FEATURES OF EARTHQUAKE CLUSTERING FROM CALCULATION OF COULOMB STRESS AROUND THE BAYAN HAR BLOCK,TIBETAN PLATEAU

Since 1997, several major earthquakes occurred around the Bayan Har block in the Tibetan plateau, providing an opportunity to further understanding the mechanism of intraplate earthquakes. What is the effect of interactions among these events on the earthquake occurrence pattern is an issue to be addressed. In this article, we use the visco-elastic Coulomb stress changes model to calculate the stress interactions among the historical events close to or large than M_S7.0 since 1893 in the Bayan Har block. We apply the relationships between the slip rate and stress accumulation rate to transform the Coulomb stress changes into the influenced time. Then we remove such influence time from the occurrence years, and analyze the effects of the earthquake interactions on the clustering patterns of the historical earthquakes in the Bayan Har block. The results show that the major earthquakes in the Bayan Har block are characterized by a quasi-period of about 16 years from 1893 to 1973 and a clustering occurrence time period from 1997 to present following a relatively long quiescence period. The Bayan Har block is still in the active period with high probabilities of major quakes. We calculate the conditional probabilities of the rupture segments that did not rupture since 1893 of the boundary faults of the Bayan Har block in the next 30 years. The following faults or fault sections seem to be of major risk:The Maqin segment and the Maqu fault of the East Kunlun fault zone, the Awanang fault, the Luocha segment of the Tazhong fault, the Moxi segment of the Xianshuihe fault, and the Dangjiang fault. Other Fault segments in the Bayan Har block without seismic events since 1893 probably also have hazard of M_S7 earthquakes in the future.     

2008年汶川MS8.0地震对周边断层地震活动的影响

为分析2008年5月12日四川汶川M_S8.0级地震对周边断层地震活动的影响,本文首先基于Burgers体黏滞松弛模型计算汶川M_S8.0级地震引起的库仑应力动态演化,分析认为2008年汶川M_S8.0级地震在周边断层上引起的库仑应力显著增加的主要有四个断层段,分别为鲜水河断裂道孚-康定段、东昆仑断裂东段玛曲段、青川断裂和龙门山断裂南段.而且震后4年内黏滞松弛引起的库仑应力变化量可能与同震变化相当,相当于再发生一次汶川地震所造成的影响,因此震后效应在分析强震影响时不应忽略.本文基于强震引起的库仑应力变化动态演化,结合背景地震发生率、由Dieterich(1994)模型给出地震发生概率,结合相关构造地质、历史地震、余震活动等方面资料的综合分析认为,上述4个断裂段地震危险性由高到低依次为鲜水河断裂道孚-康定段、龙门山断裂南段、东昆仑断裂东段玛曲段和青川断裂.     

基于库仑应力变化分析巴颜喀拉地块东端的强震相互关系

本研究基于分层黏弹介质模型,考虑同震位错效应和震后黏滞松弛效应,分析巴颜喀拉地块东端1976年松潘地震序列、2008年汶川8.0级地震、2013年芦山7.0级地震和2017年九寨沟7.0级地震等多次大地震的可能存在的触发关系,计算大地震引起的周边各主要断裂的库仑应力变化.结果显示,1976年松潘地震序列各次地震间关系密切,存在明显的相继触发作用;综合考虑同震和震后效应,汶川8.0级地震对同属于龙门山断裂带的芦山7.0级地震有触发作用,且震后效应影响不可忽略;1976年地震序列,特别是1976年8月16日7.2级地震促进了2017年8月8日九寨沟7.0级地震的发生;汶川地震对九寨沟地震的影响研究中,采用不同的汶川地震同震位错模型,计算结果有差异.综合考虑多次大地震对周边断裂带的影响,龙门山断裂带南段、鲜水河断裂带中南段、平武—青川断裂北段、灌县—安县断裂北段、文县断裂的累积库仑应力增加显著,巴颜喀拉地块东端的东昆仑断裂带东段、迭部—白龙江断裂带西段以及金沙江断裂带库仑应力亦有所增加.综合考虑各重要断裂带已有的大地震危险性分析结果和库仑应力变化计算结果,龙门山断裂带南段、鲜水河断裂带中南段、东昆仑断裂带玛沁—玛曲段和金沙江断裂带的发震紧迫性有所增强,需引起关注.     

FOCAL FAULTS AND STRESS FIELD CHARACTERISTICS OF M7.0 JIUZHAIGOU EARTHQUAKE SEQUENCE IN 2017

On August 8, 2017, Beijing time, an earthquake of M7.0 occurred in Jiuzhaigou County, Aba Prefecture, Sichuan Province, with the epicenter located at 33.20°N 103.82°E. The earthquake caused 25 people dead, 525 people injured, 6 people missing and 170000 people affected. Many houses were damaged to various degrees. Up to October 15, 2017, a total of 7679 aftershocks were recorded, including 2099 earthquakes of M ≥ 1.0. The M7.0 Jiuzhaigou earthquake occurred in the northeastern boundary belt of the Bayan Har block on the Qinghai-Tibet Plateau, where many active faults are developed, including the Tazhong Fault(the eastern segment of the East Kunlun Fault), the Minjiang fault zone, the Xueshan fault zone, the Huya fault zone, the Wenxian fault zone, the Guanggaishan-Daishan Fault, the Bailongjiang Fault, the Longriuba Fault and the Longmenshan Fault. As one of the important passages for the eastward extrusion movement of the Qinghai-Tibet Plateau(Tapponnier et al., 2001), the East Kunlun fault zone has a crucial influence on the tectonic activities of the northeastern boundary belt of Bayan Kala. Meanwhile, the Coulomb stress, fault strain and other research results show that the eastern boundary of the Bayan Har block still has a high risk of strong earthquakes in the future. So the study of the M7.0 Jiuzhaigou earthquake' seismogenic faults and stress fields is of great significance for scientific understanding of the seismogenic environment and geodynamics of the eastern boundary of Bayan Har block. In this paper, the epicenter of the main shock and its aftershocks were relocated by the double-difference relocation method and the spatial distribution of the aftershock sequence was obtained. Then we determined the focal mechanism solutions of 24 aftershocks(M ≥ 3.0)by using the CAP algorithm with the waveform records of China Digital Seismic Network. After that, we applied the sliding fitting algorithm to invert the stress field of the earthquake area based on the previous results of the mechanism solutions. Combining with the previous research results of seismogeology in this area, we discussed the seismogenic fault structure and dynamic characteristics of the M7.0 Jiuzhaigou earthquake. Our research results indicated that:1)The epicenters of the M7.0 Jiuzhaigou earthquake sequence distribute along NW-SE in a stripe pattern with a long axis of about 35km and a short axis of about 8km, and with high inclination and dipping to the southwest, the focal depths are mainly concentrated in the range of 2~25km, gradually deepening from northwest to southeast along the fault, but the dip angle does not change remarkably on the whole fault. 2)The focal mechanism solution of the M7.0 Jiuzhaigou earthquake is:strike 151°, dip 69° and rake 12° for nodal plane Ⅰ, and 245°, 78° and -158° for nodal plane Ⅱ, the main shock type is pure strike-slip and the centroid depth of the earthquake is about 5km. Most of the focal mechanism of the aftershock sequence is strike-slip type, which is consistent with the main shock's focal mechanism solution; 3)In the earthquake source area, the principal compressive stress and the principal tensile stress are both near horizontal, and the principal compressive stress is near east-west direction, while the principal tensile stress is near north-south direction. The Jiuzhaigou earthquake is a strike-slip event that occurs under the horizontal compressive stress.     

2021年青海玛多MS7.4地震同震应力场与形变台站同震阶变分布关系探讨

利用基于升、降轨InSAR形变场及余震精定位结果反演得到的同震滑动模型,通过PSGRN/PSCMP程序获得同震水平形变场及应力场分布特征,结合玛多M_S7.4地震周边形变同震阶变台站分布特征,探讨同震应力场变化与同震阶变台站分布间的关系。模拟得到的水平形变场结果显示,此次玛多地震为左旋走滑运动特征,水平形变量主要集中在巴颜喀拉块体内,其次是北部的柴达木块体;羌塘块体以及祁连块体同震水平位移量较小;昆仑山口-江错断裂作为一条NE倾向的走滑型断裂,断层上盘区域滑动量明显大于下盘,模拟得到的最大水平形变量达1380mm;形变同震阶变的台站主要集中分布在祁连山断裂带中东段以及西秦岭等地区,祁连山断裂带中东段位于此次玛多地震同震正应力变化正值区域,而西秦岭等地区则处于玛多地震同震剪切应力变化的正值区域,即出现同震阶变的台站与同震应力场变化的正值区域具有较好的一致性。     

Coseismic Coulomb failure stress changes caused by the 2017M7.0 Jiuzhaigou earthquake,and its relationship with the 2008Wenchuan earthquake

On August 8, 2017, a M7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China, resulting in significant casualties and property damage. Therefore, it is critical to identify the areas of potential aftershocks before reconstruction and re-settling people to avoid future disasters. Based on the elastic dislocation theory and a multi-layered lithospheric model, we calculate the Coulomb failure stress changes caused by the Wenchuan and Jiuzhaigou earthquakes, discuss the relationship between the Mw7.9 Wenchuan and M7.0 Jiuzhaigou earthquakes, and analyze the influence of the aftershock distribution and stress changes on the major faults in this region caused by the Jiuzhaigou earthquake. The co-and post-seismic stress changes caused by the Wenchuan earthquake significantly increased the stress accumulation at the hypocenter of the Jiuzhaigou earthquake. Therefore,the occurrence of the Jiuzhaigou earthquake was probably stimulated by the Wenchuan earthquake. The aftershock distribution is well explained by the co-seismic stress changes of the Jiuzhaigou earthquake. The stress accumulation and corresponding seismic hazard on the Maqu-Heye segment of the East Kunlun fault and the northern extremity of the Huya fault has been further increased by the Jiuzhaigou earthquake.     

2008年汶川地震的破裂模型及引起的余震活动分析

用两种发震构造的破裂位移分布模型对2008年汶川地震造成的区域主要断裂的库仑应力变化进行了模拟.通过对这两种破裂位移模型模拟结果的对比分析,表明破裂位移模型的逆冲兼右旋滑动的位移模式及南北两段分别有两个滑动量高值区这样的特点控制了区域库仑应力变化的总体分布特征.汶川地震的余震分布和计算结果还显示:所获得的区域主要断裂的...     

东昆仑断裂带地震复发间隔及地震危险性

东昆仑断裂带是青藏高原东北部一条重要的活动断裂, 构成了巴颜喀拉块体的北边界。 根据阿尼玛卿山两侧滑动速率和历史地震的差异, 将断裂带分为东西两个部分。 滑动速率由西向东递减, 近百年的历史地震产生的破裂基本覆盖了西部和东部的一部分。 随着巴颜喀拉块体周缘强震的持续发生, 作为块体北边界的东昆仑断裂带的地震空区及地震潜势研究变得更加重要。 近些年通过对东昆仑断裂带不同段的研究得到了较多的滑动速率和古地震序列数据, 为评价断裂带未来百年地震危险性提供了有利条件。 利用NB模型中的对数正态分布方法, 得到了东昆仑断裂带在未来100 a的发震概率, 研究表明, 东部(玛曲段)发震概率相对较高, 需要进一步关注。     

利用远震P波层析成像研究巴颜喀拉地块东缘及邻区的深部结构

为了揭示巴颜喀拉地块东缘及邻区的壳幔速度结构差异,获取2017年九寨沟M_S7.0地震的深部构造背景,本文收集了2009年5月至2016年8月期间四川及邻区数字测震台网的203个地震台站所记录到的远震P波走时数据,应用有限频体波走时层析成像方法,反演得到了巴颜喀拉地块东缘及邻区50—600 km深度范围内的三维壳幔P波速度结构。反演结果表明:巴颜喀拉地块东缘及邻区的壳幔速度结构具有明显的横向不均匀性和分区特征,松潘—甘孜地槽褶皱系、西秦岭和祁连山褶皱系的整体速度异常较低,研究区东部具有克拉通性质的四川盆地西北缘和鄂尔多斯地块南缘则呈明显的高速异常。上地幔P波速度结构特征差异表明松潘—甘孜地块的抬升可能与地幔上涌有关,巴颜喀拉地块东缘九寨沟震区及周边50—250 km深度范围内的上地幔存在低速异常,在400—600 km地幔过渡带深度范围内表现为明显的高速异常特征。巴颜喀拉地块向东南方向运移受到东部高速、高强度的扬子克拉通地块对青藏高原物质东向挤出的强烈阻挡,而九寨沟震区处于松潘—甘孜地块重要的北东边界断裂交会处附近,应力容易在此集中,这些因素均可能是东昆仑断裂塔藏段与岷江断裂北段交会处附近发生九寨沟M_S7.0地震的深部动力学背景。      

基于库仑应力改变和地震活动性研究巴颜喀拉块体周缘强震序列的触发关系及其构造意义

自本世纪以来,青藏高原巴颜喀拉块体周缘密集地发生了7次M_W≥6.5强震事件,包括伤亡惨重的2008年汶川M_W7.9地震和2017年九寨沟M_W6.5地震。本文根据这7次强震事件中先前地震对后续地震的库仑应力改变（dCFS）的计算结果,结合基于ETAS模型得到的背景地震活动性的变化结果,研究了强震间的触发关系,以试图解释发生在环巴颜喀拉块体的几次强震的发震机理并探讨其构造意义。结果表明,各个强震的库仑应力变化与其造成的背景地震活动性变化呈正相关,并且在这7次强震中,汶川地震对芦山地震有显著的触发作用,并造成芦山地区背景地震活动性的显著提高。同时汶川地震对九寨沟地震的发生具有一定的延迟作用,造成九寨沟地区背景地震活动性降低。除此之外,其它地震之间均无明显的触发/延迟作用或显著的背景地震活动性变化。这表明该强震序列的孕震机制主要是巴颜喀拉块体东南向持续挤压的构造运动,推断巴颜喀拉块体目前仍处于构造运动活跃期,因此包括巴颜喀拉块体周缘在内的我国西南地区未来的强震危险性值得持续关注。      

Coseismic Coulomb failure stress changes caused by the 2017 <Emphasis Type="Italic">M</Emphasis>7.0 Jiuzhaigou earthquake,and its relationship with the 2008 Wenchuan earthquake

On August 8, 2017, a M7.0 earthquake occurred in Jiuzhaigou County, Sichuan Province, China, resulting in significant casualties and property damage. Therefore, it is critical to identify the areas of potential aftershocks before reconstruction and re-settling people to avoid future disasters. Based on the elastic dislocation theory and a multi-layered lithospheric model, we calculate the Coulomb failure stress changes caused by the Wenchuan and Jiuzhaigou earthquakes, discuss the relationship between the M_w7.9 Wenchuan and M7.0 Jiuzhaigou earthquakes, and analyze the influence of the aftershock distribution and stress changes on the major faults in this region caused by the Jiuzhaigou earthquake. The co- and post-seismic stress changes caused by the Wenchuan earthquake significantly increased the stress accumulation at the hypocenter of the Jiuzhaigou earthquake. Therefore, the occurrence of the Jiuzhaigou earthquake was probably stimulated by the Wenchuan earthquake. The aftershock distribution is well explained by the co-seismic stress changes of the Jiuzhaigou earthquake. The stress accumulation and corresponding seismic hazard on the Maqu-Heye segment of the East Kunlun fault and the northern extremity of the Huya fault has been further increased by the Jiuzhaigou earthquake.     

Numerical simulation on the influences of Wenchuan earthquake on the surrounding faults

On 12 May 2008, the devastating Wenchuan earthquake struck the Longmenshan fault zone, which comprised the eastern margin of the Tibetan Plateau, and this fault zone was predominantly a convergent boundary with a right-lateral strike-slip component. After such a large-magnitude earthquake, it was crucial to analyze the influences of the earthquake on the surrounding faults and the potential seismic activity. In this paper, a complex viscoelastic model of western Sichuan and eastern Tibet regions was constructed including the topography. Based on the findings of co-seismic static slip distribution, we calculated the stress change caused by the Wenchuan earthquake with the post-seismic relaxation into consideration. Our preliminary results indicated that: (1) The tectonic stressing rate was relatively high in Kunlun mountain pass-Jiangcuo, Ganzi-Yushu, Xianshuihe and Zemuhe faults; while in the east Kunlun and Longriba was medium; also the value was less in the Minjiang, Longmenshan, Anninghe and Huya faults. As to the Longmenshan fault, the value was 0.28×10^-3 MPa/a to 0.35×10^-3 MPa/a, which is coincident with the previous long recurrence interval of Wenchuan earthquake; (2) The Wenchuan earthquake not only caused the Coulomb stress decrease in the source region, but also the stress increase in the two terminals, especially the northeastern segment, which is comparatively consistent with the aftershock distribution. Meanwhile, the high concentration areas of the static slip distribution were corresponding to the Coulomb stress reductions; (3) The Coulomb stress change caused by Wenchuan earthquake showed significant increase on five major faults, which were northwestern segment of Xianshuihe fault, eastern Kunlun fault, Longriba fault, Minjiang fault and Huya fault respectively; also the Coulomb stress on the fault plane of the Yushu earthquake was faintly increased; (4) We defined the recurrence interval as the time needed to accumulate the magnitude of the stress drop, and the recurrence interval of Wenchuan earthquake was estimated about 1 714 a to 2 143 a correspondingly.     

松潘-甘孜块体东北端强震间相互作用及地震危险性研究

松潘-甘孜块体位于中国大陆西南部、南北地震带的中段,其东段与扬子块体相接,拥有多条活动断裂带,是青藏高原北部的主要构造单元.该地区地震活动性强烈,历史上曾发生过多次灾难性地震.本文基于地震触发原理和黏弹松弛分层地壳模型,计算了松潘-甘孜块体东北端历史强震之间应力传输和相互作用的过程.模型结果显示,受之前地震导致的库仑应力场变化的影响,1879年武都地震和1976年8月23日松潘M7.2级地震震中库仑应力积累提升,将促进这些地震提前发生;1933年M7.5叠溪地震和1973年M6.5松潘地震震中库仑应力降低,前续地震的影响可能使得这两次地震的发震时间推迟;在研究历史地震对1960年漳腊M6.7级地震、1976年8月16日M7.2级和1976年8月22日M6.7级松潘地震的作用时,有效摩擦系数的取值十分重要,当有效摩擦系数取0.8时,前续地震导致的应力场变化将促进以上三次地震的发生.松潘-甘孜块体东北端的强震活动有效地增强了西秦岭北缘断裂、东昆仑断裂玛沁-玛曲段、鲜水河断裂康定-道孚段和岷江断裂中段上的库仑应力积累,将提升这些断裂今后发生地震的概率;有效降低了龙日坝断裂上库仑应力的积累,降低了该断层上发生地震的概率.松潘-甘孜块体的地震活动降低了汶川地震震中位置的库仑破裂应力,但提升了破裂面东北段的应力积累,有助于汶川地震向东北端破裂.     

鲜水河断裂带库仑应力演化与强震间关系

以鲜水河断裂带为研究区,首先验证了该断裂带上1893年以来M6.7以上地震的相互触发作用,然后采用更符合实际的分层黏弹介质模型研究强震震后黏滞松弛引起的库仑应力变化对后续地震的影响,并基于负位错理论计算鲜水河断裂带10个断层段的震间长期构造加载作用引起的断层上的应力积累.在此基础上,讨论同震、震后、震间效应引起的累积库仑应力变化与区域强震活动的关系,给出断层上库仑应力随时间的演化.结果表明,鲜水河断裂带上1893年以来发生的7次强震均在其前面一系列强震及构造应力加载的驱使下发生,同震、震后、震间三方面效应均引起了鲜水河断裂带不可忽略的库仑应力变化.对断层上的库仑应力状态的研究,可进一步为揭示地震的发生规律、找寻危险断层段提供线索.     

1900年以来巴颜喀拉块体应力演化与周缘强震关系的数值模拟研究

以巴颜喀拉块体为研究对象,考虑区域地质构造差异,主要活动断裂带,活动块体和边界断裂带的划分结果,引入深部三维速度结构,建立能反映地表起伏和岩石圈分层结构的青藏高原地区三维黏弹性有限元模型.以地壳水平运动速率观测值和最大主压应力方向测量值为约束条件重建研究区现今构造背景应力场.在此基础上模拟了自1900年以来巴颜喀拉块体周缘的7级以上强震序列,从库仑破裂应力角度研究了应力演化与强震的关系、强震之间的相互作用关系以及长期构造加载对强震的影响.研究结果表明,巴颜喀拉块体周缘强震的发生可能与震源区总应力的增加有关.2008年汶川地震导致龙门山断裂带南段应力增加,表明汶川地震对2013年芦山地震有促进作用.鲜水河断裂带上的7级以上强震序列对发生在邻近龙门山断裂带上的2008年汶川地震和2013年芦山地震有延迟作用.     

GPS结果揭示的龙门山断裂带现今形变与受力——与川滇地区其他断裂带的对比研究

本文构建川滇地区二维有限元接触模型,采用“块体加载”方法和1999-2007年GPS数据,模拟计算该区主要断裂带的形变运动,对比、分析其运动、受力特征和应力积累差异.结合区域强震研究汶川地震、芦山地震的力学背景.结果显示强震前龙门山断裂带保持低变形,右旋错动不超过1 mm·a^-1,挤压不超过0.5 mm·a^-1,明显低于其他断裂带,但其两侧应力值与其他断裂带相当,主压应力轴与断裂带走向垂直,形成很宽的挤压带,断层面法向挤压应力积累为-333.74 Pa·a^-1,为全区最高.揭示1999年以来,龙门山断裂带及巴颜喀拉块体东部的挤压应力快速增加,致使实际应力可能处于高水平并诱发地震活跃,期间强震呈丛集性,出现汶川、芦山地震接连发生的现象.     

东昆仑活动断裂带大地震之间的黏弹性应力触发研究

对青藏高原北部东昆仑破裂带大地震之间的应力转移和断层相互作用进行研究. 考虑1937年以来沿此破裂带发生的5个M≥7的地震：1937年M7.5花石峡地震，1963年MS7.1都兰地震，1973年MS7.3玛尼地震，1997年MW7.5玛尼地震和2001年MW7.8可可西里地震，模拟了黏弹性成层介质中地震断层错动产生的应力演化过程，并计算了在后续地震破裂面上产生的库仑破裂应力变化. 结果表明，前面4个地震均造成2001年可可西里地震断层面上库仑破裂应力的增加，并且中地壳和下地壳的黏弹性松弛效应使得库仑破裂应力场随着时间的推移而逐渐加强. 在计算过程中定量估计了可可西里地震发生时前面4个地震同震形变和黏弹性松弛导致可可西里地震破裂面上库仑破裂应力变化之间的比值，发现前3个地震由黏弹性松弛造成的变化远远大于同震形变所造成的变化. 可可西里地震之后应力场的模拟表明东昆仑断层中段的东大滩－西大滩断层段（位于可可西里地震破裂以东及都兰地震以西）的库仑破裂应力显著增加，变化值达0.05～0.1 MPa，预示这一地区地震危险性的增加.     

汶川地区区域构造应力场特征及汶川MS8.0地震对周围主要断层面的影响

为剖析2008年汶川M_S8.0地震对后期地震的影响及发震区域构造应力场特征,首先利用2008年5月12日—2013年4月19日汶川地震及其邻区的1660条震源机制解,同时采用同一地震多个震源机制中心解的方法筛去重复地震事件的震源机制解,最终获得911个震源机制解。其次,通过网格搜索法分段反演出区域构造应力场。结果显示:东北区主要受WNW-ESE向的挤压,西南区受W-E向的挤压,中区受WSW-ENE向的挤压。西南到东北主压应力轴方向有所变化,这可能与龙门山地区受到来自印度板块北北东方向的俯冲推挤、四川盆地的阻挡和巴颜喀拉块体东南向挤压的联合作用有关。然后,基于USGS给出的汶川M_S8.0地震的破裂模型,计算出该地震对附近强震的触发关系,结果表明,本次汶川地震对同属龙门山断裂西南端的芦山地震触发作用明显,对位于东昆仑断裂上的玛多地震也有一定的触发作用。最后,计算汶川M_S8.0地震对周围断层的同震库仑应力变化,发现本次地震造成龙门山断裂南北两端、秦岭南缘断裂、鲜水河断裂东南端、东昆仑断裂、白玉断裂的库仑破裂应力增加,龙门山断裂南北两端和秦岭南缘断裂增加最为明显,对分析地震危险性有一定的参考意义。      

The Late Pleistocene activity of the eastern part of east Kunlun fault zone and its tectonic significance

The nearly EW-trending East Kunlun fault zone is the north boundary of the Bayan Har block.The activity characteristics and the position of the eastern end of its eastward extension are of great significance to probing into the dynamic mechanism of formation of the east edge of the Tibetan Plateau,and also lay the foundation for seismic risk assessment of the fault zone.The following results are obtained by analysis based on satellite image interpretation of landforms,surface rupture survey,terrace scarp deformation survey,and terrace dating data on the eastern part of the East Kunlun fault zone:(1)the Luocha segment is a Holocene active fault,where a reverse L-shape paleoearthquake surface rupture zone of about 50 km long is located;(2)the Luocha segment is characterized by left-lateral slip movement under the compression-shear condition since the later period of the Late Pleistocene,with a rate of 7.68–9.37 mm/a and a vertical slip rate of 0.7–0.9 mm/a,which are basically in accord with the activity rate of segments on its west side.The results indicate that it is a part of eastward extension of the East Kunlun fault zone;(3)the high-speed linear horizontal slip of the nearly EW-trending East Kunlun fault zone is blocked by the South China block at east,and transforms into the vertical movement of the nearly SN-NNE trending Minjiang fault zone and the Longmenshan fault zone,and the uplift of Longmenshan and Minjiang.The area where transform of the two tectonic systems occurred confines the position of the east end;(4)Luocha segment and Maqu segment constitute the"Maqu seismic gap",so,seismic risk at Maqu segment is higher than that at Luocha segment,which should attract more attention.     

川滇菱形块体东边界库仑应力演化及强震发生概率估算

本研究基于分层黏弹介质模型,考虑强震或大地震同震位错、震后黏滞松弛及主断层段震间构造应力加载三方面效应,给出1480年以来,川滇菱形块体东边界鲜水河断裂带、安宁河断裂带、则木河断裂带和小江断裂带共20个断层段由三方面效应引起的累积库仑应力变化随时间的演化,分析强震间相互作用和强震发生的应力累积背景,定性分析各断层段的地震危险性.同时,分别采用现今台网地震目录和川滇菱形块体东边界各断层段强震复发间隔两种资料,定量计算2030年各断层段的强震发生概率;并基于摩擦本构理论,将周边强震引起的库仑应力变化量作为应力扰动,修正强震发生概率的计算结果.各断层段累积库仑应力演化的结果表明,鲜水河断裂带中部八美段、色拉哈段及南部磨西段、安宁河断裂带冕宁-西昌段、小江断裂带北部巧家-东川段和南部建水段的累积库仑应力显著增加.修正的强震发生概率计算结果显示,鲜水河断裂带中部八美-色拉哈-康定一带、安宁河断裂带冕宁-西昌段、小江断裂带南部华宁-建水一带强震发生概率较高,地震危险性值得关注.本研究基于库仑应力演化计算定性分析强震危险性的同时,基于摩擦本构律理论,结合地震引起的应力扰动和强震发生背景,定量计算修正的强震发生概率,为川滇菱形块体东边界强震危险地点及中长期发震紧迫程度判定提供方法和依据.