{"title":"Seismogenic environment and mechanism of the Yangbi MS6.4 earthquake in Yunnan, China","authors":"Mengqiao Duan , Kezhen Zuo , Cuiping Zhao , Lianqing Zhou","doi":"10.1016/j.eqs.2022.08.001","DOIUrl":null,"url":null,"abstract":"<div><p>The Yangbi <em>M</em><sub>S</sub>6.4 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 <em>v</em><sub>P</sub>, <em>v</em><sub>S</sub> and <em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> images using the <em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> consistency-constrained double-difference tomography method, which improves the accuracy of <em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> models. We focus on characteristics of <em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> images in areas with a lateral resolution of 0.1°, and reveal the seismogenic environment of the Yangbi <em>M</em><sub>S</sub>6.4 earthquake. The conclusions are as follows: (1) Low velocity and high-<em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> anomalies are revealed at different depths around the northern segment of the Red River fault. <em>v</em><sub>S</sub> and <em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> 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 <em>M</em><sub>S</sub>6.4 earthquake is located in a low-<em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> zone implying high medium strength. High-<em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> 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-<em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> body in the source region. The high-<em>v</em><sub>P</sub>/<em>v</em><sub>S</sub> 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 <em>v</em><sub>P</sub>/<em>v</em><sub>S</sub>. Meanwhile, tectonic stress incessantly accumulated in the brittle upper crust, eventually led to the <em>M</em><sub>S</sub>6.4 earthquake occurrence.</p></div>","PeriodicalId":46333,"journal":{"name":"Earthquake Science","volume":"35 4","pages":"Pages 297-310"},"PeriodicalIF":1.2000,"publicationDate":"2022-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S1674451922003482/pdfft?md5=42b0ca855b3483b8b6d600225a2d318b&pid=1-s2.0-S1674451922003482-main.pdf","citationCount":"1","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Earthquake Science","FirstCategoryId":"89","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S1674451922003482","RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q3","JCRName":"Earth and Planetary Sciences","Score":null,"Total":0}
引用次数: 1
Abstract
The Yangbi MS6.4 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 vP, vS and vP/vS images using the vP/vS consistency-constrained double-difference tomography method, which improves the accuracy of vP/vS models. We focus on characteristics of vP/vS images in areas with a lateral resolution of 0.1°, and reveal the seismogenic environment of the Yangbi MS6.4 earthquake. The conclusions are as follows: (1) Low velocity and high-vP/vS anomalies are revealed at different depths around the northern segment of the Red River fault. vS and vP/vS 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 MS6.4 earthquake is located in a low-vP/vS zone implying high medium strength. High-vP/vS 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-vP/vS body in the source region. The high-vP/vS 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 vP/vS. Meanwhile, tectonic stress incessantly accumulated in the brittle upper crust, eventually led to the MS6.4 earthquake occurrence.
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.
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● Seismic instrumentation.
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