Temporal evolution of the focal mechanism consistency of the 2021 Yangbi M_(S) 6.4 earthquake sequence in Yunnan

Using the Cut And Paste(CAP)method,we invert the focal mechanism of 38 moderate earthquakes(M_(S)≥3.0)recorded by Yunnan seismic network and analyze the corresponding focal mechanism consistency based on the minimum spatial rotation angle.Our results indicate that the M_(S)6.4 mainshock is induced by a lateral strike slip fault(with a rake angle of~-165°)and a little normal-faulting component event along a nearly vertical plane(dipping angle~79° and strike~138°).Combining our results with high resolution catalog,we argue that the seismogenic fault of this earthquake sequence is a secondary fault western to the major Weixi-Qiaohou-Weishan fault.The focal mechanism evolution can be divided into three periods.During the first period,the foreshock sequence,the focal mechanism consistency is the highest(KA<36°);during the second period which is shortly after the mainshock,the focal mechanism shows strong variation with KA ranging from 8° to 110°;during the third period,the seismicity becomes weak and the focal mechanism of the earthquakes becomes more consistent than the second period(18°<KA<73°).We suggest that the KA,to some extent,represents the coherence between local tectonic stress regime and the stress state of each individual earthquake.Furthermore,high focal mechanism consistency and high linearity of seismic distribution may serve as indicators for the identification of foreshock sequence.

An accessible seismological dataset of 2021 Yangbi M_(S)6.4 earthquake

A M_(S)6.4 earthquake occurred on 21 May 2021 in Yangbi county,Dali prefecture,Yunnan,China,at 21:48 Beijing Time(13:48 UTC).Earthquakes with an M3.0 or higher occurred before and after the main shock.Seismic data analysis is essential for the in-depth investigation of the 2021 Yangbi M_(S)6.4 earthquake sequence and the seismotectonics of northwestern Yunnan.Institute of Geophysics,China Earthquake Administration(CEA),has compiled a dataset of seismological observations from 157 broadband stations located within 500 km of the epicenter,and has made this dataset available to the earthquake science research community.The dataset(total file size:329 GB)consists of event waveforms with a sampling frequency of 100 sps collected from 18 to 28 May 2021,20-Hz and 100-Hz continuous waveforms collected from 12 to 31 May 2021,and seismic instrument response files.To promote data sharing,the dataset also includes the seismic event waveforms from 20 to 22 May 2021 recorded at 50 stations of the ongoing Binchuan Active Source Geophysical Observation Project,for which the data protection period has not expired.Sample waveforms of the main shock are included in the appendix of this article and can be downloaded from the Earthquake Science website.The event and continuous waveforms are available from the Earthquake Science Data Center website(www.esdc.ac.cn)on application.