Seismogenic environment and mechanism of the Yangbi MS6.4 earthquake in Yunnan, China

IF 1.2 4区地球科学 Q3 Earth and Planetary Sciences

Earthquake Science Pub Date : 2022-08-01 DOI:10.1016/j.eqs.2022.08.001

Mengqiao Duan , Kezhen Zuo , Cuiping Zhao , Lianqing Zhou

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引用次数: 1

Abstract

The Yangbi M_S6.4 earthquake occurred on May 21, 2021 in western Yunnan, China, where moderate earthquakes strike frequently. It exhibited a typical “foreshock-mainshock-aftershock” sequence and did not occur on a pre-existing active fault. The seismogenic environment and mechanism of this earthquake have aroused considerable research attention. In this study, we obtain the three-dimensional v_P, v_S and v_P/v_S images using the v_P/v_S consistency-constrained double-difference tomography method, which improves the accuracy of v_P/v_S models. We focus on characteristics of v_P/v_S images in areas with a lateral resolution of 0.1°, and reveal the seismogenic environment of the Yangbi M_S6.4 earthquake. The conclusions are as follows: (1) Low velocity and high-v_P/v_S anomalies are revealed at different depths around the northern segment of the Red River fault. v_S and v_P/v_S images along the Weixi-Qiaohou-Weishan fault and the buried faults on its west show obviously segmented feature. (2) The source region of the Yangbi M_S6.4 earthquake is located in a low-v_P/v_S zone implying high medium strength. High-v_P/v_S anomalies in its NW direction indicate cracks development and the existence of fluids or partial melts, which are unfavorable for stress accumulation and triggering large earthquakes. Such conditions have also prevented the earthquake sequence from extending northwestward. (3) With the southeastward extrusion of materials from the Tibetan Plateau, fluid migration was blocked by the low-v_P/v_S body in the source region. The high-v_P/v_S anomaly beneath the source region may implies that the fluids or partial melts in the middle and lower crust gradually weakened medium strength at the bottom of the seismogenic layer, and preparing the largest foreshock in the transition zone of high to low v_P/v_S. Meanwhile, tectonic stress incessantly accumulated in the brittle upper crust, eventually led to the M_S6.4 earthquake occurrence.

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云南杨壁MS6.4级地震发震环境与机制

2021年5月21日，中国云南西部中地震多发地区杨壁6.4级地震发生。它表现出典型的“前震-主震-余震”序列，并没有发生在先前存在的活动断层上。此次地震的发震环境和机制引起了人们的广泛关注。本研究采用vP/vS一致性约束双差层析成像方法获得了vP/vS三维图像，提高了vP/vS模型的精度。研究了横向分辨率为0.1°区域的vP/vS图像特征，揭示了杨壁MS6.4地震的发震环境。结果表明:(1)红河断裂北段周围不同深度均存在低速和高vp /vS异常。沿渭西-桥后-渭山断裂及其西侧隐伏断裂的vS和vP/vS图像显示出明显的分段特征。(2)杨壁MS6.4级地震震源区位于低vp /vS区，高中强度。北西向的高vp /vS异常表明裂缝发育，存在流体或部分熔体，不利于应力积累和引发大地震。这样的条件也阻止了地震序列向西北延伸。(3)青藏高原物质向东南方向挤压，源区低vp /vS体阻挡了流体运移。震源下方的高vP/vS异常可能表明，中、下地壳的流体或部分熔体在发震层底部逐渐削弱了中等强度，并在高、低vP/vS过渡带准备了最大的前震。同时，构造应力在脆弱的上地壳中不断积累，最终导致MS6.4地震的发生。

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来源期刊

Earthquake Science GEOCHEMISTRY & GEOPHYSICS-

CiteScore

1.10

自引率

8.30%

发文量

审稿时长

3 months

期刊介绍： Earthquake Science (EQS) aims to publish high-quality, original, peer-reviewed articles on earthquake-related research subjects. It is an English international journal sponsored by the Seismological Society of China and the Institute of Geophysics, China Earthquake Administration. The topics include, but not limited to, the following ● Seismic sources of all kinds. ● Earth structure at all scales. ● Seismotectonics. ● New methods and theoretical seismology. ● Strong ground motion. ● Seismic phenomena of all kinds. ● Seismic hazards, earthquake forecasting and prediction. ● Seismic instrumentation. ● Significant recent or past seismic events. ● Documentation of recent seismic events or important observations. ● Descriptions of field deployments, new methods, and available software tools. The types of manuscripts include the following. There is no length requirement, except for the Short Notes. 【Articles】 Original contributions that have not been published elsewhere. 【Short Notes】 Short papers of recent events or topics that warrant rapid peer reviews and publications. Limited to 4 publication pages. 【Rapid Communications】 Significant contributions that warrant rapid peer reviews and publications. 【Review Articles】Review articles are by invitation only. Please contact the editorial office and editors for possible proposals. 【Toolboxes】 Descriptions of novel numerical methods and associated computer codes. 【Data Products】 Documentation of datasets of various kinds that are interested to the community and available for open access (field data, processed data, synthetic data, or models). 【Opinions】Views on important topics and future directions in earthquake science. 【Comments and Replies】Commentaries on a recently published EQS paper is welcome. The authors of the paper commented will be invited to reply. Both the Comment and the Reply are subject to peer review.