2009年云南姚安6.0级地震震源机制与发震构造的分析研究

利用P波、SV波、SH波初动及其振幅比联合反演震源机制解的方法,计算了2009年7月9日发生在云南姚安6.0级地震余震序列的震源机制解,同时结合地震序列的空间分布,对姚安6.0级地震的发震断层性质和震区应力场特征进行综合分析。结果分析表明：（1）姚安6.0级地震发震断层为NWW—SEE向的直立右旋走滑断层,与美国哈佛大学的主震CMT解节面基本一致,也与余震优势方向分布一致,证明结果可靠;（2）震区主压应力场优势方向为NNW—SSE向,与其现今区域构造应力场主压应力NNW—SSE向一致,表明主震应力场主要受到现今区域构造应力场的控制,同时还有一些小的余震与主震应力场不同,表明震区应力场的多样性和复杂性;（3）结合本次地震序列的空间分布、震源机制解特征、震区断裂构造特征综合分析,综合判定姚安6.0级地震的发震构造属于马尾箐断裂。     

2009年云南姚安6.0级地震震源机制与发震构造的分析研究

利用P波、SV波、SH波初动及其振幅比联合反演震源机制解的方法,计算了2009年7月9日发生在云南姚安6.0级地震余震序列的震源机制解,同时结合地震序列的空间分布,对姚安6.0级地震的发震断层性质和震区应力场特征进行综合分析。结果分析表明：（1）姚安6.0级地震发震断层为NWW—SEE向的直立右旋走滑断层,与美国哈佛大学的主震CMT解节面基本一致,也与余震优势方向分布一致,证明结果可靠;（2）震区主压应力场优势方向为NNW—SSE向,与其现今区域构造应力场主压应力NNW—SSE向一致,表明主震应力场主要受到现今区域构造应力场的控制,同时还有一些小的余震与主震应力场不同,表明震区应力场的多样性和复杂性;（3）结合本次地震序列的空间分布、震源机制解特征、震区断裂构造特征综合分析,综合判定姚安6.0级地震的发震构造属于马尾箐断裂。     

欧亚地震带现代构造应力场及其分区特征

利用美国哈佛大学矩心矩张量目录中的2818个地震的震源机制解资料,分析了欧亚地震带及其5个分区现代构造应力场的基本特征,给出了5个分区的震源机制主压应力方向分布图。结果表明:①欧亚地震带以逆断型和走滑型断层活动为主;②地中海地震区以走滑断层活动为主,主压应力方向为SSW向;③伊朗—阿富汗—巴基斯坦地震区以逆断型断层活动为主,主压应力优势方向为NNE—NS向;④喜马拉雅地震以逆断型为主,主压应力优势方向为NS和NE向;⑤川—滇—缅地震区以走滑断层活动为主,主应力场方向为NNE向;⑥印度尼西亚地震区以逆断型断层活动为主,主压应力优势方向为NE—SSW向。各分区的主压应力方向明显受其所在区域板块运动的影响,由此推测板块运动可能是产生欧亚地震带构造应力的主要力源。     

福建仙游地震序列的震源机制解

2010年8月4日至2013年10月4日福建仙游共记录到地震1209次,其中最大地震为2013年9月4日发生的ML5.0地震。为了加强对仙游地震序列的研究,更好地了解仙游地震的发震构造及震区的区域应力场,本文利用福建数字地震台网宽频带地震记录,采用矩张量反演方法,得到仙游地震序列中ML3.5的6次地震的震源机制解。这6次地震的震源机制解结果较为一致,都为走滑型地震,断层走向为NW向,倾角陡立,主压应力轴方向为近SN向。反演得到的主压应力轴方向与福建地区的区域应力场并不一致,本文认为仙游地震是由位于震区的金钟水库蓄水造成震区应力调整而引起的。     

近震源宽频带记录的地震矩张量反演

以1985年4月18日云南禄劝地震(Ms=6.1)的15次余震为例, 使用简单介质模型进行近震源记录的地震矩张量反演, 并试图通过反演结果的讨论, 进一步明确有关方法的意义和限度。将DCS-302数字磁带加速度仪组成的小孔径流动台网获得的三分向近震源宽频带记录进行两次积分得到位移地震图, 对依据震相特征选出的信噪比较大的直达P波、直达S波和SP转换波波形在频率域进行矩张量反演。反演中采用均匀弹性半空间的格林函数。计算结果表明, 采用简单的介质模型, 选取信噪比较大的震相进行矩张量反演, 对MLL约为4-5的地震可以较好地给出震源机制解。在不十分了解详细结构的情况下, 用本文所发展的反演方法处理大量中小地震求震源机制和构造应力场是十分便利的。地震矩张量反演的结果给出禄劝地区的主压应力轴为近NNW向, 接近水平, 表明该地震与欧亚板块和印度板块边界的构造运动有关。      

2001年云南永胜6．0级地震余震序列震源机制解与震源区应力场分析

利用垂直向的Pg和Sg波的最大振幅比计算方法,计算了2001年云南永胜6.0级地震余震序列的震源机制解.通过统计方法和系统聚类分析方法,结合余震序列的震中分布,对永胜6.0级地震的震源机制解和震源区应力场的特征进行了综合分析.结果表明:(1)所得发震断层为NWW向直立右旋走滑断层,与美国哈佛大学的主震CMT解的节面一致,也与余震分布一致,证明结果比较可靠;(2)震区主压应力场方向为NNW-SSE,与其现今区域构造应力场主压应力方向(NNW向)一致,表明余震的应力场主要受主震震源应力场的控制.     

京津冀地区地壳应力场特征

基于标量断层类型值,对京津冀地区及邻区2 187个中小地震震源机制解进行分类,统计结果显示研究区震源机制类型以走滑断层和正断层为主,P轴优势方位为NEE—EW和SWW—EW向;采用MSATSI软件包反演该区1°×1°网格的精细地壳应力场,结果表明:最大主压应力轴最优解的优势方向为NEE—EW向,与P轴优势方位一致;所有网格的相对应力大小R值均小于0.5,表明京津冀地区应力状态偏拉张性质,而且最小主压应力轴的不确定度变化范围相对稳定,表明现今京津冀地区地壳应力场处于一个相对统一的NNW—SSE向的拉张作用控制下。39°N以北地区最大主压应力轴方位最优解显示一定角度的偏转,同时最大、中等、最小主压应力轴最优解推断的应力状态由西向东存在一个正断层—走滑断层—正断层的转换过程;而39°N以南地区的现今构造应力场保持稳定,最优主压应力轴呈NEE—SWW向,大部分网格应力状态显示走滑型。构造应力场的反演结果与活动构造、GPS主应变方向和剪切波分裂的快波偏振方向等相关研究结果基本一致。     

岫岩-海城Ms5.4地震序列震源机制解

应用 P波初动符号资料 ,求解得到了岫岩 -海城 5.4级地震前、主、余震 2 0个 ML ≥ 4.0的震源机制解。分析表明 ,该地区的主压应力轴 (P)大多为 NEE- SWW向 ,主张应力轴 (T)大多为 NNW- SSE向 ,P、T轴仰角基本上小于 30°,表明力轴以水平者最多。N轴大多较陡。A、B节面的走向分别为 NWW向和 NNE向。岫岩 -海城地震主要为走滑断层类型。余震震源机制解绝大多数与主震相近 ,结果比较稳定 ,表明余震的应力场主要受主震震源应力场的控制     

汶川M_W7.9和集集M_W7.6地震前应力场转换现象及其可能的前兆意义

2008年四川汶川MW7.9地震和1999年台湾集集MW7.6地震均为挤压推覆构造环境条件下发生的板内逆断层型地震。本文对比分析了两次地震前的CMT解、震区附近的中小地震震源机制解及其反演的应力场可知,集集地震主震震源机制解与用台湾内陆中西部的CMT解反演得到逆断层类型构造应力场吻合,而震区附近中小地震具有随机发生的性质,反演得到了震前与构造应力场不一致的走向滑动类型的局部应力场,但当局部应力场变化到与构造应力场一致时,数月后发生主震;同样,用青藏高原东部的CMT解震源机制反演得到走向滑动类型的构造应力场,逆冲类型的汶川主震与构造应力场的压应力轴吻合,震区附近中小地震反演得到了与构造应力场一致的区域应力场,但震前局部应力场变化为逆冲类型应力场一致时,随即发生主震。说明逆断层型主震区附近随着震源区应力积累,在震前会出现相似的应力场转换现象,当最终转换到与发生主震的应力状态一致时,表明震源区附近应力已达到相当高的应力水平,是发生大地震的征兆,应引起进一步的关注。     

中国大陆及其周边地区应力场特征

本文收集了1976—2018年发生在中国大陆及其周边地区(15°~55°N, 65°~125°E)的4303个地震震源机制解, 分析了该区震源机制解和P、 T轴空间分布特征, 并使用这些震源机制解, 反演得到了中国大陆及周边地区二维构造应力场分布。 应力场反演结果表明, 云南大部、 青藏高原大部以及华北华南大部以走滑型应力性质为主, 印度洋板块与欧亚板块的强烈碰撞控制着中国西部地区, 大量的逆断型地震集中分布在青藏高原周缘和西域活动地块的天山地区。 青藏高原内部也存在正断型地震, 且应力场方向在26°N发生了很大的变化。 位于青藏高原东构造线以南的滇缅活动块体, 最大主压应力σ₁方向在大致100°E发生突变, 由以西的NNE方向偏转到NNW方向。 中国东部的东北块体到华北块体再到华南块体, 最大主压应力方向有一个从NE向逐渐转变成EW向再变化到NW向的旋转趋势。 应力场总体结果表明, 中国东部应力场主要受到太平洋板块和菲律宾板块对欧亚大陆俯冲的作用, 中国西部主要受印度板块向北碰撞欧亚大陆的影响, 块体内部相互作用、 块体与断裂带相互作用也对应力场变化产生影响。     

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.     

北部湾地震的震源机制及地震地质条件

对北部湾地震的震源机制解和地震地质条件进行了详细分析，认为靖西－崇左断裂带过震中的北北西向断层为发震断裂，四会－吴川断裂带过震中的北东东向断层为控震构造，震源构造应力场的主压应力方向为北西－南东向，发震断层的活动方式既有垂直差异运动又有走滑运动。     

Recent Crustal Stress Field and Dislocation Along Seismic Faults in the East China Region

INTRODUCTIONThere exist many methods for studying recent crustal stress field.One of the most commonmethodsis to use focal mechanismsolution data of earthquakes to deduce the recent crustal stressfield.The method is simple and feasible and the data obtained is reliable.Yan Jiaquan,et al.(1979)usedthe method to study the recent tectonic stress field in China and its adjacent areas andgave a rough configuration and regional characteristics of the stress field.Li Qinzu(1980),WeiGuangxing,e…     

CHARACTERISTICS OF FOCAL MECHANISMS AND STRESS FIELD OF YUNNAN AREA

Using the seismic waveform data recorded by regional seismic network of Yunnan and Sichuan and the method of CAP, we calculate and obtain the focal mechanism of 268 earthquakes with the magnitude of M_L≥4.0 occurring in Yunnan during Jan. 1999 to Aug. 2014; then, we analyze the types and the regional feature of the focal mechanism of earthquakes in Yunnan, on the basis of the focal mechanism of 109 earthquakes analyzed by Harvard University. Based on the data of the above focal mechanism solutions, we adopt the method of damped regional-scale stress inversion to calculate the best-fitting tectonic stress tensor of every grid in Yunnan; and adopt the method of maximum principal stress to calculate the direction of maximum horizontal principal stress in Yunnan. The result shows that: (1)the strike-slip type is the most principal type of the earthquake focus in the study area and the second is the normal faulting type; while, the reverse-fault type is relatively small. The spatial distribution of focal mechanism is obvious. This reflects that the dynamic source and acting force are different in different parts of the study area. (2)The direction of the stress field in Yunnan shows a certain spatial continuity. Maximum horizontal principal compressive stress is mainly clockwise from north to south and counterclockwise from the west to the east. The direction of stress field shows inhomogeneity in space. There exist two stress conversion zones respectively in EW and NS direction. The inversion result of stress field shows that the stress field in Yunnan is complex and the principal stress direction changes greatly; and there are obvious differences in different regions.     

Characteristics of recent tectonic stress field in Jiashi, Xinjiang and adjacent regions

Introduction The Pamirs region where Jiashi is located is one of the most active regions of continental plate dynamics in China. Frequent earthquakes here, especially several strong earthquakes oc- curred in 1997 and 2003, have provided excellent conditions for studying the tectonic stress field in this region and a large number of results (GAO and WEN, 2000; GAO et al, 2004; XU, 2001; ZHOU et al, 2001) have been obtained. Although different methods and data were used, under- standings …     

构造"稳定"区强震长期预测的简便途径--以张北地震为例

作为强震长期预测基础的地震带、潜在震源区的划分,仍然依据地震构造类比和地震活动重复两原则。现有的强震长期预测方法在构造“稳定”区,即没有活动构造、没有历史地震(包括古地震)资料的条件下,无能为力。通过张北地震资料的分析,高精度地震定位并结合波形数据反演震源机制的结果表明：在稳定而统一的构造应力场的作用下,沿其最大剪切应力方向上的小地震集中成带,并且持续活动、震源机制的优势取向与应力场吻合,小震带便可以看作属于现今活动的震源断层,在地震长期预测工作中可以作为划分潜在震源区的依据。构造“稳定”区发生的强震属于新破裂。     

2010年4月玉树M_S7.3地震序列的断层结构

利用双差定位方法对玉树地震序列2010年4月14日至10月31日间发生的ML≥1.0地震进行双差定位,得到1545个地震的重定位结果.综合分析地震双差定位结果和玉树地震序列中强地震震源机制解,发现玉树MS7.3地震发震构造由北西向和北东东向两条相交断层组成,主震发生在北西走向的甘孜—玉树断裂带上,5月29日的MS5.9余震序列发生在北东东走向的一条隐伏断裂上,两条断裂均接近直立.甘孜—玉树断裂是羌塘地块和巴彦喀拉地块的构造边界,由于羌塘地块和巴颜喀拉地块的差异运动使甘孜—玉树断裂强耦合段应力高度积累,在应变能超过岩石强度时破裂失稳发生了MS7.3地震.主震断层的左旋滑动导致北东东向断层的正应力减小,库伦应力增加,45天后触发了MS5.9余震序列的活动.     

丽江-清镇剖面上地壳速度结构及其与鲁甸MS6.5级地震孕震环境的关系

2014年8月3日,云南省昭通-鲁甸地区发生M_S6.5级地震,造成了重大的人员伤亡和财产损失.鲁甸震区位于扬子块体的西缘,小江断裂带的东侧北东向的昭通-莲峰断裂带内.由于至今没有穿越该断裂带的人工源深地震测深剖面,而丽江-攀枝花-清镇650 km长深地震测深剖面距离鲁甸主震区不超过50 km,利用宽角地震资料的初至波震相,通过有限差分反演揭示该地区上地壳速度结构,可以为鲁甸震区的地震定位、地震孕育机制等提供深部速度模型.速度剖面显示：剖面结晶基底厚度平均为2 km左右;小江断裂带速度较低,东西两侧的速度较高;因此小江断裂带区域地壳强度比较低,加上断裂两侧的应变速率很高,所以小江断裂带和旁边的鲁甸-昭通断裂带,未来具有发生较大地震的可能,值得关注.     

利用震源机制解走向判定地震影响场长轴方向

为了评估以震源机制解走向作为影响场长轴方向的适用性,以1970—2020年145个破坏性地震为研究对象,研究各地震的震源机制解走向和极震区长轴方向之间的偏差,发现两者平均差值为17.0°;走滑型、逆断型和正断型地震分别占研究地震总数的56.6%、19.3%和6.2%,其震源机制解走向与极震区长轴方向的平均差值分别为16.4°、16.2°和20.6°;有82.8%的地震的震源机制解走向与极震区长轴走向差值小于30°,说明该方法是可行的。通过统计研究2010—2020年等震线长轴方向明显的50个强震震中附近区域历史强震震源机制解走向与极震区长轴方向差值,结果表明:有13个地震震中30 km范围内有历史强震发生,最近历史强震震源机制解走向与极震区长轴方向差值小于30°的有8个(62%)。如果在距离地震震中30 km以内发生过历史强震,则可以综合考虑距震中最近的历史强震震源机制解走向和活动断裂走向来判定影响场长轴方向。     

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.