The MS 6.8 Luding earthquake in 2022 is located on the NNW-trending Moxi segment of the Xianshuihe fault with left-lateral strike-slip behavior. This area is where the Xianshuihe, Anninghe, Daliangshan and Longmenshan faults intersect. China Earthquake Administration has identified that intersection area, among the Moxi segment of the Xianshuihe fault, the Anninghe fault, the Daliangshan fault and the southern part of the Longmenshan fault, as a high-magnitude earthquake hazard area. According to existing data on the Luding earthquake, including the focal parameters, the spatial distribution of re-located aftershocks, dominated azimuth of the earthquake intensities and earthquake-induced ground fissures, we built a 3D earthquake fault model. We found that two discontinuous NNW-trending vertical strike-slip faults with left stepping were the seismogenic faults of the Luding earthquake. Its coseismic left-lateral dislocation triggered transtensional slips and aftershocks on the NW-trending secondary faults at its northernmost tensile area. Meanwhile, local crustal coseismic shortening on the side of Mt. Gongga triggered the aftershocks on the NE- and NW-trending secondary conjugated strike-slip faults, which were confirmed by GNSS observations and InSAR deformation field around the epicenter. This earthquake rupturing pattern also controlled the spatial distribution of the earthquake intensity IX area and earthquake chain hazards. The Coulomb stress calculation shows that the Luding earthquake increases the risk of high-magnitude earthquake occurrence on the southernmost part of the Xianshuihe fault and the Anninghe fault. Finally, we suggested doing good monitoring of the Anninghe fault and the southernmost part of the Xianshuihe fault and avoiding active faults with seismogenic capacity and areas prone to earthquake-chained hazards during the site selection and planning of reconstruction.

The Xianshuihe fault zone is divided into five segments along its strike. Fault activity parameters are estimated by using crossing fault measuring data of short baselines and short leveling at sites along the fault zone. Regional dynamic gravity and GPS velocity fields are calculated by using gravity and GPS observational data of a large area covering the whole fault zone. We use the ant colony algorithm and particle swarm optimization (PSO) based on resulting data above to invert the fault activity parameters of the five fault segments, and the strike-slip component of each segment is taken as the current fault slip rate. Then we analyze the differences between the three types of the current slip rate as well as geological average slip rates of the five segments, taking the strike slip rate inverted from gravity data as the slip rate of the whole fault zone. Comparing the whole near-field fault rate with the result of short baselines and short leveling, we determine the features of fault segments measured by short baselines and short leveling, and provide the current overall strike-slip rate of the five segments and several branch faults. The resulting slip rates are as follows: (1) 9. 13 mm . a(1) on the Luhuo segment; 2. 46 mm . a (1) on the west branch fault and 5. 84 mm . a (1) on the east branch fault in the Xialatuo area. (1) 8. 57 mm . a (1) on the Daofu segment; on its southeast section, the west branch in the Goupu is 1. 78 mm . a,and the east branch is 6. 79 mm . a (3) 7. 67 mm . a (1) on the Qianning segment. (4) 6. 14 mm . a (1) on the Kangding segment. And (5) 4. 41 mm . a (1) on the Moxi segment. Moreover, we also discuss qualitatively the 3D elastic-plastic deformation model of active blocks on both sides of the fault zone covered by gravity and GPS data and permanent displacements caused by paleoand historical earthquakes.

To establish an experimental,practical and open scientific experimental platform for earthquake monitoring and prediction,with reference to that of the southern California earthquake center (SCEC),China Earthquake Administration initiated a project for an experimental field in Sichuan and Yunnan Province in 2014.The chosen area is a seismically active region in the southeastern margin of the Tibetan plateau.A series of work compiling basic maps have been launched to collect fundamental data of this area including geologic structure,earthquake geology,geophysics,geodesy, and geochemistry.The map of earthquake surface ruptures in this region is one of these basic maps. This paper presents the compilation of this map.It includes earthquake epicenters,earthquake surface ruptures,faults,strata,magmatic rocks,and geographical data.This work summarized 87 destructive earthquakes,and 22 earthquake surface rupture zones,and analyzed the distribution characterization of earthquake epicenters,strata and magmatic rocks.The content in the map is reliable and integrated.This work will provide reliable earthquake-geology data for establishing geodynamics models and other future research of the national experimental field of earthquake monitoring and prediction in Sichuan and Yunnan Province.

中国地震频度高、强度大、分布广、震源浅,地震灾害极为严重.为更好地服务于"两个一百年"奋斗目标蓝图,有效减轻地震灾害风险,助推城乡地震安全、保障"一带一路"地震灾害源调查,有力支撑国家重大战略的实施,中国地震学会地震地质专业委员会联合中国地震局活动构造与火山重点实验室于2017年12月23—24日在北京联合召开了2018年活动构造与地震地质学术年会.

The aftershocks of the 2008 Wenchuan and 2013 Lushan earthquakes delineated a prominent 60-km-long "seismic gap." The uncertainty regarding the near-future seismic potential of this seismic gap has become of increasing importance to both the scientific community and the public. Using paleoseismology, this study investigated the occurrence of the last major event in the seismic gap and then considered the future seismic potential. Based on image interpretation, trench excavation, radiocarbon and optically stimulated luminescence dating, and comparisons with historical earthquake rupture lengths, the most recent paleoearthquake (estimated magnitude: M6.5-7.0) along the Shuangshi-Dachuan Fault (SDF), which is the southern segment of the Longmen Shan Fault, was constrained to 640-1330 CE (very possibly, 876 CE). According to the most recent, geological and geophysical findings, we suggest that the seismic gap (i.e., the SDF) could be capable of generating M6.0-7.0 earthquakes, but that the likelihood of such an occurrence in the near future is not very high. (C) 2016 Elsevier Ltd. All rights reserved.

The M S6.4 Menyuan earthquake occurred on the northern side of the Lenglongling fault (LLLF) in the mid-western of the Qilian-Haiyuan fault zone on January 21, 2016. The earthquake epicenter was distant from the Minle-Damaying and Huangcheng-Shuangta faults, eastern of the Northern Qilian Shan fault zone. A near northwest-striking rupture plane intersects the two faults at a certain angle. The focal mechanism solution shows that this was a thrust-type earthquake, slightly different from the strike-slip movement with a thrust component of the LLLF. Field geological mapping, tectonic geomorphology analysis, trench excavation and 14C dating reveal that (1) the LLLF has been obviously active since the Holocene, and may behave with characteristic slip behavior and produce M W7.3–7.5 earthquakes; (2) the LLLF appears as a flower structure in terms of structure style, and dips NNE at a steep angle; and (3) the most recent earthquake event occurred after 1815–1065 a BP. An associated fault, the Northern Lenglongling fault (NLLLF), is located at the northwestern end of the LLLF. Consequently, the NLLLF was continually subject to tectonic pushing effects from the left-lateral shear at the end of the LLLF, and, accordingly, it bent and rotated outward tectonically. Subsequently, the fault deviated from the dominant rupture azimuth and activity weakened. In the late Quaternary, it behaved as a thrust fault with no obvious deformation at the surface. This is indicated by the arc shape, with a micro-protrusion northeastward, and no geologic or geomorphic signs of surface rupturing since the late Quaternary. However, such faults could still rupture at depth, producing moderate-strong earthquakes. The geometric and kinematic properties of the NLLLF are in good agreement with the occurrence and kinematic properties of nodal plane 2, and with the distribution characteristics of the aftershocks and seismic intensity. Therefore, the NLLLF is a more suitable seismogenic structure for the M S 6.4 Menyuan earthquake. In addition, the thrust movement of the NLLLF accommodates subsequent movement of the LLLF. During the historical evolution of the NLLLF, the LLLF and the NLLLF have affected the local topography through tectonic uplift.

通过浅层地震勘探和钻孔联合剖面探测,揭示了信宜-廉江断裂带东支西南段隐伏断裂的存在.2条浅层地震勘探剖面资料显示,信宜-廉江断裂带东支西南段隐伏断裂的上断点埋深和垂直断距分别为60m和4～7m(L5-1和L5-2测段,横山镇剖面)、85m和5～ 8m(L5-3测段)、73m和3～5m(L6测线,田头仔村剖面),均断错了第四系底部.2条钻孔联合剖面揭示了上断点埋深和垂直断距分别为66m和7.5m(横山镇剖面)、75m和5m(田头仔村剖面),其中横山镇钻孔剖面显示断裂带宽约27m.采用电子自旋共振方法对钻孔联合剖面中的第四系年代进行测定,显示信宜-廉江断裂带东支西南段隐伏断裂最新活动时代为早更新世晚期(田头仔村剖面)到中更新世早期(横山镇剖面).由横山镇钻孔联合剖面和田头仔村钻孔联合剖面获得的滑动速率分别为0.1 mm/a和0.013mm/a.基岩出露区沙井断层剖面的断面上发育有2期断层泥,由电子自旋共振方法测得晚期的断层泥年龄为(348±49)ka,沿断面还发育有近水平擦痕,反映断裂的最新活动方式以右旋走滑运动为主.

Coulomb stress changes along the Xianshuihe fault induced by the Wenchuan,Lushan and Kangding earthquakes are calculated and compared with long term tectonic loading rates in order to assess seismic potential change on the fault due to these earthquakes.The results show that the Kangding earthquake was advanced and delayed by the Wenchuan and Lushan earthquakes,respectively.Most of the Coulomb stress changes along the Xianshuihe fault are due to the Wenchuan and Kangding earthquakes.Under a linear stress loading assumption,advance/delay times of earthquake recurrence are calculated along the fault.In the case assumingμ′=0,the earthquake recurring times could be advanced by approximately 0-5years at locations between Bamei and Moxi(except the rupture zone of the Kangding earthquake),and delayed by 0-4years at the other regions,respectively.Ifμ′=0.4,the advance times of earthquake recurrence are estimated as 0-6years in the range between Daofu and Zhuyaozihaizi,and the delay times are calculated to be 0-2years out of the range.As our knowledge is so limited about the rheological structures on both sides of the Xianshuihe fault,the impact of its variation on the results is also investigated.Our research shows that the lower the viscosities of the lower crust and the upper mantle,the larger the Coulomb stress change due to viscous relaxation would be,and the more rapidly it changes along fault strike.Furthermore,the contribution of the viscous relaxation is comparable to that of coseismic rupture,resulting in advance/delay times of earthquake recurrence of up to 3years.

The 26 November 2005 Jiujiang-Ruichang, Jiangxi, Ms 5.7 earthquake occurred in a seismotectonic setting of moderate earthquake. The northwest-trending Xiangfan-Guangji fault (XFG) does not enter into the epicenter vicinity, but the northeast-trending Ruichang-Wuning fault (RWF) as a regional fault extends to the epicenter nearby, appearing as the Ruichang basin and its marginal faults. Tilting of the Ruichang Basin (RCB) in the Quaternary was controlled by the RCB southeast-marginal, buried fault (RSMBF). Shallow geophysical survey reveals that the RSMBF caused an offset of the reflection layers. Drill hole columnar section demonstrates that there are about 1012 m displacement in the lower section of the middle-Pleistocene Series along the RSMBF, but no disruption is found in the upper section of the middle-Pleistocene Series. The RSMBF not only has activity in the Quaternary, but also coincides with the nodal plane I from the focal mechanism of the Jiujiang-Ruichang Ms 5.7 earthquake. This evidence, including aftershock distribution and isoseismic lines, strongly suggests that the RSMBF might be the seismogenic tectonics. The RWF is discontinuous at the surface, and consists of three en echelon Quaternary basins, which are the Ruichang, Fanzhen and Wuning basins. Three moderate earthquakes, the Fanzhen ML 4.9 earthquake, the Yejiapu ML 4.1 earthquake and the Jiujiang-Ruichang Ms 5.7 earthquake, have happened in the basins since 1995. The seismogenic tectonics of the Jiujiang-Ruichang Ms 5.7 earthquake is not isolated, but may be controlled by the RWF at depth, the slip of which causes the accumulation of energy for earthquake occurrence.

In this paper, we discuss the differences of dynamic environment, neo-tectonics, seismogenic models, Quaternary tectonic movement and geophysical field of the South China, and their roles in dividing diffuse seismicity provinces. Considering the actual seismo-tectonic features, the conditions for evaluating the magnitudes of diffuse earthquakes are introduced systematically. As to the maximum historical earthquake with no relation to a known seismogenic tectonics in a diffuse seismicity province, two approaches are provided to determine the magnitude of diffuse earthquake. As to the relationship between the diffuse earthquakes magnitudes with the general intensity of seismic and tectonic activity, a comprehensive explanation is provided. The consistency of seismo-tectonic environment is the basis for comparison of diffuse seismicity in different province. Based on the evaluation methods and basal information, the results about the division of diffuse seismicity provinces and diffuse earthquake magnitudes are obtained.

The Kunlun Fault, an active fault on the border between the Bayan Har and Kunlun-Qaidam blocks, is one of the major left lateral strike-slip faults in the Tibetan Plateau. Previous research has not reached a consensus on agreeable slip rates along much of its length and the slip rate gradient along the eastern part, both of which play critical roles in a range of models for the eastward extrusion and thickened crust of the Tibetan Plateau. New slip rates have been determined at sites along the eastern part of the Kunlun Fault by dating deposits and measuring atop displaced fluvial terrace risers. Field investigations and interpretation of satellite images reveal geometrical features of the fault and the late Quaternary offset, new earthquake ruptures and surface-rupturing segmentation, from which long-term slip rates and earthquake recurrence intervals on the fault are estimated. The tectonic geomorphology method has determined that the long-term horizontal slip rates on the Tuosuohu, Maqin and Maqu segments from west to east are 11.2±1, 9.3±2, and 4.9±1.3 mm/a while their vertical slip rates are 1.2±0.2, 0.7±0.1, and 0.3 mm/a in the late Quaternary. Results indicate that the slip rates regularly decrease along the eastern ∼300 km of the fault from >10 to <5 mm/a. This is consistent with the decrease in the gradient such that at the slip rate break point is at the triple point intersection with the transverse fault, which in turn is transformed to the Awancang Fault. The vector decomposition for this tectonic transformation shows that the western and eastern branches of the Awancang Fault fit the slip-partitioning mode. The slip rate of the southwestern wall is 4.6 mm/a relative to the northeastern wall and the slip direction is 112.1°. The mid-eastern part of the Kunlun Fault can be divided into three independent segments by the A’nyêmaqên double restraining bend and the Xigongzhou intersection zone, which compose the surface rupture segmentation indicators for themselves as well as the ending point of the 1937 M7.5 Tuosuohu earthquake. The average recurrence interval of the characteristic earthquakes are estimated to be 500–1000 a, respectively. The latest earthquake ruptures occurred in AD 1937 on the western Tuosuohu segment, as compared to ∼514–534 a BP on the Maqin segment, and ∼1055 to 1524 a BP on the Maqu segment. This may indicate a unidirectional migration for surface rupturing earthquakes along the mid-eastern Kunlun Fault related to stress triggered between these segments. Meanwhile, the long-term slip rate is obtained through the single event offset and the recurrence interval, which turn out to be the same results as those determined by the offset tectonic geomorphology method, i.e., the decreasing gradient corresponds to the geometrical bending and the fault’s intersection with the transverse fault. Therefore, the falling slip rate gradient of the mid-eastern Kunlun Fault is mainly caused by eastward extension of the fault and its intersection with the transverse fault.

<正>作为"位于亚洲大陆东南部强烈变形场中的左旋剪切破裂带,撕裂了高耸的青藏高原的东南部边缘,在中国大陆内部新构造格局中占据着突出位置"的青藏高原东缘一条重要的左旋走滑断裂带,鲜水河断裂带有着丰富的历史地震记录、较清晰的地貌特征和地表破裂形迹,是开

China Earthquake Urban Active Fault Surveying Project is a national important scientific and engineering project in recent years.Its map achievement,which includes 1:250,000 regional seismotectonic map and 1: 50,000active fault distribution map of twenty cities,is an important integrated document and will be utilized in seismological and geologic research,protecting against earthquake,and relief of disaster.However,these maps are not drawn in uniform standards.As a result,there is lack of normalization in stratigraphic division,map information expression and map layout.The lack of standardization will lead to further problems when publishing and utilizing these documents because of the diverse information expression. This paper discusses the design philosophy,data scheme and expression,cartographic generalization,illustration standard and mapping procedure of the 1:250,000 regional seismotectonic maps and 1: 50,000 urban active fault distribution maps.The map information is from urban active fault databases,which are based on ArcGIS Geodatabase technique,and the mapping procedure is based on ArcGIS mapping template technique.Therefore,the paper also introduces the mapping procedure in ArcGIS software and references the information organization in urban active fault database. Since cooperation among industries,universities and geological research institutions becomes increasingly prominent,the mapping achievement of active fault surveying is in urge of standardization and normalization.The work in this paper is based on years of work of active fault survey project.We have collected suggestions and advices from first-line technological staff to scientific experts,and then revised our work in many details.It is expected that this work can promote the standardization and normalization of the active fault map achievements.

基于卫星影像解译和野外考察测量, 本文对东昆仑断裂带中东部的3条次级断裂(托索湖断裂、玛沁断裂和玛曲断裂)的滑动速率以及全新世以来的古地震活动特征进行了分析研究.

2008年5月12日,汶川Mw 7.9级地震在青藏高原东缘沿龙门山逆冲断裂带中段形成了两条NE向和一条NW向逆冲走滑型地表破裂.依据同震地表陡坎形态特征,将其分为8种类型:逆断层陡坎、上盘垮塌陡坎、挤压推覆陡坎、右旋挤压推覆陡坎、断层相关褶皱陡坎、后冲挤压陡坎、上冲叠覆陡坎和局部正断层陡坎.汶川地震所形成的同震地表破裂主要由以逆冲为主的映秀破裂段和兼具逆冲、右旋走滑的北川破裂段两部分组成,这两个破裂段分别对应于Mw 7.8与Mw 7.6级地震事件;它们还可进一步细分为分别对应于Mw 7.5、Mw 7.7、Mw 7.0和Mw 7.5等4个次级事件的4个次级破裂段.这些次级破裂段的级联破裂可以用来解释为什么汶川地震的持续时间长达110 s.余震震源机制分析结果表明,发震断层的倾角随深度的增加而变缓,且从西南向北东逐渐变陡可以用来解释走滑分量增加的成因.此次大地震还表明,沿青藏高原东缘地形抬高的主要驱动力可能是地壳挤压缩短,而不一定是下地壳物质流动和膨胀引起上地壳的隆升.

Based on in-situ measurements of the earthquake surface ruptures and surveys of building damage associated with the Wenchuan earthquake along the measured profile, various types of earthquake surface ruptures and their associated features of building damages are analyzed in this paper. Moreover, the relationship between the gradient of the surface deformation and the building damage degree is quantitatively discussed. The results indicate that, regardless of fault scarp type, the surface rupture or strong deformation would be localized within an average width of 10 similar to 30 m across the seismogenic fault. The most direct factor affecting the building damages is the gradient of surface deformation in the site, where the building is located. Generally speaking, at a site where the gradient of surface deformation is equal to or larger than 0.1, the buildings will be completely destroyed; at a site where the gradient ranges from 0.07 to 0.1, the buildings will be subjected to serious damage, and at a site where the gradient ranges from 0.03 to 0.07, the buildings with a certain seismic resistance will be subject to a moderate damage, resulting in tilting and deformation, but generally will not be collapsed, while at a site where the gradient is less than 0.03, the buildings with a certain seismic resistance may suffer generally from light damage or even remains intact.

Based on in‐situ measurements of the surface ruptures caused by the Wenchuan M s 8.0 earthquake in 2008, incorporating with the surveys of building damages along the measured profile, various types of earthquake surface ruptures and the associated features of building damages are analyzed. Moreover, the relationship between the gradient of surface deformation and the damage degree of buildings is quantitatively discussed. The results indicate that regardless of the type of fault scarp, the surface rupture or strong deformation would be localized within an average width range of 10~30 m across the seismogenetic fault. The most direct factor affecting the damage of buildings is the gradient of surface deformation at the site where the buildings are located. Generally speaking, at the site where the gradient of surface deformation is equal to or larger than 0.1, the buildings will be completely destroyed; at a site where the gradient ranges from 0.07 to 0.1, the buildings will be subjected to serious damage; at a site where the gradient ranges from 0.03 to 0.07, the buildings will be subject to moderate damage, resulting in tilting and deformation, but generally will not collapse, while at a site where the gradient is less than 0.03, the buildings with a certain seismic resistance may suffer generally from light damage or even remains intact.