Source Characteristics and Path Attenuation for the Yangbi, China Seismic Sequence in 2021

• Published in: Pure and applied geophysics Vol. 179; no. 8; pp. 2721 - 2733
• Main Authors: Zhou, Ying, Wang, Hongwei, Wen, Ruizhi, Miao, Tianming, Cui, Jianwen
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.08.2022; Springer Nature B.V
• Subjects: Aftershocks; Anelasticity; Attenuation; Decay; Decay rate; Distance; Earth and Environmental Science; Earth Sciences; Earthquakes; Frequency ranges; Geophysics/Geodesy; Seismic activity; Sequencing; Shaking; Spectra; China; spectral analysis; source characteristics; path attenuation; Earthquake ground motion
• ISSN: 0033-4553; 1420-9136
• DOI: 10.1007/s00024-022-03077-x

On 21 May 2021, an M 6.4 earthquake occurred in Yangbi county, west of Yunnan Province, China. The Yangbi seismic sequence was initiated on 18 May and reached its climax as the occurrence of the M 6.4 mainshock. It was a typical foreshock-mainshock-aftershock sequence. A total of 1043 strong-motion recordings during 44 events from this sequence were selected and utilized for the spectral decomposition to separate the path attenuation and source spectra. The path attenuation curves are overall close to the simplest distance decay form described by R −1 . The path attenuations were further represented by the combination of the geometric spreading and anelastic attenuation. Geometric spreading of R −0.37 was retrieved, indicating slower distance decay at local distances. The larger area close to the epicenter tends to undergo strong ground shaking. The quality factors obtained were regressed as Q s ( f ) = 64.27 f 0.76 in the frequency range of 0.25–20 Hz, lower than those reported for the whole Yunnan region, indicating faster attenuation at large distances in the study region. The seismic moments, corner frequencies, and stress drops were estimated from the inverted source spectra. The stress drops for the Yangbi seismic sequence were mainly in the range of 0.5–3.0 MPa. The mainshock had the largest stress release (~ 2.7 MPa). The strong foreshocks and aftershocks with M w  ≥ 5.0 had higher stress drops (~ 1.5–2.5 MPa) than those of small events with M w  < 5.0 (~ 0.1–1.5 MPa). We inferred that the strong foreshocks and aftershocks with high stress releases may not rupture the same fault activated by the mainshock, while they may occur in various fault branches.