Volume 44 Issue 3
Jun.  2022
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Zeng X W,Zhao X Y,Li M Y,Li W J,Tang H,Yuan Y. 2022. Variation of b-value before and after Yangbi four MS≥5.0 earthquakes on May 21,2021. Acta Seismologica Sinica,44(3):401−412 doi: 10.11939/jass.20210129
Citation: Zeng X W,Zhao X Y,Li M Y,Li W J,Tang H,Yuan Y. 2022. Variation of b-value before and after Yangbi four MS≥5.0 earthquakes on May 21,2021. Acta Seismologica Sinica44(3):401−412 doi: 10.11939/jass.20210129

Variation of b-value before and after Yangbi four MS≥5.0 earthquakes on May 21,2021

doi: 10.11939/jass.20210129
  • Received Date: 2021-07-29
  • Rev Recd Date: 2021-10-25
  • Available Online: 2022-04-11
  • Publish Date: 2022-06-27
  • Four MS≥5.0 earthquakes occurred successively in Yunnan Yangbi from 21:21 to 22:31 on May 21, 2021, which are MS5.6, MS6.4, MS5.0 and MS5.2, respectively. Based on the earthquakes recorded in focal area of Yangbi earthquake and its vicinity from January 1, 2015 to June 4, 2021, we estimated the b-value by the maximum likelihood method. Then, we analyzed the spatial distribution of b-value before and after Yangbi earthquakes and got the views below. Firstly, an earthquake swarm occurred three days before the Yangbi earthquakes, then, the b-value near the focal area of Yangbi earthquake decreased rapidly after the earthquake swarm. It may indicate that the strength of crustal medium was close to the critical state of fracture. Secondly, the four MS≥5.0 earthquakes distribute along the edge of the abnormal area with low b-value. Thirdly, the b-value of the focal area increased obviously after the Yangbi earthquakes. It indicates that the regional stress has been released and the risk of strong earthquake is reduced in the short term. Fourthly, there are two b-value abnormal areas 40 km and 70 km northwest of the Yangbi earthquakes. It means that there is a risk of strong earthquakes in the abnormal areas in the future.


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