction on the ESR theoretical basis and the measuring process of dose rate(D) and equivalent dose(ED),and then,reviews the sunlight bleaching characteristics and the applications in Quaternary geochronology of different ESR signal centers.The E'-center ESR signal increases with the sunlight bleaching during first 72 hours,it is not suitable for the sediment dating.Ge-center ESR signal is bleachable and can be reset after several hours sunlight bleaching,so,it is the most light sensitive signal center.However,it is very difficult to measure the Ge-center ESR signal in laboratory because it is very weak.Al-center can attenuate 20 percent after 2 hours sunlight bleaching and after tens to hundreds of hours bleaching it still maintains a stable residual signal,50-80 percent.The remnant signals are not equal under different sediment environment.We usually gain a bigger age using Al-center ESR signal for the uncertain remnant.Ti-center ESR signals can be totally bleached after tens to hundreds of hours sunlight bleaching,and this ESR signal also has enough intensity for measurements.According to the review of all the ESR signal centers' sunlight bleaching characteristics and several successful application examples,we suggest that Ti-center ESR signal is more suitable than others for the ESR dating of Quaternary sediment.

Volume strain for the saturated rock in the undrained condition under tide force is studied in this paper with mechanical balance equation of linear elastic medium.The equation relating to pore pressure in confined aquifer responding to tide generating height(TGH)is proposed,and the coefficient(E) in this equation is defined with a clear physical meaning.In combination with the formula proposed by Hsieh(1987) for the amplitude ratio (A) and phase shift (α₁) of well water level response to pore pressure,the formula is derived for the amplitude ratio M(=EA)and phase shift α(=α₁+α₂) of well water level response to TGH.M and α can be calculated by measured water level and theoretical earth tide data.Assuming the phase shift(α₂) of pore pressure to TGH approximates zero,the transmissivity(T)of the aquifer,the amplitude ratio(A)and response coefficient(E) can be in turn determined by M and α.As an example,Chuan 18and 06 well data are used to calculate M and α, and to estimate T,A and E,and the changes of A,E and M with T are analyzed.

In this paper,we calculate receiver functions of body wave under the 14 stations in Shaanxi Province from 3-component digital waveform data of teleseismic earthquake events and obtain the thickness and Poisson ratio in crust of this area through H-kappa stacking.Through analysing the characteristics of crustal structure in Shaanxi Province,we discuss the relationship between seismic activity,crustal structure and geological structure in Shaanxi Province.The results show that(1)Crustal thickness in western Shaanxi is thicker than that in the east.Crustal thickness in the south and north of Shaanxi(≥40km)is larger than that in Weihe Basin,middle Shaanxi(about 34～40km).Among 14 stations,the crust beneath Huayin station is the thinnest(34km),which locates on the boundary between eastern Weihe Basin and Shanxi Province,and the biggest thickness(48km)appears beneath Longxian station at the northwestern end of Weihe Basin.(2)Poisson ratio in Shaanxi Province is about 0.24～0.29,which may be related to rock compositions.Poisson ratio in the north of Weihe Basin has higher values than those in the south.(3)There exist some relations between seismic activity and geological structure.The Weihe Basin with frequent earthquakes locates in a compound position of several tectonic systems.The Hanzhong Basin and Ankang Basin in the south of Shaanxi are controlled by several major faults,where the seismicity is relatively low.Seismic activity in northern Shaanxi is the lowest because of stable geological structure.Poisson ratio reflects material composition of earth interior.Our analysis suggests that seismic activity in the region with high Poisson ratio is higher than that with low Poisson ratio.

The paper studies the coseismic changes of water level and water temperature caused by the M_S 8.0 Wenchuan earthquake.The differences of water level and water temperature variations caused by the M_S 8.5 Sumatra earthquake on Sep.12,2007 and the M_S 8.0 Wenchuan earthquake on May 12,2008 are analyzed.The result shows that the well water level change caused by Wenchuan earthquake is dominated by rising.Spatial distribution of wells with water level rising or descending exhibits regional difference.The proportion of wells is higher with water level and water temperature changes in the same directions than in the reverse direction.Water temperature mainly dropped when water level fluctuated.Compared to remote earthquake,near earthquake caused bigger changes in water level and water temperature in wells.Coseismic changes of all the well water level and most of water temperature kept the same direction regardless of distance,magnitude,focal mechanism of earthquakes or epicentral directions,though water temperature direction changes occurred only at some peculiar wells.The water temperature direction changes were caused by changes of artesian condition and water level response from fluctuations to steps.The direction of water level changes might be controlled mainly by both local geological structures and hydro-geological conditions of the well.However,the direction of water temperature relates with mixing of water in the well,the location of the water temperature probe and other factors.The mechanisms of water temperature coseismic change are more complicated.

In this paper,the method for inversing the kinematics parameters of a fault zone from seismic moment tensors is discussed and applied to the study of the present kinematics characteristics of Xianshuihe Fault zone and Fenwei Fault zone. The results show that the Xianshuihe Fault zone extends in the direction of N16癢 and is compressed in the direction of N74癊. The average sinistral motion rate is about 10.9 mm/a. The Fenwei Fault zone extends in N20癢 and is compressed in N78癢 direction. The average dextral motion rate is about 0.24mm/a. Comparing the results mentioned above to the geological information and the GPS results,it is found that the motion directions of fracture zone are basically agreeable,but the slip rate is less than that of the latter two,especially in the Fenwei Fault zone. Three reasons may explain this phenomenon,firstly,the time when the data are collected is different; secondly,all strain energy produced by geological body is assumed to be released by means of the stick slip,instead of creep-slip of the fault; and thirdly there were totally 14 earthquakes of magnitude greater that 5 occurring in the sampled time period,among which there was only one earthquake of maximum over 6 and the largest event is M 6.2. The motion rate of the fault zone calculated from seismic moment tensors is less than the average rate drawn by geological information. This shows that the strain energy of the geological body has not been released completely. So there exists high seismic risk. In addition,the motion rate of the Fenwei Fault zone is less than that of the Xianshuihe Fault zone,indicating that the level of seismicity and the energy released by earthquake of the former is less than that of the latter.

The earthquake occurred in Jiezhou,Gansu Province on July 1,1879 (May 12,Guangxu 5,Qing Dynasty) is one of the largest earthquake events in Chinese history. The effect of this event spread over more than ten provinces. According to historical data,the magnitude of this earthquake has been estimated to be 8 or 71/2,and the macroscopic epicenter has been located at Mianshanheba (104.7E,33.2N),south of Wudu,Gansu Province,with type II precision of estimation (≤25km error). As the earthquake occurred in the areas of high mountain ridges difficult to be approached,it has not been studied in detail so far. It is one of the 3M=8 earthquakes in China that their relation to active faults had not been revealed so far. Recently,we have found that in satellite images a NNE-trending lineament can be clearly observed along the northern foot of the Shuikeng Mountains to the northeast of Wenxian County,Gansu Province. It extends eastward from Shifang Village to the northwest of Wenxian County,passing through Liangjiaba,Malian River,Fanjiaba,Miaobeihou,Guanjiagou,Jianzuishan Mountains,Shuikengya,northern slope of the Fangmashan Mountains,Songjia Mountains and Shenjiana'an,and then gradually becomes unclear after crossing through the Bailongjiang River and turning northward at 500m downstream from the Majiaba. The lineament has a total length of about 30km,among which about 21km can be identified to be surface fracture zone (from the bank of the Bailongjiang River to the top of the western hills of Guanjiagou). The lineament offsets left-laterally a series of ridges and gullies. In comparison with geologic data of this region,this lineament image coincides well with the NEE-trending Fanjiaba-Linjiang Fault. The interpretation of satellite images for the whole region and re-collation of historical records about this earthquake have confirmed that the Fanjiaba-Linjiang Fault bears a close relation to the southern Wudu earthquake,and is most probably the causative fault of this earthquake. This study,therefore,provides new insights into the following aspects,such as the occurrence and mode of motion of the causative fault,the length of surface ruptures,the amount and variation of horizontal displacement along the fault,the location of macroscopic epicenter,the probable magnitude of the event and the distribution of seismic hazards etc. All these results have led to the satisfactory solution of outstanding issue about the causative fault of the 1879 southern Wudu earthquake. They are also of great importance to seismic risk assessment in the border areas of Gansu,Qinghai and Sichuan Provinces as well as in southeast Gansu Province.

On the basis of analyses to the many observational data, abnormal changes of the hydrogeochemistry precursor are classified into three basic types of curves. Comparing these curves with the hydrodynamic dispersion curves, it is suggested that the transmission mechanism of hydrogeochemistry is actually a hydrodynamic dispersion. Application of the theory on hydrodynamic dispersion in the study of transmission mechanism of hydrogeochemistry precursor information is also discussed in this paper.

The origin and reversal of the Earth’s magnetic field is still a puzzle in geophysics. There are two reasons for this,one is that the physical process in the Earth’s core can not be observed directly,and another is that scarce studies were carried out in combining paleomagnetic data with magnetohydrodynamics. Based on paleomagnetism and αω dynamo theory,some new results are obtained in this paper: (1) Lorentz force results in negative feedback in the dynamo process in the Earth’s core; (2) westward drift of the geomagnetic field is determined by the difference of rotation between the Earth’s coie and mantle: (3) α effect makes the geomagnetic dipole tilt at some angles with respect to the axis of rotation.

This paper presents the results of detailed paleomagnetic study on the ophiolite of Danfeng group in Qinling erogenic zone. The paleomagnetic pole position and paleolati-tude of Danfeng group have been located on the basis of the origin and formation age of remanence,as well as the impact of metamorphism and deformation on the characteristic component. The origin and evolution of Danfeng group have also been discussed.