Anomalous Seismic Noises from the December 9, 2020 MW = 5.6 KUDARA Earthquake in the Baikal Basin

Studies have been conducted on the variations of microseismic noise recorded by broadband and short-period seismic stations in the area of South Baikal before and after the large December 9, 2020 Kudara earthquake with M w = 5.6. Ten days before the earthquake, there was a gradual increase of oscillation amplitudes in the frequency range from 0.01 to 0.1 Hz, with an increasing background observed also during 4 days after the main shock (period from December 1, 2020 to January 12, 2021). The maximum amplitude increase is 19.5 against the background. During this time, there were recorded 48 aftershocks. The analysis of direction of particle motion in seismic waves over the reporting period showed an abrupt change in the orientation of oscillations, which is fully consistent with the azimuth for the main shock epicenter. The analysis of seismograms over the next period (from December 13) did not show similar effects in the microseismic noise field. Apparently, the microseismic noise field reflected the process of slow faulting before the earthquake and after the main shock with subsequent attenuation.