The Eryuan area is located in the central part of the northwest Yunnan region on the southeastern edge of the Qinghai-Xizang Plateau. The geological structure in the area is complex, including the Weixi-Qiaohou-Weishan Fault and Honghe Fault, as well as the Longpan-Qiaohou Fault and Heqing-Eryuan Fault, which intersect in an “X” shape. The geothermal activity in the area is also active and exhibits strong fault structural characteristics. Earthquake activity is also frequent in the Eryuan area. Since 2013, multiple earthquakes with M_S≥5.0 have occurred on the west side of the Weixi-Qiaohou-Weishan Fault. Given the complex geological and geothermal background and seismic activity in the Eryuan area, we use the seismic travel time data recorded by the Yunnan Regional Seismic Network and the Northwest Yunnan Dense Array from January 1, 2008, to July 20, 2023, V_P/V_S model consistency-constrained DD tomography method to obtain the 3D V_P, V_S, and V_P/V_S models and relocation results in the Eryuan and its surrounding areas. The research results indicate that: 1)based on the relocation results, the dense small seismic cluster develops at the intersection of the Weixi-Qiaohou-Weishan Fault, Honghe Fault, and Heqing-eryuan Fault deserves special attention. Four earthquakes with M_S≥5.0 that have occurred since 2013 are mainly distributed on the west side of the Weixi-Qiaohou-Weishan Fault, with an NNW-SSE trend distribution. The fault system at the western boundary of the Sichuan-Yunnan block is very complex, and its seismic risk deserves our special attention. 2)Based on the tomography results, the widely distributed low-velocity anomalies in the upper crust of the study area may be related to the crustal material migration pathway caused by the escape of the Sichuan-Yunnan diamond block towards SSE. 3)Combining imaging results with geochemical research results for inference, the high V_P/V_S below 10km depth beneath the small seismic cluster at the intersection of the Weixi-Qiaohou-Weishan Fault, Honghe Fault, and Heqing-Eryuan Fault may correspond to hot spring geothermal fluids. Moreover, the circulation process of hot spring fluids in complex fault systems may have penetrated to a depth of 7~10km below the seismic cluster, accompanied by some small earthquakes. However, there is no imaging evidence of fluid within a depth of 5~7km where some earthquakes are densely distributed. The occurrence of these earthquakes may be related to the distribution of brittle rocks, but it cannot be ruled out that fluid may have a potential infiltration effect on them in the future. Based on the results of velocity structure, they are combined with pre-existing seismology research results. It is found that the Eryuan earthquake sequences on March 3 and April 17, 2013 were mainly located within low V_P, low V_S, and low V_P/V_S anomaly. Generally, if there is fluid present, V_S decreases faster than V_P, resulting in high V_P/V_S. So low V_P/V_S indicates that low V_S is not caused by fluids, which may be due to lithology. Therefore, the imaging evidence indicates that there is no fluid in the region where the sequence is located, thus inferring that the occurrence of the sequence is not directly related to the fluid. The M_S5.1 Yangbi earthquake sequence on March 27, 2017, is spatially close to the Eryuan sequence and also has the same velocity structure characteristics, so it may not be directly related to fluids. The mainshock and some aftershocks of the M_S5.1 Yunlong earthquake sequence on May 18, 2016, were mainly located in high V_P, high V_S, and relatively high V_P/V_S regions. High V_S indicates that it is not the fluid that causes relatively high V_P/V_S. It is speculated that there may not be fluid in the region where the mainshock is located, and the fluid did not directly participate in the occurrence process of the sequence.

Earthquake catalog is the foundational data for analyzing seismic activity, assessing seismic hazard, and studying earthquake prediction. The majority of historical earthquake records are sourced from historical documents, with a significant portion of these records found in local gazetteers. Compiling historical literature is an essential way in analyzing seismic activity because historical accounts of earthquakes often provide more detailed and accurate information than geological data. Among these sources, analyzing relevant content in local gazetteers, such as the historical development of local governance, military garrison, official records, and descriptions of disasters and auspicious events, plays a crucial role in seismic activity research. This article aims to acquire historical earthquake records by consulting local gazetteers, folk books, and other historical sources containing natural, social, and political records. These records serve as historical foundations for analyzing the completeness of seismic data records.

The border region between Sichuan, Yunnan, and Tibet is located in the northwest secondary block of the Sichuan-Yunnan block, which is one of the areas with frequent strong earthquakes in China. The Xianshuihe fault zone and the Jinshajiang fault zone are the northeastern and northwestern boundary faults of the Sichuan-Yunnan block, respectively. They are large-scale and highly active fault zones formed due to the eastward escape of the Tibetan plateau caused by the relative movement between the Indian and Eurasian plates. Previous studies on active tectonics have shown that major earthquakes with magnitudes of 8 and above, as well as over 80% of strong earthquakes with magnitudes of 7, mainly occur in the boundary zones of active blocks with intense structural deformation and high stress accumulation. Moreover, the known active faults in the study area, such as the Batang fault and Litang fault, are also major faults that significantly have influence on the occurrence strong earthquakes. The Sichuan-Yunnan-Tibet adjacent region is home to significant infrastructure, including the Sichuan-Tibet railway and hydropower stations. Analyzing the completeness of earthquake data in the border region of Sichuan, Yunnan, and Tibet can contribute to the assessment of fault hazards and the analysis of regional seismic activity trends. This, in turn, can help minimize the damage caused by earthquakes to critical infrastructure and further enhance the safety and security of people’s lives and properties.

This study reviewed the local gazetteers of 44 counties in the border region between Sichuan, Yunnan, and Tibet, and summarized the establishment and historical evolution of each county. Based on the analysis of the road evolution from Sichuan to Tibet and from Yunnan to Tibet, we examined the significant roles of important transportation hubs and nodes, such as stations, pond flood, and grain platforms, in regarding of recording earthquakes. Combining various historical sources and previous research on the completeness of earthquake data in the region, we conducted a comprehensive analysis to determine the probable starting years for the availability of seismic records of magnitude 7 and above in the Xianshuihe area and the three parallel rivers area. Additionally, based on the data of the length and short axis of isoseismal lines from 88 earthquakes, an elliptical model was used to derive the seismic intensity attenuation relationship for the Sichuan-Yunnan block. By placing the fitted isoseismal lines of magnitude 6 and 7 earthquakes in the study area, we analyzed their impact range, providing a spatial dimension basis for the completeness analysis of seismic data.

This article provides a comprehensive analysis and demonstration of the complete starting years of seismic data in the border region between Sichuan, Yunnan, and Tibet from both temporal and spatial perspectives. The results indicate that due to the establishment of grain stations and Tangxun along the Sichuan-Tibet road, as well as the appointment of officials, several counties in the Xianshuihe area, including Kangding, Luhuo, Garzê, Litang, and Yajiang, were developed between 1719 and 1736. At the same time, there are relatively abundant historical documents related to earthquakes in the Xianshuihe area. Local chronicles, reports from governors and resident ministers, written records in Tibetan temples, and accounts from lamas have documented earthquake surveys, disaster assessments, and relief efforts. By combining these historical sources with the analysis of intensity attenuation relationships in the Sichuan-Yunnan block, the affected areas of earthquakes with magnitudes 6 and 7 can be determined that the period from 1719 to 1736 marks the starting years with complete M≥7 earthquake data in the Xianshuihe area. The towns of Batang, Mangkang, and Changdu in the three parallel rivers area are also significant nodes and hubs along the road to Tibet. They were established with administrative institutions and granaries between 1719 and 1728, and the road network extensively covered Tangxun in the region. In considering the seismic records and historical sources in the three parallel rivers area, as well as referencing the recording capabilities of granaries, administrative institutions, and Tangxun in the Xianshuihe area, and estimating the potential recorded seismic magnitudes based on the intensity attenuation relationships of the Sichuan-Yunnan block, it can be suggested that the period from 1719 to 1728 is a possible starting point for complete earthquake data with M≥7 in the three parallel rivers area. In areas farther away from the road to Tibet, such as Jiangda, Gongjue, Baiyu, Xinlong, and the northern regions of Batang and Litang, as well as the large contiguous regions of Derong, Xiangcheng, Daocheng, and Jiulong, the eastern boundary is the Xianshuihe fault zone, while the area between the two zones is divided by the northeast-oriented Batang fault. Previous seismic geological investigations have found that within the aforementioned regions, the influence of the Jinshajiang fault zone extends along the Batang-Derong-Benzilan line. In remote areas away from the road and with sparse population, the possibility of individual earthquakes with magnitudes above 7 occurring but being missed cannot be ruled out. However, in other areas not located on active fault zones, it can be considered unlikely to experience earthquakes with magnitudes above 7. Based on the analysis of the data, the starting years of earthquakes with a magnitude of 6 and above should be the same as those of earthquakes with a magnitude of 7 and above. However, according to the analysis of the average occurrence rate of earthquakes per year, there is a significant lack of records for earthquakes of magnitude 6 and above. This may be due to the sparsely populated and vast nature of the Tibetan region during historical times, limited administrative capabilities of officials, and lack of earthquake historical records and documents. Therefore, it is not possible to determine the exact starting year for complete data on earthquakes of magnitude 6, which would be the same as for earthquakes of magnitude 7 and above.

14 survey lines, with a total of 167 measuring points, were laid out in the northern section of the Red River Fault, the Longpan-Qiaohou Fault, the Heqing-Eryuan Fault, the eastern piedmont fault of Yulong Mountains, and the Lijiang-Jianchuan Fault in the northwest of Yunnan Province, China. Cross-fault soil gas radon, hydrogen, and carbon dioxide have been measured on the above-mentioned faults. The concentration intensity and distribution characteristics of soil gas in the study area were calculated and analyzed. The results show that:
(1)The concentrations and distribution patterns of soil gas radon and hydrogen vary greatly in different faults. The concentrations of radon vary from 6.18Bq/L to 168.32Bq/L, while that of hydrogen are between 7.72ppm to 429ppm, and carbon dioxide are from 0.73% to 4.04%.
(2)The average results of soil gas measurement show that the concentrations of radon are higher than 40kBq/m³ in the sampling sites of Yinjie, Niujie, Gantangzi, while the concentrations of radon in En’nu and Tiger Leaping Gorge measuring lines are smaller; The concentrations of hydrogen are higher than 60ppm in the sampling sites of Yangwang village, Houqing, Dawa, Yangcaoqing and Tiger Leaping Gorge, while the concentrations in Gantangzi and Niujie measuring lines are smaller.
(3)The spatial distribution characteristics of soil gas concentration in faults in northwest Yunnan are obvious, and the intensity of radon and hydrogen concentrations in different active fault zones vary greatly. The intensities of radon and hydrogen concentration are higher and have good consistency in Yinjie and Yangwang village measuring lines located in the northern section of the Red River Fault, the Houqing survey line located in Longpan-Qiaohou Fault, Dawa survey line in the Lijiang-Jianchuan Fault and Yangcaoqing in the south of Chenghai Fault. The soil gas concentration in such sample sites is high and the degassing ability is strong, indicating the different activity characteristics of different segments of the above faults to some extent.
Under the action of tectonic stress, the fault will slip and the rock properties and material structure of the fault will change, thus causing changes of underground material, gas transport channel and transport mode, which is characterized by the change of the concentration and distribution characteristics of escaped soil gas. Combined with the active characteristics of faults, slip rate and geomorphological features, the characteristics of concentration and spatial distribution of two soil gases(radon and hydrogen)are discussed, and the following conclusions are obtained.
(1)There is a large difference in the concentration of escaped soil gas from different faults in the study area, indicating that the content of soil gas is controlled by regional geochemical background values, and there are certain differences in the gas concentration of different sections of the same fault, indicating that the local concentration/flux change is greatly affected by the transport.
(2)The concentration of fault soil gas is related to fault activity, and for different faults, the higher the degree of fault activity is, the higher the concentration of fault gas will be. From the point of fault gas concentration characteristics, the concentrations in the survey lines in the northern section of the Red River Fault and Heqing-Eryuan Fault in the study area vary greatly, suggesting that the fault segmentation is obvious. Compared with other faults, the northern section of the Red River Fault has a higher concentration of soil gas, indicating that the fault is more active. However, there is no simple linear relationship between the soil gas concentration and the fault slip rate, and it may also depend on its material source, transport channel structure, etc.
(3)The concentration of soil hydrogen at the outcrop of faults(especially normal faults and strike-slip faults)is generally higher, which shows that hydrogen has better indicative significance in revealing the location of fault rupture, and the distribution pattern of soil gas radon concentration is a good indicator for analyzing the characteristics of fault movement.

Ocean earthquakes pose a serious threat to the security of the economic construction in coastal areas and the marine resource exploitation of China, so building proper seismicity models for China seas and adjacent regions is one of the focuses of the next generation seismic zoning map of China. Different from mainland China, there is lack of multidisciplinary data for the sea areas, such as seismic geology and geophysical exploration, thus the earthquake catalogue is the most important basic data for analyzing its seismic activity characteristics. Recently, a unified catalogue was compiled by researchers for China seas and neighboring regions, which provides a basis for further work.
The Smoothed Seismicity Model (SSM) is a classic model based on earthquake catalogue and has become a basic model for the United States National Seismic Hazard Map. The Adaptively Smoothed Seismicity Model (ASSM) is an improved version of SSM. Compared with SSM, ASSM has optimized the value algorithm of the kernel function, thereby improving the model’s capability on mid- and long-term earthquake forecast. Due to the outstanding performance of ASSM in the CSEP project, it has become a research hotspot for seismologists. Based on a further improved ASSM algorithm and the newly compiled catalogue, this study established for the first time an adaptively smoothed seismicity model for China seas and adjacent areas.
First, similar to most studies on mid-to-long-term seismicity models, we removed the foreshocks and aftershocks from the catalogue. Then we used seismic zones as the unit to estimate the start and end time of completely recorded earthquakes in different magnitude intervals. Furthermore, the maximum likelihood method was used to estimate the seismic activity parameters such as a-value and b-value for every seismic zone. On this basis, an improved adaptively smoothed algorithm was used to build the model. The function of probability gain per earthquake was applied to evaluate the performance of models under different parameter settings. Finally, our model was compared with the traditional SSM, and the advantages and limitations of our model were analyzed.
Results show that: Compared with SSM, our model has a better performance on the probability gain function, and this advantage is not affected by the minimum magnitude(M_min)of the input earthquakes. When M_min is set as M4.0, our model achieves its best performance. The performance of the model does not necessarily improve as M_min decreases or the number of earthquakes increases. This indicates that we need to comprehensively consider the distribution of earthquakes in the study area and the integrity of the earthquake catalogue when selecting parameters. The algorithm used in this study can make full use of seismic data with varying record level over time and space, and has a certain application value in seismic hazard analysis and mid- and long-term earthquake forecast. Meanwhile, our model can be used as one of the basic models to analyze the seismic hazard for China’s maritime areas, and provide technical support for the compilation of seismic zoning maps in China’s sea areas. In addition, the completeness analysis results and seismic activity parameters obtained by this study can also provide references for other peer research.
Since ASSM is only based on historical and instrumental earthquake catalogues, it has certain limitations. For example, it cannot calculate the upper limit of the magnitude and reflect the distribution of faults, nor can it consider the time-dependence of the recurrence of large earthquakes. Therefore, this model can be used alone to describe the occurrence probability of small to moderately strong earthquakes, and it can also be used as one of the important factors to determine the spatial distribution functions for potential seismic source zones. However, when conducting seismic hazard analysis, it is recommended to combine the results of other disciplines such as geology and geodesy to form a hybrid model, so as to further improve the applicability and effectiveness of the model.

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

b-value in the magnitude-frequency(G-R)relationship plays a vital role in seismicity research and seismic hazard analysis, and the most commonly used techniques to simulate it are least square approach and maximum likelihood method. Least square method is simple and easy to apply, therefore widely used in China. However, many researches show that there exist some limits in least square estimation of b-value. Earthquakes with different magnitudes are not equally weighted in this method, and larger events have higher weights, so b-value is vulnerable to the fluctuation of several big earthquakes; meanwhile, least square method needs to divide magnitude intervals artificially. With a small sample size, data points could be not enough if the magnitude interval is too wide, and events in a magnitude interval may be lacking if it is divided to be too narrow. Especially for incremental G-R relationship, it is possible that N(M_i)equals 0 in an interval with large magnitude, so log(N(M_i))loses meaning and has to be ignored, resulting in a low b-value. Therefore, under certain conditions, maximum likelihood method is recommended as an effective substitution or supplementary for least square estimation of b-value. Among numerous previous researches on maximum likelihood estimation of b-value, lots of equations have been provided, based on varied implicit assumptions and different ways of solution. A brief overview is first presented for these equations, and classification and summary are provided based on whether taking account of the effect of binned magnitude, with finite maximum magnitude, using unequal observation periods for different magnitude intervals, and with analytic solution or not. Following this, a total of 6 influential factors are analyzed, such as binning magnitude, measurement errors of magnitude, sample size, magnitude span, minimum completeness magnitude and fore- and aftershocks. At last, reasonable suggestions are provided for using those equations properly. The equations of Aki(1965), Utsu(1965), Page(1968)and Kijko and Smit(2012)are based on assumption that magnitudes are continuous random variables, and have no corrections for this, so these equations are not recommended here. For simplicity, the equations of Utsu(1966)or Tinti and Mulargia(1987)can be used, but magnitude span should be greater than 2.5 due to without finite maximum magnitude in the formulas. For researchers having capability to write code and calculate numerically, Weichert(1980)or Bender(1983)'s algorithm could be utilized. Especially when it is required to apply data with different observation periods for varied magnitudes, the formula of Weichert(1980)is recommended. This study contributes to more accurately understand and use different formulas of estimating b-value by maximum likelihood technique, which can be used as reference for peers.

The Chaohu-Tongling area in Anhui Province is a typical moderate-to-strong earthquake active area in the mainland of China. Four earthquakes occurred in this area, displayed as a NNE-trending zonal distribution, including the 1585 M5(3/4) Chaoxian earthquake and the 1654 M5(1/4) Lujiang earthquake, which formed a striking moderate-to-strong seismic activity zone. Field survey, shallow geophysical prospecting, drilling data, collection and dating of chronology samples and comprehensive analysis of fault activity indicate that the Fanshan, Xiajialing and Langcun faults are not active since Quaternary. The NNE-trending Tongling Fault is a buried middle-Pleistocene fault, but it can produce moderate-to-strong earthquakes and control the evolution and development of three en echelon geologic structures. The intensity of the four earthquakes is characterized by southward progressive decrease, which is in accordance with the characteristics that the subsidence range of Wuwei Basin is obviously larger than that of Guichi Basin to its south since late Cenozoic. In terms of deep structure, the characteristics of spatial distribution of Tongling Fault indicate that it corresponds to a NNE-striking Bouguer gravity anomaly gradient belt. So there is a spatial correspondence between the middle-Pleistocene Tongling Fault, the en echelon structures, the differential movement of the neotectonics, the Bouguer gravity anomaly gradient belt and the moderate-to-strong seismic activity belt in the Chaohu-Tongling area, indicating that they should be the tectonic indications of occurrence for moderate-to-strong earthquakes.

On 10 June 1856, an M61/4 earthquake occurred between Qianjiang, Chongqin and Xianfeng, Hubei, resulting in severe geologic hazard including a series of large-scale landslides. Based on previous work, combining field investigations and remote sensing imagery, we have mapped the locations of three landslides triggered by this event, dominated by slumps. Our field work included observations to every failure slopes and occurrence, lithology and joints of rocks in the surroundings. We also employed an unmanned air plane to take pictures of the study area, yielding high-resolution DEM and DOM data which permit to generate terrain contours with a 2m interval. With these field investigations, we have described the sizes and forms of each slump mass in detail, and studied their generation mechanisms. Our research suggests the following natural conditions are responsible for these seismic landslides. 1)In a tectonic stress field characterized by NW-SE directed principal compressive stress, the slopes received a seismic acceleration from NW to SE in a short time. 2)Strata dip in a direction consistent with the seismic motion, thus the slope was easy to slide along stratum interfaces. 3)The two sets of joints existing in rocks experienced long-term weathering, resulting in connection of partial structural planes and destruction to the intactness of rock bodies.

The seismogenic structure of the Lushan earthquake has remained in suspensed until now. Several faults or tectonics, including basal slipping zone, unknown blind thrust fault and piedmont buried fault, etc, are all considered as the possible seismogenic structure. This paper tries to make some new insights into this unsolved problem. Firstly, based on the data collected from the dynamic seismic stations located on the southern segment of the Longmenshan fault deployed by the Institute of Earthquake Science from 2008 to 2009 and the result of the aftershock relocation and the location of the known faults on the surface, we analyze and interpret the deep structures. Secondly, based on the terrace deformation across the main earthquake zone obtained from the dirrerential GPS meaturement of topography along the Qingyijiang River, combining with the geological interpretation of the high resolution remote sensing image and the regional geological data, we analyze the surface tectonic deformation. Furthermore, we combined the data of the deep structure and the surface deformation above to construct tectonic deformation model and research the seismogenic structure of the Lushan earthquake. Preliminarily, we think that the deformation model of the Lushan earthquake is different from that of the northern thrust segment ruptured in the Wenchuan earthquake due to the dip angle of the fault plane. On the southern segment, the main deformation is the compression of the footwall due to the nearly vertical fault plane of the frontal fault, and the new active thrust faults formed in the footwall. While on the northern segment, the main deformation is the thrusting of the hanging wall due to the less steep fault plane of the central fault. An active anticline formed on the hanging wall of the new active thrust fault, and the terrace surface on this anticline have deformed evidently since the Quaterary, and the latest activity of this anticline caused the Lushan earthquake, so the newly formed active thrust fault is probably the seismogenic structure of the Lushan earthquake. Huge displacement or tectonic deformation has been accumulated on the fault segment curved towards southeast from the Daxi country to the Taiping town during a long time, and the release of the strain and the tectonic movement all concentrate on this fault segment. The Lushan earthquake is just one event during the whole process of tectonic evolution, and the newly formed active thrust faults in the footwall may still cause similar earthquake in the future.

Focal mechanism solutions, distribution of aftershocks and field investigation suggest that the 3 August 2014 Ludian, Yunnan M_S6.5 earthquake was spawned by the NW-trending steep left-slip fault that stretches along Baogunao-Xiaohe. The landsides, dominated by avalanches, induced by the shock are distributed in a rectangular area(15km×12km)with a NW-orientated long axis. The bedrock avalanches at many sites indicate that the primary direction of ground motion changes from SE in the north to SN in the south. The distribution of landslides triggered by the shock can be explained by the following two models of seismogenic structure: 1)Left-lateral strike-slip faulting occurred on a generally NW-trending arc-like fault, which caused seismic ground motion with the direction changing gradually from SE in the north to near-SN in the south; and 2)in addition to the left-lateral slip of the NW-trending fault, the NE-trending fault has also contributed to the hazard, which thrust from NW toward SE. So the Ludian M_S6.5 event was the result of the joint action of both the NW and NE directed faults, of which the NW left-lateral slip fault is the dominant and the NE thrust fault is the secondary. Another evidence is that most aftershocks are distributed linearly in NW direction, meanwhile some are clustered in nearly NE around the epicenter, which also implies the possibility that both faults moved simultaneously during the event. Besides, focal mechanism solutions of a lot of earthquakes in the Yongshan-Zhaotong area, northeastern Yunnan Province, where the epicenter of the 2014 Ludian M_S6.5 event is located, indicate that the seismogenic faults are primarily dominated by thrust faulting, associated with strike-slip faulting.

The Zhaotong-Ludian Fault zone, composed mainly of three right-step en echelon faults, namely, the Zhaotong-Ludian Fault, the Sayuhe Fault and the Longshu Fault, strikes 40°～60° on the whole, with the Sayuhe Fault and the Longshu Fault dipping SE and the Zhaotong-Ludian Fault dipping NW, and they all together constitute a complicated thrust fault system. Based on years of field investigation results of geology and geomorphography, we elaborate the late Quaternary active features, the geological and geomorphic evidences of the latest activity of the Zhaotong-Ludian Faults. Our observation shows that: the late Cenozoic basins along the Zhaotong-Luian Fault zone are obviously dominated by the fault; there are many neo-active fault landforms, such as, flat and straight fault troughs, directional aligned fault facets and fault scarps, and the upper Pleistocene to Holocene strata are offset by the fault. The fault zone has been active since the late Quaternary. For example, the fault at Daqiaobian dislocated a set of strata of the Pliocene, and middle to upper Pleistocene, with an apparently reverse character. The fault trending NE is developed in the Holocene diluvium with oblique striation on the fault plane at Guangming Village. Deposits with an OSL age of(23.4±1.8)ka BP on T2 terrace of a small river near Beizha town was offset by the fault. There is a fault scarp trending NE 40°, 0.5～2.0m in height, on the first terrace of the Longshu River near the Longshu Village. Several Quaternary faults are revealed by the trench which offset the late Pleistocene to Holocene strata and there are three poleo-earthquake events discovered in the trench. At Yanjiao Village the gravel layer has risen steeply and is aligned in a line because of squeezing effect of the fault; the rivers and ridges nearby are synchronously offset dextrally up to 30～40m. The fault zone is dominated by reverse faulting with a small amount of right-lateral motion. Besides, there are some NW-trending faults interweaving with the NE-trending fault zone, some of which are active since late Quaternary as well, and they are the conjugate structures with the NE-trending faults. Surface deformation, such as NE- and NW-trending ground fissures and reverse scarp landforms, has been generated in the epicenter area of the 2014 Ludian M6.5 earthquake, the distribution of which is in consistence with the NE- and NW-trending faults. Because of far-field deformation response and energy exchange and transfer between blocks, the Liangshan active sub-block formed on the east of the Sichuan-Yunnan block, and the Zhaotong-Ludian Fault zone lies in the forefront of the SE movement of this sub-block. On account of its distinct location and its complicated geometric structure, the Zhaotong-Ludian Fault zone is one of main carriers of the tectonic deformation of the Liangshan active sub-block to absorb and accommodate the strains produced by the block's SE movement, and is the southern boundary of the Liangshan sub-block. From the point of view of the regional tectonic positions and the kinematic characteristics, the relation of Zhaotong-Ludian Fault zone to the Liangshan active sub-block is exactly as the relation of the Longmanshan Faults to Bayan Har block. Consequently, the Zhaotong-Ludian Fault zone has an important significance in the division of active block boundaries and the regional tectonic framework, and meanwhile, it is also an important seismogenic structure in the northeastern Yunnan.

Geological disaster distribution induced by the 2013 M_S7.0 Lushan earthquake shows clear hanging wall effect and direction effect under reverse fault motion. No surface rupture was found in the post-earthquake emergency field surveys. We developed a detailed geo-spatial database of 2230 rock falls and landslides based on post-earthquake field surveys and examination of high-resolution aerial photographs across the disaster area. Landslides triggered by earthquake, dense aftershocks and isoseismal map provide clues to study the unrevealed causative fault.Statistics show that rock falls and landslides have a dominant slide direction of southeast(135°～144°), which is perpendicular to the strike of the causative fault. This result is consistent with the focal mechanisms. From distribution and density of seismic disasters, the macroscopic epicenter was relocated on the northern edge of Baosheng Town, ～3.6 km from the instrumental location. The probable surface rupture may appear on the edge of dense region of coseismic landslides and aftershocks, paralleling to the Shuangshi-Dachuan Fault. Because of difference in weatherability of rocks, linear cliffs or high-angle topography are formed between different strata or igneous rocks, and these regions are susceptible to rock falls and landslides under the action of strong earthquake.

This paper mainly studies the distribution of structural deformation and stress under the motion of thrust fault due to the effect of stress normal to the strike direction. As an example,we build the finite element model of central fault of Longmen Shan Fault zone,the Yingxiu-Qingchuan Fault. The finite element model is the model of single inverse fault. During the study,we compute the variations of surface deformation and stress fields near to the fault due to the thrust motion of Yingxiu-Qingchuan Fault in the process of Wenchuan earthquake. In the computation,we apply the frictional contact element and curved surface geometry to simulating the fault plane to obtain the variations of stress components and displacement field which are normal to strike direction and ground surface. In order to get the stress value of the hanging fall of the Yingxiu-Qingchuan Fault,we also apply the static dislocation model to the computation. Through the computation,we find that the displacement field along the strike direction can exist even if there is no initial stress load along the strike,but the value of this deformation is tiny. So we believe the displacement field along the strike may stem from the transverse deformation due to the extrusion of thrust fault; The structure deformation normal to the strike direction resulting from the thrust motion of inverse fault does not reach to maximum value at the zone near the fault,but the structure deformation normal to the ground surface can reach the maximum at the zone near to the fault; Generally,under the compression stress effect,the amount of crustal shortening is much bigger than that of uplift deformation at the zone near to the inverse fault,and the value of compression stress is much bigger than that of stress normal to ground surface along the fault plane. Furthermore,variation of stress on the inverse fault plane occurs mainly at the area where the dip angle of fault plane changes.

The June 24th 2012 Ninglang-Yanyuan M_S 5.7 earthquake happened at 30km northwest of the Lijiang-Xiaojinhe Fault, a region seismically active in history and prone to earthquake in northwestern Yunnan. Tectonics in the earthquake region is complex,where two groups of faults are developed,trending NW and NE,respectively,and distributed in a chessboard pattern. Field survey results reveal that there are the NW-trending Yongning Fault and the NE-trending Rigulu-yanwa Fault developed near the epicenter,both are active in late Pleistocene.The Yongning Fault,composed of Wenquan Fault,Yongning Fault,and Alaao Fault,shows obvious fault landforms and clear linear features on satellite imagery.The fault has played an obvious control role in the development of the Yongning Quaternary Basin and Lugu Lake Basin,with several hot springs developed along the fault. Several tributaries of Qiansuo River run along the fault,and there are dextral displacements observed in many parts of the rivers along the fault,such as between Baqi and Haiyijiao,Shancuo village east of Rigulu. Near Alaao,the fault offset the late Pleistocene deposit on the T₂ terrace,and the latest TL age of the offset stratum is (21.19±1.80)ka,indicating it is a normal with dextral strike-slip,late Pleistocene active fault.The Rigulu-Wayan Fault has played a noticeable control role in the development of the Tertiary Basins such as Wayan,Rigulu,and Lijiazui and the Quaternary Basin of Yongning. It offset the mid Pleistocene and the upper Pleistocene strata. Between Zhongwadu and Lijiazui,several streams were synchronously displaced left-laterally. There are obvious signs showing the fault was active in the late Pleistocene,dominated by sinistral strike-slip. According to the focal mechanism solutions,the Ninglang-Yanyuan M_S 5.7 earthquake is of normal faulting with dextral strike-slip,the attitude of the NW nodal plane is basically consistent to the Yongning Fault,and the seismic rupture pattern is identical to the kinematical characteristic of Yongning Fault.The major axis of the isoseismals,the linear distribution of intensity Ⅷ anomaly sites and the direction of tectonic ground fissures are all consistent to the strike of Yongning Fault. Through analysis,it is believed that Yongning Fault is the seismogenic fault of Ninglang-Yanyuan M_S 5.7 earthquake. Furthermore,the 1996 Lijiang M7.0 earthquake,the 1976 Zhongdian M5.5 earthquake and this M5.7 earthquake all have apparent normal dip-slip component. These earthquakes are located in the periphery of the neo-tectonic uplift of Haba Snow Mountain and Yulong Snow Mountain. Based on analyses of regional topography,the normal faulting in this area is most likely related to the gravitational potential energy resulting from the big topography contrast.

The Xiannüshan Fault zone,lying along the western margin of Huangling anticline,is one of the most important fault zones in Three Gorges reservoir area. The fault experienced strong activities during Cenozoic. Whether the fault zone crosses the Yangtze River is one of the key problems in previous studies,as it has significant influence on the assessment of geological hazards and earthquake stability in the reservoir area. Based on tectonic and geomorphic observations along this fault zone around Baixianchi in Changyang County,Huangkou in Zigui County,together with the comparisons between the geology in Guizhou and Quyuan Town in the north bank of Yangtze River and the Xiannüshan Fault zone,it is suggested that the north end of this fault zone locates around Huangkou village and doesnt traverse the Yangtze River northward.
The details are as follows: ① On the basis of field data collection,it is found that the Xiannüshan Fault zone,which stretches 80km,underwent thrust movement in Cenozoic,resulting in ravines and fault scarps,topographically. Whereas,on the northern bank of Yangtze River,faults are rarely found,and most of the faults are developed in the Jurassic strata,without topographical effects. Therefore,the Xiannüshan Fault zone has not stretched to the north bank of Yangtze River.②Fault gouge and tectonite zone were found developed on Xiannüshan Fault zone at Baixianchi village,but only tectonite zone was found at Zhouping village. There are also some branch faults close to the northern end of the fault zone. So,the activity of the fault zone weakened from south to north in Cenozoic. The fault zone extends northward and dies out at Huangkou. It doesnt stretch forward any longer as indicated by continuous strata,sparse joints,and small folds,etc.

On 14 November 2001,an extraordinarily large earthquake(M_S 8.1)occurred on the Hoh Sai Hu segment of the eastern Kunlun Fault,northern Tibetan Plateau. The seismogenic fault,Hoh Sai Hu segment,is a left-lateral fault with a high slip rate in the geological history,and the average slip rate reaches(14.8±2.8)mm/a since the late Pleistocene. Different slip rates of Hoh Sai Hu segment can affect the fault motion in the future. So,the paper analyzes the effect of different slip rates and different initial friction coefficients on the fault surface of the Hoh Sai Hu segment of eastern Kunlun Fault on the rupture behaviors of the fault. In the research,we apply the single degree of spring block model controlled by the rate- and state-dependent frictional constitutive laws. Using the fault dislocation model and based on ancient earthquake researches,historical earthquakes data and the achievements of previous researchers,we obtained the parameters of the model. Through the numerical simulation of rupturing motion of the Hoh Sai Hu segment in the future 6500 years under different slip rates,we find that a faster annual slip rate will shorten the recurrence interval of earthquake. For example,the earthquake recurrence interval is 2100a at a slip rate of 0.014m/a,which agrees with previous research results,but,the recurrence interval will be 1000～1500a and 2100～2500a,corresponding to the slip rates of 0.018m/a and 0.008m/a,respectively. Slip rate of fault has no regular effect on the coseismic slip rate and displacement of fault in an earthquake. The initial friction coefficient on the fault surface has effect on earthquake recurrence interval. A smaller initial friction coefficient will lengthen earthquake recurrence interval. At the same time,the smaller initial friction coefficient will lead to larger slip rate and displacement of fault when earthquake occurs.

A destructive earthquake occurred around Changde,Hunan Province,south-central China in 1631.The previous research of this earthquake yielded 4 different epicenter locations and isoseismal intensity maps.The authors replotted the isoseismals of this event based on checking historical earthquake records,in which the intensity value of the innermost isoseismal is Ⅷ.We concluded that the depth of this earthquake is from 15km to 18km.The basic considerations of our conclusion are as follows:a.This earthquake occurred in an area of lacustrine and fluvial deposits,with the magnitude of M 6¹/2;b.The geometrical center of the innermost isoseismal is the epicenter;c.The depth of epicenter is about 15 to 18km,which is based on the statistical relation between magnitude,depth of the earthquake source and epicenter intensity as well as Xie's statistical result.Finally,the authors discussed the influences of different ground conditions on the textual research and identification of historical data.

The 12 May 2008 Wenchuan Earthquake created about 240km-long surface fault ruptures along the Central Fault and about 72km along the Mountain Front Fault,two of the three sub-parallel secondary faults of Longmenshan thrust faults striking NE-SW,according to field investigation of surface faulting.From north to south,most of the widths of intense surface rupture zones are less than 40m,and above 1/2 are between 10～30m.Many buildings along fault surface ruptures were destroyed,including those with frame structure or reinforced concrete structure,and we also find some houses or buildings have withstood the strong earthquake and its aftershocks for their excellent performance of earthquake-resistance.The distance between fault scarps and the buildings are from 10 to 30 meters.Based on the field investigation,on the widths of surface rupture zones of historical strong earthquakes,and considering "crustal shortening" for inverse faulting and other various uncertainties,it is suggested that safety distance away from active fault in rebuilding is 25m.Within this distance,only one or two-storeyed buildings with higher standard of earthquake-resistance can be constructed,and public buildings,like schools and hospitals should be prohibited to build.

The neotectonic movement and characteristics of fault activity in the Anqing-Ma'anshan section of the Changjiang River valley are analyzed on the basis of data obtained from field investigation,shallow seismic prospecting and drilling. The results show that during neotectonic time this river valley section and its both sides as a whole was dominated by weak and intermittent uplift movement. As a consequence,owing to the effect of the activity of NE-and NNE-trending faults,relatively strong vertical differential movement occurred in Wuwei-Anqing area during Paleogene-Neogene,and had continued to early and middle Pleistocene. The NE-NNE-trending and NW-trending faults were developed in the bed rocks of the valley and its both sides. The former was formed during Indo-Chinese epoch,while the later was formed during Yanshan epoch. The most recent active period of the larger faults controlling the development of Cenozoic Basins is middle Pleistocene,while the newest activity of the relatively small faults developed within pre-Cenozoic group is pre-Quaternary. The Quaternary system in the valley is \{10～\}50m thick,consisting mainly of Pleistocene-Holocene deposits. The isopach of these deposits is smoothly distributed,indicating normal valley deposition. Seismic activity along the valley and its both sides is relatively weak,and historically only 4 destructive earthquakes have been recorded. Among these events,the largest one is the M5(3/4) earthquake occurring at Chaohu in 1585,and the other events including one with M5(1/4) and two with M4(3/4). Since the beginning of instrumental records in 1970,the largest magnitude that has been recorded so far is ML 3.7. All these results may provide better constraints on the assessment of the crustal stability for this river valley section.

In 1556, a strong earthquake with magnitude 8¹/₄ occurred in Huaxian, Shaanxi Province. The earthquake destroyed many places in Shaanxi Province and its adjacent regions, and also affected above 100 counties in Gansu Province, Hebei Province, Shandong Province and etc. According to historical documents, an earthquake was also recorded in Yueyang district, about 700km away from the Huaxian earthquake epicenter on the same day. Was it an isolated event or influenced by the Huaxian earthquake? It is a controversial problem.A lot of historical earthquake records of Yueyang district and its adjacent regions have been collected and studied, including the border area between Hunan Province and Hubei Province. The records for the 1556 AD Yueyang earthquake in “Annals of Yuezhou” in Longqing time of Ming Dynasty were judged to be more accurate than other historical documents. Earthquake recorded in 1556 AD in Yueyang district was a felt event with less strength. In analyzing historical materials, two principles for cases of earthquake records lacking have to be adopted: 1)Local annals to be used shall have other earthquake records. That means the annals writers paid attention to earthquake events; 2)Other types of disasters were recorded in the period of time when the earthquake occurred. That means there were no other kinds of historical disaster events influencing the records of earthquake.There were no earthquake records in counties like Tongshan, Tongchen, Puxi, Chongyang, Gongan, Shishou in the 34th year of Jiajing reign (1556 AD). It can be concluded that the earthquake records in Yueyang district in 1556 were not the effect of the Huaxian earthquake in Shaanxi Province in the same year. It was an isolated event. At last, according to records of local annals, the earthquake epicenter and magnitude are determined.

Lying on the eastern margin of the Tibetan Plateau,the northwestern Yunnan Province has attracted many tourists all over the world for its beautiful scenery and maltinational cultures. At the same time,however,it is also famous for frequent destructive earthquakes that have caused serious loss of life and properties. With rapid economic development,deficiency of electric power in China has become very serious. Therefore,it is inevitable to build a lot of hydropower stations in southwestern China,where hydropower resources are very abundant. A series of dams are planed to construct along the Jinshajiang River. The seismic safety evaluation should be done before the construction of hydropower station,while the appropriate delineation of potential seismic source (PSS) is a key point of the evaluation. In the probabilistic seismic hazard analysis,the distribution and upper bound magnitude of the PSS affect the determination of the design parameters in different engineering sites. For this reason,we have collected the former research results and the data obtained from recent geologic investigation on engineering sites of a series of hydropower stations and on regional seismicity. In order to get an insight into the seismotectonic indicator for the northwestern Yunnan Province,we have analyzed the seismogenic structures of several typical strong earthquakes,including the 1515 Yongsheng M 7^3/4,1925 Dali M 7.0 and 1996 Lijiang M 7.0,and delineate again the PSS for the northwestern Yunnan Province. The following principles and methods have been applied to the delineation of PSS: In the region where strong earthquake has occurred,upper bound magnitude of PSS is determined in the light of “Earthquake Recurrence” principle; in the region where seismogenic structures are clear but no strong earthquake was recorded,PSS are delineated according to“Tectonic Analog”principle; in the region where the segmentation of active fault has been studied thoroughly,the PSS can be demarcated precisely; early-middle Pleistocene faults can be taken as tectonic indicator for moderate-strong earthquake; in the region of buried active fault,images of seismic activity and geophysical anomaly can be used to determine the extension direction of the PSS. In the studied region,21 PSS are delineated with different upper bound magnitude,among which 1 is of upper bound magnitude 8.0,3 are of magnitude 7.5,9 are of magnitude 7.0,and 8 are of magnitude 6.5.

Geographic Information System (GIS) technique provides a powerful tool for managing,manipulating,analyzing and displaying space related data set. The compilation of seismic zoning map requires a vast amount of spatially referenced data. Therefore,the application of GIS to the seismic zo￣ning work allows the users to take advantage of various functions of GIS into the seismic zoning work. This paper introduces briefly the procedure and results of GIS application in the compilation of the New Seismic Zoning Map of China (2001). The GIS Database of the New Seismic Zoning Map includes three sub-databases: 1. Sub-database for seismic environment and potential seismic sources,including: (1)Earthquake catalog; (2)Quaternary active faults; (3)Cenozoic basins; (4)Earthquake mechanism; (5)Geophysical anomalies and deep structure; (6)Seismotectonic provinces and zones; (7)Potential seismic sources. 2. Sub-database for earthquake ground motion and seismic attenuation,including: (1)Seismic intensity and isoseism; (2)Observed seismic intensity; (3)Strong ground motion. 3. Sub-database for the results of probability calculation of seismic parameters.

By analyzing the seismicity in Kuqa depression,north Tarim Basin,some active basement faults are inferred from the distribution of earthquake epicenters in several profiles.The different deformation characteristics between the cover and the basement,as well as their reasons are investigated by comparing the locations of surface structures and basement faults,combined with some other results of deformation and kinematic research in this region.The following conclusions can be drawn from the present study: (1)The distribution of earthquake epicenters indicates that active basement faults exist along the tectonic grain corresponding to that of the surface structures of the Qiulitage-Yaken tectonic belt in Kuqa depression.In the basement beneath the East and West Qiulitage anticlines,there exist the East,North and South Qiulitage deep faults.Moreover,in the basement beneath the Yiqikelike anticline and Yaken anticline there exist the Yiqikelike and Yaken deep faults.These facts may imply that the development of surface structures was controlled by the deep structures. (2)It is revealed that a NE-trending deep strike slip fault is developed along the line from the west end of the Yiqikelike anticline to the Dongqiu No.5 well,and a NW-trending deep fault is developed on the west side of Baicheng.These two active deep faults cut the tectonic grain of the region,and might be responsible for the segmentation of tectonics in Kuqa depression,probably has led to the greater contraction at the middle segment of Kuqa depression(Kuqa-Baicheng)and smaller contraction at east and west segments.(3)The different characteristics of media result in the different deformation between the cover and the basement.The strength of the lithosphere at the basement of Kuqa depression is extremely high,so that deformation of the basement here is dominated by brittle fracturing and the generation of earthquake.The strength of the sedimentary rocks in the cover is much weaker,which may cause the plastic flow of the rocks under the action of long-period intense compression from the orogenic belt.And especially with the existence of coal or salt layers of extremely weak strength in the cover,a large scale aseismic detachment may occur along these weak layers.

Previous studies suggested that the Kuqa, Xinjiang M7.4 earthquake of 1949 is associated with the NEE trending Qiulitage Fault of the active tectonic zone at the southern foot of the Tianshan Mountain. Recently we have made a more detailed analysis of the seismotectonic setting of this event based on new data and results of crustal seismic sounding, petroleum geology, and research of active faults. Our work indicates that the underthrusting of the Tarim block beneath the Tianshan, as well as faulted block uplift and lateral overthrusting and spreading of the upper crust of Tianshan have given rise to the development of the Kuqa basin and thrust-fold system along the southern margin of the Tianshan Mountain. All these are thin-skinned structures developed in the sedimentary cover. The NE-trending Kuqa-Yixi No.1 Well Fault is an important transfer fault in the Kuqa basin, which is located in the NE-trending Urumqi-Kuqa-Keping tectonic zone. The results of seismological research on the M7.4 earthquake indicate that the earthquake bears no relation to the Qiulitage Fault, but is related to the Kuqa-Yixi No.1 Well Fault.

The Tianshan Mountains are a late Cenozoic rejuvenated mountain range in central Asia. The Urumqi Range front Depression is located along the northern margin of the Tianshan Mountains, consisting of a series of reverse fault-and-fold zones that form a typical thin skinned structural system. The southern Junggar Fault separates the Tianshan Mountains from the Urumqi Depression, in which three rows of reverse fault-and-fold zones are developed. From south to north, the three fault-and-fold zones are named Qigu reverse fault-and-fold zone, Manas reverse fault-and-fold zone and Dushanzi reverse fault-and-fold zone, respectively. Except for the anticlines in Qigu reverse fault-and-fold zone, the other anticlines in the Manas and Dushanzi reverse fault-and-fold zones are fault propagation fold. The shallow seismic exploration profiles show that the anticline consists of an overthrust fault zone, backward reverse fault and two partial anticlines. Four oil seismic exploration profiles show that the lower detachment fault exists in the Jurassic coal bearing strata, and the upper detachment fault exists in Paleogene strata. Some active folds are only formed on the ramps at the front of detachment fault. 2D electrical structure, deep seismic reflection profiling and crustal velocity structure across the northern Tianshan piedmont indicate that the active multilayered thrust tectonic system in the Urumqi Depression joins to a low-velocity(low resistance)layer through a brittle ductile transition zone in the crust of the Tianshan. The low-velocity layer in the upper crust of the Tianshan may be an active ductile shear zone. The brittle ductile transition zone under the Qigu reverse fault fold belt is the key link between the deep-seated active ductile shear zone and the shallow brittle fracture, and it is also the place of strong earthquake generation. The active surface structures in Manas earthquake region recorded only a part of the information of the activities of the deep-seated ductile shear zone.

It is known that strong earthquakes are usually associated with regional active tectonics and certain geophysical anomalies reflecting the features of regional deep structures. In this paper, the Bayes formula in statistic is used to quantify the relationship between the earthquake and the factors of seismogenic environment. These factors include active fault, Quaternary basin, Bouguer anomaly and geomagnetic anomaly.

Being a sub-system of Information System on Seismic Zonation in China, GIS on seismic environment and potential seismic source zone includes data of seismology, geophysics, earthquake records, seismic zonation and etc. It can provide service for earthquake research by querying, computer-aid mapping and statistic analysing. Furthermore, extra subroutines give ways to seismicity and obtaining seismic parameters for different seismic areas.