2022年四川马尔康MS6.0强震群重定位及发震断层探讨

doi:10.3969/j.issn.0253-4967.2023.04.012

摘要/Abstract

摘要：

2022年四川马尔康强震群是中国有地震台网记录以来, 巴颜喀拉块体东部马尔康地区首次出现的地震频度高、时空分布集中、爆发性较强且震级强度大的罕见强震群活动。文中通过双差定位方法对该震群序列进行了重定位, 利用gCAP方法测定了M_S≥3.6地震的震源机制及矩心深度, 然后根据震源机制结果分析了马尔康地区应力体系与这些地震震源机制的关系, 最后根据重定位结果进行了断层面拟合。结果显示, 马尔康震群序列震中区域主要沿NW向优势分布, 整个震群序列的平均初始破裂深度为9.8km, 深度剖面反映地震相对密集的区域主要介于0~15km深度之间, 震群中震级最大的 M_S6.0 地震的初始破裂深度为12.5km, 几乎位于震群序列密集区的底端。其震源机制节面I的走向为150°, 倾角为79°, 滑动角为7°; 节面Ⅱ的走向为59°, 倾角为83°, 滑动角为169°; 矩心深度为9km。其余M_S≥3.6地震的震源机制均为走滑型, 震源机制节面的倾角为71°~86°, 且相同走向的各个节面的倾向也有所不同, 其矩心深度为5~9km, P轴方位为NWW向, 且倾伏角近水平。M_S≥3.6地震震源机制NW向节面的相对剪应力均显著大于NE向节面, 且NW向节面的正应力均小于NE向节面, 表明这些地震更容易在NW向的节面上产生走滑错动。拟合后的断层面参数揭示震群中大部分地震活动可能受到马尔康断裂附近至少2条近NW走向的平行伴生断层控制, 倾角约为88°, 且具有左旋运动性质。结合已有的区域地质构造推测, 马尔康震群可能为NW向和NE向共轭断层发震, 其中NW向断层控制了大多数地震活动。

关键词: 马尔康震群, 重定位, 震源机制, 滑动特性, 发震断层

Abstract:

The 2022 M_S6.0 Maerkang earthquake swarm in Sichuan Province is the first rare strong swarm activity with high frequency, concentrated spatial and temporal distribution, strong explosive and strong magnitude in Maerkang area in the eastern segment of Bayan Har block in China seismic network records. It is also another significantly strong earthquake event in Bayan Har block after the M_S7.4 Maduo earthquake on May 22, 2021. The M_S6.0 Maerkang earthquake on June 10, 2022 not only broke the 33-year record without M_S≥6.0 earthquakes within 100km of the epicenter, but also broke the historical record without M_S≥6.0 earthquakes within 50km of the epicenter. The earthquake swarm is mainly located in the nearly “T” shaped conjugate fault structure area composed of the NW strike Maerkang fault and NE strike Longriba fault in the Bayan Har block. This area is a relatively rare region for moderate and strong earthquakes in the history. Therefore, it is of great significance to analyze and discuss the possible seismogenic faults of the Maerkang strong earthquake sequence for the study of seismogenic structures and the risk of strong earthquakes in the weak seismic region of Bayan Har block.

The earthquake swarm was relocated by double-difference method, and focal mechanisms and centriod depths of M_S≥3.6 earthquakes were calculated by using gCAP inversion method. Then the relationship between the stress system in the Malkang area and these earthquake focal mechanisms was analyzed, and fault plane was fitted by using relocation results. Maerkang earthquake swarm is mainly distributed along NW direction, and the initial rupture depth is 9.8km on average. Depth profiles show that earthquakes are mainly concentrated at depth between 0km to 15km. The most earthquakes of early-stage occurred in 48 hours. The mid-stage and late-stage earthquakes are located less than 15km in depth and move to the northwest of the epicenters. Initial rupture depth of the largest M_S6.0 earthquake is 12.5km, which is almost at the bottom of the dense area. The focal mechanism of M_S6.0 earthquake is 150° in strike, 79° in dip, and 7° in rake on nodal plane Ⅰ, and 59° in strike, 83° in dip, and 169° in rake on nodal plane Ⅱ, with the centroid depth of 9km. Other focal mechanisms of M_S≥3.6 earthquake are strike-slip types. Dips of nodal plane of focal mechanism range from 71° to 86°, and there exist different dip directions for one strike of every nodal plane. All azimuths of P axis are in NWW direction, and the plunges are nearly horizontal. The focal mechanisms of M_S≥3.6 earthquakes show that the tectonic environment is very favorable for NE or NW strike faults to generate the strike-slip movement. Centriod depths range from 5 to 9km, which are lower than the average depth of 9.8km of relocation, indicating that these earthquakes mainly ruptured from deep to shallow. The relative shear stress of the NW nodal plane are significantly greater than that of the NE nodal plane, and the normal stress of the NW nodal plane was smaller than that of the NE nodal plane, indicating more possibility of strike-slip dislocation on the NW nodal plane. The fault plane fitting results reveal that there are obviously two nearly parallel and nearly NW strike earthquake belts in the epicenter area. Fitted fault plane parameters of the belt in the north branch show the strike 333°, the dip 88°, the slide -22°, and the belt in the south branch show the strike 331°, dip 88°, and slide -23°. It is indicated that the fault properties of these two earthquake belts are basically the same, revealing that most of earthquake activities of the swarm may be controlled by at least two parallel structures near the Maerkang fault with the NW strike, dip 88° and left-lateral strike-slip. Combined with the existing regional geological structure, it is inferred that the Maerkang earthquake swarm may be induced by the NW and NE strike conjugate faults, and the NW strike faults control most of the earthquake activities.

Key words: Maerkang earthquake swarm, Earthquake relocation, Focal mechanism, Sliding property, Seismic fault

许英才, 郭祥云. 2022年四川马尔康M_S6.0强震群重定位及发震断层探讨[J]. 地震地质, 2023, 45(4): 1006-1024.

XU Ying-cai, GUO Xiang-yun. RELOCATION OF THE 2022 M_S6.0 MAERKANG EARTHQUAKE SWARM IN SICHUAN PROVINCE AND ITS SEISMIC FAULT ANALYSIS[J]. SEISMOLOGY AND GEOLOGY, 2023, 45(4): 1006-1024.

图/表 14

图 1 马尔康 MS6.0 震群的震中位置、区域地质构造及M≥6.0历史地震分布五角星为震群序列中最大地震 MS6.0 及次大地震 MS5.8 的震中, 其余黑点为余震震中。MEKF 马尔康断裂; LRBF 龙日坝断裂; YKF 玉科断裂; DRF 达日断裂; MD-GDF 玛多-甘德断裂; JZF 久治断裂; XSHF 鲜水河断裂; MJF 岷江断裂; HYF 虎牙断裂; TZF 塔藏断裂; LMSF 龙门山断裂。除龙日坝断裂据参考文献(徐锡伟等, 2008; 陈长云等, 2013)改绘外, 其余断层来自文献(邓起东等, 2003)

Fig. 1 Epicenters of the MS6.0 Maerkang earthquake swarm, regional geological structure and distribution of historical M≥6.0 earthquakes.

图 2 马尔康 MS6.0 震群的M-t图及日频次图

Fig. 2 Plots of M-t and daily earthquakes frequency of the MS6.0 Maerkang earthquake swarm.

表 1 马尔康地区的P波速度模型

Table 1 P-wave velocity model of the Maerkang region

层号	1	2	3	4	5	6	7	8	9	10	11	12
H/km	0	5	10	15	20	25	30	35	40	50	60	65
V_P/km·s^-1	5.08	5.19	5.64	5.84	5.79	5.79	5.94	5.99	6.08	6.70	7.25	7.55

图 3 重新定位后马尔康 MS6.0 震群的震中分布及深度剖面图

Fig. 3 Epicentral distribution and depth of the MS6.0 Maerkang earthquake swarm after relocation.

表 2 马尔康震群序列MS≥3.6地震的震源机制2个节面解及矩心深度

Table 2 Parameters of two nodal planes from focal mechanism and centrid depth of MS≥3.6 earthquakes from Maerkang swarm

序号	地震事件时间	M_S	M_W	H_W /km	节面Ⅰ			节面Ⅱ
					走向 /(°)	倾角 /(°)	滑动角 /(°)	走向 /(°)	倾角 /(°)	滑动角 /(°)
1	2022-06-10,00:03:24	5.8	5.4	6	323	72	4	232	86	162
2	2022-06-10,00:21:17	4.4	4.6	6	147	80	19	54	71	169
3	2022-06-10,01:28:34	6.0	5.7	9	150	79	7	59	83	169
4	2022-06-10,03:27:00	5.2	4.8	8	155	81	10	63	80	171
5	2022-06-10,04:37:26	4.4	4.5	6	338	73	9	245	81	163
6	2022-06-10,04:54:33	3.9	4.0	8	333	72	14	239	77	161
7	2022-06-14,18:11:10	4.4	4.4	5	147	76	17	53	74	165

图 4 马尔康 MS6.0 地震震源机制拟合误差随深度的变化图

Fig. 4 Variation of fitting error with focal depth of the MS6.0 Maerkang earthquake.

图 5 马尔康 MS6.0 地震的震源机制解及观测波形(黑)与理论波形(红)拟合图台站名旁边的数值为方位角(°); 下方左侧为震中距(km), 右侧为偏移时间(s); 波形下方分别为理论波形(红)与实际波形(黑)的相对移动时间(s)及波形相关系数(%)

Fig. 5 Focal mechanism solution of the MS6.0 Maerkang earthquake and fitting diagram of observed waveform(black)and theoretical waveform(red).

图 6 震群序列MS≥3.6地震的震源机制及震中地震序号按地震发生时间正序排序

Fig. 6 Focal mechanisms and epicenters of MS≥3.6 earthquake swarm.

图 7 马尔康震群序列MS≥3.6地震震源机制节面的走向、倾角、滑动角, P轴和T轴的方位及倾伏角参数玫瑰图

Fig. 7 Rose diagrams of strike, dip, rake of nodal planes, and azimuth and plunge of P-axis and T-axis from focal mechanisms of MS≥3.6 earthquake swarm.

图 8 马尔康 MS5.8、 MS6.0 及 MS5.2 地震不同作者或机构的震源机制结果与本文结果的对比马尔康地震的各种震源机制, 按震源机制中心解的最小空间旋转角排序, 除本文结果之外,其余不同作者、机构的震源机制结果来自Seismology小组①（① https://mp.weixin.qq.com/s/lLvTKGnb4guMglf5_7BV6Q。）

Fig. 8 Comparison of the focal mechanism results of MS5.8, MS6.0 and MS5.2 Maerkang earthquakes calculated with other's work.

图 9 马尔康地区的应力体系与震群MS≥3.6地震的震源机制关系图方形网格区域内为在不同形状断层面下模拟的震源机制、相对剪应力和正应力分布, 7个红色震源机制中粗弧线为该节面的形状, 其旁边的数字为对应的地震序号

Fig. 9 Relationship between regional tectonic stress system and focal mechanism of the Maerkang MS≥3.6 earthquakes.

图 10 震源机制2个节面的相对剪应力及正应力随MS≥3.6地震序号的变化图红色实线和蓝色实线分别代表NW向节面Ⅰ和NE向节面Ⅱ的应力变化, 震源球旁的值为地震震级MS

Fig. 10 Variations of relative shear stress and normal stress on the two nodal planes of focal mechanism with MS≥3.6 earthquake sequence number.

图 11 马尔康震群的断层面拟合 a 所选取的北、南支2个地震丛集区, b、 c 分别为北支和南支地震丛集区的断层面拟合。其中, 对于图b和c中的各图, 左上分图为地震水平分布, 右上分图为地震在该剖面的投影图, 左下分图为垂直于断层面的横截面投影,右下分图为地震到断层面的距离

Fig. 11 Fault plane fitting of Maerkang earthquake swarm.

图 12 本文推测的马尔康 MS6.0 震群的发震断层及错动方式左侧图震源机制为震源球在水平剖面的下半球投影, 右侧图震源机制为震源球在该深度垂直剖面的投影

Fig. 12 Inferred possible seismic fault and rupture pattern of the MS6.0 Maerkang earthquake swarm.

参考文献 30

[1]	陈长云. 2014. 巴颜喀拉地块东部及其邻区块体运动及块体边界带形变特征[D]. 北京: 中国地震局地质研究所: 1-80.
	CHEN Chang-yun. 2014. Block motion and deformation of boundary faults of active blocks in eastern Bayan Har block and its adjacent regions[D]. Institute of Geology, China Earthquake Administration, Beijing: 1-80 (in Chinese).
[2]	陈长云, 任金卫, 孟国杰, 等. 2013. 巴颜喀拉块体东部活动块体的划分、形变特征及构造意义[J]. 地球物理学报, 56(12): 4125-4141.
	CHEN Chang-yun, REN Jin-wei, MENG Guo-jie, et al. 2013. Division, deformation and tectonic implication of active blocks in the eastern segment of Bayan Har block[J]. Chinese Journal of Geophysics, 56(12): 4125-4141 (in Chinese).
[3]	邓起东, 冉勇康, 杨晓平, 等. 2003. 中国活动构造图(1︰400万)[CM]. 北京: 地震出版社.
	DENG Qi-dong, RAN Yong-kang, YANG Xiao-ping, et al. 2003. Map of Active Tectonics in China(1︰4 000 000)[CM]. Seismological Press, Beijing (in Chinese).
[4]	杜明甫. 2020. 阿坝地区小震精定位及其活动构造意义[D]. 成都: 成都理工大学:30-34.
	DU Ming-fu. 2020. Location of small seismic essence in Aba area and its active structural significance[D]. Chengdu University of Technology, Chengdu: 30-34 (in Chinese).
[5]	韩立波, 蒋长胜, 包丰. 2012. 2010年河南太康 M_S4.6 地震序列震源参数的精确确定[J]. 地球物理学报, 55(9): 2973-2981.
	HAN Li-bo, JIANG Chang-sheng, BAO Feng. 2012. Source parameter determination of 2010 Taikang M_S4.6 earthquake sequences[J]. Chinese Journal of Geophysics, 55(9): 2973-2981 (in Chinese).
[6]	何玉林, 龚宇, 伍先国. 1997. 四川抚边河断裂的活动特征[J]. 地震地质, 19(1): 31-36.
	HE Yu-lin, GONG Yu, WU Xian-guo. 1997. Activity features of the Fubian River Fault in Sichuan Province[J]. Seismology and Geology, 19(1): 31-36 (in Chinese).
[7]	罗艳, 赵里, 曾祥方, 等. 2015. 芦山地震序列震源机制及其构造应力场空间变化[J]. 中国科学(D辑), 45(4): 538-550.
	LUO Yan, ZHAO Li, ZENG Xiang-fang, et al. 2015. Focal mechanisms of the Lushan earthquake sequence and spatial variation of the stress field[J]. Science in China(Ser D), 58(7): 1148-1158.
[8]	万永革. 2019. 同一地震多个震源机制中心解的确定[J]. 地球物理学报, 62(12): 4718-4728.
	WAN Yong-ge. 2019. Determination of center of several focal mechanisms of the same earthquake[J]. Chinese Journal of Geophysics, 62(12): 4718-4728 (in Chinese).
[9]	万永革. 2020. 震源机制与应力体系关系模拟研究[J]. 地球物理学报, 63(6): 2281-2296.
	WAN Yong-ge. 2020. Simulation on relationship between stress regimes and focal mechanisms of earthquakes[J]. Chinese Journal of Geophysics, 63(6): 2281-2296 (in Chinese).
[10]	万永革, 沈正康, 刁桂苓, 等. 2008. 利用小震分布和区域应力场确定大震断层面参数方法研究及其在唐山地震序列中的应用[J]. 地球物理学报, 51(3): 793-804.
	WAN Yong-ge, SHEN Zheng-kang, DIAO Gui-ling, et al. 2008. An algorithm of fault parameter determination using distribution of small earthquakes and parameters of regional stress field and its application to Tangshan earthquake sequence[J]. Chinese Journal of Geophysics, 51(3): 793-804 (in Chinese).
[11]	魏娅玲, 蔡一川. 2018. 四川地区地震震源机制解及震源深度特征: 以中等强度地震为例[J]. 地震工程学报, 40(S1): 6-17.
	WEI Ya-ling, CAI Yi-chuan. 2018. Characteristics of focal mechanisms and focal depths of earthquakes in Sichuan region: A case study of moderate earthquakes[J]. China Earthquake Engineering Journal, 40(S1): 6-17 (in Chinese).
[12]	熊熊, 许厚泽, 滕吉文. 2001. 青藏高原物质东流的岩石层力学背景探讨[J]. 地壳形变与地震, 21(2): 1-6.
	XIONG Xiong, XU Hou-ze, TENG Ji-wen. 2001. Investigation on lithospheric mechanical background of eastward mass flow of Tibetan plateau[J]. Crustal Deformation and Earthquake, 21(2): 1-6 (in Chinese).
[13]	徐锡伟, 闻学泽, 陈桂华, 等. 2008. 巴颜喀拉地块东部龙日坝断裂带的发现及其大地构造意义[J]. 中国科学(D辑), 38(5): 529-542.
	XU Xi-wei, WEN Xue-ze, CHEN Gui-hua, et al. 2008. Discovery of the Longriba fault zone in eastern Bayan Har block, China and its tectonic implication[J]. Science in China(Ser D), 51(9): 1209-1223.
[14]	姚华建. 2020. 中国川滇地区公共速度模型构建: 思路与进展[J]. 中国科学(D辑), 50(9): 1319-1322.
	YAO Hua-jian. 2020. Building the community velocity model in the Sichuan-Yunnan region, China: Strategies and progresses[J]. Science in China (Ser D), 63(9): 1425-1428.
[15]	易桂喜, 龙锋, 梁明剑, 等. 2019. 2019年6月17日四川长宁 M_S6.0 地震序列震源机制解与发震构造分析[J]. 地球物理学报, 62(9): 3432-3447.
	YI Gui-xi, LONG Feng, LIANG Ming-jian, et al. 2019. Focal mechanism solutions and seismogenic structure of the 17 June 2019 M_S6.0 Sichuan Changning earthquake sequence[J]. Chinese Journal of Geophysics, 62(9): 3432-3447 (in Chinese).
[16]	易桂喜, 龙锋, 闻学泽, 等. 2015. 2014年11月22日康定M6.3地震序列发震构造分析[J]. 地球物理学报, 58(4): 1205-1219.
	YI Gui-xi, LONG Feng, WEN Xue-ze, et al. 2015. Seismogenic structure of the M6.3 Kangding earthquake sequence on 22 Nov. 2014, Southwestern China[J]. Chinese Journal of Geophysics, 58(4): 1205-1219 (in Chinese).
[17]	易桂喜, 赵敏, 龙锋, 等. 2021. 2021年9月16日四川泸县 M_S6.0 地震序列特征及孕震构造环境[J]. 地球物理学报, 64(12): 4449-4461.
	YI Gui-xi, ZHAO Min, LONG Feng, et al. 2021. Characteristics of the seismic sequence and seismogenic environment of the M_S6.0 Sichuan Luxian earthquake on September 16, 2021[J]. Chinese Journal of Geophysics, 64(12): 4449-4461 (in Chinese).
[18]	张国庆, 祝意青, 梁伟锋. 2022. 青藏高原东缘扶边河断裂周边地壳密度及垂向构造应力特征[J]. 地震地质, 44(3): 578-589. doi: 10.3969/j.issn.0253-4967.2022.03.002. DOI
	ZHANG Guo-qing, ZHU Yi-qing, LIANG Wei-feng. 2022. The crustal density structures and isostatic additional stress around the Fubianhe fault on the eastern margin of Tibet Plateau[J]. Seismology and Geology, 44(3): 578-589 (in Chinese).
[19]	郑斯华. 1995. 青藏高原地震的震源深度及其构造意义[J]. 中国地震, 11(2): 99-106.
	ZHENG Si-hua. 1995. Focal depth of earthquakes under the Tibetan plateau and its tectonic implication[J]. Earthquake Research in China, 11(2): 99-106 (in Chinese).
[20]	郑勇, 马宏生, 吕坚, 等. 2009. 汶川地震强余震(M_S≥5.6)的震源机制解及其与发震构造的关系[J]. 中国科学(D辑), 39(4): 413-426.
	ZHENG Yong, MA Hong-sheng, LÜ Jian, et al. 2009. Source mechanism of strong aftershocks(M_S≥5.6)of the 2008/05/12 Wenchuan earthquake and the implication for seismotectonics[J]. Science in China(Ser D), 52(6): 739-753.
[21]	中国地震局. 2022. 中国地震局发布四川马尔康6.0级震群地震烈度图[EB/OL].(2022-06-13)[2022-09-28]. https: //www.cea.gov.cn/cea/xwzx/fzjzyw/5662853/index.html
	China Earthquake Administration. 2022. China Earthquake Administration released a seismic intensity regionalization map of Sichuan Malkang M6.0 earthquake swarm[EB/OL].(2022-06-13)[2022-09-28]. https: //www.cea.gov.cn/cea/xwzx/fzjzyw/5662853/index.html(in Chinese).
[22]	中国地震局编. 1998. 地震现场工作大纲和技术指南[M]. 北京: 地震出版社.
	China Earthquake Administrationeds. 1998. Brief and Technique Guideline on Earthquake Process[M]. Seismological Press, Beijing (in Chinese).
[23]	周荣军, 何玉林, 马声浩, 等. 1999. 四川小金抚边河断裂的晚第四纪活动特征[J]. 地震研究, 22(4): 376-381.
	ZHOU Rong-jun, HE Yu-lin, MA Sheng-hao, et al. 1999. Late Quaternary active characteristics of Fubianhe fault in Sichuan's Xiaojin[J]. Journal of Seismological Research, 22(4): 376-381 (in Chinese).
[24]	朱艾斓, 徐锡伟, 周永胜, 等. 2005. 川西地区小震重新定位及其活动构造意义[J]. 地球物理学报, 48(3): 629-636.
	ZHU Ai-lan, XU Xi-wei, ZHOU Yong-sheng, et al. 2005. Relocation of small earthquakes in western Sichuan, China and its implications for active tectonics[J]. Chinese Journal of Geophysics, 48(3): 629-636 (in Chinese).
[25]	Aki K. 1984. Asperities, barriers, characteristic earthquakes and strong motion prediction[J]. Journal of Geophysical Research: Solid Earth, 89(B7): 5867-5872.
[26]	Liu Y, Yao H J, Zhang H J, et al. 2021. The Community Velocity Model V.1.0 of southwest China, constructed from joint body and surface-wave travel-time tomography[J]. Seismological Research Letters, 92(5): 2972-2987. https://doi.org/10.1785/0220200318.. DOI URL
[27]	Waldhauser F, Ellsworth W L. 2000. A double-difference earthquake location algorithm: Method and application to the northern Hayward fault, California[J]. Bulletin of the Seismological Society of America, 90(6): 1353-1368. DOI URL
[28]	Wan Y G. 2010. Contemporary tectonic stress field in China[J]. Earthquake Science, 23(4): 377-386. DOI URL
[29]	Zhu L P, Ben-zion Y. 2013. Parametrization of general seismic potency and moment tensors for source inversion of seismic waveform data[J]. Geophysical Journal International, 194(2): 839-843. DOI URL
[30]	Zhu L P, Rivera L A. 2002. A note on the dynamic and static displacements from a point source in multilayered media[J]. Geophysical Journal International, 148(3): 619-627. DOI URL