Xinxiang-Shangqiu Fault starts from Yuhekou in the west and extends eastward into Anhui Province through Xinxiang, Yanjin, Fengqiu, Lankao, Minquan, Shangqiu and Xiayi, with a total length of about 400km and a general strike of NWW. It is a regional concealed fault in Henan Province and a boundary fault between northern North China depression and southern North China depression.

This study focuses on the Fengqiu section of Xinxiang-Shangqiu Fault, which is the boundary structure between the Kaifeng sag, Neihuang uplift and Dongpu sag. Controlled by the NE-NEE trending Changyuan Fault and Yellow River Fault at its east and west end, this fault section has a length of about 30km and controls the Mesozoic to early Cenozoic sedimentation in the Kaifeng sag and the south side of Dongpu sag.

In this paper, the shallow structural characteristics and Quaternary activities of Fengqiu section of the Xinxiang-Shangqiu Fault are revealed by the combination of reflection seismic exploration and drilling detection. Two shallow seismic exploration profiles and one composite drilling geological section are arranged across the fault.

The results of shallow seismic exploration show that the Fengqiu section of Xinxiang-Shangqiu Fault is NWW trending. It is a north-dipping normal fault accompanied by several nearly parallel normal faults, and the fault is still active since the Quaternary.

In the composite drilling geological section at Yaowu, the latest faulted stratum is a clay layer between borehole YW5 and YW7, and the buried depth of the upper breakpoint is between 57.00~61.50m. Combined with the dating results of the collected samples, it is comprehensively judged that the latest activity age of Fengqiu section is the middle of late Pleistocene. Since the middle of late Pleistocene, the whole region is in a relatively stable tectonic period. It is verified that the comprehensive detection method of shallow seismic exploration with drilling can effectively find out the accurate location of hidden faults.

The zone with strong vertical differential movement is often the zone where earthquakes occur. The vertical differential movement between Kaifeng sag and Neihuang uplift is very strong, and the difference reaches nearly 1^{}000 meters since Neogene. Moreover, the structural pattern of the main strong earthquakes in the North China Plain is characterized by zoning in NE direction and segmentation in NW direction, especially at the intersections of NWW-trending faults and NE-trending faults. The Xinxiang-Shangqiu Fault intersects with a series of NE-NEE trending faults, including Tangdong, Changyuan, Yellow River and Liaolan faults from west to east. The Fengqiu section is at the intersection with the Changyuan Fault and the Yellow River Fault, and is located in the Fengqiu M6.5 potential seismic source area of the North China plain seismic belt. The intersection of two groups of Quaternary active faults is a favorable place for the preparation and generation of moderate and strong earthquakes. Therefore, the research results provide seismological basis for the site selection of major engineering projects, urban planning and construction in this area, and have reference value for discussing the geodynamic issues such as deep and shallow structural relationship and structural evolution of Xinxiang-Shangqiu Fault.

The Anqiu-Juxian Fault is the latest active fault in Tanlu fault zone, which is also the seismogenic fault of Tancheng M8.5 earthquake in 1668. In order to probe the shallow structure and the characteristics of faults in the eastern graben of Tanlu fault zone, we applied the high-resolution shallow seismic reflection method with multifold overlaying and stacking. In addition, we laid out two shallow seismic reflection lines across the Anqiu-Juxian Fault and the eastern graben of Tanlu fault zone. The shallow seismic profiles clearly reveal the stratigraphic interface morphology and shallow fault characteristics. The results show that the eastern graben of Tanlu fault zone is a graben basin consisting of multiple faults, and the thickness of Quaternary strata and graben structure characteristics are obviously affected and controlled by Changyi-Dadian Fault F₁ and Baifenzi-Fulaishan Fault F₂. Also, the eastern and western sides of the graben are the basement uplift areas, and the sediment thickness of the Quaternary strata in uplift areas is less than 30m. There are thick Cenozoic strata deposited in the barben, the stratigraphic morphology changes greatly laterally, showing an inclined form which is shallow in the west and deep in the east, and the Cenozoic strata are in angular unconformity contact with the overlying strata. The deepest part of Quaternary strata in the graben is located near the horizontal distance of 7400m, and its depth is about 190m. The Anqiu-Juxian Fault revealed by the shallow seismic reflection profile is composed of two branch faults dipping in opposite direction, which merge into one fault in the deep section. According to the discernible buried depth of the upper breakpoints of these faults and the characteristics of the Quaternary activity, the activity of Baifenzi-Fulaishan Fault on the western boundary of the eastern graben of Tanlu fault zone is relatively weak and the discernible depth of the upper breakpoint is 53m, we infer that the Baifenzi-Fulaishan Fault is a pre-Quaternary fault. The Changyi-Dadian Fault on the eastern boundary of the eastern graben of Tanlu fault zone not only cut the bedrock’s top interface, but also revealed signs of dislocation since Quaternary. The discernible depth of the upper breakpoint of Changyi-Dadian Fault is about 26~33m. The Anqiu-Juxian Fault is the latest active fault in the study area, which possess the characteristics of large scale and large penetration depth. The fault controls the deposition of the Cenozoic strata in the graben and plays an important role in the formation of the the eastern graben of Tanlu fault zone. The discernible depth of the upper breakpoint of Anqiu-Juxian Fault is about 17~22m. Therefore, we infer that the active ages of Changyi-Dadian Fault and Anqiu-Juxian Fault are the late Pleistocene and Holocene, respectively. The research results can provide seismological evidence for further understanding of activity mode and activity age of the seismogenic fault of the 1668 Tancheng M$8\frac{1}{2}$ earthquake, as well as the near-surface characteristics and activity of the Banquan segment of the Tanlu fault zone.

Based on the seismic data from temporary stations and regional stations in the northwestern area of Yunnan, the paper performs high-resolution detection and high-precision location on continuous waveforms recorded from February 25, 2018 to July 31, 2019 using waveform correlation methods and analyzes the seismicity characteristics of the Weixi-Qiaohou Fault in the northern section of the Red River fault zone. Studies have shown that the Weixi-Qiaohou Fault exhibits weak seismic activity currently, except for some special fault locations(such as terraces, intersections, etc.), but there may be a hidden steep-dip right-lateral strike-slip fault along the west side of the fault. Small earthquakes are frequent along the fault. The distribution of seismic activity and focal mechanism solutions indicate that this fault is a right-lateral strike-slip fault with a steep dip. Statistical parameters, such as seismic frequency, energy release rate and b-value, indicate that the seismic activity in the Weixi-Qiaohou Fault and its surrounding areas is relatively stable, and the regional stress enhancement is not obvious. The b-value is relatively high in most areas, and low b-value areas are mainly distributed in some special fault locations(such as terraces, intersections, etc.), but the scale is generally small. The statistical results of the ETAS model show that more than 40% of seismic activity may be affected by external factors such as deep fluid disturbance and remote strong earthquake triggering. This shows that the role of external trigger mechanisms in seismic activity cannot be ignored. The external triggering seismic activity factors are related to the disturbance of deep fluid activity and the dynamic triggering of long-distance strong earthquakes. Therefore, we believe that the Weixi-Qiaohou Fault is currently not active, but on the hidden branch fault to its west, small earthquake activity is clustering and has a tendency to increase. So, when assessing the seismic risk of the fault, comprehensive analysis shall be made on the activity of the main fault and the branch fault to its west.

3-D V_P and V_S images of southern Philippines at the 0~100km depths are generated by inverting a large number of travel-time data from the International Seismological Centre(1960-2017)through seismic tomography method. The results show lateral variation exists in the crust and upper mantle:High V_P and V_S anomalies emerge in mid-west Mindanao and Bohol Island, which might be caused by the combined action of huge magmatism and ophiolite accretion in the lower crust; low velocity anomalies of the upper mantle in the west of Mindanao are consistent with locations of volcanoes on the surface. It, thus, could be inferred that the low velocity anomaly is closely related to magmatic activity. The dense earthquake distribution along plate margin extending to 100km coincides with the strong activity of the Philippine Sea Plate which is located in the northeast and southeast of Mindanao. Relative weak activity of Sulawesi Sea Basin is presented simultaneously. The subduction of the Philippine Sea Plate is mostly concentrated in the crust and the top of the uppermost mantle.
Our tomographic images show that lateral heterogeneities exist in the crust and uppermost mantle of the southern Philippines. Low V_P and V_S anomalies emerge in Philippine Trench and Cotabato Trench, in contrast, high V_P and V_S anomalies appear in shallow crust of land area where a large number of earthquakes and magmatic activities develop. This may reflect strong tectonic processes between the Philippine Sea Plate and Philippine Mobile Belt.
Low V_P and V_S anomalies in the crust of eastern Mindanao coinciding with the location of volcanoes on the surface may show partial melting of crust material caused by dehydration of the subducting Philippine Sea Plate. Such a similar phenomenon can be also seen in the south of Negros Island and Cotabato Trench. Thus we infer that active tectonic behaviors are constrained within the crust of the Philippine Sea Plate, Sulu Sea Basin and Sulawesi Basin.Low V_P and V_S anomalies of the mantle in the mid-west of Mindanao island are associated with magmatic activity which may be caused by a collision between the east and west part of Mindanao at 5Ma. The fracture system in the west of Mindanao provides the possible passage ways of mantle hot material upwelling, coinciding with the model of geothermal distribution in this area. According to the geochemical analysis, ophiolite observed in Sanbaoyan and the western part of Mindanao could indicate material composition from crust to upper mantle on Eurasian continental margin which may show the evidence of rapid expansion environment of mid-ocean ridge. High V_P and V_S anomalies in the mantle of northeast and southeast of Mindanao coinciding with the distribution of massive earthquake along boundaries show a well agreement with the shape of the Philippine Sea Plate. Dense earthquake distribution in south Mindanao at 100km shows the Philippine Sea Plate has strong activity and stress accumulation in the upper mantle. On the contrary, the seismicity in southwest Mindanao and Cotabato Trench reduces rapidly at the depth from 50km to 100km, revealing weak subduciton and stress release of Sulawesi Basin in the mantle.

Based on the seismic data collected from regional permanent stations and 6 temporal stations, we analyzed the seismic activity from October 2008 to July 2011 in Rongchang area. On the basis of HypoDD relocated results, we used Match&Locate method to detect and located the micro-earthquakes. We obtained the focal mechanism solutions of some earthquakes with M_L ≥ 3.5 by using CAP method. Then we analyzed the temporal-spatial distribution of earthquakes and discussed the characteristics of micro-seismicity before the M_L5.1 earthquake occurring on September 10, 2010. We totally detected 3 354 micro-earthquake events, which are nearly 5 times of the earthquakes in the seismic catalog issued by China Earthquake Networks Center. The magnitude of the detected events is mostly from M_L-1 to 1, and the focal depth is from 2 to 4km. The magnitude-frequency analysis shows that the catalog completeness is obviously improved after adding the detected earthquakes, with the lowest magnitude decreasing from M_L1.0 to 0.3. The earthquakes hypocenters are mainly clustered along faults or buried faults and in a dominant depth range consistent with the depth of injection wells, and also show a tendency of lateral extension from injection wells. The focal mechanism solutions of 9 earthquakes of M_L ≥ 3.5 presented reverse faulting, as the same as the preexisting faults, indicating that earthquakes were surely related to reactivation of the faults. The strike, dip and rate of the causative faults separated in wide ranges, which indicates not only obvious changes in structure and strike of preexisting faults but also the effect of increasing pore pressure on the local stress field. Before the M_L5.1 earthquake on September 10 of 2010, seismicity firstly showed clustering in time and covered the most part of the seismogenic fault in space. Then an obvious seismic quiescence occurred and lasted about 3 months. The phenomenon is consistent with the mechanism of creep sliding and resistance-uniformization along the fault zone, suggested on the basis of laboratory experiments, and it may be one of patterns of sub-instability along fault zone. However, such explanation needs to be further confirmed.

As one of the rhombic blocks in North China, Kaifeng depression is on the south of the northern Huabei depression and in the north of the southern Huabei depression, bounded by Xinxiang-Shangqiu Fault and Zhengzhou-Kaifeng Fault, respectively. So far, the activity of Zhengzhou-Kaifeng Fault during Kainozoic era and the relationship between Zhengzhou-Kaifeng Fault and Xinxiang-Shangqiu Fault is still unknown. We interpreted several deep seismic profiles across Taikang uplift and Kaifeng depression on the basis of the strata sequence exposed by the 8 drill holes in the related area. The outcomes indicate that the Zhengzhou-Kaifeng Fault strikes EW on the whole, presenting undulating feature in plain, with a length about 154km. The profiles show the dip angle of the fault is steeper in the shallow than that in the deep, with an obvious "L-shaped" turning point. In Paleogene, the fault was a normal fault. In its hanging wall, the Kaifeng depression, there deposited hundreds of meters of Eogene. After middle Himalayan movement, Zhengzhou-Kaifeng Fault converted to a strike-slip fault, the dip angle became steeper, but the activity became weaker. The Zhengzhou-Kaifeng Fault ended its activity before Quaternary. As a response to the compression in the footwall caused by the sustained sinistral shearing, there developed a series of NW-trending, en echelon wide and gentle folds. Then, the activity in Kaifeng depression shifted to its north boundary.

On 23 September 2016, two earthquakes with magnitude of M4.9 and M5.1 occurred successively near Litang city in Sichuan Province, southwestern China. These two events are located between two large-scale fault zones, i.e., the Jinshajiang and Litang faults, in the northwest of the Sichuan-Yuannan active block, eastern Tibetan plateau. Based on the phase data and waveform data from the Sichuan regional seismic network, the M4.9 and M5.0 mainshocks and 390 aftershocks have been relocated using the multi-step locating method, and the focal mechanism solutions and centroid depths for the two mainshocks were calculated by the CAP waveform inversion method. From the spatial distribution of the relocated aftershocks and fault plane solutions of the two mainshocks, combining with the seismic intensity map and tectonic setting, we suggested that the two earthquakes were generated by the E-W trending northward dipping Hagala fault. The nodal plane consistent with the strike and dip of the Hagala fault is interpreted as the coseismic rupture plane with a dip angle of 44° for both the M4.9 and M5.1 earthquakes. And we inferred that the M4.9 and M5.1 earthquakes may be resulted from the nearly E-W striking Hagala normal faulting in the upper crust between the Litang and Batang regions due to the continuous eastward extrusion of the material of the Qiangtang block in the west.

On the basis of dividing and comparison of the Neogene strata and their bottoms revealed by 7 drill holes in Taikang area, we completed 101 seismic profiles with a total length of 4991km. Seismic data were compared and interpreted. The results indicate that Xinzheng-Taikang Fault, as a blind fault extending from Xinzheng to Taikang, which was considered as an EW striking fault from Xuchang to Taikang before, is the boundary of Taikang uplift and Zhoukou depression, controlling the sedimentation since Neogene Period. So we named the fault the Xinzheng-Taikang Fault, which is composed of two branches, mainly, the east and west branches. The west branch strikes northwest, dipping northeast with steep angles, and the fault plane extending more than 140km in length. As revealed on the seismic profiles, the eastern segment of the west branch is normal fault, while the west segment of the branch shows characteristics of strike-slip fault. The east branch trends NW-NEE, dipping SW-SSE with the length of about 50km. Two branches form a minus flower structure, indicating the strike slip-extension tectonic background. The bottom of Neogene strata is offset about 120m by the east branch, 20m by the west branch, and the bottom of Quaternary is probably offset too. Meanwhile, latest studies suggest that the composite strip of the two branches of Xinzheng-Taikang Fault, which is a tectonic transfer zone, is the subduction zone between the two strike-slip faults. The tectonic stress tends to be released by the east-west branch fault, and the zone should be the seismogenic structure for the recent seismicity in Taikang area. In 2010, the latest earthquake ofM_S4.7 occurred in this area, causing 12 people wounded. The seismogenic structure was considered to be the Xinzheng-Taikang Fault. So locating the fault exactly is of great importance to disaster prevention.

The Anqiu-Juxian Fault is a major branch fault and an active prominent fault of the Yishu Fault belt. The spatial distribution, geometric features and the latest activities of the Anqiu-Juxian Fault are studied by field survey and mapping in this study. The northern segment of the Anqiu-Juxian Fault between Juxian and Changyi can be divided into four segments, namely from north to south, the Changyi-Nanliu segment, the Anqiu-Mengtuan segment, the Qingfengling segment and the Mengyan segment. These segments are left-step en echelon arranged, and each of the fault segments consists of right-step en echelon arranged sub-segments. The Changyi-Nanliu segment is about 31km long and composed of 4 sub-segments in right-step en-echelon arrangement, namely, Wenshan sub-segment, Zhuli sub-segment, Shuangguan-Meicun sub-segment and Nanliu sub-segment, from north to south. The length of these sub-segments is 5km, 7km, 10km and 9km, respectively. The width of the stepover between them is about 2～3km. The Changyi-Nanliu segment generally strikes～15°, and the fault plane dips both west and east with dip angle 70°～80°. This segment offsets the widely distributed eolian yellow or orange fine sand and silt that were formed in the latest late Pleistocene, and it also offsets the mid-Holocene grey-yellow clay. The latest active age of the Changyi-Nanliu segment is the middle and late Holocene. This segment is characterized by right-lateral strike-slip motion with thrust and normal fault component, and the normal faulting activity is usually younger than the reverse faulting activity. The Anqiu-Mengtuan segment is about 50km long and exposes～21km. It strikes 15°～20°with the major fault plane dipping NWW with dip angle 70°～80°. This fault segment is characterized by right-lateral strike-slip motion with west-to-east thrust component. The segment can also be divided into two sub-segments, namely, the 13km long Anqiu-Guangong sub-segment and the 8km long Anshang-Mengtuan sub-segment, as in right-step en echelon arrangement, with a stepover of about 3km in width. The youngest offset stratum along the Anqiu-Mengtuan segment is the late Pleistocene, so, its latest active age is the late Paleocene and early Holocene. The Qingfengling segment is about 32km long, striking 15°～20°, dipping mainly southeast and partly west with dip angles more than 60° generally. This segment is characterized by right-lateral strike-slip motion with minor thrust component. It is composed of 4 sub-segments, which are the Xiaodianzi-Henhushan sub-segment, Kushan-Chezhuang, Maobu and Wangtaizi sub-segment, respectively from north to south. The length of these sub-segments is 6km, 8km, 14km and 4km, respectively. The former three sub-segments are aligned right-laterally. The Qingfengling segment offsets the upper late Pleistocene and the early Holocene strata; its latest active age is the early Holocene. The Mengyan segment exposes about 20km, striking 20° and dipping northwest with dip angle ～70°. It is also characterized by right-lateral strike-slip motion with thrust component, and its latest active age is the early Holocene.
The only historical earthquake that occurred on the north segment of the Anqiu-Juxian Fault between Juxian and Changyi is the 70BC Anqiu M7 earthquake. However, paleo-earthquake researches show that several strong earthquakes occurred along the Qingfengling segment and the Mengyan segment between the latest late Pleistocene to early Holocene. The time of the latest strong earthquake is ～3 500a BP, 2 084a BP (-70BC), ～10 000a BP, ～10 000a BP on the Changyi-Nanliu segment, Anqiu-Mengtan segment, Qingfengling segment, and Mengyan segment, respectively. Since the strong earthquake recurrence interval is still not known for each segment, the exact time for the next strong earthquake can't be predicted. However, according to the geometric features, latest active age, latest activity features, historic earthquake data and paleoearthquake documents of this active fault, the 4 segments do have seismotectonic conditions for generating M≥7 earthquake, and the potential earthquake risk does exist and may be rather high and imperative. Thus, the fault activities and the potential earthquake hazard should be considered during future earthquake hazard prevention and prediction.

The Qi-Chu earthquake,occurring in 179 BC(the first year of Hanwen Emperor,Han Dynasty),is a contentious historical earthquake event. Its basic parameters have not been determined. According to former researches on administrative division in Han Dynasty and analysis on historical earthquake records,the paper presents a discussion on the basic parameters of this earthquake event. A comprehensive method is developed to determine the epicenter,focusing on the border area between Qi and Chu States and the direct line of their capitals,and also considering other conditions from historical data. Moreover,based on results of seismic and geological investigation,the paper verifies the rationality of location of the epicenter from the seismotectonic point of view.Firstly,considering the frequent regime changes in Han Dynasty,the paper tries to recover the then administrative divisions and the boundary between Qi State and Chu State around the first year of Hanwen Emperor. Secondly,we analyzed carefully the range of the region indicated by historical earthquake records as "29 mountains collapsed and water burst during the Qi-Chu earthquake",and compared the spatial distribution and intensity of damage caused by other historical earthquakes to obtain important constraints for determining the location and magnitude of this event. It is suggested by textual analysis that the Qi-Chu earthquake ought to be the magnitude 7 earthquake occurring in the southern area of Pingyi County(N35.2?,E117.6?)on June 6,179 BC.Thirdly,geological structures and active faults around the epicenter area of Qi-Chu earthquake are studied by analyzing satellite image and geological data. As the earthquake was ruled out from the Tanlu Fault zone,it is considered that the Cangni active fault probably is the seismogenic structure of the Qi-Chu earthquake. Nearby the epicenter,the Cangni active fault with clear landforms and greatest displacement has controlled the development of the Baiyan Basin and offset the late Quaternary sediments.

Recognition of natural deformation during excavating ancient ruins and tomb is an important work of tracing or enriching the history and the historic records about prehistoric deformation.Recently,the earthquake department in cooperation with the cultural relic archaeology department conducted the special excavation research at the archaeological site of Gaixia ruins,Guzhen,Anhui,and discovered fault and cracks,which are demonstrated by preliminary study to be the vestiges of two coeval strata deformation events.The high speed deformation characteristic possibly represents two strong earthquake events,and the time is approximately in the Late Dawenkou culture stage.The crack was formed earlier than the fault.The discovery is the first in the eastern China.This work has filled the gap of research on recognition of natural dislocation event in Late Dawenkou culture stage and may improve the recognition of seismological relics in cultural stratum of human being in eastern China,especially in the transition belt between the north and south of China in the Changjiang-Huaihe area.

A 240km-long co-seismic surface rupture was produced along the Beichuan-Yingxiu Fault during the 2008 Wenchuan earthquake.We made a detailed survey at representative sites along the surface rupture and analyzed the data based on the geometry between the benchmark and deformation.The co-seismic vertical slip,horizontal dip-slip shortening,strike slip and moving direction of the hanging-wall were calculated based on the survey data of these sites.Results show that the spatial distribution of the co-seismic deformation of the fault varies a lot along the fault.The maximal horizontal slip,as we got till now,is located in the Shenxigou site of Hongkou with a value of 4.98m,and the maximal strike slip is also located in the same site with a value of 4.5m.The maximal vertical displacement is located to the northeast of Shenxigou with a value of 5.7～6.7m.The average horizontal slip for the NE trending fault is 1～2m,and the average vertical slip is 3m.But horizontal and vertical slip for the NW-trending branch from Xiaoyudong to Caoba is only 0.5～1.5m.The data from Leigu town show that the gravity deformation resulting from the fault-related landslide was perhaps superimposed on the tectonic one.The dip angles of the fault at the surveyed sites calculated from the horizontal shortening and vertical displacement indicate that the Beichuan-Yingxiu Fault is a steep dipping reverse fault with some strike-slip.From the comparison between field results and geophysical inversion,we believe that the spatial distribution of co-seismic fault-slip is related to the barriers and rupture process along the fault plane.

Field investigations show that the M_S8.0 Wenchuan earthquake of 12^th May 2008 ruptured two NW-dipping imbricate reverse faults along the Longmenshan Fault zone at the eastern margin of the Tibetan Plateau.This earthquake generated a 240km long surface rupture along the Beichuan-Yingxiu Fault characterized by right-lateral oblique faulting and a 90km long surface rupture along the Guanxian-Jiangyou Fault characterized by dip-slip reverse faulting.Maximum vertical and horizontal dispacements of 6.2m and 4.9m,respectively,were observed along the Beichuan-Yingxiu Fault,whereas a maximum vertical displacement of 3.5m occurred along the Guanxian-jiangyou Fault.This co-seismic surface rupture pattern,involving multiple structures,is among the most complicated of recent great earthquakes.Its surface rupture length is the longest among the co-seismic surface rupture zones for reverse faulting events ever reported.Aftershocks recorded by local network clearly outline the hanging wall of the Beichuan-Yingxiu Fault and indicate that the fault dips about 47? to the west.Industry seismic lines,in addition to surface ruptures and aftershocks,allow us to build a 3D model for the rupture geometry that shows crustal shortening is the dominant process along the Longmen Shan to accommodate long-term deformation.Oblique thrusting accomplished by the earthquake indicates that the east-southeastward extrusion of Tibet Plateau accommodates,in part,the continuing penetration of the Indian plate into the Eurasian plate,and this extrusion is transformed at the eastern margin of the Tibetan Plateau into crustal thickening and shortening along the Longmenshan Fault zone that is responsible for the growth of high topography in the region.

Based on the optical dating and paleomagnetic testing results,we make a chronostratigraphic research of Huanghua depression and Cangxian uplift which are two tectonic units of Tianjin area.In this paper,we establish a Quaternary stratigraphic section and make a new division of the Quaternary strata.The result shows that the two tectonic units have similar sedimentation histories,but many differences exist.On the one hand,both units have received transgression since the Quaternary and some marine strata formed to various extents,which indicates different transgression sedimentation histories between them;on the other hand,the Quaternary stratigraphic sequences of the two units are greatly different,indicating different sedimentation histories,and consequently,the type and thickness of sediments are obviously different,so they belong to different sedimentary units.The study also shows the depths of bottom interfaces of Holocene,upper Pleistocene and middle Pleistocene as 19m,45m and 103m,respectively in hole BZ1 in Huanghua depression and 13m,30m and 56m respectively in hole BZ2 and hole TN3 in Cangxian uplift.The depth of bottom interface of the Quaternary is about 162m,much smaller than the result of the previous Quaternary strata division.

It is the first time that several profiles of acoustic survey have been conducted across the Qianliyan Fault in the northern part of the South Yellow Sea. According to the difference of the late Quaternary fault activities revealed by the acoustic survey,the Qianliyan Fault may be divided by the Chaoliandao Fault into two segments. The southern segment is not active since the late Pleistocene,no offset in late Pleistocene strata has been observed on the acoustic profiles to the southeast of Rizhao. The northern segment is active in the late Pleistocene,normal faults are observed on the acoustic profiles west of Qianliyan island and offset the middle and upper part of the late Pleistocene layers,but no offset has been found in the latest Pleistocene and Holocene strata. In addition,it is found that the Qianliyan Fault offsets the late Pleistocene strata in the sea region 15km east of Shidao,Rongcheng County. In summary,the northern segment of the Qianliyan Fault is active in the latest Pleistocene in the sea region from the west of Qianliyan Island to the east of Shidao. Besides the Qianliyan Fault,other faults develop in the region to the southeast of the Qianliyan Island,which show obvious late Pleistocene active evidence. Therefore,the relative uplift status of the block where the Qianliyan Island lies on may be related to the late Pleistocene tectonic activities including that of the Qianliyan Fault. Both modern and history seismicity are relatively week in the region along the Qianliyan Fault. Since the establishment of the seismograph network in this region,no earthquake with magnitude equal or larger than 5and no small earthquake clusters have occurred along the Qianliyan Fault and in the surrounding area. The only historic earthquake is the 1932 M6(1/2) southern Yellow Sea earthquake which occurred in the sea region 28km southeast of the Qianliyan Fault. It is obviously that the seismicity is not concordant with the late Pleistocene active features of the Qianliyan Fault. Above all,the Qianliyan Fault is over 100km long from the Qianliyan Island to the offshore near Shidao and it is obviously active in the latest Pleistocene,the probability of the occurrence of a some M6.5 earthquake along the Qianliyan Fault should be considered in the practice of earthquake prediction and seismic hazard analysis.

The urban area in the eastern China region is mostly covered by the relatively thick loose Quaternary deposits,below which,in many cities,there exist many considerably large buried faults.In these thick-Quaternary-covering areas,does the date of the upper layers dislocated by the buried faults represent the latest faulting? In this paper,based on the integrated analysis on the data of geology,geophysics and earthquakes of cities in the east of China,including Xingtai and Tangshan,we discussed the relation between the upper offset point and the latest activity times of the buried faults in these areas covered by thick Quaternary.Our study shows,in the area with very thick recent deposits in East China,one should not determine the latest faulting of one fault fully according to the younger layers displaced by the fault.To a fault running through the area covered with thick young deposits,its latest active period should be determined comprehensively by the tectonic settings,the controlling of the fault to the young strata,the youngest layer displaced by the fault,the thickness of the young deposits,seismicity and modern tectonic stress field,etc.

The western Qinling Fault zone is one of the main left-lateral strike-slip active faults in northeastern Tibet. At site of Huangxianggou, the behavior of the fault zone shows typical strike-slip movement. Detailed analysis on the amounts of the offset of the late Quaternary landforms and geologic bodies along the fault shows that at Huangxianggou the maximum horizontal displacement since the late of late-Pleistocene is about 40～60m, and the minimum is 6～8m which is possibly the amount of one principal slip associated with one large earthquake event. And it is also inferred that the amounts of the displacement along the fault can be grouped, and between the groups there is a stable increment of 6～8m. The grouping and the increment of amounts of the offsets suggest that this fault segment displays an activity associated with characteristic earthquakes, and the 7 groups of the displacement values represent 7 characteristic events on the fault. Analysis on the microgeomorphology related to the faulting, such as periodic sag-ponding and deformed pluvial fans, also suggests the corresponding events. Thus it can be inferred, the activity of the fault zone has been dominated by several strong movements since late Late-Pleistocene.

The Yishu Fault zone is a part of the Tanlu Fault zone that passes through Shandong Province and the northern area of Jiangsu. It is composed of 5 nearly parallel faults among which the Anqiu-Juxian Fault is the most important and prominent active fault since late Pleistocene and is usually considered to be the seismogenic fault of the 70 BC M 7 Anqiu earthquake and the 1668 AD M 8¹/₂ Tancheng earthquake. By detailed research in recent years, e.g. the active fault mapping implemented during the “Eighth Five-Year Plan” period, we have gained thorough knowledge of the middle segment of the Anqiu-Juxian Fault to the south of Juxian, while the knowledge of the segment to the north of Juxian has been poor, even no active fault profiles have ever been found. Recent discoveries about the geometry and activity of the Anqiu-Zhuli segment of the Anqiu-Juxian Fault are introduced in this paper. The segment consists of the Nanliu sub-segment, the Shuangguan-Meicun sub-segment and the Zhuli sub-segment. All these sub-segments are distributed along the linear boundary line between hilly area and plain, or locate in the eastern slope of the NNE-trending hills. These fault segments are featured with right-lateral strike-slip movement combined with dip component, and their latest activity age is late Pleistocene to early Holocene. In conclusion, The Anqiu-Juxian Fault is the predominant active structure between Juxian and Changyi in the north of Shandong, and it should have some connections with the occurrence of the 70 BC M 7 Anqiu earthquake. Since the elapsed time is nearly 2100 years, the future earthquake risk in this area shall be emphasized.

The Kunlunshan M_s 8.1 earthquake of 2001 is a large earthquake produced by a large-scale intraplate strike slip faulting. Field observation shows that the surface rupture of this earthquake is about 426km long,and the maximum sinistral displacement is about 6m. As compared with the other similar intraplate large earthquakes,its rupture length is extraordinarily longer but its horizontal displacement is relatively small. The distribution of horizontal displacement along the surface ruptures is markedly controlled by fault structure. At the section where the horizontal displacement is small,the vertical displacement is also smaller,and no transformation of horizontal and vertical displacements is observed. This feature is also different from that of the other earthquakes. The relationship among rupture length,displacement and seismic magnitude follows a certain empirical equation,in which the ratio between the average displacement amount and rupture length is called "Ultimate linear strain",and is constantly within the range of 10^-5 for the rupture in the earth's crust. This feature can be used as criterion for testing the independency and integrality of the rupture segments. In this paper,we calculated the "ultimate linear strain" of the entire rupture zones and sub-segments of several large earthquakes,including the 1920 Haiyuan earthquake,1951 Bong Co earthquake,1932 Changma earthquake and 2001 Kunlunshan earthquake. The results show that average values of ultimate linear strain of the Haiyuan,Bong Co and Changma earthquakes are approximately close to the statistic value,but the values of ultimate linear strain of their sub-segments are significantly higher. In contrast,the value of ultimate linear strain for the entire surface rupture of the Kunlunshan earthquake is much lower than the statistic value,but the values of ultimate linear strain of its four sub-segments,except the west Taiyanghu segments,are close to the statistic value. Therefore,the Kunlunshan earthquake (M_s 8.1) should be produced by four relatively independent faulting events,instead of a uniform faulting. These characters provide geological evidence supporting the deduction that the Kunlunshan earthquake is successively triggered multiple earthquake events,rather than a single earthquake.

The 14 November,2001 M_S8.1 West Kunlun Pass Earthquake is the largest event associated with the longest surface rupture that has occurred in the Tibetan Plateau since 1951. We made 291 surficial left lateral slip measurements and 111 net vertical slip measurements along the main fault zone. The displacement on the main fault strand is dominated by left lateral strike slip of 2.7m in average,with vertical slip component of mostly less than 1m. The maximum left lateral slip is 6.4m,with as much as 5.1m of vertical slip component. Sinistral surficial slip is quite variable along the main strand of the rupture at distance scales ranging from a few tens of meters to a few hundreds of kilometers,with slip gradient ranging between 10^-1～10^-4. The slip variations over short length scales (tens of meters to a few kilometers) might be caused by variations in thickness of unconsolidated sediments,fault strike and slip of the previous earthquake,distributed non brittle deformation and secondary fractures,complexities in fault geometry,and perhaps by measurement error. Despite this short wavelength variability,there is fairly regular long wavelength (tens to hundreds of kilometers) behavior to the east of the Buka Daban Peak. One notable characteristic of slip distribution along the faults is that very large surficial slips (as large as 5～6 meters) were observed at 5～6 sites located at different surface rupture segments in asymmetry to their left lateral slip functions. Slip on each of these rupture segments diminishes away from the highest slip site to its terminations with different slip gradients. This asymmetric distribution of slips may indicate the propagation direction of the rupture along the faults. This long wavelength variation in slip might be influenced by fault geometry,while the segmentation of the surface rupture zone might play a key role. It should be pointed out that the surficial slip (at both short and long length scales) is only a near field slip measured in the field by using tape measure. Therefore,it should be considered as a minimum value,and may represent the real variations in the amount of brittle slip on visible fractures at the surface,but it potentially underestimates the actual slip produced by the earthquake and slip distribution over the whole surface rupture due to the difficulty in identifying distributed non brittle deformation. This calls for caution in discriminating between one or multiple discrete events and in estimating the size of past and future earthquakes by using displaced deposits in trenches or offset geomorphologic features along strike slip prehistoric fault ruptures.

Taipingzhuang observation well is one of the wells that has been observed for over ten years and has experienced some earthquake cases.In recent years,the ground water level has significantly fallen due to large amount exploitation of underground water,and especially geothermal exploitation around the Taipingzhuang observation well.This paper presents the analysis of the annual behavior of water level,water temperature,escaped gases and fault gases of the Taipingzhuang observation well,on the basis of the normal behavior in former years and the tectonic setting of the well.The analysis shows that the variation of water level and water temperature depends on the rainfall at the recharge area of the well,and the variation of water temperature is affected also by local rainfall.Especially,the withdrawal of newly drilled wells around the observation well greatly affects the variation of water level,water temperature and escaped gases of the observation well.After eliminating the effects of rainfall and human factors,the observed data of the Taipingzhuang well will still be useful for the prediction of seismic regime in Beijing region. After eliminating interference factors,the water level and water temperature of Taipingzhuang well for the year of 2002 was consistentwith the normal annual behavior of the well,and no significant anomalywas observed.The water level in 2002 was lower in winter and higher in summer and autumn,in consistence with the ordinary annual behavior of the well.However,the rise of water level of the well after the end of heating period in spring was very slow,and the risen water level was4m lower than the highest level in the same period of 2001.This might be attributed to the pervasive water level drop in Beijing region,and especially to the large amount exploitation of hot water around Taipingzhuang area. H₂ content of the escaped gases in the Taipingzhuang observation well begins to increase anomalously with the withdrawal of hot water in winter,and than decreases to normal value at the end of heating period in March.This phenomenon can be attributed to the following reasons:The large amount exploitation of hot water causes the significant drop of water level,which in turn causes the decrease of pore pressure in the layer;in this condition the gases will expand and H₂ may remove rapidly,causing the increase of H₂ content in escaped gases.In addition,the gases from the depth are concentrated mainly in the space above the aquifer,and the drop of water level will cause the escape of these stored gases,and hence the increase of H₂ content.

Recently, remarkable rare gas anomalies have been observed in the water of Baolong and Tai-ping-zhuang wells in Beijing area, and Xialiao No.1 well in Xiaxian County, Shanxi Province. All these three wells are located in North China. According to the characteristics of rare gas anomalies in the three wells and the relationship between the anomalies and groundwater levels, theoretical analysis and experimental study have been carried out to gain an insight into the genesis of the anomalies. The results of experiments show that the volume of gases in the pores and fractures varies significantly with the evolution of groundwater dynamic condition. We find that the gas volume will expanse about 0.009 0% when the water level drops for 100mm. This may indicate that the anomalies of rare gases in these three wells are resulted from the expansion of gas volume and escape of gases due to the drop of groundwater level and the decrease of pore fluid pressures. It is proposed, therefore, that the rare gas anomalies discussed in this paper should not be earthquake precursor, but are anomalies caused by interference factors.

A series of studies have been carried out to gain an insight into the Quaternary fault activities in Qingdao City and its surrounding area. The spatial distribution, geomorphic features and the features of the structural planes of the faults, as well as the relation between the faults and Quaternary strata have been studied in detail. Moreover, the ages of the relevant fault zone materials and unfaulted overlying Quaternary deposits have been dated by TL and/or ESR methods. This paper summarizes the achievements of these recent studies. It is concluded that the NE trending faults in Qingdao City and its surrounding area share some similarities in their dimension, orientation, age of faulted rocks, mode of motion, and age of the latest faulting. Their latest active period was in the mid late stage of middle Pleistocene. The faults have no longer been active since late Pleistocene. Moreover, in this area no fault of other strikes has been found to be active since late Pleistocene. According to historical earthquakes, the current activity of small earthquakes and Quaternary fault activities in this area, it is suggested that there's no condition for the occurrence of M_S≥6 earthquakes within this area, but it would not be surprising if an M_S≈5 earthquake should occurs in the future.

Zhangzhou basin is the largest Quaternary fault basin in Fujian Province. Five earthquakes of magnitudes 5 1/2, 6 1/2, 6 1/4, 5.0 and 5 1/4 had successively occurred in this basin in 1067, 1185, 1445, 1549 and 1601. It is an area with highest intensity and frequency of historical earthquakes in Fujian Province. In this paper we discuss the latest tectonic motion and the seismic risk of this basin on the basis of the analysis of the rejuvenation of the basin, fault activity, neotectonic differential movement within the basin and the periodicity of strong earthquakes. We have also compared this basin with the other basins or plains in the coastal areas of Fujian Province. It is found that since the late Pleistocene the basin has got rid of the constraint of the NE-trending faults to continue its propagation toward the southeast. At that time, the NE-trending faults within the basin were dominated by strong dextral strike slip with dip-slip component, while the NW-trending faults were dominated by sinistral strike slip with dip-slip component. Elevation and subsidence have frequently occurred in this basin since late Quaternary. As a result, the early Holocene alluvial deposits overlapped the late Pleistocene alluvial beds, forming the first level terrace. The lower part of the late Pleistocene beds is still below the present river level. The elevation of some early Holocene deposits is higher than that of the middle Pleistocene deposits, indicating that during the late Pleistocene time the amplitude of subsidence was greater than the amplitude of elevation in this basin. The differential movement within the basin was very intensive. In elevated area the level of early Holocene alluvial deposits is 20m higher than the river level, while in subsided area the top of these alluvial deposits is 27 10m below the earth's surface, resulting in a height difference of 47 10m between the two. The latest historical earthquake in this basin has occurred for 400 years, which exceeds greatly the 52～260 years interval of strong earthquakes in this area. This area, therefore, is a high seismic risk area. As compared with the other basins and plains in the coastal areas of Fujian Province, this basin has some peculiarities, and that is why 5 strong earthquakes had occurred here. It is expected that a destructive earthquake may occur in this area in the future. Moreover, the historical strong earthquakes in this basin all occurred directly beneath the city, causing more severe damage than the earthquakes of the other types.

Unconsolidated Quaternary sediments are widely distributed on the Earth surface. As active faults usually disturb the Quaternary sediments, the study of the deformation styles of these sediments is therefore of great significance to the assessment of fault activity and property. Oriented samples of unconsolidated Quaternary sediments deformed by faulting have been collected from some typical active fault profiles. They were solidified in lab by filling epoxy resin diluted by acetone with solidified agent. Oriented thin sections were cut according to the primitive orientations of the samples in the field. Deformation features of the samples were observed carefully under optical microscope. An attempt has been made to identify the deformation microstructures of the samples, which may reflect the features of faulting. The observations show that the deformation in unconsolidated Quaternary sediments can be classified into two styles: fracturing and flow. The fracturing deformation is represented by parallel slip bands, straight slip planes, broken mineral grains etc, while the flow deformation is characterized by flow structures, mineral grain rotation, drag structure of clay minerals and others. The deformation style and property of unconsolidated Quaternary sediments depend to a large extent on the characteristics of the sediments themselves. Unconsolidated Quaternary sediments are composed mainly of clastic grains and clays. They can be considered as a visco-elastic body, and may behave as elastic-plastic materials. The duration of applied force has a great effect on the deformation behavior of unconsolidated Quaternary sediments. It means that strain rate plays an important role in the deformation behavior of unconsolidated Quaternary sediments. It is suggested that the fracturing deformation is generated by high strain rate event such as earthquake, while the flow deformation is generated by low strain rate event such as creep slip. The detailed observation of deformation styles of unconsolidated Quaternary sediments,therefore, may provide important information on the kinetic process of faulting.

Invisible faults often developed in Quaternary unconsolidated sediments including concealed faults and die-out faults, which lead to complexity and multi-solution for paleoearthquake research. In this paper, original-state directional samples related to invisible or die-out faults are collected from some typical paleoearthquake profiles and solidified in laboratory. Microstructures have been observed after grinding slides in three-dimension coordinate system. Some indicators of invisible faults have been found in micrscopic field. The mechanisms of die-out faults have also been studied. It is suggested that according to microstructural observation, to confirm or negate the existence of concealed faults or to trace the terminated levels of die-out faults, can help us determine the age and periods of paleoearthquake events more accurately combining with macroscopic observation and age dating.

By detailed field geological survey, combining with analyses of the basic parameters, focal mechanism solution, the characteristics of the earthquake sequence and macroseismic damage investigation of the 1995 Cangshan M_S5.2 earthquake, we propose that the seismogenic structure of the event is the Wanjiazhuang fault The magnitude of this event does correspond with the scale and activity of the fault and the seismotectonic background

Based on explaining satellite pictures,five main faults in the Tai'an region,Shandong Province have been investigated According to age research,it is found that the piedmont fault of Taishan is a late Pleistoncene active fault with the latest active age of (1.42±12)×10⁴a B.P. The seismogenic structure of the Taishan earthquake occurred in 1831 B.C. is discussed It is suggested that this earthquake may be related to the activities of the piedmont fault of Taishan and may be a medium earthquake (M ≤6.5) without surface ruptures

his paper present the anomalies of underground fluid in the Taipingzhuang well of Beijing suburbs which appeared several times before the Zhangbei Shangyi M 6.2 earthquake.Though these anomalies seem to be related to Zhangjiakou M 4.2 earthquake of May 25,1997 and Wulatehouqi M 5.0 earthquake on October 21,1997,we consider that the anomalies and the earthquakes should be regarded as the respond to crust activity in the north area of North China and increase of stress in the regional stress field.So it can be identified as the intermediate short term precursor of Zhangbei Shangyi M_s 6.2 earthquake January 10,1998.

The effect of underlying bedrock slope on the seismic ground motion is indicated by the seismic microregionalization for the study area.Two-dimentional inversion has been used in the seismic model and the author has worked out an extending program SAP 5.The main results are as follows:vertical ground motion is significant;distributions of horizontal motion vary with the distance of the bedrock from the center of the basin;the spectra show a regular variation;input of multi-directional seimic waves shows larger effect than does input of mono-directional seismic waves on the ground motion.As indicated by data the effect of underlying bedrock slope on the ground motion is significant compared with the site condition.