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Russian Geology and Geophysics

2003 year, number 10


V.N. Tabulevich, V.A. Potapov, E.N. Chernykh, and N.N. Drennova
Institute of the Earth's Crust, Siberian Branch of the RAS,
128 ul. Lermontova, Irkutsk, 664033, Russia
Keywords: Seismicity, foreshocks, aftershocks, rift, Lake Baikal
Pages: 1045-1052


Nucleation of large (M = 5-6) earthquakes in the Baikal basin was investigated from data on the M = 1.1 M = 2.2 and 2.2 < M < 3.3 foreshock activity. The seismic process was constrained between the first foreshocks and the decay of aftershocks on the basis of specially introduced parameters that represent the behavior of groups of small shocks associated with the main event. These parameters, including grouping radius (rc), distance from grouping center (C) to a M = 5-6 epicenter, scatter (rb), frequency, and apparent migration velocity, were applied to analyze the foreshock and aftershock activity of the 25 February 1999 earthquake in southern Lake Baikal. The seismic process was the most active in the epicentral zone 20-30 km offshore near the Listvyanka bay. The behavior of foreshocks changed 15 days before the main shock. Their grouping center migrated with time approaching the epicenter of the future event. Short-term precursors were observed only before the 25 February 1999 earthquake in South Baikal basin, and other offshore events in Central and North Baikal were not preceded by detectable foreshock activity. Small events related with nucleation of larger earthquakes have a number of specific features and may be useful in earthquake prediction.