云南洱源地区地壳三维精细速度结构成像

doi:10.3969/j.issn.0253-4967.2024.01.010

摘要/Abstract

摘要：

云南洱源地区地处青藏高原东南缘的滇西北地区中部, 区内地质构造复杂, 多条断裂交会穿过, 且地热活动活跃, 显示出很强的断裂构造特征。地区内地震活动频繁, 2013年以来在维西-乔后-巍山断裂西侧发生了多个5级以上地震。文中利用云南区域固定台网和滇西北密集台阵记录的2008年1月1日—2023年7月20日发生在洱源地区的地震走时数据, 采用波速比模型一致性约束的双差层析成像方法, 获得了云南洱源及其周边区域的地壳三维V_P、 V_S和V_P/V_S模型及地震重定位结果。结果表明: 1)在龙蟠-乔后断裂以东, 维西-乔后-巍山断裂、红河断裂和鹤庆-洱源断裂交会处聚集了大量小地震, 缺乏中强地震。从现有的层析成像结果分析认为浅层发生的部分小地震可能与地热流体无直接关系, 而从浅层向深层逐渐变高的V_P/V_S值可能暗示深部存在流体, 深部流体可能在循环流动过程中逐渐渗透到浅层岩石中, 并与部分密集小地震的发生有关。2)2013年以来发生的4个5级以上地震均发生在维西-乔后-巍山断裂西侧, 并呈NNW-SSE走向分布, 表明川滇块体西边界断裂系统的地震危险性有所增大。3)2013年3月3日和4月17日发生的洱源地震序列主要位于低V_P、低V_S和低V_P/V_S值的异常体内。一般而言, 如存在流体, 则V_S比V_P下降得更快, 从而导致高V_P/V_S值, 而低V_P/V_S则表明低V_S并非由流体所致。因此, 现有的成像证据表明地震序列所处区域并不存在流体, 从而推断地震序列的发生与流体无直接关系。空间上与洱源地震序列接近的2017年3月27日 M_S5.1 漾濞地震序列也具有相同的速度结构特征, 因此也可能与流体无直接联系。2016年5月18日发生的 M_S5.1 云龙地震序列的主震和部分余震主要位于高V_P、高V_S和V_P/V_S相对高值区内, 高V_S表明并非因存在流体而导致出现相对高的V_P/V_S值, 据此推测主震及周围的余震所处区域可能不存在流体, 流体并未直接参与到地震序列的发生过程中。

关键词: 洱源地区, 双差层析成像, 三维速度结构, V_P/V_S

Abstract:

The Eryuan area is located in the central part of the northwest Yunnan region on the southeastern edge of the Qinghai-Xizang Plateau. The geological structure in the area is complex, including the Weixi-Qiaohou-Weishan Fault and Honghe Fault, as well as the Longpan-Qiaohou Fault and Heqing-Eryuan Fault, which intersect in an “X” shape. The geothermal activity in the area is also active and exhibits strong fault structural characteristics. Earthquake activity is also frequent in the Eryuan area. Since 2013, multiple earthquakes with M_S≥5.0 have occurred on the west side of the Weixi-Qiaohou-Weishan Fault. Given the complex geological and geothermal background and seismic activity in the Eryuan area, we use the seismic travel time data recorded by the Yunnan Regional Seismic Network and the Northwest Yunnan Dense Array from January 1, 2008, to July 20, 2023, V_P/V_S model consistency-constrained DD tomography method to obtain the 3D V_P, V_S, and V_P/V_S models and relocation results in the Eryuan and its surrounding areas. The research results indicate that: 1)based on the relocation results, the dense small seismic cluster develops at the intersection of the Weixi-Qiaohou-Weishan Fault, Honghe Fault, and Heqing-eryuan Fault deserves special attention. Four earthquakes with M_S≥5.0 that have occurred since 2013 are mainly distributed on the west side of the Weixi-Qiaohou-Weishan Fault, with an NNW-SSE trend distribution. The fault system at the western boundary of the Sichuan-Yunnan block is very complex, and its seismic risk deserves our special attention. 2)Based on the tomography results, the widely distributed low-velocity anomalies in the upper crust of the study area may be related to the crustal material migration pathway caused by the escape of the Sichuan-Yunnan diamond block towards SSE. 3)Combining imaging results with geochemical research results for inference, the high V_P/V_S below 10km depth beneath the small seismic cluster at the intersection of the Weixi-Qiaohou-Weishan Fault, Honghe Fault, and Heqing-Eryuan Fault may correspond to hot spring geothermal fluids. Moreover, the circulation process of hot spring fluids in complex fault systems may have penetrated to a depth of 7~10km below the seismic cluster, accompanied by some small earthquakes. However, there is no imaging evidence of fluid within a depth of 5~7km where some earthquakes are densely distributed. The occurrence of these earthquakes may be related to the distribution of brittle rocks, but it cannot be ruled out that fluid may have a potential infiltration effect on them in the future. Based on the results of velocity structure, they are combined with pre-existing seismology research results. It is found that the Eryuan earthquake sequences on March 3 and April 17, 2013 were mainly located within low V_P, low V_S, and low V_P/V_S anomaly. Generally, if there is fluid present, V_S decreases faster than V_P, resulting in high V_P/V_S. So low V_P/V_S indicates that low V_S is not caused by fluids, which may be due to lithology. Therefore, the imaging evidence indicates that there is no fluid in the region where the sequence is located, thus inferring that the occurrence of the sequence is not directly related to the fluid. The M_S5.1 Yangbi earthquake sequence on March 27, 2017, is spatially close to the Eryuan sequence and also has the same velocity structure characteristics, so it may not be directly related to fluids. The mainshock and some aftershocks of the M_S5.1 Yunlong earthquake sequence on May 18, 2016, were mainly located in high V_P, high V_S, and relatively high V_P/V_S regions. High V_S indicates that it is not the fluid that causes relatively high V_P/V_S. It is speculated that there may not be fluid in the region where the mainshock is located, and the fluid did not directly participate in the occurrence process of the sequence.

Key words: Eryuan area, double-different tomography, 3D velocity structure, V_P/V_S

曹颖, 钱佳威, 黄江培, 周青云. 云南洱源地区地壳三维精细速度结构成像[J]. 地震地质, 2024, 46(1): 162-183.

CAO Ying, QIAN Jia-wei, HUANG Jiang-pei, ZHOU Qing-yun. CRUSTAL FINE VELOCITY STRUCTURE IN THE ERYUAN AREA, YUNNAN FROM DOUBLE-DIFFERENT TOMOGRAPHY[J]. SEISMOLOGY AND GEOLOGY, 2024, 46(1): 162-183.

图/表 9

图1 研究区地质构造背景 a 研究中所使用的台站分布, 右上角插图显示了川滇块体结构; b 研究区内地震、主要断层及温泉点分布。图a中黑色框为研究区, 橙色三角形表示固定台站, 黄色三角形表示用于地震序列监测的流动台站, 粉色三角形表示滇西北密集台阵的流动台站, 图b中的红色五角星表示MS≥5.0地震震中, 绿色圆圈表示4.0≤MS<5.0地震震中, 黑色圆点表示M≥0.0地震震中, 红色震源球为MS≥5.0地震的震源机制解(来自GCMT①（① https://www.globalcmt.org/。）), 蓝色正方形表示温泉点(自王云等, 2019), 紫色正方形表示主要市县。F1维西-乔后-巍山断裂; F2红河断裂; F3龙蟠-乔后断裂; F4鹤庆-洱源断裂; F5苍山山前断裂

Fig. 1 Tectonic background in the study area.

图2 a 研究区内P波射线分布; b S波射线分布; c P波和S波震相时距曲线; d 网格节点分布

Fig. 2 Distribution of P-wave seismic ray paths(a), distribution of S-wave seismic ray paths(b), time-distance curves of P- and S-wave phases(c), distribution of the grid nodes(d).

图3 使用L-curve选取最优光滑权重(a)和阻尼因子(b)与反演前(白色)、后(灰色)P波走时残差(c)和S波走时残差(d)的变化直方图

Fig. 3 Selection of smoothing factor(a)and optimal damping factor(b)and comparison of travel time residuals before(white histogram)and after(gray histogram)inversion for P-wave(c)and S-wave(d).

图4 地震重定位结果在X(a)、 Y(b)和Z方向(c)上的误差直方图

Fig. 4 Uncertainty histograms of earthquake relocations in the X (a), Y (b) and Z (c) directions.

图5 不同深度处的棋盘测试分辨率结果 a VP; b VS; c VP/VS。白色五角星表示MS≥5.0地震, 白色实线表示DWS=100, 黑色实线表示断层。F1维西-乔后-巍山断裂; F2 红河断裂; F3 龙蟠-乔后断裂; F4 鹤庆-洱源断裂; F5 苍山山前断裂

Fig. 5 Recovered results of the checkerboard test at various depths.

图6 地震重定位结果分布 a 重定位后的地震震中分布; b、 c 地震分别在纬度和在经度方向的深度分布情况; d 震源深度分布直方图。AA'和BB'为2条测线的位置。F1 维西-乔后-巍山断裂; F2 红河断裂; F3 龙蟠-乔后断裂; F4 鹤庆-洱源断裂; F5 苍山山前断裂

Fig. 6 Distribution of earthquake relocated events.

表1 本文与其他研究重定位结果的比较

Table1 A comparison of relocation results from this study and other’s

5级以上地震	本文重定位结果	其他研究的重定位结果
2013-03-03洱源M_S5.5地震	25.952°N, 99.780°E, 7.9km	25.952°N, 99.779°E, 7.5km(赵小艳等, 2014)
2013-04-17洱源M_S5.0地震	25.902°N, 99.798°E, 9.9km	25.900°N, 99.800°E, 8.5km(赵小艳等, 2014)
2016-05-18云龙M_S5.1地震	26.095°N, 99.586°E, 13.8km	无具体位置,深度约15km(李姣等, 2017)
2017-03-27漾濞M_S5.1地震	25.891°N, 99.790°E, 10.8km	无具体位置,深度约15km(李姣等, 2020)

图7 不同深度处的VP(a)、 VS(b)和VP/VS(c)模型水平切片白色五角星表示MS≥5.0地震震中, 白色实线表示DWS=100, 黑色实线表示断层。F1 维西-乔后-巍山断裂; F2 红河断裂; F3 龙蟠-乔后断裂; F4 鹤庆-洱源断裂; F5 苍山山前断裂

Fig. 7 Horizontal slices of the VP(a), VS(b)and VP/VS(c)images at various depths.

图8 垂直剖面AA'(a)和BB'(b)的VP、 VS和VP/VS分布黑点表示地震, 白色实线表示DWS=100

Fig. 8 The distribution of VP, VS and VP /VS on the vertical profile AA'(a)and BB'(b).

参考文献 57

[1]	白志明, 王椿镛. 2003. 云南地区上部地壳结构和地震构造环境的层析成像研究[J]. 地震学报, 25(2): 117—127.
	BAI Zhi-ming, WANG Chun-yong. 2003. Tomographic investigation of the upper crustal structure and seismotectonic environments in Yunnan Province[J]. Acta Seismologica Sinica, 25(2): 117—127 (in Chinese).
[2]	白志明, 王椿镛. 2004. 云南遮放—宾川和孟连—马龙宽角地震剖面的层析成像研究[J]. 地球物理学报, 47(2): 257—267.
	BAI Zhi-ming, WANG Chun-yong. 2004. Tomography research of the Zhefang-Binchuan and Menglian-Malong wide-angle seismic profiles in Yunnan Province[J]. Chinese Journal of Geophysics, 47(2): 257—267 (in Chinese).
[3]	常祖峰, 常昊, 李鉴林, 等. 2016a. 维西-乔后断裂南段正断层活动特征[J]. 地震研究, 39(4): 579—586.
	CHANG Zu-feng, CHANG Hao, LI Jian-lin, et al. 2016a. The characteristic of active normal faulting of the southern segment of Weixi-Qiaohou Fault[J]. Journal of Seismological Research, 39(4): 579—586 (in Chinese).
[4]	常祖峰, 常昊, 李鉴林, 等. 2021. 维西-乔后断裂全新世活动与古地震[J]. 地震地质, 43(4): 881—898. doi: 10.3969/j.issn.0253-4967.2021.04.009.
	CHANG Zu-feng, CHANG Hao, LI Jian-lin, et al. 2021. Holocene activity and paleoearthquakes of the Weixi-Qiaohou Fault[J]. Seismology and Geology, 43(4): 881—898 (in Chinese). DOI
[5]	常祖峰, 常昊, 臧阳, 等. 2016b. 维西-乔后断裂新活动特征及其与红河断裂的关系[J]. 地质力学学报, 22(3): 517—530.
	CHANG Zu-feng, CHANG Hao, ZANG Yang, et al. 2016b. Recent active features of Weixi-Qiaohou Fault and its relationship with the Honghe Fault[J]. Journal of Geomechanics, 22(3): 517—530 (in Chinese).
[6]	胡家富, 苏有锦, 朱雄关, 等. 2003. 云南的地壳S波速度与泊松比结构及其意义[J]. 中国科学(D辑), 33(8): 714—722.
	HU Jia-fu, SU You-jin, ZHU Xiong-guan, et al. 2003. S-wave velocity and Poisson’s ratio structure of crust in Yunnan and its implication[J]. Science in China(Ser D), 33(8): 714—722.
[7]	黄小巾, 吴中海, 李家存, 等. 2014. 滇西北裂陷带的构造地貌特征与第四纪构造活动性[J]. 地质通报, 33(4): 578—593.
	HUANG Xiao-jin, WU Zhong-hai, LI Jia-cun, et al. 2014. Tectonic geomorphology and Quaternary tectonic activity in the northwest Yunnan rift zone[J]. Geological Bulletin of China, 33(4): 578—593 (in Chinese).
[8]	贾佳. 2020. 洱源地区地壳三维P波速度精细结构研究[D]. 北京: 中国地震局地球物理研究所:9—49.
	JIA Jia. 2020. 3D P-wave velocity structure of crust in the Eryuan area[D]. Graduate Institute of Geophysics, China Earthquake Administration, Beijing: 9—49 (in Chinese).
[9]	阚荣举, 张四昌, 晏凤桐, 等. 1977. 我国西南地区现代构造应力场与现代构造活动特征的探讨[J]. 地球物理学报, 20(2): 96—109.
	KAN Rong-ju, ZHANG Si-chang, YAN Feng-tong, et al. 1977. Discuss on modern tectonic stress field and the tectonicactivity features in southern region, China[J]. Acta Geophysica Sinica, 20(2): 96—109 (in Chinese).
[10]	雷兴林, 王志伟, 马胜利, 等. 2021. 关于2021年5月滇西漾濞 M_S6.4 地震序列特征及成因的初步研究[J]. 地震学报, 43(3): 261—286.
	LEI Xing-lin, WANG Zhi-wei, MA Sheng-li, et al. 2021. A preliminary study on the characteristics and mechanism of the May 2021 M_S6.4, Yangbi earthquake sequence, Yunnan, China[J]. Acta Seismologica Sinica, 43(3): 261—286 (in Chinese).
[11]	李姣, 姜金钟, 付虹. 2017. 2016年云南云龙 M_S5.0 地震序列精定位研究[J]. 国际地震动态, (8): 35—36.
	LI Jiao, JIANG Jin-zhong, FU Hong. 2017. Research on relocation of Yunnan Yunlong M_S5.0 earthquake sequence in 2016[J]. Recent Developments in World Seismology, (8): 35—36 (in Chinese).
[12]	李姣, 姜金钟, 杨晶琼. 2020. 2017年漾濞 M_S4.8 和 M_S5.1 地震序列的微震检测及重定位[J]. 地震学报, 42(5): 527—542.
	LI Jiao, JIANG Jin-zhong, YANG Jing-qiong. 2020. Microseismic detection and relocation of the 2017 M_S4.8 and M_S5.1 Yangbi earthquake sequence, Yunnan[J]. Acta Seismologica Sinica, 42(5): 527—542 (in Chinese).
[13]	林元武. 1993. 红河断裂带北段温泉水循环深度与地震活动性的关系探讨[J]. 地震地质, 15(3): 193—206.
	LIN Yuan-wu. 1993. A discussion on the relation of circulation depth of hot spring water to seismic activity on the northern segment of the Honghe fault zone[J]. Seismology and Geology, 15(3): 193—206 (in Chinese).
[14]	林元武. 1994a. 滇西地震带大理—剑川段中强地震迁移规律及其原因探讨[J]. 地震研究, 17(2): 136—142.
	LIN Yuan-wu. 1994a. Discussion on regularity of strong-moderate earthquake migration and its cause in Dali-Jianchuan segment of seismic belt in western Yunnan[J]. Journal of Seismological Research, 17(2): 136—142 (in Chinese).
[15]	林元武. 1994b. 温泉热储温度对断裂的弱化作用及其对地震活动性的影响[J]. 地震学报, 16(2): 251—257.
	LIN Yuan-wu. 1994b. The weakening effect of hot spring thermal storage temperature on faults and its impact on seismic activity[J]. Acta Seismologica Sinica, 16(2): 251—257 (in Chinese). DOI URL
[16]	刘毅. 2020. 洱源地震震源区及周边精细速度结构和地震重定位研究[D]. 北京: 中国地质大学:10—43.
	LIU Yi. 2020. Fine velocity structure and earthquake relocation in source and peripheral area of Eryuan earthquake[D]. Graduate China University of Geosciences, Beijing: 10—43 (in Chinese).
[17]	上官志冠. 1988. 滇西实验场区主要活动断裂地球化学特征[J]. 地震地质, 10(4): 134—141.
	SHANGGUAN Zhi-guan. 1988. Geochemical characteristics of the main active faults in Western Yunnan Earthquake Prediction Test Site[J]. Seismology and Geology, 10(4): 134—141 (in Chinese).
[18]	上官志冠, 高松井. 1987. 滇西实验场区温泉碳同位素地震地球化学特征[J]. 地震, (6): 25—35.
	SHANGGUAN Zhi-guan, GAO Song-jing. 1987. Seismo-geochemical characteristics of carbon isotope in hot spring in Dianxi Experimental Field[J]. Earthquake, (6): 25—35 (in Chinese).
[19]	王博, 周永胜, 钟骏, 等. 2022. 滇西北构造地热特征及对地震活动的影响[J]. 地球物理学报, 65(9): 3419—3433.
	WANG Bo, ZHOU Yong-sheng, ZHONG Jun, et al. 2022. Tectonic geothermal feature of Northwest Yunnan and the influence on seismic activity[J]. Chinese Journal of Geophysics, 65(9): 3419—3433 (in Chinese).
[20]	王光明, 吴中海, 彭关灵, 等. 2021. 2021年5月21日漾濞 M_S6.4 地震的发震断层及其破裂特征: 地震序列的重定位分析结果[J]. 地质力学学报, 27(4): 662—678.
	WANG Guang-ming, WU Zhong-hai, PENG Guan-ling, et al. 2021. Seismogenic fault and it’s rupture characteristics of the 21 May, 2021 Yangbi M_S6.4 earthquake: Analysis results from the relocation of the earthquake sequence[J]. Journal of Geomechanics, 27(4): 662—678 (in Chinese).
[21]	王云, 冉华, 李其林, 等. 2019. 滇西北裂陷区地热及构造活动特征研究[J]. 矿物岩石地球化学通报, 38(5): 923—930.
	WANG Yun, RAN Hua, LI Qi-lin, et al. 2019. A study on characteristics of geothermal and tectonic activities in the northwest Yunnan rifting zone, western China[J]. Bulletin of Mineralogy, Petrology and Geochemistry, 38(5): 923—930 (in Chinese).
[22]	徐锡伟, 闻学泽, 郑荣章, 等. 2003. 川滇地区活动块体最新构造样式及动力学来源[J]. 中国科学(D辑), 33(S1): 151—162.
	XU Xi-wei, WEN Xue-ze, ZHENG Rong-zhang, et al. 2003. Pattern of latest tectonic motion and dynamics of faulted blocks inYunnan and Sichuan[J]. Science in China(Ser D), 33(S1): 151—162 (in Chinese).
[23]	颜鹍, 李如陶, 李四海. 1997. 滇西地震预报实验场区温泉地球化学与断裂活动的关系[J]. 大地构造与成矿学, 21(2): 129—136.
	YAN Kun, LI Ru-tao, LI Si-hai. 1997. The relationship between tectonic activities and geochemistry of hot springs in Western Yunnan Earthquake Study Test Site[J]. Geotectonica at Metallogenia, 21(2): 129—136 (in Chinese).
[24]	杨军, 苏有锦, 李孝宾, 等. 2015. 2013年洱源 M_S5.5 地震序列M_L≥3. 4地震的震源机制解研究[J]. 地震研究, 38(2): 196—202.
	YANG Jun, SU You-jin, LI Xiao-bin, et al. 2015. Research on focal mechanism solutions of M_L≥3. 4 earthquakes of Eryuan M_S5. 5 earthquake sequence in 2013[J]. Journal of Seismological Research, 38(2): 196—202 (in Chinese).
[25]	张培震, 王敏, 甘卫军, 等. 2003a. GPS观测的活动断裂滑动速率及其对现今大陆动力作用的制约[J]. 地学前缘, 10(S1): 81—92.
	ZHANG Pei-zhen, WANG Min, GAN Wei-jun, et al. 2003a. Slip rates along major active faults from GPS measurements and constraints on contemporary continental tectonics[J]. Earth Science Frontiers, 10(S1): 81—92 (in Chinese).
[26]	张培震, 邓起东, 张国民, 等. 2003b. 中国大陆的强震活动与活动地块[J]. 中国科学(D辑), 33(S1): 12—20.
	ZHANG Pei-zhen, DENG Qi-dong, ZHANG Guo-min, et al. 2003b. Active tectonic blocks and strong earthquakes in China[J]. Science in China(Ser D), 33(S1): 12—20 (in Chinese).
[27]	赵小艳, 付虹. 2014. 2013年洱源 M_S5.5 和 M_S5.0 地震发震构造识别[J]. 地震学报, 36(4): 640—650.
	ZHAO Xiao-yan, FU Hong. 2014. Seismogenic structure identification of the 2013 Eryuan M_S5.5 and M_S5.0 earthquake sequence[J]. Acta Seismologica Sinica, 36(4): 640—650 (in Chinese).
[28]	Bao X W, Sun X X, Xu M J, et al. 2015. Two crustal low-velocity channels beneath SE Tibet revealed by joint inversion of Rayleigh wave dispersion and receiver functions[J]. Earth and Planetary Science Letters, 415: 16—24. DOI URL
[29]	Cao Y, Jin M P, Qian J W, et al. 2023. Crustal structure and seismicity characteristics based on dense array monitoring in northwestern Yunnan, China[J]. Physics of the Earth and Planetary Interiors, 340: 107047. DOI URL
[30]	Chen C H, Wang W H, Teng T L. 2001. 3D velocity structure around the source area of the 1999 Chi-Chi, Taiwan, earthquake: Before and after the mainshock[J]. Bulletin of the Seismological Society of America, 91(5): 1013—1027. DOI URL
[31]	Du J G, Cheng W Z, Zhang Y L, et al. 2006. Helium and carbon isotopic compositions of thermal springs in the earthquake zone of Sichuan, Southwestern China[J]. Journal of Asian Earth Sciences, 26(5): 533—539. DOI URL
[32]	Eberhart-Phillips D, Michael A J. 1993. Three-dimensional velocity structure, seismicity, and fault structure in the Parkfield Region, central California[J]. Journal of Geophysical Research: Solid Earth, 98(B9): 15737—15758.
[33]	Efron B, Gong G. 1983. A leisurely look at the bootstrap, the jackknife, and cross-validation[J]. The American Statistician, 37(1): 36—48. DOI URL
[34]	Efron B, Tibshirani R. 1991. Statistical data analysis in the computer age[J]. Science, 253(5018): 390—395. PMID
[35]	Guo H, Zhang H J, Froment B. 2018. Structural control on earthquake behaviors revealed by high-resolution V_P/V_S imaging along the Gofar transform fault, East Pacific Rise[J]. Earth and Planetary Science Letters, 499: 243—255. DOI URL
[36]	Jiang J Z, Li J, Fu H. 2018. Seismicity analysis of the 2016 M_S5.0 Yunlong earthquake, Yunnan, China and its tectonic implications[J]. Pure and Applied Geophysics, 176(3): 1225—1241. DOI
[37]	Lei X L, Xie C D, Fu B H. 2011. Remotely triggered seismicity in Yunnan, southwestern China, following the 2004 M_W9.3 Sumatra earthquake[J]. Journal of Geophysical Research: Solid Earth, 116(B8): B08303.
[38]	Liu M, Li H Y, Zhang M, et al. 2022. Investigation of the 2013 Eryuan, Yunnan, China M_S5.5 earthquake sequence: aftershock migration, seismogenic structure and hazard implication[J]. Tectonophysics, 837: 229445. DOI URL
[39]	Moos D, Zoback M D. 1983. In situ studies of velocity in fractured crystalline rocks[J]. Journal of Geophysical Research: Solid Earth, 88(B3): 2345—2358.
[40]	Nadeau R, Antolik M, Johnson P, et al. 1994. Seismological studies at Parkfield Ⅲ: Microearthquake clusters in the study of fault-zone dynamics[J]. Bulletin of the Seismological Society of America, 84(2): 247—263.
[41]	Paige C C, Saunders M A. 1982. LSQR: An algorithm for sparse linear equations and sparse least squares[J]. ACM Transactions on Mathematical Software(TOMS), 8(1): 43—71.
[42]	Ross Z E, Hauksson E, Ben-Zion Y. 2017. Abundant off-fault seismicity and orthogonal structures in the San Jacinto fault zone[J]. Science Advances, 3(3): e1601946. DOI URL
[43]	Schorlemmer D, Wiemer S, Wyss M. 2005. Variations in earthquake-size distribution across different stress regimes[J]. Nature, 437(7058): 539—542. DOI
[44]	Tapponnie R P, Peltze R G, Dain A L, et al. 1982. Propagating extrusion tectonics in Asia: New insights from simple experiments with plasticine[J]. Geology, 10(12): 61—66. DOI URL
[45]	Thurber C, Eberhart-Phillips D. 1999. Local earthquake tomography with flexible gridding[J]. Computers & Geosciences, 25(7): 809—818. DOI URL
[46]	Thurber C H. 1993. Local earthquake tomography: Velocities and V_P/V_S theory, in Seismic Tomography: Theory and Practise[M]. Chapman and Hall, New York: 563—583.
[47]	Thurber C H, Brocher T M, Zhang H J, et al. 2007. Three-dimensional P wave velocity model for the San Franciso Bay region, California[J]. Journal of Geophysical Research: Solid Earth, 112(B7): B07313.
[48]	Um J, Thurber C. 1987. A fast algorithm for two-point seismic ray tracing[J]. Bulletin of the Seismological Society of America, 77(3): 972—986. DOI URL
[49]	Wessel P, Luis J F, Uieda L, et al. 2019. The generic mapping tools version 6[J]. Geochemistry, Geophysics, Geosystems, 20(11): 5556—5564. DOI
[50]	Yang Y, Yao H J, Wu H X, et al. 2020. A new crustal shear-velocity model in Southwest China from joint seismological inversion and its implications for regional crustal dynamics[J]. Geophysical Journal International, 220(2): 1379—1393.
[51]	Zhang H J, Thurber C H. 2003. Double-difference tomography: The method and its application to the Hayward Fault, California[J]. Bulletin of the Seismological Society of America, 93(5): 1875—1889. DOI URL
[52]	Zhang H J, Thurber C H. 2006. Development and applications of double-difference seismic tomography[J]. Pure and Applied Geophysics, 163(2): 373—403. DOI URL
[53]	Zhang H J, Thurber C H. 2007. Estimating the model resolution matrix for large seismic tomography problems based on Lanczos bidiagonalization with partial reorthogonalization[J]. Geophysical Journal International, 170(1): 337—345. DOI URL
[54]	Zhang H J, Thurber C H, Bedrosian P. 2009. Joint inversion for V_P, V_S and V_P/V_S at SAFOD, Parkfield, California[J]. Geochemistry, Geophysics, Geosystems, 10(11): Q11002.
[55]	Zhao D P, Kanamori H, Negishi H, et al. 1996. Tomography of the source area of the 1995 Kobe earthquake: Evidence for fluids at the hypocenter?[J]. Science, 274(5294): 1891—1894. PMID
[56]	Zhao D P, Hasegawa A, Horiuchi S. 1992. Tomographic imaging of P and S wave velocity structure beneath northeastern Japan[J]. Journal of Geophysical Research: Solid Earth, 97(B13): 19909—19928.
[57]	Zhao D P, Santosh M, Akira Yamada. 2010. Dissecting large earthquakes in Japan: Role of arc magma and fluids[J]. Island Arc, 19(1): 4—16. DOI URL