CHUYA EARTHQUAKES (2003, SEPTEMBER 27 - OCTOBER 1) AS A KEY FOR ESTIMATION SE ALTAI PALEOSEISMICITY
дата публикации: 2004
A number of severe seismic shocks (maximal M = 7.5) occurred in SE Altai in September-October 2003. They were the most powerful earthquakes in the modern history of the Altai mountain country. We can consider newly formed relief destructions as a key for estimation of paleoseismicity of this region.The Altai mountains are an active suture zone of Western Siberian, Mongolian and Dgungarian lithospheric plates. Orogenic processes occurred there repeatedly in the Permian- the Early Triassic, the Jurassic - the Early Cretaceous and in the Cenozoic (Novikov, 2001). Molasses of modern submontane and intermontane depressions point at the beginning of Cenozoic activation in the Late Palaeogene. The last great tectonic stage took place between the Middle and the Late Pleistocene and it is revealed by correlation between glacial and tectonic relief elements (Vysotsky, 1997; Agatova, 2003). But paleoseismicity traces such as large rockfalls, landslides and powerful talus are mainly preserved in relief after degradation of last glaciation (from the end of the Late Pleistocene). Most of paleoseismodislocations are concentrated in SE part of Russian Altai. This part is the north edge of the highest axial section of the Altai mountain country. Analysis of large scale (1:50 000) geomorphologic maps of the key territories shows the fact that the paleoseismodislocations are confined to borders of tectonic blocks with different altitude which form Chuya and Kuray intermontane depressions and framing ridges.Epicenters of the September-October earthquakes were also located on the south-west border of Chuya depression. The relief deformations in main epicenter zone correspond to grade 9 earthquake. A comparison of modern seismic induced geomorphologic effects with the ancient rockfalls and landslides confirms their seismic nature. This comparison allows us to estimate the intensity of paleoseismicity as grade 11-12 earthquakes.The concentration of the ancient and the modern seismic induced relief destructions in the South-East Altai indicates that at least since the end of the Late Pleistocene the axial part of Altai elevation is not less tectonically active than its borders.This study was supported by the Russian Foundation for Basic Research (N 02-05-64786).
первоисточник: 32nd International Geological Congress, Florence, Italy, August 20-28, 2004: Abstracts Volume