The March 29, 2019 Earthquake in the Western Part of the Tunka Rift Basin System: Source Parameters and Macroseismic Eff
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March 29, 2019 Earthquake in the Western Part of the Tunka Rift Basin System: Source Parameters and Macroseismic Effects Ya. B. Radziminovicha, *, A. I. Seredkinab, V. I. Melnikovaa, and N. A. Gilevac aInstitute bPushkov
of the Earth’s Crust, Siberian Branch, Russian Academy of Sciences, Irkutsk, 664033 Russia Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow, 108840 Russia c Baikal Branch, Geophysical Survey, Russian Academy of Sciences, Irkutsk, 664033 Russia *e-mail: [email protected]
Abstract—The paper considers one of the perceptible earthquakes that occurred on March 29, 2019, in the western part of the Tunka rift basin system. The epicenter of this seismic event was localized within the Hoytogol basin. The earthquake source parameters were as follows: hypocentral depth (h = 36–37 km), scalar seismic moment (M0 = 1.6 × 1016 N m), moment magnitude (Mw = 4.8), and focal mechanism—were determined using joint inversion of surface wave amplitude spectra and polarities of P-wave first arrivals. The focal mechanism demonstrates the predominance of combined thrust and strike-slip movements, indicating uplifting tectonic movements in the Hoytogol basin. The shaking from the earthquake was felt within a vast area, with an intensity of up to I = III at epicentral distances up to 490 km. Macroseismic data were obtained using different methods, including an interactive questionnaire hosted on the website of the Baikal Branch of GS RAS. Analysis of the macroseismic data made it possible to formulate the goal of refining the regional macroseismic field equation. Keywords: Tunka rift basin system, seismicity, earthquake, macroseismic data, macroseismic equation DOI: 10.3103/S0747923920060067
lar, for problems related to refinining seismic hazard and seismic risk assessment.
INTRODUCTION The Tunka rift basin system and its mountain frame, which structurally represent the southwestern flank of the Baikal Rift Zone (BRZ), are characterized by relatively high seismic activity (Fig. 1). On the one hand, it is well known that sources of strong earthquakes can occur in this region, and these earthquake sources represent a direct hazard for populated areas, industrial facilities, and transport infrastructure in southern Cis-Baikalia (Golenetskii, 1998). On the other hand, data on strong earthquakes (including their macroseismic effects) are still insufficient as of today. Therefore, any perceptible seismic event can be considered a valuable source of new information. The earthquake that occurred on March 29, 2019, in the western part of the Tunka rift basin system is one of such events; it was felt within a large area covering the west of the Republic of Buryatia and southern Irkutsk oblast (Fig. 2). In epicentral location and energy class, this was close to the event of September 17, 2003 (Mw = 4.9), known as Hoytogol earthquake (Pavlenov et al., 2007; Mel’nikova et al., 2009): therefore, the earthquake of March 29, 2019, was called Hoytogol-II. In addition to
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