2003年大姚6.2级、6.1级地震序列震源位置及震源区速度结构的联合反演

采用震源位置和速度结构的联合反演方法确定2003年大姚6.2级、6.1级地震序列的分布和震源区的速度结构.该方法首先确定研究区的速度结构,然后在该速度结构的基础上对地震重新定位.结果表明:① 大姚6.2级地震序列明显分为地震较密集的东南段和地震较稀疏的北西段,而且这两段存在一定的错动,速度结构也显示出高、低速交界带在错动处具有转折特点;② 大姚6.2级地震序列在深度上呈"V"字形分布,这与该地区呈倒三角形分布的低速体相对应,即余震主要分布在高、低速交界带附近;③ 大姚6.2级、6.1级地震的破裂区都位于倒三角形低速体的东南侧,6.2级地震沿高、低速交界带往下破裂,而6.1级地震沿高、低速交界带往上破裂;④ 6 km深度的速度分布显示震源区具有高、低速度体交替呈四象限分布特征,而且余震主要沿北西向的高低速交界带分布;⑤ 大姚6.2级主震的东南侧的高、低速交界带处的低速体速度值较北西侧低速值高,其对6.2级地震往东南方向破裂具有阻碍作用,即东南侧处于能量积累状态,有利于6.1级地震的发生.     

阜阳M_S4.3地震震源深度的确定及地震成因分析

2015年3月14日在安徽阜阳地区发生了M_S4.3地震,随后发生3月23日M_s3.6余震.主震造成2人死亡13人受伤.房屋倒塌155间,受损1万多间.主震震级不大,而造成的灾害巨大.本文使用CAP方法反演了两次地震的震源机制解和震源深度,结果显示两次地震的震源机制解和深度一致.主震的机制解节面Ⅰ走向110°,倾角75°,滑动角—10°;节面Ⅱ走向202°,倾角80°,滑动角—164°;矩震级M_w4.3,余震矩震级M_w3.7,反演最佳深度均为3 km.最佳深度时波形拟合相关系数较高,表明反演结果是可靠的.使用sPn和sPL深度震相进一步分析了两次地震的震源深度.结果显示,选取的7个台站的sPn震相与Pn震相的平均到时差为1 s,对应的震源深度为3 km.震中距为36 km的利辛台的sPL震相与Pg震相到时差约为1.1 s,对应震源深度约3~4 km之间.两种深度震相分析的震源深度与CAP方法的结果一致,表明本文给出的阜阳地震震源深度为3 km左右基本是可靠的.本次地震造成较大灾害的原因很可能与地震震源较浅有关.阜阳地区地壳结构相对稳定,地质构造演化形成3 km厚的沉积层,本次地震可能是区域应力作用下发生在沉积层里的一次地震.     

廊固凹陷深部剪切破裂构造的地震学证据

基于区域地震台网观测数据,采用近震波形反演方法,确定2018年2月12日河北永清M4.3地震的最佳双力偶源震源机制解为:节面Ⅰ走向297°,倾角58°,滑动角-32°;节面Ⅱ走向45°,倾角63°,滑动角-144°;是一个略带正断分量的右旋走滑地震.结合近震转换波测定主震的震源深度在19km附近.地震序列的双差定位结果显示:永清地震序列震中呈北东向窄带展布,表明此次地震主要向北东向破裂;深度集中分布在17～19km,整体形态近于铅直,显示发震断裂具有走向北东、倾向南东、倾角陡立的特征,与节面Ⅱ的性质比较吻合,推测节面Ⅱ为发震断层面.将发震断层面参数与震源区附近断裂性质进行对比分析,形成了关于廊固凹陷附近区域地震构造的一些认识:(1)推测永清地震的发震构造不是地壳浅部发育的先存正断裂,而是震源区下方一条地壳尺度的深断裂,该深断裂为新生断裂,具有右旋走滑正断性质,倾角陡峭、近于直立、宽度较大,向上与夏垫断裂相通.(2)综合震源区附近多条深地震反射剖面探测结果,推测永清地震的发震断裂与新夏垫断裂同属一条断裂,称为:新夏垫深断裂.该断裂从夏垫向西南方向延伸至文安,并可能与霸县—束鹿—邯郸断裂带相联系,总长度超过150km.(3)基于2006年文安M5.1地震与2018年永清M4.3地震在震源机制上的相似性及震源位置上的关联性,结合区域构造条件,认为两次地震的发震构造均为新夏垫深断裂.(4)根据研究区几次显著地震的震源深度分布特征,参考区域断层构造、电性结构和流变学模型,推测活化克拉通块体新生断裂的脆韧性转换界面深度在15km附近.     

区域宽频地震波形反演所揭示的2022年青海门源MS6.9地震震源破裂过程

基于有限断层模型反演方法,利用区域宽频带数据反演了2022年1月青海门源M_S6.9地震的震源破裂过程,并结合地质构造与地震重定位结果判断发震断层走向.综合反演结果表明:此次地震的发震断层走向为WNW向,主要以走滑为主;破裂主要发生在震源两侧,可能存在着双侧破裂,在震后2 s和9 s出现破裂极大值,最大错动量约为1.5 m,位于深度约6km处,发生明显破裂的深度约为16 km,地表破裂长度约20 km;此次地震释放的标量地震矩为1.23×10¹⁹N·m,相当于矩震级M_W6.7,地震能量主要在前15 s释放;发震断层面的倾角为84.6°,接近于垂直,由于破裂范围较大,所以发生明显错动分布的地表投影也长达34 km.     

2009年7月24日西藏尼玛西南MS5.6地震研究

主要研究2009年7月24日西藏尼玛西南MS5.6地震的基本参数、地震序列特征、震源参数、发震构造等;利用震中附近600km范围内台站测定参数研究地震的震源机制解,与哈佛大学给出的震源机制解较一致,且与通过现场考察的发震断层走向具有一致性。研究认为本次地震发生在冈底斯山—拉萨块体内部,断裂为NNW向,主要受张应力作用产生左旋走滑正断层活动。此外还分析了震前地震学条带异常特征,结束表明,震前1年出现NW向条带非常显著,研究结论为该地区今后地震预测提供科学依据。     

2014 年云南盈江Ms 6.1 地震震源机制研究

利用中国数字地震台网记录的区域宽频带波形,通过频率域和时间域多步反演,研究了2014年云南盈江Ms6.1地震基于点源模型的震源机制解和有限断层模型.考虑到使用不同的波形资料类型和简化的一维速度模型等因素对震源参数反演结果的影响,进行了大量的测试比较.结果表明,使用近震波形和本区域简化一维速度模型M1,波形拟合误差最小.基于点源模型的震源机制解显示此次地震发震断层面参数分别为:走向176°/倾角84°/滑动角-173°,表现为一次右旋走滑错动为主的事件.矩心在水平方向上位于震中(24.99°N,97.84.E)北东向约7km,最佳波形拟合矩心深度7km.平均总标量地震矩M0为7.56×1017N·m,计算成矩震级为Mw5.8.进一步模拟高达0.5Hz的高频波形,获得了盈江地震的有限断层模型,结果显示此次地震未表现出明显的破裂方向性.破裂半径约10km,整个破裂面积为267.2km2,平均滑动量约0.05m,破裂在5 s内释放了大多数能量.震后0～2s内,破裂以孕震点为中心向四周同时扩展,在深度7～ 17km内释放了部分能量.2s后,破裂朝断层面顶部和沿走向两侧进一步延伸,约5s后破裂基本停止.     

1995年河北沙城ML4.1地震发震断层参数测定

在一维单侧有限移动震源模式下, 根据拐角频率的方位变化, 利用最小二乘法研究了1995年7月20日河北沙城ML4.1地震的发震断层面参数. 结果表明, 这次地震的断层面破裂方向为224°, 与余震分布和震源机制的NE向节面一致. 地震马赫数v/c约为1.85, 即平均破裂速度大于S波速度, 为一次超速破裂. 若取横波速度为3.5 km/s, 则破裂长度约为1 km. 因此, 这次地震破裂以超S波速的速度从北东向西南方向传播了约1 km.     

广西北流Ms5.2地震发震构造研究

2019年10月12日广西北流县发生5.2级地震,震源深度10 km。该地震在华南地区地震活动逐渐增强背景下发生,地震序列类型为前—主余型。根据震中附近断裂带分布、震源机制解、余震分布、地震烈度图、建筑物震害调查等结果,对广西北流5.2级地震发震构造特征进行了初步探讨。研究结果表明,北西走向的米场—石窝断裂带为该地震发震断裂带。     

利用区域宽频地震数据反演2021年5月云南漾濞MS6.4地震震源破裂过程

本文基于有限断层模型反演方法,利用区域宽频带数据反演了2021年5月云南漾濞M_S6.4地震的震源破裂过程,结果显示:此次地震的发震断层走向为SE向,主要以右旋走滑为主.破裂主要发生在震源东南侧,最大错动量约为0.55 m,位于深度约9 km处,发生明显破裂的深度约达13 km.此次地震释放的标量地震矩为1.48×10¹⁸N·m,相当于矩震级M_W6.05.地震能量主要在前11 s释放.在深度为6~8 km处破裂速度有明显的变快,可能加剧了地表的震动.     

利用区域宽频地震数据反演2021年5月云南漾濞MS6.4地震震源破裂过程

本文基于有限断层模型反演方法,利用区域宽频带数据反演了2021年5月云南漾濞M_S6.4地震的震源破裂过程,结果显示:此次地震的发震断层走向为SE向,主要以右旋走滑为主.破裂主要发生在震源东南侧,最大错动量约为0.55 m,位于深度约9 km处,发生明显破裂的深度约达13 km.此次地震释放的标量地震矩为1.48×10¹⁸N·m,相当于矩震级M_W6.05.地震能量主要在前11 s释放.在深度为6~8 km处破裂速度有明显的变快,可能加剧了地表的震动.     

Evolution of 3D velocity structure before Dayao <Emphasis Type="Italic">M</Emphasis>=6.2 and <Emphasis Type="Italic">M</Emphasis>=6.1 earthquakes in 2003

In this paper the crustal velocity structure are imaged at the annual scale for determining the evolution of 3D velocity structure before the Dayao earthquakes in 2003, and the relation between physical variation of medium and cause of earthquake occurrence is discussed. Checkerboard resolution tests show that the spatial resolution at 15 km depth is approximate 0.6 around Dayao. Error analyses show that the error (Approximate 0.02 km/s) at the focus area is far smaller than the magnitude (approximate 0.15 km/s) of velocity variation. Results of the studies show that a NNW-striking juncture zone of high-and low-velocity is formed before Dayao earthquake, whose strike is basically consistent with that of aftershock distribution of Dayao earthquakes and the focal mechanism, and the hypocenters lie on the high-velocity side of juncture zone. Furthermore, there is a low-velocity body under the hypocenters after Dayao earthquakes. The evolution of velocity structure provides restriction for discussing the circumstances of earthquake gestating and occurring.     

Evolution of 3D velocity structure before Dayao M=6.2 and M=6.1 earthquakes in 2003

Introduction The Sichuan-Yunnan rhombic block (KAN et al, 1977) located to the southeast of Qinghai-Xizang (Tibetan) sub-plate is one of the most seismically active tectonic regions and ac- tive region of strong earthquakes to monitor (MA et al, 1987). Af…     

唐海—商都地震台阵剖面下方的地壳上地幔S波速度结构研究

2006年底,我们沿“张渤地震带”布设了一条从唐海—北京—商都的宽频带地震台阵剖面.本文利用台阵记录的远震波形资料,通过接收函数和面波联合反演对剖面下方100 km深度范围内地壳上地幔S波速度结构进行了研究.结果表明剖面东段莫霍面深度约30～34 km,西段深度约38～42 km,平原与山区的过渡地带地壳厚度变化较快.地壳内部10～20 km深度范围内存在多个低速体.在唐山7.8级地震震区附近Moho面出现小幅度隆起,中地壳存在明显的S波低速体.张家口以西,剖面下方10～20 km范围内存在两个S波低速体,张北6.2级地震发生在这两个低速体之间狭小的高速区. 在观测剖面附近,历史上发生的4个大震都与壳内低速体的分布有关. 张家口以东,上地幔普遍存在低速层,顶部埋深在60~80 km之间,并表现出明显的东部浅西部深的特点.     

晋冀鲁豫交界地区震源位置及震源区速度结构的联合反演

利用邯郸数字台网记录到的2001—2008年间460次M_L≥1.0地震的1861条P波到时数据, 采用震源位置和速度结构联合反演方法确定晋冀鲁豫交界地区(35.0°~38.0°N, 113.0°~116.0°E)地震的震源位置分布和该区域的速度结构。 结果表明: ① 经过重新定位后, P波走时的均方根残差(RMS)由反演前的1.35 s降到反演后的0.45 s。 定位偏差在EW方向上平均为0.031 km, 在NS方向上平均为0.029 km, 在垂直方向上平均为0.060 km。 ② 邢台震区的中小地震明显呈NEE向分布, 深度主要集中分布在7~14 km范围内; 磁县震区中小震分布相对复杂, 具有NEE和NWW两个展布方向, 震源深度主要集中在8~18 km范围内, 总体上晋冀鲁豫交界地区中小地震深度呈现北部浅南部深的趋势。 ③ 反演得到了晋冀鲁豫交界地区的速度结构, 在邢台地震极震区下方7~14 km处存在低速层, 与1966年邢台7.2级地震的震源深度一致;在磁县地震极震区下方13~18 km处也存在低速层与1831年磁县7.5级地震震源深度一致, 且磁县震区下方的速度结构比邢台震区更为复杂。     

Three-dimensional crustal P-wave velocity structure in the Yangbi and Eryuan earthquake regions,Yunnan, China

A magnitude 5.5 earthquakes occurred in Eryuan County, Dali Bai Autonomous Prefecture, Yunnan Province, China, on March 3. And a magnitude 5.0 earthquake occurred in the same place on April 17, 2013, i.e., 45 days later. Then, on May 21, 2021, multiple earthquakes, one with magnitude 6.4 and several at 5.0 or above, occurred in Yangbi County, Dali Bai Autonomous Prefecture, Yunnan Province, China. All of these occurred in the Weixi-Qiaohou-Weishan fault zone. In this study, 1,874 seismic events in Yangbi and Eryuan counties were identified by automatic micro-seismic identification technology and the first arrivals were picked up manually. Following this, a total of 11,968 direct P-wave absolute arrivals and 73,987 high-quality P-wave relative arrivals were collected for joint inversion via the double difference tomography method. This was done to obtain the regional three-dimensional fine crustal P-wave velocity structure. The results show that the travel time residuals before and after inversion decreased from the initial –0.1–0.1 s to –0.06–0.06 s. The upper crust in the study area, which exhibited a low-velocity anomaly, corresponded to the basin region; this indicated that the low-velocity anomaly in the shallow part of the study area was affected by the basin. Results also showed some correlation between the distribution of the earthquakes and velocity structure, as there was a low-velocity body Lv1 with a wide distribution at depths ranging from 15–20 km in the Yangbi and Eryuan earthquake regions. In addition, earthquakes occurred predominantly in the high-low velocity abnormal transition zone. The low-velocity body in the middle and lower crust may be prone to concentrating upper crustal stress, thus leading to the occurrence of earthquakes.     

2014年三峡秭归M4.5、M4.7震群序列定位及震源区三维P波速度结构研究

采用双差层析成像方法,对2014年3月27日M4.7和3月30日M4.5秭归震群重定位显示:0～5 km深度层P波高速区分布在仙女山断裂北中段和九畹溪断裂北段,天阳坪断裂一带为低速区;8 km深度层高速区分布在九畹溪断裂东侧,仙女山断裂较低;11 km层高速区仅分布在高桥断裂和周家山—牛口断裂之间地带。在地震集中区的下方(即8～12 km处)存在分布较为稳定的低速区,较大地震事件主要分布在高速区或高低速区交界地带,低速区内则很少有地震分布。局部高速体的存在为岩石发生瞬间破裂提供了物质基础,其与低速体间的梯度带是发震构造常发育的区域。研究区内的仙女山断裂北段、九畹溪断裂正是在该梯度带内发育的两条活动断裂。本地震序列的自地表至5 km和5～10 km深度范围内均有大量破裂存在表明,浅层地震仍在水库渗透范围内,而深部地震则与流体渗透无关。此次地震活动同时存在水库诱发地震和构造地震存在。     

study on crustal velocity structure beneath kouquan fault and adjacent area

Through simultaneous inversion of earthquake hypocenters and velocity structure, we obtained the precise locations of earthquakes occurring from 1981 to 2013 in northern Shanxi and the 3D velocity structure, and analyzed emphatically the Kouquan Fault. The result of earthquake relocation shows that earthquakes are concentrated in the central-north segment of Kouquan Fault and the distribution is sparse towards both south and north end of the fault, which indicates that the strong activity is in the central-north segment of Kouquan Fault and the seismicity becomes weaker towards both ends. The result of velocity structure shows that the earthquake concentrated segment of Kouquan Fault is on the side of relative low-velocity area in the high-velocity body, and the south segment of Kouquan Fault is the continuous low velocity. We can recognize the velocity gradient zone from the obvious depression near the Kouquan Fault, which, as we preliminarily speculate, may be the evidence of the presence of Kouquan Fault(or basement detachment)at the deep part. The parallel velocity profile (velocity ratio profile) to Kouquan Fault shows that the earthquake cluster in the central-north segment of Kouquan Fault is located in the abrupt change zone from high to low velocity(from high to low velocity ratio).     

Fine S wave velocity structure beneath Iwate volcano, northeastern Japan, as derived from receiver functions and travel times

A genetic algorithm inversion of receiver functions derived from a dense seismic network around Iwate volcano, northeastern Japan, provides the fine S wave velocity structure of the crust and uppermost mantle. Since receiver functions are insensitive to an absolute velocity, travel times of P and S waves propagating vertically from earthquakes in the subducting slab beneath the volcano are involved in the inversion. The distribution of velocity perturbations in relation to the hypocenters of the low-frequency (LF) earthquakes helps our understanding of deep magmatism beneath Iwate volcano. A high-velocity region (dV_S/V_S=10%) exists around the volcano at depths of 2–15 km, with the bottom depth decreasing to 11 km beneath the volcano’s summit. Just beneath the thinning high-velocity region, a low-velocity region (dV_S/V_S=−10%) exists at depths of 11–20 km. Intermediate-depth LF (ILF) events are distributed vertically in the high-velocity region down to the top of the low-velocity region. This distribution suggests that a magma reservoir situated in the low-velocity region supplies magma to a narrow conduit that is detectable by the hypocenters of LF earthquakes. Another broad low-velocity region (dV_S/V_S=−5 to −10%) occurs at depths of 17–35 km. Additional clusters of deep LF (DLF) events exist at depths of 32–37 km in the broad low-velocity zone. The DLF and ILF events are the manifestations of magma movement near the Moho discontinuity and in the conduit just beneath the volcano, respectively.     

基于密集台阵的青藏高原东北缘地壳精细结构及九寨沟地震震源区结构特征分析

基于青藏高原东北缘密集宽频带野外流动观测台阵以及固定台站资料,利用双差层析成像方法对地震位置和研究区的地壳速度结构进行了反演.最终用于联合反演的地震事件合计9644个.结果显示青藏高原东北缘速度结构具有明显的横向不均匀性.从整体上看,青藏高原地区表现为低速异常,鄂尔多斯表现为高速异常,而扬子地块亦表现为高速异常.不同深度处速度结构表现不一致,同一深度处P波速度结构和S波速度结构也有明显差异.由西秦岭北缘断裂带、临潭-宕昌断裂以及礼县-罗家堡断裂围限的地震活动强烈的区域中,P波速度结构由深度0 km时呈现的低速异常,逐渐过渡到5 km时高低速相间分布的特征;而S波速度结构在此区域中,由近地表0 km时高低速相间分布的特征,逐渐过渡到30 km时几乎表现为低速异常.2017年8月8日九寨沟7级地震所在的塔藏断裂、岷江断裂和雪山断裂围限区域,在深度20 km处的P波速度结构和周围存在明显差异,九寨沟地震处于高速异常与低速异常的过渡带内.此外,2013年7月22日发生在青藏高原东北缘的岷漳县6.6级地震,震源区所在的临潭-宕昌断裂附近的P波速度结构在15 km深度处也有明显特征,震源位置所在区域也处于高低速过渡带.该区域这种地壳内部高低速过渡带可能是应力比较容易积累而发生中强地震的一个重要场所.     

Crustal structure in and around the region of the 1995 Kobe Earthquake deduced from a wide-angle and refraction seismic exploration

Abstract The 1995 Kobe (Hyogo-ken Nanbu) earthquake (M_JMA 7.2, M_w 6.9) occurred on Jan. 17, 1995, at a depth of 17 km, beneath the areas of southern part of Hyogo prefecture and Awaji Island. To investigate P-wave velocity distribution and seismological characteristics in the aftershock area of this great earthquake, a wide-angle and refraction seismic exploration was carried out by the Research Group for Explosion Seismology (RGES) . The profile including 6 shot points and 205 observations was 135 km in length, extending from Keihoku, Northern Kyoto prefecture, through Kobe, to Seidan on Awaji Island. The charge of each shot was 350–700 kg. The P-wave velocity structure model showed a complicated sedimentary layer which is shallower than 2.5 km, a 2.5 km-thick basement layer whose velocity is 5.5 km/s, overlying the crystalline upper crust, and the boundary between the upper and lower crust.
Almost all aftershock hypocenters were located in the upper crust. However, the structure model suggests that the hypocenters of the main shock and some aftershock clusters were situated deeper than the boundary between the upper and lower crust. We found that the P-velocity in the upper crust beneath the northern part of Awaji Island is 5.64 km/s which is 3% lower than that of the surrounding area. The low-velocity zone coincides with the region where the high stress moment release was observed.