GROWTH STRATA REVEAL THE QUATERNARY TECTONIC FEATURE OF GUDIAN FAULT IN SONGYUAN,SONGLIAO BASIN,CHINA

Because of the frequent seismic activity in Songyuan in recent years, the modes of tectonic movement in this area since the Quaternary have attracted increasing consideration. This paper selects the Gudian Fault which locates between the southeast uplift and central depression of Songliao Basin as the research object. We discussed the Quaternary structural characteristics of the Gudian Fault using growth strata. Using the data of deep seismic reflection prospecting for oil, we determined the location, geometry and kinematics characteristics of the Gudian Fault. And using the shallow seismic reflection prospecting data, the combined drilling exploration data and TL data, we determined precisely the inversion tectonics feature of the fault since late Cenozoic. Based on the above data, we believe that the Gudian Fault is dominated mainly by thrust-folding since Quaternary. A set of growth strata is recognized by shallow seismic reflection exploration data. According to the overlap of growth strata and the relationship between deposition rate and uplift rate, we confirm that the uplift rate of Gudian Fault in the early of Early Pleistocene is less than 0.15mm/a. And according to the offlap of growth strata and the relationship between deposition rate and uplift rate, the uplift rate of the Gudian Fault is more than 0.091mm/a in the late of Early Pleistocene and more than 0.052mm/a in middle Pleistocene. According to the chronological data, it is determined that the uplift rate of the Gudian Fault is 0.046mm/y since 205ka.     

NEW EVIDENCES FOR LATE QUATERNARY ACTIVITY IN THE SOUTHERN SEGMENT OF THE YISHU-TANGTOU FAULT,THE TAN-LU FAULT ZONE,AND ITS TECTONIC IMPLICATION

The Tan-Lu Fault Zone(TLFZ), a well-known lithosphere fault zone in eastern China, is a boundary tectonic belt of the secondary block within the North China plate, and its seismic risk has always been a focus problem. Previous studies were primarily conducted on the eastern graben faults of the Yishu segment where there are historical earthquake records, but the faults in western graben have seldom been involved. So, there has been no agreement about the activity of the western graben fault from the previous studies. This paper focuses on the activity of the two buried faults in the western graben along the southern segment of Yishu through combination of shallow seismic reflection profile and composite drilling section exploration. Shallow seismic reflection profile reveals that the Tangwu-Gegou Fault(F₄)only affects the top surface of Suqian Formation, therefore, the fault may be an early Quaternary fault. The Yishui-Tangtou Fault(F₃)has displaced the upper Pleistocene series in the shallow seismic reflection profile, suggesting that the fault may be a late Pleistocene active fault. Drilling was implemented in Caiji Town and Lingcheng Town along the Yishui-Tangtou Fault(F₃)respectively, and the result shows that the latest activity time of Yishui-Tangtou Fault(F₃)is between(91.2±4.4)ka and(97.0±4.8)ka, therefore, the fault belongs to late Pleistocene active fault. Combined with the latest research on the activity of other faults along TLFZ, both faults in eastern and western graben were active during the late Pleistocene in the southern segment of the Yishu fault zone, however, only the fault in eastern graben was active in the Holocene. This phenomenon is the tectonic response to the subduction of the Pacific and Philippine Sea Plate and collision between India and Asian Plate. The two late Quaternary active faults in the Yishu segment of TLFZ are deep faults and present different forms on the surface and in near surface according to studies of deep seismic reflection profile, seismic wave function and seismic relocation. Considering the tectonic structure of the southern segment of Yishu fault zone, the relationship between deep and shallow structures, and the impact of 1668 Tancheng earthquake(M=8(1/2)), the seismogenic ability of moderate-strong earthquake along the Yishui-Tangtou Fault(F₃)can't be ignored.     

钻探揭示的黄河断裂北段活动性和滑动速率

黄河断裂是银川盆地内展布最长、切割最深的一条深大断裂,也是银川盆地的东边界。由于其北段呈隐伏状,因此,该段的活动性和滑动速率长期未知,影响了对盆地演化和地震危险性的认识。文中选择具有石油地震勘探基础的陶乐镇为研究场点,以人工浅层地震勘探结果为依据,在黄河断裂北段布设了一排钻孔联合剖面,并对标志层进行年代测试,获得了断裂的活动时代和滑动速率。结果表明,黄河断裂北段在晚更新世末期或全新世有过活动,在（28.16±0.12）ka BP 以来的累积位移为0.96m,晚第四纪以来的平均滑动速率为0.04mm/a,该值明显低于南段灵武断层（0.24mm/a）;尽管向下切割了莫霍面,黄河断裂晚第四纪活动强度和发震能力均要低于切割相对浅的贺兰山东麓断裂;黄河断裂可能在新生代之前已经强烈活动并深切莫霍面,新生代以来,银川盆地的构造活动迁移分解到以贺兰山东麓断裂为主的多条断裂之上,地壳双层伸展模型可解释银川盆地现今深浅部构造活动间的联系。     

NEW EVIDENCES OF HOLOCENE ACTIVITY IN THE JIANGSU SEGMENT OF ANQIU-JUXIAN FAULT OF THE TANLU FAULT ZONE

Anqiu-Juxian Fault is an important fault in the Tanlu fault zone, with the largest seismic risk, the most recent activity date and the most obvious surface traces. It is also the seismogenic fault of the Tancheng M8 1/2 earthquake in 1668. There are many different views about the southern termination location of surface rupture of the Tancheng earthquake and the Holocene activity in Jiangsu segment of this fault. Research on the latest activity time of the Jiangsu segment of Anqiu-Juxian Fault, particularly the termination location of surface rupture of the Tancheng earthquake, is of great significance to the assessment of its earthquake potential and seismic risk. Based on trench excavation on the Jiangsu segment of Anqiu-Juxian Fault, we discuss the time and characteristics of its latest activity. Multiple geological sections from southern Maling Mountain to Chonggang Mountain indicate that there was an ancient seismic event occurring in Holocene on the Jiangsu segment of Anqiu-Juxian Fault. We suggest the time of the latest seismic event is about(4.853±0.012)~(2.92±0.3)ka BP by dating results. The latest activity is characterized by thrust strike-slip faulting, with the maximum displacement of 1m. Combined with the fault rupture characteristics of each section, it is inferred that only one large-scale paleo-earthquake event occurred on the Jiangsu segment of Anqiu-Juxian Fault since the Holocene. The upper parts of the fault are covered by horizontal sand layers, not only on the trench in the west of Chonggang mountain but also on the trench in Hehuan Road in Suqian city, which indicates that the main part of the Jiangsu segment of Anqiu-Juxian Fault was probably not the surface rupture zone of the 1668 Tancheng M8 1/2 earthquake. In short, the Jiangsu segment of Anqiu-Juxian Fault has experienced many paleo-earthquake events since the late Pleistocene, with obvious activity during the Holocene. The seismic activities of the Jiangsu segment of Anqiu-Juxian Fault have the characteristics of large magnitude and low frequency. The Jiangsu segment of Anqiu-Juxian Fault has the deep tectonic and seismic-geological backgrounds of big earthquakes generation and should be highly valued by scientists.     

松原市扶余北隐伏活动断裂地震潜势研究

扶余肇东断裂带是松辽盆地中一条重要的隐伏发震断裂带,2006年和2014年在此断裂带上发生了多次近6级地震,地震活动主要集中在断裂的东北段和查干花段。在2012—2014年的松原市活断层探测工作中,探明扶余肇东断裂带东北段经过松原市区,该段呈近EW向,具有明显的分段性和独立性,将其命名为扶余北断裂。通过三维物探资料和浅层人工探测,确定了扶余北断裂的空间展布和剖面特征,并利用联排钻孔探测和光释光测年技术,确定该断裂存在晚更新世以来的活动;利用石油物探资料获得的基岩面破裂规模,对扶余北断裂的地震潜势进行了估计,并进行了概率性地震危险性研究。     

PALEOEARTHQUAKES ALONG PUXIONG FAULT OF DALIANGSHAN FAULT ZONE DURING LATE QUATERNARY

Daliangshan fault zone (DFZ) constitutes an indispensable part of Xianshuihe-Xiaojiang fault system which is one of the main large continental strong earthquake faults in China.Puxiong Fault,the east branch of middle segment of DFZ,is the longest secondary fault.Its paleoseismic activity plays an important role in evaluating regional seismic activity level and building countermeasures of preventing and reducing the earthquake damage.The active fault mapping as well as the study of paleoseismological trench in recent years illustrates that Puxiong Fault is a slightly west-dipping high-angle left-lateral strike-slip fault with strong activity since late Pleistocene.Two trenches excavated across this fault reveal 2 and 3 paleoearthquakes that ruptured the fault at 8206 BC-1172 AD,1084-1549 AD,and 17434-7557 BC,1577-959 BC and 927-1360 AD,respectively.The OxCal model combining the results from both trenches and the another one in previous study across the fault with the historical earthquake record yields the elapsed time of~0.7ka of the latest paleoearthquake event,and the interval time is~2.3ka between the last two events.In the model,the penultimate event is considered to be recorded in all trenches.As all the three trenches are located at north part of the Puxiong Fault whose strike is apparently different from the south part,the~57km long north secondary segment is supposed to be the seismogenic structure of the paleoearthquake.According to the empirical scaling laws between magnitude and rupture length,the magnitude of the surface ruptured paleoearthquake is estimated to be more than M7 with the coseismic displacement~3.5m.However,the difference between the time of the paleoearthquake events on the middle and south segments of DFZ illustrates their independence as earthquake fracture units,and furthermore,the lower connectivity and the new generation of DFZ.     

RESEARCH ON THE CHARACTERISTICS OF QUATERNARY ACTIVITIES OF SU-XI-CHANG FAULT

Running across the urban areas of Changzhou, Wuxi and Suzhou, the NW-trending Su-Xi-Chang Fault is an important buried fault in Yangtze River Delta. In the respect of structural geomorphology, hilly landform is developed along the southwest side of the Su-Xi-Chang Fault, and a series of lakes and relatively low-lying depressions are developed on its northeast side, which is an important landform and neotectonic boundary line. The fault controlled the Jurassic and Cretaceous stratigraphic sedimentary and Cenozoic volcanic activities, and also has obvious control effects on the modern geomorphology and Quaternary stratigraphic distribution. Su-Xi-Chang Fault is one of the target faults of the project "Urban active fault exploration and seismic risk assessment in Changzhou City" and "Urban active fault exploration and seismic risk assessment in Suzhou City". Hidden in the ground with thick cover layer, few researches have been done on this fault in the past. The study on the activity characteristics and the latest activity era of the Su-Xi-Chang Fault is of great significance for the prevention and reduction of earthquake disaster losses caused by the destructive earthquakes to the cities of Changzhou, Wuxi and Suzhou. Based on shallow seismic exploration and drilling joint profiling method, Quaternary activities and distribution characteristics of the Su-Xi-Chang Fault are analyzed systematically. Shallow seismic exploration results show that the south branch of the Su-Xi-Chang Fault in Suzhou area is dominated by normal faulting, dipping to the north-east, with a dip angle of about 60° and a displacement of 3~5m on the bedrock surface. The north branch of the Su-Xi-Chang Fault in Changzhou area is dominated by normal faulting, dipping to the south, with a dip angle of about 55°~70° and a displacement of 4~12m on the bedrock surface. All breakpoints of Su-Xi-Chang Fault on the seismic exploration profiles show that only the bedrock surface was dislocated, not the interior strata of the Quaternary. On the drilling joint profile in the Dongqiao site of Suzhou, the latest activity of the south branch of Su-Xi-Chang Fault is manifested as reverse faulting, with maximum displacement of 2.9m in the upper part of Lower Pleistocene, and the Middle Pleistocene has not been dislocated by the fault. The fault acts as normal fault in the Pre-Quaternary strata, with a displacement of 3.7m in the Neogene stratum. On the drilling joint profile in the Chaoyang Road site of Changzhou, the latest activity of the north branch of Su-Xi-Chang Fault is manifested as reverse faulting too, with maximum displacement of 2.8m in the bottom layer of the Middle Pleistocene. The fault acts as normal fault in the Pre-Quaternary strata, with a displacement of 10.2m in the bedrock surface. Combining the above results, we conclude that the latest activity era of Su-Xi-Chang Fault is early Middle Pleistocene. The Su-Xi-Chang Fault was dominated by the sinistral normal faulting in the pre-Quaternary period, and turned into sinistral reverse faulting after the early Pleistocene, with displacement of about 3m in the Quaternary strata. The maximum magnitude of potential earthquake on the Su-Xi-Chang Fault is estimated to be 6.0.     

2012年6月24日宁蒗-盐源MS5.7地震发震构造刍议

2012年6月24日宁蒗-盐源M_S5.7地震,位于丽江-小金河断裂西北30km。区域范围内历史上地震频繁,为滇西北地震多发区。震区断裂构造复杂,主要发育NW向、NE向2组断裂,呈棋盘格式展布。经野外实地考察,震中附近发育NW向永宁断裂和NE向日古鲁-岩瓦断裂2条晚更新世活动断裂。永宁断裂由温泉断层、永宁断层和阿拉凹断层组成。在卫星影像上线性特征清晰,断层地貌明显。断裂对永宁、泸沽湖第四纪盆地具有严格的控制作用,沿线多处发育温泉。前所河的多条支流顺断层发育,八七—海衣角一带、日古鲁东山厝附近,多处河流右旋位错。阿拉凹一带断错T₂阶地上更新统沉积,被错地层最新年龄(TL)为(21.19±1.80)ka,是一条以右旋走滑兼正断性质的晚更新世活动断层。日古鲁—岩瓦断裂对岩瓦、日古鲁、利家咀等古近纪、新近纪盆地和永宁第四纪盆地有着明显的控制作用,断错中更新世和上更新世地层。中挖都—利家咀一带,有多条小溪呈现出同步左旋位错特征。断裂在晚更新世有着明显的活动迹象,以左旋走滑运动为主。据震源机制解结果,此次地震为正断兼右旋走滑型地震,NW向节面产状与永宁断裂基本吻合,地震破裂型式与永宁断裂运动学特征一致。地震烈度长轴方向、Ⅷ度烈度异常点线性分布以及构造地裂缝方向均与永宁断裂走向一致。分析认为,永宁断裂为此次地震的发震构造。此外,1996年丽江7.0级地震、1976年中甸5.5级地震以及本次5.7级地震,均具有明显的正倾滑分量。这些地震多分布在哈巴雪山和玉龙雪山新构造隆起周缘。根据区域地形条件分析,该地区的正断层运动作用很可能与地形巨大反差引起的重力势能有关。     

镇江地区主要NW向断裂的第四纪活动性

五峰山-西来桥断裂和丹徒-建山断裂是镇江地区2条主要的NW向断裂,可能与镇江多次破坏性地震相关。文中通过浅层地震勘探和钻孔联合剖面探测方法,对五峰山-西来桥断裂和丹徒-建山断裂的展布特征及第四纪活动性进行了系统研究。五峰山-西来桥断裂在浅层地震剖面上倾向NE,倾角约为60°,断距约为5~9m,以正断活动为主;大路镇场地上,该断裂断错的最新地层为中更新统底部,位错量为2m,判断五峰山-西来桥断裂的最新活动时代为中更新世早期。丹徒-建山断裂在浅层地震剖面上倾向SW,倾角约为50°~55°,断距约为2~7m,以正断活动为主;访仙镇场地上,中更新统之上的地层没有被断错的迹象,中更新统底部可能被断层影响,判断丹徒-建山断裂的最新活动时代为早更新世—中更新世早期。     

STUDY ON TANGSHAN-HEJIAN-CIXIAN EARTHQUAKE FAULT ZONE BY SHALLOW SEISMIC EXPLORATION METHOD

The location of the buried faults, the fault broken layers and the depth of breakpoints in the Tangshan-Hejian-Cixian seismotectonic zone are not clear. We implemented 4 shallow seismic exploration profiles on the Daming Fault, Cangxi Fault, and Dachengdong Fault. Line DZ1 is located on the Daming Fault in the southeast of Daming County. Five breakpoints were dectectd, which are all normal faults, with depths of 95~125m and displacements about 6~12m, offsetting late Pleistocene but not the Holocene. Line DZ2 is located in the east of Xianxian County to dectect the Cangxi Fault. Three breakpoints were detected, all are normal faults, with depths of 170~190m and displacements about 7~10m. The upper breakpoints of the three faults cut the middle Pleistocene. The lines DZ3 and DZ4 are located in the west of Litan Town, Dacheng County. Four breakpoints were detected, with the upper breakpoint depth of 120~130m and displacements about 5~15m. They are all normal faults, and the upper breakpoints of the faults cut the Pleistocene strata.
The result of the exploration of Cixian-Daming Fault is not consistent with the buried depth 1 200m proposed by XU Hua-ming. It is proved that the activity of the fault is also consistent with the overall activity of the Cixian-Daming Fault, which is an active fault since late Pleistocene.
The Dachengdong Fault and Cangxi Fault offset the middle Pleistocene strata. Although the late Pleistocene active faults are generally defined as active faults in the practice of active tectonics research in China, strong earthquakes in eastern China have shorter recurrence period, and earthquakes of magnitude 6 or so may also occur in some middle Pleistocene active faults.
During the compilation of GB18306-2015 “Seismic ground motion parameter zonation map of China”, there were no late Pleistocene active faults in the M6~6.5 potential source areas in eastern China. Therefore, we believe that the Dachengdong and Cangxi faults still have the ability to generate earthquake of magnitude 6 or so, and the faults have some similarities with the seismogenic structures of Xingtai earthquake swarm. Under the action of the latest tectonic stress field, the “deep faults” tearing ruptured successively and expanded upwards, resulting in stress migration and loading between two neighbouring en-echolon concealed faults, so, the Dachengdong and Cangxi faults are the product of this three-dimensional rupture process. The Dachengdong Fault is a “newly-generated” fault resulting from the tearing rupturing and upward expanding of the pre-existing concealed “deept faults” in the middle and lower curst.     

USING DEFORMED FLUVIALTERRACES OF THE QINGYIJIANG RIVER TO STUDY THE TECTONIC ACTIVITY OF THE SOUTHERN SEGMENT OF LONGMENSHAN FAULT ZONE

On 20 April 2013, a destructive earthquake, the Lushan M_S7.0 earthquake, occurred in the southern segment of the Longmenshan Fault zone, the eastern margin of the Tibetan plateau in Sichuan, China. This earthquake did not produce surface rupture zone, and its seismogenic structure is not clear. Due to the lack of Quaternary sediment in the southern segment of the Longmenshan fault zone and the fact that fault outcrops are not obvious, there is a shortage of data concerning the tectonic activity of this region. This paper takes the upper reaches of the Qingyijiang River as the research target, which runs through the Yanjing-Wulong Fault, Dachuan-Shuangshi Fault and Lushan Basin, with an attempt to improve the understanding of the tectonic activity of the southern segment of the Longmenshan fault zone and explore the seismogenic structure of Lushan earthquake. In the paper, the important morphological features and tectonic evolution of this area were reviewed. Then, field sites were selected to provide profiles of different parts of the Qingyijiang River terraces, and the longitudinal profile of the terraces of the Qingyijiang River in the south segment of the Longmenshan fault zone was reconstructed based on geological interpretation of high-resolution remote sensing images, continuous differential GPS surveying along the terrace surfaces, geomorphic field evidence, and correlation of the fluvial terraces. The deformed longitudinal profile reveals that the most active tectonics during the late Quaternary in the south segment of the Longmenshan Fault zone are the Yanjing-Wulong Fault and the Longmenshan range front anticline. The vertical thrust rate of the Yanjing-Wulong Fault is nearly 0.6~1.2mm/a in the late Quaternary. The tectonic activity of the Longmenshan range front anticline may be higher than the Yanjing-Wulong Fault. Combined with the relocations of aftershocks and other geophysical data about the Lushan earthquake, we found that the seismogenic structure of the Lushan earthquake is the range front blind thrust and the back thrust fault, and the pop-up structure between the two faults controls the surface deformation of the range front anticline.     

郯庐断裂带白山-卅铺段第四纪以来的活动习性

根据构造地貌遥感解析,发现郯庐断裂带沿庐江白山到桐城卅铺一线显示1组平行断层,现场地震地质调查验证其为1组活动断层。通过断层剖面观测、样品采集及样品测试分析和宏微观构造分析,结果表明,郯庐断裂带在白山—卅铺一带第四纪以来仍具有黏滑、蠕滑交替的变形活动。其中,在柯坦—卅铺一带,最年轻的水系被NE向断层组右旋扭折,其断层物质的微观观测和测龄结果表明该断裂段第四纪时的活动具有脆、塑性过渡变形特征,强烈活动时间处于早、中更新世;而白山剖面断层泥年龄测试结果则反映相应断层段在中、晚更新世曾有过较强烈的活动。断层泥超微(SEM)和显微观测结果亦表明该断裂段曾发生黏滑、蠕滑交替的构造变形事件,且表现为先黏滑后蠕滑;结合水系呈现缓慢扭折表征,近年来沿断裂有不少微震发生,表明郯庐断裂带在白山—卅铺段的最新滑移方式主要表现为蠕滑,也就是说,该段积累的应力以蠕滑或微震等方式缓慢释放,据此推测未来一定时期内不易孕育强烈地震     

关于芦山7.0级地震在龙门一带是否存在同震地表破裂的讨论

4.20芦山地震后,有学者在芦山县龙门乡发现一系列的线性裂缝和砖块的旋转变形等"地震地表破裂迹象",由此推测芦山—龙门一线存在隐伏逆断裂,并认为该断裂有可能是此次地震的发震断裂。因此,进一步探讨芦山—龙门一线是否存在潜在的发震断裂,无论是对研究芦山7.0级地震的发震断裂,还是对灾区的重建指导都十分重要。在龙门乡开展了地质灾害调查、跨谷地的地质剖面实测,槽探和人工地震勘探等工作。结果显示:至少在800m深度范围内,不存在芦山-龙门隐伏断裂。此带上的地裂缝等现象不是由断层位错引起,而更可能是地震动在阶地陡坎附近造成的地基或边坡效应所致。     

Seismogenic tectonics of the Qian-Gorlos earthquake in Jilin Province,China

The Qian-Gorlos earthquake, which occurred in the Songliao basin in Jilin Province in 1119 AD, was the largest earthquake to occur in NE China before the 1975 Haicheng earthquake. Based on historical records and surface geological investigations, it has been suggested previously that the earthquake epicenter was in the Longkeng area. However, other workers have considered the epicenter to be in the Halamaodu area based on the landslides and faults found in this region. No seismogenic structure has yet been found in either of these two regions. We tried to detect active faults in the urban areas of Songyuan City, where the historical earthquake was probably located. One of the aims of this work was to clarify the seismogenic structure so that the seismic risk in the city could be more accurately evaluated. The area was investigated and analyzed using information from remote sensing and topographic surveys, seismic data from petroleum exploration, shallow seismic profiles, exploratory geological trenches on fault outcrops, and borehole data. The geophysical data did not reveal any evidence of faults cutting through Cretaceous or later strata under the Longkeng scarp, which has been suggested to be structural evidence of the Qian-Gorlos earthquake. The continuous fault surfaces on the back edge of terraces in the Halamaodu area stretch for >3.5 km and were probably formed by tectonic activity. However, results from shallow seismic profiles showed that the faults did not extend downward, with the corresponding deep structure being identified as a gentle kink band. A new reverse fault was found to the west of the two suggested epicenters, which presented as a curvilinear fault extending to the west, and was formed by two groups of NE- and NW-trending faults intersecting the Gudian fault. Three-dimensional seismic and shallow seismic data from petroleum exploration revealed its distinct spatial distribution and showed that the fault may cut through Late Quaternary strata. Exploration boreholes and later geomorphological studies provided further proof of this. Based on these results and analysis, the Gudian fault was confirmed as having been an active fault since the Late Quaternary, with the possibility of earthquakes of magnitude >7 in the future. The Qian-Gorlos earthquake was most probably the result of breakage on one or two sections of this 66-km-long fault.     

Analysis of Paleoseismic Events of Dahuzhuang Trench at the Xiadian Fault

The Xiadian Fault is a very important concealed active fault in the Beijing Plain. It is the seismogenic fault of the Sanhe-Pinggu M_S8.0 earthquake in 1679. The ancient earthquake sequence in the long historical period is of great significance to understand accurately the activity characteristics of the fault and effectively reduce the earthquake disaster risk in Beijing. We have re-interpreted the Dahuzhuang trench, and identified three layers of buried paleosol, six collapsed wedges and one sand liquefaction event. Further, through the comparison with the landmark strata and paleo-earthquake events revealed by other trenches on the fault, an ancient earthquake sequence with a long historical period of the Xiadian Fault was established:since the 31ka, the Xiadian Fault has 11 occurrences of earthquake events (including the 1679 earthquake), and the average recurrence interval is about 2.8ka. The paleo-seismic sequence also shows that there is an ancient earthquake cluster period from 25ka to 15ka, and there are 5 strong earthquakes in the cluster period. The average recurrence interval is about 2.0ka, which reflects the phase difference of the Xiadian Fault activity.     

前郭MS5.8和松原MS5.7地震震源区地壳速度结构与孕震环境

为了解2013年11月23日吉林前郭M_S5.8和2018年5月28日吉林松原M_S5.7地震震源区的地壳速度结构及其孕震环境,本研究收集了东北地区CEA固定台站、NECESSArray流动台站和五大连池WAVESArrary流动台站的连续波形数据,使用背景噪声成像方法,获得了前郭地震和松原地震震源区地壳S波速度结构.结果显示,这两个地震主要发生在相对高波速异常区,而震源区下方存在明显低波速异常,且该低速层呈北北东走向,并有向北延展的趋势.结果表明,震源区相对高波速异常区易于积累能量孕育地震,而震源区下方的低波速异常可能代表了流体作用.这种流体作用会降低断层面有效正应力从而触发地震.这种流体作用可能和太平洋板块深俯冲至我国东北地区（包括前郭地震和松原地震震源区）下方的地幔转换内形成"大地幔楔"结构与动力学密切相关.在"大地幔楔"结构中,由于地幔转换带中滞留板块脱水作用和地幔角流作用,容易形成热湿物质上涌,进而导致松辽盆地中北部岩石圈物质拆沉、地幔流体入侵至中下地壳、然后作用于断裂带,从而导致了两个震源区中强度地震的发生.     

SLIP RATES OF THE RIYUE MT. FAULT AT DEZHOU SEGMENT SINCE LATE PLEISTOCENE

The Riyue Mt. Fault is a secondary fault controlled by the major regional boundary faults (East Kunlun Fault and Qilian-Haiyuan Fault). It lies in the interior of Qaidam-Qilianshan block and between the major regional boundary faults. The Riyue Mt. fault zone locates in the special tectonic setting which can provide some evidences for recent activity of outward extension of NE Tibetan plateau, so it is of significance to determine the activity of Riyue Mt. Fault since late Pleistocene to Holocene. In this paper, we have obtained some findings along the Dezhou segment of Riyue Mt. Fault by interpreting the piedmont alluvial fans, measuring fault scarps, and excavating trenches across the fault scarp. The findings are as follows:(1) Since the late Pleistocene, there are an alluvial fan f_p and three river terraces T₁-T₃ formed on the Dezhou segment. The abandonment age of f_p is approximately (21.2±0.6) ka, and that of the river terrace T₂ is (12.4±0.11) ka. (2) Since the late Pleistocene, the dextral strike-slip rate of the Riyue Mt. Fault is (2.41±0.25) mm/a. In the Holocene, the dextral strike-slip rate of the fault is (2.18±0.40) mm/a, and its vertical displacement rate is (0.24±0.16) mm/a. This result indicates that the dextral strike-slip rate of the Riyue Mt. Fault has not changed since the late Pleistocene. It is believed that, as one of the dextral strikeslip faults, sandwiched between the the regional big left-lateral strike-slip faults, the Riyue Mt. Fault didn't cut the boundary zone of the large block. What's more, the dextral strike-slip faults play an important role in the coordination of deformation between the sub-blocks during the long term growth and expansion of the northeast Tibetan plateau.     

唐山地震发震构造的浅层地震探测

利用浅层地震探测方法,研究了唐山地震区１年前出现在卫星图像上的异常现象与发震构造的关系,探讨地震中长期预测的途径。结果表明：唐山地震断层是一条倾向ＮＷ的右旋走滑第四纪同生断裂,它错断了全新统,晚更新统,中更新统,和早更新统地层。     

安徽淮南地区明龙山-上窑断裂第四纪活动特征

明龙山-上窑断裂是一条逆走滑性质的第四纪活动断裂,长约68km,走向300°-315°。本文在卫星影像解译的基础上,通过野外调查,确定了该断裂的几何展布和分段特征,初步将断裂分为明龙山、上窑、凤阳山3条次级断裂段。通过对断裂经过处的采石场进行详细追索,我们对典型断层剖面进行了描述并采集了断层泥ESR样品,得到的测年结果为（243±24）ka和（126±15）ka,由于淮南地区是典型的中等强度地震活动区,断层晚第四纪以来活动强度较弱,这些测年结果虽不能代表断层最后一次微弱活动的时代,但可以确定断层最后一次强烈活动时代为中更新世晚期至晚更新世早期。结合前人对1831年凤台M_S 6?级地震极震区位置、等震线形态研究及本文对极震区附近断裂展布和活动性的对比分析,我们认为明龙山-上窑断裂为本次地震发震构造的可能性最大。     

THE NEW ACTIVITY OF TAN-LU FAULT ZONE IN SEGMENT OF DAHONGSHAN SINCE LATE QUATERNARY

The relationship between the latest activity of active fault and seismic events is of the utmost importance. The Tan-lu fault zone in eastern China is a major fault zone, of which the active characteristics of the segments in Jiangsu, Shandong and Anhui has been the focus of research. This study takes the Dahongshan segment of the Tanlu Fault in Sihong County as the main research area. We carried out a detailed geological survey and excavated two trenches across the steep slope on the southwest side of the Dahongshan. Each trench shows fault clearly. Combining the comparative analysis of previous work, we identified and cataloged the late Quaternary deformation events and prehistoric earthquake relics, and analyzed the activity stages and behavior of this segment. Fault gonge observed in the trench profiles shows that multiple earthquake events occurred in the fault. The faulting dislocated the Neogene sandstone, black gravel layer and gray clay layer. Brown clay layer is not broken. According to the relations of dislocated stratums, corresponding ¹⁴C and OSL samples were collected and dated. The result indicates that the Dahongshan segment of the Tanlu Fault has experienced strong earthquakes since the late Quaternary. Thrust fault, normal fault and strike-slip fault are found in the trenches. The microscopic analysis of slices from fault shows that there are many stick-creep events taking place in the area during the late Quaternary. Comprehensive analysis shows that there have been many paleoearthquakes in this region since the late Quaternary, the recent active time is the late Pleistocene, and the most recent earthquake event occurred in(12~2.5ka BP). The neotectonic activity is relatively weak in the Anhui segment(south of the Huaihe River)of Tanlu fault zone. There are difficulties in the study of late Quaternary activity. For example, uneven distribution of the Quaternary, complex geological structure, larger man-made transformation of surface and so on. The progressive research may be able to promote the study on the activity of the Anhui segment of Tanlu fault zone.