Geological, Geophysical and Macroseismic Data on the September 28, 2019, M w = 5.1 Earthquake That Occurred at the North
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ogical, Geophysical and Macroseismic Data on the September 28, 2019, Mw = 5.1 Earthquake That Occurred at the Northeast of the Baikal Rift A. I. Seredkinaa, *, Ya. B. Radziminovichb, V. I. Melnikovab, and N. A. Gilevac aPushkov
Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences, Moscow, Troitsk, 108840 Russia b Institute of the Earth’s Crust, Siberian Branch of the Russian Academy of Sciences, Irkutsk, 664033 Russia cBaikal Branch, Federal Research Center Geophysical Survey, Russian Academy of Sciences, Irkutsk, 664033 Russia *e-mail: [email protected] Abstract—This paper considers the September 28, 2019 earthquake that occurred on the northeastern flank of the Baikal Rift Zone (BRZ), called the Lenger earthquake after its location. The seismic moment tensor and hypocentral depth of the event are calculated from data on surface wave amplitude spectra with additional information on P-wave first-arrival polarities recorded at regional stations. The hypocentral depth is 11– 12 km, the moment magnitude Mw = 5.1, and the scalar seismic moment M0 = 5 × 1016 N m. The earthquake source is formed under the influence of horizontal submeridional extension and subhorizontal NE–SW compression. The latter approximately coincides with the azimuth of the fast S-wave velocity in the upper mantle obtained from SKS-splitting and surface wave tomography data. The Lenger earthquake was felt at epicentral distances of more than 600 km. Comparison of its macroseismic effects with effects of other strong seismic events in the study area demonstrates that the regional macroseismic field equation should be actualized for the territory of the northeastern flank of the BRZ. Analysis of the obtained data, along with the available information on the stress-strain field of the crust of this area indicates that the geodynamical pattern of the conjunction zone of the northeastern flank of the BRZ and the Olekma–Stanovoi orogenic system influences the low-active Transbaikalia block. However, due to low tectonic activity, the tectonic stress accumulation period sufficient for the occurrence of relatively strong seismic events is larger than in regions with high-level tectonic activity. Keywords: earthquake, seismic moment tensor, surface waves, macroseismic data, seismotectonic deformations, anisotropy, Baikal rift DOI: 10.3103/S0747923920060080
INTRODUCTION On September 28, 2019, southeast of the seismically active areas of the northeastern flank of the Baikal Rift Zone (BRZ), which borders the Olekma–Stanovoi seismic belt, a fairly strong earthquake was recorded (Mw = 5.1), named the Lenger after its location (the epicenter is located in the upper reaches of the Lenger River). It is noteworthy that this event occurred at some distance from the known epicentral fields: the Chara, Charuoda, and Olekma, characterized by increased seismic activity (Fig. 1). Paleoseismogeological studies have shown that destructive earthquakes with a recurrence period of 100– 1000 years have occurred repeatedly during
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