THE SEISMOGENIC FAULT OF THE 2021 YUNNAN YANGBI MS6.4 EARTHQUAKE

doi:10.3969/j.issn.0253-4967.2021.03.015

Abstract

Abstract: The May 21, 2021 Yangbi M_S6.4 earthquake occurred at the western boundary of the Chuandian tectonic block in southeast Tibetan plateau. The structural background is complex, with multiple active faults distributed around the epicenter area. Focal mechanism and seismic waveform inversion reveal that this earthquake is right-lateral strike-slip type with a NW-trending rupture plane. This accords with the strike and motion directions of the Weixi-Qiaohou and Red River faults along the western boundary of the Chuandian block.
We made a careful field investigation along the Weixi-Qiaohou Fault and around the epicenter area, and did not find any obvious earthquake surface rupture. But we observed a NW-trending ground fissure zone near the epicenter area to the west of the Yangbi County. This zone is divided into two sections, the Yangkechang-Paoshuitian section in the northwest and the Xiquewo-Shahe section in the southwest. These sections have a length of 2.5~3km and 3~3.5km, respectively, and are separated by a ~6km gap. They are characterized by NW-trending ground fissures with a width of several meters to tens meters. The formation of these fissures is inferred to be related to the tectonic movement under the ground, and the fissures have the following features: 1)they are not affected by the topography and cut the slope and range upward; 2)they are continuous and concentrated in a zone with a strike of NW 310°~320°, which is consistent with the belt of aftershocks and differs from the gravity fissures that usually have no regular strikes; 3)they usually have a plane dipping towards upslope(southwest), opposite to the valley; 4)they present shear property, not tensional. This zone thus is interpreted to be the surficial expression of the seismogenic fault of the Yangbi M_S6.4 earthquake.
Moreover, satellite image and field observation suggest that a~30km long linear structure with a NW strike traverses the epicenter area, which may suggest an undiscovered fault. Relocation of small earthquakes shows that the aftershocks are concentrated in a NW-trending belt that is consistent with the linear structure. Furthermore, the fissure zone lies in the northeast side of the aftershock belt, which suggests that the earthquake fault dips SW. Such a dip direction coincides with that of the observed fissure plane, and also agrees with the results from the focal mechanism and InSAR inversion. Both the focal mechanism and the waveform inversion result suggest that the Yangbi earthquake is a right-lateral strike-slip type, which is consistent with the type of the observed ground fissures. No displacement is observed on the fissures, with is also consistent with the InSAR inversion results that suggest the rupture did not break the surface. In addition, there is no coseismic deformation observed along the Weixi-Qiaohou Fault, which may indicate this fault did not move during this earthquake.
Based on our field investigation, in combination with the focal mechanism, aftershock distribution, and InSAR and GNSS inversion results, the seismogenic fault for this Yangbi M_S6.4 earthquake is believed to be a NW-trending(310°~320°)fault with a length of~30km, named as the Yangkechang-Shahe Fault. According to the location, size, and motion of the fault, it is suggested that the Yangkechang-Shahe Fault is a secondary fault of the Weixi-Qiaohou fault system. This fault has a slightly SW-dipping plane, and is dominated by right-lateral strike-slip motion, which may be a younger fault developed during the westward expansion of the western boundary of the Chuandian block.

Key words: Yangbi M_S6.4 earthquake, the seismogenic fault, ground fissure zone, the Weixi-Qiaohou Fault

摘要： 2021年5月21日的漾濞6.4级地震发生在青藏高原东南缘川滇块体的西边界, 震中地区分布有多条活动断裂, 构造较为复杂。震源机制解和地震波形反演显示该地震为右旋走滑型, 破裂面走向NW, 与川滇块体西边界的维西-乔后、红河断裂带的运动性质和走向一致。在野外调查中没有发现明显的地震地表破裂, 只在漾濞县城西侧震中区一带发育一条NW向地表裂缝带, 分为间隔约6km的北西和南东2段, 长度分别为2.5~3km和3~3.5km, 分析认为此裂缝带为本次地震发震断裂活动在地表的表现。而维西-乔后断裂在漾濞6.4级地震中未见同震变形, 说明该断裂在此次地震中没有活动。根据野外地质调查结果, 并结合他人关于震源机制解、余震精定位、 InSAR和GNSS形变观测等结果进行综合分析, 认为维西-乔后断裂西侧的一条NW向次级断裂是此次漾濞6.4级地震的发震构造, 该断裂走向310°~320°, 长约30km, 以右旋走滑运动为主, 断裂面陡立, 略向SW倾, 可能为川滇块体西边界向W扩展中形成的较新构造。

关键词: 漾濞6.4级地震, 发震构造, 地表裂缝带, 维西-乔后断裂

CLC Number:

P315.2

LI Chuan-you, ZHANG Jin-yu, WANG Wei, SUN Kai, SHAN Xin-jian. THE SEISMOGENIC FAULT OF THE 2021 YUNNAN YANGBI M_S6.4 EARTHQUAKE[J]. SEISMOLOGY AND GEOLOGY, 2021, 43(3): 706-721.

李传友, 张金玉, 王伟, 孙凯, 单新建. 2021年云南漾濞6.4级地震发震构造分析[J]. 地震地质, 2021, 43(3): 706-721.

References

[1] 常祖峰, 张艳凤, 周青云, 等. 2014. 2013年洱源M_S5.5地震烈度分布及震区活动构造背景研究[J]. 中国地震, 30(4): 560—570.
CHANG Zu-feng, ZHANG Yan-feng, ZHOU Qing-yun, et al. 2014. Intensity distribution characteristics and active tectonic background in area of the 2013 Eryuan M_S5.5 earthquake[J]. Earthquake Research in China, 30(4): 560—570(in Chinese).
[2] 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).
[3] 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).
[4] 国家地震局地质研究所, 云南地震局. 1990. 滇西北地区活动断裂 [M]. 北京, 地震出版社: 69—128.
Institute of Geology, SSB and Seismological Bureau of Yunnan Province. 1990. Active Faults in the Northwest Yunnan Region [M]. Seismological Press, Beijing: 69—128(in Chinese).
[5] 虢顺民, 张靖, 李祥根, 等. 1984. 云南红河断裂带北段断裂位错与地震重复发生的时间间隔[J]. 地震地质, 6(1): 1—12.
GUO Shun-min, ZHANG Jing, LI Xiang-gen, et al. 1984. Fault displacement and recurrence intervals of earthquakes at the northern segment of the Honghe fault zone, Yunnan Province[J]. Seismology and Geology, 6(1): 1—12(in Chinese).
[6] 虢顺民, 计凤桔, 向宏发, 等. 2001. 红河活动断裂带 [M]. 北京: 海洋出版社: 89—108.
GUO Shun-min, JI Feng-ju, XIANG Hong-fa, et al. 2001. Red River Active Fault Zone [M]. China Ocean Press, Beijing: 89—108(in Chinese).
[7] 虢顺民, 向宏发, 计凤桔, 等. 1996. 红河断裂带第四纪右旋走滑与尾端拉张转换关系研究[J]. 地震地质, 18(4): 301—309.
GUO Shun-min, XIANG Hong-fa, JI Feng-ju, et al. 1996. A study on the relation between Quaternary right-lateral slip and tip extension along the Honghe Fault[J]. Seismology and Geology, 18(4): 301—309(in Chinese).
[8] 李西, 冉勇康, 陈立春, 等. 2016. 红河断裂带南段全新世地震活动证据[J]. 地震地质, 38(3): 596—604.
LI Xi, RAN Yong-kang, CHEN Li-chun, et al. 2016. The Holocene seismic evidence on southern segment of the Red River fault zone[J]. Seismology and Geology, 38(3): 596—604(in Chinese).
[9] 潘睿, 姜金钟, 付虹, 等. 2019. 2017年云南漾濞M_S5.1及M_S4.8地震震源机制解和震源深度测定[J]. 地震研究, 42(3): 338—348.
PAN Rui, JIANG Jin-zhong, FU Hong, et al. 2019. Focal mechanism and focal depth determination of Yunnan Yangbi M_S5.1 and M_S4.8 earthquakes in 2017[J]. Journal Seismological Research, 42(3): 338—348(in Chinese).
[10] 任俊杰, 张世民, 侯治华, 等. 2007. 滇西北通甸-巍山断裂中段的晚第四纪滑动速率[J]. 地震地质, 29(4): 756—764.
REN Jun-jie, ZHANG Shi-min, HOU Zhi-hua, et al. 2007. Study of late Quaternary slip rate in the mid-segment of the Tongdian-Weishan Fault[J]. Seismology and Geology, 29(4): 756—764(in Chinese).
[11] 万佳威, 李滨, 谭成轩, 等. 2019. 中国地裂缝的发育特征及成因机制研究: 以汾渭盆地、河北平原、苏锡常平原为例[J]. 地质论评, 65(6): 1383—1396.
WAN Jia-wei, LI Bin, TAN Cheng-xuan, et al. 2019. Characteristics and mechanism of earth fissures in China: A case study of Fenhe River-Weihe River Basin, Hebei plain and Suzhou-Wuxi-Changzhou plain[J]. Geological Review, 65(6): 1383—1396(in Chinese).
[12] 王阎昭, 王恩宁, 沈正康, 等. 2008. 基于GPS资料约束反演川滇地区主要断裂现今活动速率[J]. 中国科学(D辑), 38(5): 582—597.
WANG Yan-zhao, WANG En-ning, SHEN Zheng-kang, et al. 2008. GPS-constrained inversion of present-day slip rates along major faults of the Sichuan-Yunnan region, China[J]. Science in China(Ser D), 38(5): 582—597(in Chinese).
[13] 汪一鹏, 沈军, 王琪, 等. 2003. 川滇块体的侧向挤出问题[J]. 地学前缘, 10(S1): 188—192.
WANG Yi-peng, SHEN Jun, WANG Qi, et al. 2003. On the lateral extrusion of Sichuan-Yunnan block(Chuandian block)[J]. Earth Science Frontiers, 10(S1): 188—192(in Chinese).
[14] 向宏发, 虢顺民, 张晚霞, 等. 2007. 红河断裂带南段中新世以来大型右旋位错量的定量研究[J]. 地震地质, 29(1): 34—50.
XIANG Hong-fa, GUO Shun-min, ZHANG Wan-xia, et al. 2007. Quantitative study on the large scale dextral strike-slip offset in the southern segment of the Red River Fault since Miocene[J]. Seismology and Geology, 29(1): 34—50(in Chinese).
[15] 张建国, 谢英情, 金明培, 等. 2009. 中越红河断裂活动性研究 [M]. 昆明: 云南科技出版社.
ZHANG Jian-guo, XIE Ying-qing, JIN Ming-pei, et al. 2009. Red River Fault Activity in China and Vietnam [M]. Science and Technology Publishing House, Kunming(in Chinese).
[16] 张克亮, 甘卫军, 梁诗明, 等. 2021. 2021年5月21日M_S6.4漾濞地震GNSS同震变形场及其约束反演的破裂滑动分布[J]. 地球物理学报, 64(7): 2253—2266.
ZHANG Ke-liang, GAN Wei-jun, LIANG Shi-ming, et al. 2021. Coseismic displacement and slip distribution of the May 21, 2021 M_S6.4, Yangbi earthquake derived from GNSS observations[J]. Chinese Journal of Geophysics, 64(7): 2253—2266(in Chinese).
[17] 朱俊江, 詹文欢, 唐诚, 等. 2003. 红河断裂带活动性研究[J]. 华南地震, 23(2): 13—19.
ZHU Jun-jiang, ZHAN Wen-huan, TANG Cheng, et al. 2003. Study on activity of the Red River fault zone[J]. South China Journal of Seismology, 23(2): 13—19(in Chinese).
[18] Allen C R, Gillespie A R, Yuan H, et al. 1984. Red River and associated faults, Yunnan Province, China: Quaternary geology, slip rates, and seismic hazard[J]. Geological Society of America Bulletin, 95(6): 686—700.
[19] Leloup P H, Harrison T M, Ryerson F J, et al. 1993. Structural, petrological and thermal evolution of a Tertiary ductile strike-slip shear zone, Diancang Shan, Yunnan[J]. Journal of Geophysical Research: Solid Earth, 98(B4): 6715—6743.
[20] Leloup P H, Lacassin R, Tapponnier P, et al. 1995. The Ailao Shan-Red River shear zone(Yunnan, China), Tertiary transform boundary of IndoChina[J]. Tectonophysics, 251(1-4): 3—10.
[21] Li Z, Wang Y, Gan W, et al. 2020. Diffuse deformation in the SE Tibetan plateau: New insights from geodetic observations[J]. Journal of Geophysical Research: Solid Earth, 125(10): e2020JB019383.
[22] Replumaz A, Lacassin R, Tapponnier P, et al. 2001. Large river offsets and Plio-Quaternary dextral slip rate on the Red River Fault(Yunnan, China)[J]. Journal of Geophysical Research: Solid Earth, 106(B1): 819—836.
[23] Sarkar I. 2004. The role of the 1999 Chamoli earthquake in the formation of ground cracks[J]. Journal of Asian Earth Sciences, 22(5): 529—538.
[24] Savage J C, HastieL M. 1976. Surface deformation associated with dip slip faulting[J]. Journal of Geophysical Research, 71(20): 4897—4904.
[25] Schoenbohm L, Burchfiel B, Chen L, et al. 2006. Miocene to present activity along the Red River Fault, China, in the context of continental extrusion, upper-crustal rotation, and lower-crustal flow[J]. Geological Society of America Bulletin, 118(5-6): 672—688.
[26] Shen Z K, Lü J, Wang M, et al. 2005. Contemporary crustal deformation around the southeast borderland of the Tibetan plateau[J]. Journal of Geophysical Research, 110(B11): B11409.
[27] Shi X H, Sieh K, Weldon R, et al. 2018. Slip rate and rare large prehistoric earthquakes of the Red River Fault, southwestern China[J]. Geochemistry Geophysics Geosystem, 19(7): 2014—2031.
[28] Tapponnier P, Lacassin R, Leloup P H, et al. 1990. The Ailao Shan/Red River metamorphic belt: Tertiary left-lateral shear between IndoChina and South China[J]. Nature, 343(6257): 431—437.
[29] Wang E Q, Burchfiel B, Royden L, et al. 1998. The Cenozoic Xianshuihe-Xiaojiang, Red River, and Dali fault systems of southwestern Sichuan and central Yunnan, China [G]. Geological Society of America Special Paper: 327.
[30] Wang M, Shen Z K. 2020. Present-day crustal deformation of continental China derived from GPS and its tectonic implications[J]. Journal of Geophysical Research: Solid Earth, 125: e2019JB018774.
[31] Zhang P Z, Shen Z K, Wang M, et al. 2004. Continuous deformation of the Tibetan plateau from global positioning system data[J]. Geology, 32(9): 809—812. doi: 10.1130/G20554.1.

THE SEISMOGENIC FAULT OF THE 2021 YUNNAN YANGBI M_S6.4 EARTHQUAKE

2021年云南漾濞6.4级地震发震构造分析

RichHTML

PDF (PC)

Knowledge

Abstract

Cite this article

share this article

References

Related Articles 2

Recommended Articles

Metrics

Comments

[1]	WANG Shao-jun, LIU Yun-hua, SHAN Xin-jian, QU Chun-yan, ZHANG Guo-hong, XIE Zhao-di, ZHAO De-zheng, FAN Xiao-ran, HUA Jun, LIANG Shi-ming, ZHANG Ke-liang, DAI Cheng-long. COSEISMIC SURFACE DEFORMATION AND SLIP MODELS OF THE 2021 M_S6.4 YANGBI(YUNNAN, CHINA)EARTHQUAKE [J]. SEISMOLOGY AND GEOLOGY, 2021, 43(3): 692-705.
[2]	WEI Qiang, XU Li-sheng, LI Chun-lai, FANG Li-hua, FU Hong. A RESTUDY OF THE SEISMOGENIC FAULTS OF THE 2014 LUDIAN M_S6.5 EARTHQUAKE SEQUENCE [J]. SEISMOLOGY AND GEOLOGY, 2017, 39(2): 374-389.