四川芦山2022年6月 MS6.1 地震的发震构造及其与2013年4月 MS7.0 地震关系的探讨

doi:10.3969/j.issn.0253-4967.2023.05.012

地震地质 ›› 2023, Vol. 45 ›› Issue (5): 1233-1246.DOI: 10.3969/j.issn.0253-4967.2023.05.012

• 研究论文 • 上一篇

四川芦山2022年6月 M_S6.1 地震的发震构造及其与2013年4月 M_S7.0 地震关系的探讨

陈翰林¹^,²⁾(), 王勤彩²⁾^,^*(), 张金川³⁾, 刘瑞丰¹⁾

¹⁾ 中国地震局地球物理研究所, 北京 100081
²⁾ 中国地震局地震预测研究所, 北京 100036
³⁾ 江苏省地震局, 南京 210014

收稿日期:2023-01-17 修回日期:2023-03-31 出版日期:2023-10-20 发布日期:2023-11-23
通讯作者: *王勤彩, 女, 1966年生, 研究员, 主要研究方向为地震学, E-mail: wangqc@ief.ac.cn。
作者简介:
陈翰林, 男, 1982年生, 2009年于中国地震局地震预测研究所获地球物理专业硕士学位, 助理研究员, 现主要研究方向为数字地震学, E-mail: blesschl@126.com。
基金资助:
中国地震局地震预测研究所基本科研业务专项(2021IEF0603); 中国地震局地震预测研究所基本科研业务专项(CEAIEF2022030100); 陕西省自然科学基础研究计划项目(2021JM-600)

DISCUSSION ON SEISMOGENIC STRUCTURE OF THE JUNE 2022 M_S6.1 EARTHQUAKE AND ITS RELATIONSHIP WITH THE APRIL 2013 M_S7.0 EARTHQUAKE IN LUSHAN, SICHUAN PROVINCE

CHEN Han-lin¹^,²⁾(), WANG Qin-cai²⁾^,^*(), ZHANG Jin-chuan³⁾, LIU Rui-feng¹⁾

¹⁾ Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
²⁾ Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China
³⁾ Jiangsu Earthquake Agency, Nanjing 210014, China

Received:2023-01-17 Revised:2023-03-31 Online:2023-10-20 Published:2023-11-23

摘要/Abstract

摘要：

文中对2013年4月—2022年7月发生在芦山震区的地震进行重定位, 并反演了芦山2022年6月1日 M_S6.1 地震的震源机制解。芦山 M_S6.1 地震序列的震源深度北浅南深, 断层长约10km, 自深向浅破裂。通过分析芦山震区的发震构造和地震活动特征, 认为震源断层为一条走向NE、倾向SE的盲逆冲断层, 其与2013年 M_S7.0 地震走向NE、倾向NW的主逆冲断层及其上盘走向NE、倾向SE的反向逆冲断层共同组成双层“Y”字形结构。进一步综合分析库仑应力变化, 认为2013年芦山 M_S7.0 地震对2022年芦山 M_S6.1 地震具有抑制作用。

关键词: 芦山地震, 地震精定位, 震源机制, 发震构造

Abstract:

In this paper, we relocated earthquakes occurred from April 2013 to July 2022 in Lushan seismic zone, inversed focal mechanism solution of the Lushan M_S6.1 earthquake on June 1, 2022 and discussed the seismogenic structure of the Lushan M_S6.1 earthquake and its relationship with the M_S7.0 earthquake in April 2013.

The results of the focal mechanism solution show that the Lushan M_S6.1 earthquake in 2022 is a thrust earthquake. The strike, dip and azimuth of nodal plane Ⅰ are 228°, 46° and 104° and for nodal plane Ⅱ are 28°, 46° and 76° respectively. The results of earthquake relocation show that the focal depth of the Lushan M_S6.1 earthquake sequence is shallow in the north and deep in the south, the fault length is about 10km. The focal depth is mainly concentrated between 10km to 19km. The fault dip is southeast with an angle of 60°. The initial rupture point of the main shock of the Lushan M_S6.1 earthquake is at a depth of 20km, located at the deepest part of the fault. The fault ruptured from deep to shallow. The Lushan M_S7.0 earthquake occurred on April 2013 strikes northeast and dips northwestward, but there exists a reverse fault in the aftershock sequence that has the same direction of strike but the opposite direction of dip. This reverse fault is consistent with the strike and dip of the M_S6.1 earthquake occurred in June 2022. It appears as two parallel faults in the profile. In addition to the reverse fault on the west side, the embryonic of another reverse fault seems to appear on the east side of the middle of earthquake sequence. These faults are about 10km away from the surface. The distribution of earthquakes in two northwest-oriented depth profiles shows that the dip angles of the main shock and the reverse fault of the M_S7.0 earthquake is different at different locations, and these faults are not simple straight planar sections. From one year after occurrence of the M_S7.0 earthquake to occurrence of the M_S6.1 earthquake, the seismic activity on the main fault decreased but the seismic activity on the reverse fault on the west side of the M_S7.0 earthquake sequence was more active during this period, most of the seismic activity occurred near the reverse fault that is parallel to the M_S6.1 earthquake fault.

By analyzing the seismogenic structure and seismic activity characteristics of the Lushan seismic zone, we concluded the Lushan M_S6.1 earthquake on June 1, 2022 is caused by a blind thrust fault with strike towards northeast and dip towards southeast, located 10km away from the surface. It has the opposite directions of strike and dip of the Longmenshan Fault. The epicenters of the Lushan M_S7.0 earthquake in April 2013 and the M_S6.1 earthquake in June 2022 are located near the surface exposure traces of the Shuangshi-Dachuan Fault and the Xiaoguanzi Fault, respectively. However, according to the analysis of the relocation aftershock depth in profile, the aftershock extension to the surface does not coincide with the surface exposure positions of the Shuangshi-Dachuan Fault and the Xiaoguanzi Fault. Therefore, the seismogenic faults of these two earthquakes are not the Shuangshi-Dachuan Fault and the Xiaoguanzi Fault, but two blind reverse faults. The Shuangshi-Dachuan Fault near the M_S6.1 earthquake sequence and the main shock fault of the 2013 M_S7.0 earthquake are thrust faults dipping northwest, while the Lushan M_S6.1 seismogenic fault has opposite direction of dip. The seismogenic fault of the Lushan M_S6.1 earthquake and the main thrust fault of the 2013 M_S7.0 earthquake, which strikes northeast and dips northwest with the reverse thrust fault of the hanging wall, which strikes northeast and dips southeast, together form a double layer Y-shaped structure. These faults are all blind thrust faults and belong to the Qianshan-Shanqian Fault system in the southern segment of the Longmenshan fault zone. The seismogenic structure in the Lushan seismic zone is a complex fault system composed of one main northeast strike fault with dipping northwest, and three faults dipping southeast.

From one year after occurrence of the Lushan M_S7.0 earthquake to the occurrence of the Lushan M_S6.1 earthquake, most of earthquakes in the Lushan seismic zone occurred near a reverse fault which is parallel to the Lushan M_S6.1 earthquake seismogenic fault. These earthquakes are located in the area where the coulomb stress change caused by the M_S7.0 earthquake acts as loading effect. The Lushan M_S6.1 earthquake sequence is mainly distributed in the area where the coulomb stress change plays an unloading role caused by the Lushan M_S7.0 earthquake. The research results showed that the coulomb rupture stress caused by the Lushan M_S7.0 earthquake on the seismic nodal plane of the M_S6.1 earthquake has a restraining effect on the M_S6.1 Lushan earthquake.

Key words: Lushan earthquake, precise earthquake relocation, focal mechanism, seismogenic structure

陈翰林, 王勤彩, 张金川, 刘瑞丰. 四川芦山2022年6月 M_S6.1 地震的发震构造及其与2013年4月 M_S7.0 地震关系的探讨[J]. 地震地质, 2023, 45(5): 1233-1246.

CHEN Han-lin, WANG Qin-cai, ZHANG Jin-chuan, LIU Rui-feng. DISCUSSION ON SEISMOGENIC STRUCTURE OF THE JUNE 2022 M_S6.1 EARTHQUAKE AND ITS RELATIONSHIP WITH THE APRIL 2013 M_S7.0 EARTHQUAKE IN LUSHAN, SICHUAN PROVINCE[J]. SEISMOLOGY AND GEOLOGY, 2023, 45(5): 1233-1246.

图/表 7

图1 芦山震区及周围台站、断裂分布和震中分布结果图1a中黑色三角为区域固定台站, 绿色三角为流动台站, 红色五角星为芦山2013年4月20日 MS7.0 地震和2022年6月1日 MS6.1 地震震中, 青蓝色线条为水系, 蓝色线条为断裂。 F1陇东断裂; F2五龙断裂; F3小关子断裂; F4双石-大川断裂; F5新开店断裂; F6名山断裂; F7汉王场断裂; F8三苏场断裂; F9龙泉山断裂; F10抚边河断裂; F11北川-映秀断裂; F12汶川-茂汶断裂; F13金汤弧形断裂; F14玉树断裂; F15鲜水河断裂; F16泸定断裂; F17宝新厂-凰仪断裂; F18天全断裂; F19三合断裂; F20荣经断裂; F21玉农希-盐水断裂; F22广元-大邑断裂; F23浦江-新津断裂; F24洛水-都江堰断裂。图1b为芦山震区, 黑色点为2013年4月20日—2022年7月25日芦山震区地震目录的震中分布

Fig. 1 Location of stations, distribution of faults and epicenters in Lushan seismic zone and surrounding areas.

图2 2022年6月1日 MS6.1地震震源机制解反演使用的波形拟合情况图中波形最左侧为台站代码, 台站代码下方为震中距(km)和相对偏移时间(s)。黑色波形为观测波形, 红色波形为理论波形, 每个窗口波形左下方的2行数字分别代表波形拟合时观测波形与理论波形之间的时间偏移量(s)及相关系数(%)。震源机制解拟合误差随震源深度的变化图中左下角数字为最佳震源深度(km)和深度误差(km), 震源球上方数字为通过相应震源深度计算得到的矩震级

Fig. 2 Waveform fitting for inversion of focal mechanism solution of the MS6.1 earthquake on June 1, 2022.

图3 精定位后 MS6.1 地震序列的震中及深度分布剖面图 a 震中分布图; b 深度分布图; c AA'剖面图; d BB'剖面图。图a中红色实线为断层剖面线, 紫色五角星为2022年6月1日 MS6.1 地震震中, 紫色沙滩球为 MS6.1 地震的震源机制解。图d中的蓝线为断层, 紫色沙滩球为震源机制解2个节面在BB'剖面上的投影, 沙滩球中倾向SE的线为 MS6.1 主震断层的横断面

Fig. 3 Profile of epicenter and depth distribution of magnitude MS6.1 earthquake sequence after precise location.

图4 芦山震区的震级-频度分布图

Fig. 4 Plot of magnitude-frequency of earthquakes in Lushan seismic zone.

图5 芦山震区震级和月频度随时间的变化 a 2013年4月—2022年7月芦山震区震级随时间的变化; b 2013年4月—2022年7月芦山震区月频度随时间的变化; c 2015年1月—2022年7月芦山震区月频度随时间的变化

Fig. 5 Magnitude and monthly frequency in Lushan seismic zone with time.

图6 2013年4月—2022年7月芦山震区地震的重定位结果 a 芦山震区的断裂、震中分布及剖面位置; b AA'剖面上的结果; c BB'剖面上的结果; d CC'剖面上的结果; e 深度统计分布; f MS7.0 地震发生1a后至 MS6.1 地震发生前BB'剖面上的结果。图6a中的断裂编号名称同图1, 图6a—d中的黑点为2013年4月20日—2022年5月31日期间发生的地震, 绿点为2022年6月1日—7月25日期间发生的地震, 图6f中的黑点为2014年4月—2022年5月31日期间发生的地震。图6a、 c、 f中的紫色五角星和沙滩球为2022年6月1日 MS6.1 地震的震中位置和震源机制解, 红色五星和沙滩球为2013年4月20日 MS7.0 地震的震中位置和震源机制解(李文超等, 2018)。图6c、 f中的沙滩球为震源机制解2个节面在BB'剖面上的投影。图6c、 d、 f中的红线为根据地震分布解译出的断层

Fig. 6 Relocation results in Lushan seismic zone for earthquakes from April 2013 to July 2022.

图7 芦山震区地震的时空演化图 a MS7.0 地震后7h的地震时空演化; b MS7.0 地震后10d的地震时空演化; c MS7.0 地震后至2019年12月的地震时空演化; d MS7.0 地震后至2022年7月的地震时空演化。图e、 f、 g、 h为图a、 b、 c、 d在BB'剖面上的投影。图中的红色五星为2013年4月20日 MS7.0 地震、 ML4.4地震、 2019年5月2日ML4.9地震和2022年6月1日 MS6.1 地震的震中, 青蓝色点为精定位后不同时段的震中位置

Fig. 7 Time-space evolution of earthquakes in Lushan seismic zone.

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四川芦山2022年6月 M_S6.1 地震的发震构造及其与2013年4月 M_S7.0 地震关系的探讨

DISCUSSION ON SEISMOGENIC STRUCTURE OF THE JUNE 2022 M_S6.1 EARTHQUAKE AND ITS RELATIONSHIP WITH THE APRIL 2013 M_S7.0 EARTHQUAKE IN LUSHAN, SICHUAN PROVINCE

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