The September 21, 2020, Mw=5.5, Bystraya Earthquake in the Southern Baikal Region: Preliminary Results of Instrumental and Macroseismic Observations

We consider the September 21, 2020, M-w = 5.5 seismic event, which occurred in the eastern part of the Tunka rift basin system and was followed by a relatively strong mb = 4.6 aftershock. The earthquake epicenter is localized within the Bystraya basin in the zone of prolonged seismic quiescence and is possibly confined to the Main Sayan fault zone. The hypocentral depth, according to the solution of the Baikal Branch, United Geophysical Survey, Russian Academy of Sciences (UGS RAS), is estimated as h = 18 km. The focal mechanisms of the main shock and strong aftershock are characterized by almost pure strike-slip movements, which agrees well with modern ideas about the tectonics of the area. The maximum shaking intensity observed in the populated areas closest to the epicenter is estimated at VI-VII on the MSK-64 scale. A shaking intensity of V and IV was observed in populated areas at distances over 180 and 500 km, respectively. This earthquake made it possible to obtain new data on the dynamic ground motion parameters. The maximum peak ground acceleration (PGA) of 187 cm/s(2) was recorded at the Talaya seismic station, which is the highest value for the territory of the Southern Baikal Region during the digital period of earthquake detection.