THE 25 FEBRUARY 1999 SOUTH BAIKAL EARTHQUAKE: SEISMOTECTONICS AND REGIONAL GEODYNAMICS

Abstract

The South Baikal earthquake of 25 February 1999 had the main shock in the southwestern part of Lake Baikal. The source of a normal-slip mechanism was associated with the Obruchev (Primorsky)/Angara fault node. This was the strongest shock (Mpsp = 6.0) in southern Baikal region over the past forty years after the Mlh = 6.8 Central Baikal earthquake of 1959. The main shock, followed by a long sequence of aftershocks with different mechanisms, reached an intensity of VII-VIII at the epicenter, VI-VII in villages 15 to 30 km away on the northwestern and southeastern sides of Baikal, and IV-VI in neighboring towns of Irkutsk, Angarsk, and Ulan Ude. The earthquake occurred in the region for which a fifteen years pending seismic risk was predicted in 1994.