PALEOSEISMODISLOCATIONS AND RELATED PALEOEARTHQUAKES ALONG THE MAJOR SAYAN FAULT ZONE

Abstract

Detailed paleoseismological investigations were carried out by cutting seismodislocation zones with trenches (nine at three sites) to estimate the number of paleoearthquakes and their absolute age. The detailed structure, morphology, and parameters of deformations are given. The Holocene left-lateral strike-slip displacements are 4-10 (one act), 18-22, 30-37, and, possibly, 60-70 m. Six faulting paleoevents have been distinguished, which occurred less than 400, -600, -1800, -4700, -7600, and -9800 years ago. Seismodeformations dated at 9800, 7600, and 4700 years are traceable over a distance of 60 km. Paleoevents that occurred 1800 and 600 years ago are imprinted in seismodeformations over a length of 46 km, and the youngest paleoearthquake is fixed at two segments, 3 and 19 km long, over a distance of 40 km. Magnitudes (M) of paleoevents are determined by the length (L), displacement (D), and parameter (LD) of related seismodislocations. The maximum M values vary from 7.6 to 8.0. The recurrence periods of earthquakes are 1200-2900 years, averaging 2300 years.