The 9 November 2002 Earthquake in the Northeast of the Russian Plate (Komi Republic)

摘要

The East European Platform (EEP) is characterized by a rather weak seismicity. The south of the Komi Republic is the most seismically active territory in the northeast of the EEP. The 1939 Sysola earthquake (grade 7), one of the strongest earthquakes in the European north of the 20th century, occurred there. Many world's seismic stations recorded an earthquake in the Priluzsky region of the republic on 9 November 2002, but it was not thoroughly studied and is not considered in literature. In this work we recalculate the parameters of the earthquake hypocenter, substantiate its tectonic nature, construct its focal mechanism, and describe its tectonic position. For processing, we used data on 86 seismic phases from 58 stations with epicentral distances from 5.9 to 57 degrees, azimuth angles from 1.5 to 341.7 degrees, and the maximum azimuthal gap of 70 degrees. The following parameters of the hypocenter were obtained: t(0) = 06 h 47 min 17.9 s, 59.93 degrees N, 49.76 degrees E, R-minor = 7.7 km, R-major = 10.7 km, Az(major) = 20 degrees, h = 16 km, and M-s = 3.4. The earthquake is localized in the upper crust and is confined to the zone of the junction of the eastern slope of the Sysola arch and the western flank of the Kirov-Kazhim aulacogen of the Volga-Ural anteclise of the Russian Plate. We have established a strike-slip fault focal mechanism of the earthquake, which corresponds to the latest stress field of the region. The estimated axis parameters (value, azimuth, plunge) are as follows: T = 0.707, 90.0, 0; N = 0, 0, 39.792; and P = -0.707, 180.0, 50.208. The plane parameters (strike, dip, slip) are estimated at 327, 57, -140 degrees for the first plane and 213, 57, -40 degrees for the second plane. The recorded seismic events in the northeast of the Russian Plate indicate that the platform area is not seismically passive. The performed research shows that recent seismotectonic processes are related to the structure and state of the Earth's crust within the platform.