MECHANISM OF THE 2015 PISHAN,XINJIANG, MS6.5 MAINSHOCK AND RELOCATION OF ITS AFTERSHOCK SEQUENCES

Using the digital broadband seismic data recorded by Xinjiang network stations, we obtained focal mechanism of the July 3 Pishan, Xinjiang, M_S6.5 earthquake with generalized Cut and Paste(gCAP)inversion method. The strike, dip and rake of first nodal plane are 97°, 27°, 51°, and the second nodal plane are 318°, 70°, 107°. The centroid depth and moment magnitude are calculated to be 12km and 6.4. Combining with the distribution of aftershocks, we conclude that the first nodal plane is the seismogenic fault, and the main shock presents a thrust earthquake at low angle. We relocated 1014 earthquakes using the double-difference algorithm, and finally obtained 937 relocated events. Our results show that the earthquake sequences clearly demonstrate a unilateral extension about 50km nearly in NWW direction, and are mainly located above 25km depth, especially the small earthquakes are predominately located at the shallow parts. Furthermore, the focal depth profile shows a southwestward dipping fault plane at the main shock position, suggesting listric thrust faulting, which is consistent with the dip of the mainshock rupture plane. The spatial distribution of aftershocks represents that the Tarim block was thrust under the West Kunlun orogenic belt. In addition, the dip angle of the fault plane gradually increases along the NWW direction, possibly suggesting a gradual increase of strike-slip component during the NWW rupturing process. From above, we conclude that the Pishan M_S6.5 earthquake is the result of Tibet plateau pushing onto the Tarim block from south to north, which further confirms that the continuous collision of India plate and Eurasia plate has strong influence on the seismic activity in and around the Tibet plateau.     

2013年10月31日吉林前郭M5.8震群研究

2013年10月31日在吉林省前郭县查干花镇先后发生5.5级和5.0级地震,之后于2013年11月22日、23日又在原地分别发生了5.3级和5.8级、5.0级地震,形成震群活动。震群地震发生在东北断块区松辽断陷带中央坳陷区内,极震区长轴呈北东向展布。本次震群序列共记录1 356次地震,包括5次5级以上地震,记录到完整的地震序列。余震呈NW向密集条带状分布,震群震源断错性质为带有走滑分量的逆冲型错动,综合分析认为,前郭震群地震可能受北东向扶余—肇东断裂和北西向查干泡—道字井断裂控制,其破裂面为北西向,发震构造可能是震源区基底深部一条NW向隐伏逆冲断裂（查干泡—道字井断裂）。前郭5.8级震群在震前出现一部分测震学异常,而前兆异常更丰富,表现为由外围向震中区逐渐逼近,地震发生后前兆异常又表现出由震中区向外围扩散的特征;在时间上,先是从2010年以来出现以破年变为特征的中期趋势异常,逐渐由趋势异常向短期异常再向临震异常演化,临震异常主要以加速转折下降为主。      

基于区域地震波形的2017年新疆精河MS6.6地震破裂方向性及发震构造研究

2017年8月9日的新疆精河MS6.6地震是近年来天山北缘发生的最大地震,震中位于由多条逆冲断层组成的库松木契克断裂带内.由于震源较深、构造形变复杂、区域地震台站相对稀疏,仅根据震源机制解、余震分布和InSAR观测结果等难以直接判定发震构造.本文针对倾滑型地震发展了一种基于区域地震波形的破裂方向性测定方法,利用余震作为参考地震进行路径校正,根据主震和参考地震的波形时移差和Pn-Pg到时差分别确定主震在水平方向和深度方向的破裂尺度,进而推断同震破裂的延展方向和延伸尺度.本文在反演了主震的点源参数后,应用新发展的方法测定了地震的破裂方向性.点源反演结果显示,精河地震是一个发生在中地壳的高角度逆冲地震,矩震级约6.2,质心深度21km,震源持续时间5.5s,两个双力偶节面分别为102°/45°/106°(NP1)和259°/47°/74°(NP2).破裂方向性分析结果显示,地震的破裂面为南倾的NP1节面,地震沿着破裂起始点向西南方向、向下破裂,总破裂长度约11.5km,其中,沿深度的破裂范围约7km,沿水平的破裂范围约9km,平均破裂速度约2.1km·s-1.综合区域地质资料、卫星影像等判定本次地震的发震断层为精河南断层,地震可能只破裂了断层的下段(17~25km),并未破出地表.     

2014年新疆于田MS7.3地震序列重定位及其发震构造初步研究

2014年2月12日在新疆于田县发生了M_S7.3地震,主震前一天在震区发生了M_S5.4前震,震后余震活动频繁,由于震区台站十分稀疏和不均匀、地壳速度结构复杂,台网常规定位结果精度有限,很难从中获得序列的空间分布特征和活动趋势的正确认识.本文首先利用位于震区附近的于田地震台5年记录的远震波形数据,采用接收函数方法研究了震区附近的地壳结构,建立了震源区的地壳速度模型.在此基础上,联合震相到时和方位角对2014年于田M_S7.3地震序列(从2014年02月11日-2014年04月30日,共计577次地震)进行了重新绝对定位.结果显示,(1) 重定位后的前震和主震震中位置明显向地表破裂带及其附近的阿尔金分支断裂(南肖尔库勒断裂和阿什库勒-肖尔库勒断裂)靠近,两者相距5.4 km,主震位置为36.076°N、82.576°E,震源深度为22 km, 前震位置为36.055°N、82.522°E,震源深度为19 km;(2) 本文重定位结果显示,余震序列沿NEE-SWW展布,优势分布长度约73 km、宽度约16 km,平均震源深度为14.8 km,其中77%的余震分布在地表破裂带的西南端,这部分余震中少数沿阿什库勒-肖尔库勒断裂分布,绝大多数沿北东东向的南肖尔库勒断裂分布,位于地表破裂带东北端的余震沿阿什库勒-肖尔库勒断裂分布,但发生在地表破裂带的余震极少;重定位后,位于地表破裂带西南侧的震中分布由台网目录的近南北向变为北东向,与地表破裂带、南肖尔库勒断裂和阿什库勒-肖尔库勒断裂走向一致;(3) 沿重定位剖面的地震分布,可推断位于地表破裂带西南段的南肖尔库勒断裂与位于北东段的阿什库勒-肖尔库勒断裂倾向反向,南肖尔库勒断裂的倾向为SE,阿什库勒-肖尔库勒断裂的倾向为NW,这与本次地震野外考察得到的断裂性质一致.综合重定位结果、地表破裂带分布、震源机制解、南肖尔库勒断裂和阿什库勒-肖尔库勒断裂的性质认为,2014年于田M_S7.3地震的发震构造为阿尔金断裂西南尾段的两条分支断裂——南肖尔库勒断裂和阿什库勒-肖尔库勒断裂.     

2022年1月8日青海门源M6.9地震余震精确定位与断层面拟合

利用青海和周边87个地震台站于2022年1月8—13日记录的青海门源M6.9地震主震及680次余震资料,经双差地震定位重新进行震源位置的修定,获得633个地震重新定位后的震源信息。结果显示,此次地震的余震分布明显以昌马—俄博断裂南末梢端为界分为东、西两段,西段呈近EW向沿托勒山断裂东段分布,东段呈NWW向沿冷龙岭断裂西段分布。重新定位前余震初始震源深度集中分布在5~15 km,重新定位后变化为在0~20 km深度范围内偏正态分布。根据重新定位后余震分布特点并参考地表破裂带的展布,依据成丛地震发生在断层附近的原则,选取2个矩形区域,基于这2个区域内重新定位后的震源信息,利用模拟退火与高斯\|牛顿相结合的算法进行断层面拟合计算,完整地获得每一个拟合区域的断层面参数。结果表明托勒山断裂东段断层面与冷龙岭断裂西段断层面分别为长约15 km总体走向为近EW向的高倾角左旋走滑断裂与长约12 km总体走向为NWW向的高倾角大型左旋走滑断裂。此次青海门源地震可能是上述两断层面末端相互挤压共同破裂形成的。     

2021年吴忠—灵武ML3.6震群重新定位及震源机制研究

2021年7月18日—8月7日,宁夏吴忠—灵武地区发生M_L3.6显著震群活动。本文利用多阶段定位方法对该震群进行了重新定位,并根据gCAP方法反演了2021年7月20日灵武M_L3.6地震的震源机制及震源矩心深度,采用Snoke方法计算了震群中3次M_L3.0以上地震的震源机制,测定了同一地震多个震源机制的中心解。结果表明,该震群中最大的地震即7月20日02时40分M_L3.6地震的震源机制为节面Ⅰ走向289°,倾角72°,滑动角?22°,节面Ⅱ走向26°,倾角69°,滑动角?161°,震源矩心深度为12 km,初始破裂深度为12.5 km;7月20日03时15分M_L3.2地震的震源机制为节面Ⅰ走向290°,倾角82°,滑动角?2°,节面Ⅱ走向20°,倾角88°,滑动角?172°,初始破裂深度为11.9 km;7月21日04时55分M_L3.1地震的震源机制为节面Ⅰ走向285°,倾角53°,滑动角2°,节面Ⅱ走向194°,倾角88°,滑动角143°,初始破裂深度为11.6 km,这些地震震源机制的主压应力轴主要为NE向。该震群序列的震源深度主要相对集中在7—15 km之间,其中M_L3.0以上地震的震源深度主要介于11—13 km,震源深度剖面显示震群相对集中的区域由深到浅大体呈现近似于陡立的展布。本文进一步研究发现区域应力场在灵武M_L3.6地震震源机制NNE向节面产生的相对剪应力为0.393,而在NWW向节面产生的相对剪应力为0.945。结合地质构造和已有断层资料初步分析认为,若NNE向的崇兴隐伏断裂为灵武M_L3.6地震的发震断层,则表明崇兴断裂可能是一条断裂薄弱带,地震破裂方式主要为右旋走滑;若NWW向的未知隐伏断裂为发震断层,则表明NWW向断裂可能为该地震在区域应力场下的剪应力相对最大释放节面,其破裂方式为左旋走滑。      

2017年西藏米林MS6.9地震发震构造初探

2017年11月18日在西藏米林发生了M_S6.9地震,目前尚未发现地表破裂带,发震构造尚不明确.震源机制解表明该次地震为逆冲型地震.精定位结果显示余震集中在加拉白垒东北坡上一个NW走向的长约36 km、宽约8 km的狭长条带之内.余震条带的走向及长度严格受到派乡构造岩片NE边界走向及长度的控制,垂直于该条带的地震剖面清晰地揭示出一条倾向NE的低倾角逆冲断层面,结合震源机制解及GPS同震位移场的已有结果,初步推断它可能就是发震断层面.雅鲁藏布江大拐弯上游加拉-米林河段两岸的湖相基座阶地面和山脊线在南迦巴瓦、加拉白垒脚下都发生了倾向SW的翘起变形,发震断层面构成了其上盘加拉白垒、南迦巴瓦强烈隆升区与其下盘地貌发生翘起变形的弱隆升区的分界面,推断加拉白垒峰沿着这一断层面不断地逆冲、隆升,以此来调节其两侧的不均匀挤出,而下盘近断层处的褶皱、拖曳等作用逐渐造成了阶地面、山脊线的翘起、弯曲变形.基于夷平面的区域变形分析,认为雅江缝合带作为主干断裂带从整体上控制着印度板块与欧亚板块在东构造结地区的碰撞-挤压格局.印度板块东北犄角的强烈顶撞引起了东构造结附近强烈的断块运动,嘉黎断裂带北侧的地壳显著增厚,主夷平面随之发生裂解.与此同时,由于碰撞带来的强烈挤压,派乡构造岩片、多雄拉变质穹隆沿着缝合带大拐弯内侧不均匀地挤出,南迦巴瓦、加拉白垒随之隆升.此次的米林地震仅仅是该不均匀挤出过程所引发的一次具体的事件,是派乡构造岩片内部的一条次级断层发生的一次逆冲运动造成的.此外,紧邻此次余震条带的南迦巴瓦NEE边界以及SE边界是一个潜在的地震空区,其未来地震危险性值得关注.     

STUDY ON THE SEISMOGENIC FAULT AND DYNAMICS PARAME-TERS OF THE 2014 MS6.6 JINGGU EARTHQUAKE IN YUNNAN

On October 17, 2014, a M_S6.6 earthquake occurred in Jinggu, Yunnan. The epicenter was located in the western branch of Wuliang Mountain, the northwest extension line of Puwen Fault. There are 2 faults in the surrounding area, one is a sinistral strike-slip and the other is the dextral. Two faults have mutual intersection with conjugate joints property to form a checkerboard faulting structure. The structure of the area of the focal region is complex. The present-day tectonic movement is strong, and the aftershock distribution indicates the faulting surface trending NNW. There is no obvious surface rupture related to the known fault in the epicenter, and there is a certain distance from the surface of the Puwen fault zone. Regional seismic activity is strong. In 1941, there were two over magnitude 7.0 earthquakes in the south of the epicenter of Jinggu County and Mengzhe Town. In 1988, two mainshock-aftershock type earthquakes occurred in Canglan-Gengma Counties, the principal stress axes of the whole seismic area is in the direction of NNE. Geological method can be adopted to clarify the distribution of surficial fracture caused by active faults, and high-precision seismic positioning and spatial distribution characteristics of seismic sequences can contribute to understand deep seismogenic faults and geometric features. Thus, we can better analyze the three-dimensional spatial distribution characteristics of seismotectonics and the deep and shallow tectonic relationship. The focal mechanism reveals the property and faulting process to a certain extent, which can help us understand not only the active property of faults, but also the important basis for deep tectonic stress and seismogenic mechanism. In order to study the fault characteristic of the Jinggu earthquake, the stress field characteristics of the source area and the geometric parameters of the fault plane, this paper firstly uses the 15 days aftershock data of the Jingsuo M_S6.6 earthquake, to precisely locate the main shock and aftershock sequences using double-difference location method. The results show that the aftershock sequences have clustering characteristics along the NW direction, with a depth mainly of 5~15km. Based on the precise location, calculations are made to the focal mechanisms of a total of 46 earthquakes including the main shock and aftershocks with M_L ≥ 3.0 of the Jinggu earthquake. The double-couple(DC)component of the focal mechanism of the main shock shows that nodal plane Ⅰ:The strike is 239°, the dip 81°, and the rake -22°; nodal plane Ⅱ, the strike is 333°, the dip 68°, and the rake -170.31°. According to focal mechanism solutions, there are 42 earthquakes with a focal mechanism of strike-slip type, accounting for 91.3%. According to the distribution of the aftershock sequence, it can be inferred that the nodal plane Ⅱ is the seismogenic fault. The obtained focal mechanism is used to invert the stress field in the source region. The distribution of horizontal maximum principal stress orienation is concentrated. The main features of the regional tectonic stress field are under the NNE-SSW compression(P axis)and the NW-SE extension(T axis)and are also affected by NNW direction stress fields in the central region of Yunnan, which indicates that Jinggu earthquake fault, like Gengma earthquake, is a new NW-trending fault which is under domination of large-scale tectonic stress and effected by local tectonic stress environment. In order to define more accurately the occurrence of the fault plane of the Jinggu earthquake, with the precise location results and the stress field in the source region, the global optimal solution of the fault plane parameters and its error are obtained by using both global searching simulated annealing algorithm and local searching Gauss-Newton method. Since the parameters of the fault plane fitting process use the stress parameters obtained by the focal mechanism inversion, the data obtained by the fault plane fitting is more representative of the rupture plane, that is, the strike 332.75°, the dip 89.53°, and the rake -167.12°. The buried depth of the rupture plane is 2.746km, indicating that the source fault has not cut through the surface. Based on the stress field characteristics and the inversion results of the fault plane, it is preliminarily believed that the seismogenic structure of the Jinggu earthquake is a newly generated nearly vertical right-lateral strike-slip fault with normal component. The rupture plane length is about 17.2km, which does not extend to the Puwen fault zone. Jinggu earthquake occurred in Simao-Puer seismic region in the south of Sichuan-Yunnan plate. Its focal mechanism solution is similar to that of the three sub-events of the Gengma earthquake in November 1988. The seismogenic structure of both of them is NW-trending and the principal stress is NE-SW. The rupture plane of the Jinggu main shock(NW direction)is significantly different from the known near NS direction Lancang Fault and the near NE direction Jinggu Fault in the study area. It is preliminarily inferred that the seismogenic structure of this earthquake has a neogenetic feature.     

芦山7.0级地震序列的震源位置与震源机制解特征

基于中国国家和四川区域数字地震台网记录,采用HypoDD方法精确定位了四川芦山M_L2.0级以上地震序列的震源位置,采用CAP方法反演了36次M_L4.0级以上地震的最佳双力偶震源机制解,并利用小震分布和区域应力场拟合了可能存在的发震断层面参数,从而综合分析了芦山地震序列的震源深度、震源机制和震源破裂面特征,探讨可能的发震构造.结果显示,7.0级主震的震源位置为30.30°N、102.97°E,初始破裂深度为15 km左右,震源矩心深度为14 km左右,最佳双力偶震源机制解的两组节面分别为走向209°/倾角46°/滑动角94°和走向23°/倾角44°/滑动角86°,可视为纯逆冲型地震破裂,绝大多数M_L4.0级以上余震的震源机制也表现出与主震类似的逆冲破裂特征.M_L2.0级以上余震序列发生在主震两侧,集中分布的长轴为30 km左右,震源深度主要集中在5～27 km,M_L3.5级以上较大余震则集中分布在9～25 km的深度上,并揭示出发震断层倾向北西的特征.利用小震分布和区域应力场拟合得到发震断层参数为走向207°/倾角50°/滑动角92°,绝大多数余震发生在断层面附近10 km左右的区域.综合地震序列分布特征、主震震源深度和已有破裂过程研究结果,可以推测主震破裂过程自初始点沿断层的两侧扩展破裂,南侧破裂比北侧稍长,滑动量主要集中在初始破裂点附近,可能没有破裂到地表.综合本文研究成果、地震烈度分布和现有的科学考察结果,初步推测发震构造为龙门山山前断裂,也不排除主震震中东侧还存在一条未知的基底断裂发震的可能性.     

Fault plane parameters of Sanhe-Pinggu M8 earthquake in 1679 determined using present-day small earthquakes

The great Sanhe-Pinggu M8 earthquake occurred in 1679 was the largest surface rupture event recorded in history in the northern part of North China plain. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method. Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake, and referring to the morphology of the long axis of the isoseismal line obtained by the predecessors, we selected a strip-shaped zone from the relocated earthquake catalog in the period from 1980 to 2009 to invert fault plane parameters of this earthquake. The inversion results are as follows: the strike is 38.23°, the dip angle is 82.54°, the slip angle is -156.08°, the fault length is about 80 km, the lower-boundary depth is about 23 km and the buried depth of upper boundary is about 3 km. This shows that the seismogenic fault is a NNE-trending normal dip-slip fault, southeast wall downward and northwest wall uplift, with the right-lateral strike-slip component. Moreover, the surface rupture zone, intensity distribution of the earthquake and seismic-wave velocity profile in the focal area all verified our study result.     

盖州青石岭地震序列发震构造初探

利用双差定位方法对盖州青石岭震群2012年2月至2015年8月的地震活动进行了重新定位,并使用CAP方法和P波初动法计算了M_L≥4.0地震的震源机制解,之后结合盖州地区的地震地质资料,分析了青石岭震群的发震构造.结果表明:青石岭震群在平面上呈NW向分布,地震活动主要分布在6 km×3 km的矩形范围内,震源深度为7—10 km;较大地震的震源机制解的走向与精定位后地震的优势分布方向一致;综合分析双差定位结果、震源机制解和发震区的地震地质等资料,初步认为九寨—盖县北段西北侧存在NW向次级铲式正断层,青石岭震群即为该断层在区域应力场作用下不断地左旋走滑-拉张错动造成的.      

四川木里小震群活动特征研究

本文通过对四川木里地区地震震源位置的重新确定,反演了较大地震震源机制解,结果显示：①重定位后的小震群震中分布成带状,地震震源深度分布在0—12km范围内;②经过对震群空间分布进行仔细分析,认为其发震构造是小金河断裂西侧的一条NWW向分支断裂;③3次4.0级以上地震震源参数存在明显差异,浅源逆冲事件表现有受垂直方向应力（重力）作用的特征,走滑事件表现出与区域应力构造活动有关。     

浙江珊溪水库2014年震群活动发震机理研究

本文使用双差定位法对2014年9月12日至12月30日浙江珊溪水库发生的4184次地震进行重定位,并采用CAP方法对11次M_L≥3.0地震事件的震源机制解进行反演,讨论了震群序列的活动特征及其与断裂之间的关系,分析了水库水位与地震之间的关系.重新定位的结果显示,在空间分布上,2014年震群序列发生在2006年震群序列NW向延伸的方向上,两者形成一条线性条带,该条带平行分布于双溪—焦溪垟断裂南侧.重定位得到的震源主要在0.7—6 km深度范围内分层分布,垂直于地震条带走向的震源剖面刻画出的结构面以高角度倾向SW.震源机制解结果显示多数地震为走滑型,均存在一个与地震条带走向一致的NW向节面,呈右旋走滑错动性质.考虑到断裂的定位误差,线性分布的震群活动极有可能沿双溪—焦溪垟断裂的破裂面活动,精定位的震源位置和震源机制刻画出了该断裂的几何结构和活动性质.但由于多数地震的震源深度在6 km以上,因此震群活动不能归为双溪—焦溪垟断裂活动的结果,即双溪—焦溪垟断裂不是这两次震群的发震构造,而且仍然属于水库诱发地震,而水库地震存在激发该断裂发生构造地震的可能.水库水位上升或者下降与震群活动关系不大,震群活动有随时间进一步增强的趋势, 可能是库水沿库底断层破裂面长期渗透和扩散增加了孔隙压所致.      

2021年西藏比如MS6.1地震序列发震构造分析

利用双差定位方法对西藏比如M_S6.1地震序列141次M_L≥2.0地震进行重新定位,采用CAP波形反演方法获得主震的震源机制解,并运用最小空间旋转角方法比较不同机构发布的震源机制解的差异。重新定位后主震震中位置为(31.924°N,92.824°E),靠近余震区中心,震源深度为12.8 km;余震分布沿NE向展布,长约18 km。沿NE向深度剖面结果显示,在主震右上方存在5 km×10 km的近椭圆形地震破裂空区。主震的震源机制解为正断兼走滑型,最佳矩心深度为9.3 km,矩震级为5.98。结合重新定位后余震分布、主震与历史地震震源机制解及地质构造背景等分析,认为具有左旋运动性质的安多南缘断裂可能是该次地震序列的主要发震构造。     

内蒙古敖汉旗震群的微震匹配定位及其发震断层研究

内蒙古敖汉旗地区在2018—2019年间曾发生多次小震丛集活动,不同地震事件的波形记录易相互交叠,导致地震目录缺失。针对以上问题,采用匹配定位（Match & Locate）方法,对台网遗漏地震进行识别、检测与定位,并通过CAP方法反演敖汉旗震群最大地震的震源机制解,利用匹配定位后的小震分布定量地拟合发震断层面参数,从而综合判定敖汉旗震群的发震断层面几何形态和发震构造。结果显示:通过匹配定位方法共识别、定位405个小震事件,是原有地震目录事件的5.4倍,震群主体沿NW?SE向展布于红山—八里罕断裂与赤峰—开源断裂相交区域的东侧,震源深度集中于8—10 km。断层拟合结果和最大地震震源机制解表明敖汉旗震群的发震构造应是一条左旋走滑型隐伏正断层,断层面走向为157°,倾角为84°。综合分析红山—八里罕断裂和赤峰—开源断裂的断层性质和活动特征,认为敖汉旗震群的发震断层可能是这两条深大断裂在不断活动中相互作用而形成。      

2014年秭归M_S4.5和M_S4.9地震震源与发震构造特征

2014年3月27日和30日湖北秭归县发生了三峡水库蓄水以来该地区最大的2次地震,文中通过多种方法分析了2次地震的震源与发震构造特征。采用Kiwi方法反演2次地震的矩张量解,该方法中使用了湖北和重庆测震台网14个宽频带波形记录和6层地壳速度结构模型,反演结果显示,2次地震观测谱和波形与理论谱和波形拟合得比较好,非拟合误差数0.57,表明反演结果是可靠的。2次地震均为走滑兼少量逆冲错动,但前一地震为左旋走滑,后一地震为右旋走滑,矩张量解中DC成分偏少而ISO成分多可能是库水对地下介质物性影响的反映。同时也使用三峡台网15个子台记录的波形资料,采用双差定位法重新精定位了从3月27日至4月27日时段内超过500次地震序列事件,结果显示余震序列分布方向为NNW向和NE向,但主要集中在NE向,并分别沿NNW和NE向作了深度剖面,剖面显示震源深度为4.5~10.0km,余震在深部呈现2个较明显的断面,与震源机制解NE向节面产状一致。野外现场宏观烈度调查指出,Ⅴ度极震区等震线为一椭圆,长轴NWW向,短轴NE向,结合野外现场考察结果和震源区地质构造背景,综合推断仙女山断裂北端的NE向破裂面为2次地震的发震断面,余震序列的NE和NNW向分布、剖面上发震层的形态和深度特征表明,这次地震活动受到了仙女山断裂和九畹溪断裂活动的控制与影响。     

STUDY ON SOURCE PARAMETERS OF THE 8 AUGUST 2017 M7.0 JIUZHAIGOU EARTHQUAKE AND ITS AFTERSHOCKS,NORTHERN SICHUAN

On August 8, 2017, a strong earthquake of M7.0 occurred in Jiuzhaigou County, Aba Prefecture, northern Sichuan. The earthquake occurred on a branch fault at the southern end of the eastern section of the East Kunlun fault zone. In the northwest of the aftershock area is the Maqu-Maqin seismic gap, which is in a locking state under high stress. Destructive earthquakes are frequent along the southeast direction of the aftershocks area. In Songpan-Pingwu area, only 50~80km away from the Jiuzhaigou earthquake, two M7.2 earthquakes and one M6.7 earthquake occurred from August 16 to 23, 1976. Therefore, the Jiuzhaigou earthquake was an earthquake that occurred at the transition part between the historical earthquake fracture gap and the neotectonic active area. Compared with other M7.0 earthquakes, there are few moderate-strong aftershocks following this Jiuzhaigou earthquake, and the maximum magnitude of aftershocks is much smaller than the main shock. There is no surface rupture zone discovered corresponding to the M7.0 earthquake. In order to understand the feature of source structure and the tectonic environment of the source region, we calculate the parameters of the initial earthquake catalogue by Loc3D based on the digital waveform data recorded by Sichuan seismic network and seismic phase data collected by the China Earthquake Networks Center. Smaller events in the sequence are relocated using double-difference algorithm; source mechanism solutions and centroid depths of 29 earthquakes with M_L≥3.4 are obtained by CAP method. Moreover, the source spectrum of 186 earthquakes with 2.0≤M_L≤5.5 is restored and the spatial distribution of source stress drop along faults is obtained. According to the relocations and focal mechanism results, the Jiuzhaigou M7.0 earthquake is a high-angle left-lateral strike-slip event. The earthquake sequence mainly extends along the NW-SE direction, with the dominant focal depth of 4~18km. There are few shallow earthquakes and few earthquakes with depth greater than 20km. The relocation results show that the distribution of aftershocks is bounded by the M7.0 main shock, which shows obvious segmental characteristics in space, and the aftershock area is divided into NW segment and SE segment. The NW segment is about 16km long and 12km wide, with scattered and less earthquakes, the dominant focal depth is 4~12km, the source stress drop is large, and the type of focal mechanism is complicated. The SE segment is about 20km long and 8km wide, with concentrated earthquakes, the dominant depth is 4~12km, most moderate-strong earthquakes occurred in the depth between 11~14km. Aftershock activity extends eastward from the start point of the M7.0 main earthquake. The middle-late-stage aftershocks are released intensively on this segment, most of them are strike-slip earthquakes. The stress drop of the aftershock sequence gradually decreases with time. Principal stress axis distribution also shows segmentation characteristics. On the NW segment, the dominant azimuth of P axis is about 91.39°, the average elevation angle is about 20.80°, the dominant azimuth of T axis is NE-SW, and the average elevation angle is about 58.44°. On the SE segment, the dominant azimuth of P axis is about 103.66°, the average elevation angle is about 19.03°, the dominant azimuth of T axis is NNE-SSW, and the average elevation angle is about 15.44°. According to the fault profile inferred from the focal mechanism solution, the main controlling structure in the source area is in NW-SE direction, which may be a concealed fault or the north extension of Huya Fault. The northwest end of the fault is limited to the horsetail structure at the east end of the East Kunlun Fault, and the SE extension requires clear seismic geological evidence. The dip angle of the NW segment of the seismogenic fault is about 65°, which may be a reverse fault striking NNW and dipping NE. According to the basic characteristics of inverse fault ruptures, the rupture often extends short along the strike, the rupture length is often disproportionate to the magnitude of the earthquake, and it is not easy to form a rupture zone on the surface. The dip angle of the SE segment of the seismogenic fault is about 82°, which may be a strike-slip fault that strikes NW and dips SW. The fault plane solution shows significant change on the north and south sides of the main earthquake, and turns gradually from compressional thrust to strike-slip movement, with a certain degree of rotation.     

1303年山西洪洞8级地震震源断层研究

1303年在山西洪洞附近发生的8级巨大地震, 是中国根据现存较为详细的文献记载史料所确定的最早的一次8级地震。 这次地震距今已有700多年的历史, 而地震所在区域至今仍有持续不断的小地震活动。 本文根据地震破裂区1981年至2013年的中小地震精定位地震目录, 采用震源断层面拟合方法, 反演得到了1303年山西洪洞地震的震源断层面参数: 走向19.3°、 倾角88.5°、 滑动角-170.0°。 断层面长75.5 km, 宽26.2 km, 深度为地下11.12 ～37.35 km。 将地震破裂区的地震精确定位资料以近东西向的洪洞断裂为界划分为地震北段和地震南段, 分段进行地震震源断层拟合, 反演得到洪洞地震北段震源断层面参数: 走向13.7°、 倾角76.6°、 滑动角-157.6°。 断层面长32.7 km, 宽21.7 km, 深度为地下11.97～32.86 km; 南段震源断层面参数: 走向20.3°、 倾角87.1°、 滑动角-154.6°。 断层面长45.9 km, 宽16.6 km, 深度为地下9.32 km～25.50 km。 无论是分段还是不分段, 反演得到的洪洞地震震源断层均是右倾的近直立断层, 属于右旋走向滑动性质。 分段计算得到的地震北段震源断层深度比南段更深, 将反演得到的震源断层与临汾盆地深部构造最新研究成果进行了分析对比, 北段震源断层深度及倾角大小与深地震剖面推测得到的深大断裂几乎相同。 震源断层在地表的投影与洪洞地震的高烈度区能够较好地对应。     

2017—2018年吉林松原地震序列研究

本文利用主地震相对定位法,对2017年7月18日—2018年7月15日期间发生在2018年松原M_S5.7地震震中附近的地震进行了重新定位,并对松原地震序列进行了分析,得到如下结果:① 松原地震破裂面的走向为SW向,倾角较陡,接近直立,倾向为NW向;② 研究区范围内的地震震源深度大部分比主震浅;③ 主震发生前的地震显示出震源深度逐渐加深的过程,主震发生后,地震的震源深度则逐渐变浅。根据上述结果,结合研究区的地震构造背景及松原地震震源机制解的综合分析结果表明,本次地震的破裂面走向为NE?SW向,其发震断层可能为一条NE?SW向的隐伏断层。      

2019年1月12日新疆疏附5.1级地震序列重定位及发震构造研究

基于新疆区域数字地震台网震相观测报告, 采用双差定位方法对2019年新疆疏附M_S5.1地震序列M_L≥1.0地震进行重定位, 采用CAP波形反演方法, 获得了主震的震源机制解和震源矩心深度, 进而综合分析了本次地震可能的发震构造。 结果表明, 疏附5.1级地震震源位置为39.59°N, 75.57°E, 初始破裂深度为18 km, 震源矩心深度为18 km。 重定位后的地震序列呈两个优势方向展布, 分别为NEE向和NE向分支, NEE向为主要的余震优势分布区域, 呈长约13 km窄带状分布在喀什断裂附近。 另一条优势分布为沿NE向长度约9 km, 这可能与喀什断裂阶区有关。 深度剖面显示, 地震震源深度主要集中分布在8~20 km。 沿NEE走向深度剖面显示, 疏附5.1级地震破裂于深部, 余震沿优势分布的震源深度自SWW向NEE呈现逐渐加深的变化特征。 垂直于震中优势分布的深度剖面显示, 本次地震发震断层面倾向为N倾。 震源机制解显示本次地震断错类型为逆冲型, 结合震源深度剖面特征推断节面Ⅰ为本次地震的发震断层面。 综合地震序列空间分布特征、 震源机制以及震源区地质资料, 推测此次地震的发震构造可能为喀什断裂, 余震向浅部扩展。