THE PLEISTOSEIST ZONE AND TECTONIC POSITION OF THE CHUYA EARTHQUAKE CENTER IN 2003

Abstract

The earthquake on September 27, 2003 (11:33 GMT), in southeastern Gornyi Altai was the strongest one (M = 7.5) the region has ever seen. In terms of magnitude, only the Mongolian earthquake on December 9, 1761 (M = 7.7), is comparable with this event. However, this earthquake epicenter has been approximately determined. Therefore, one cannot rule out that it took place in Mongolia rather than Gornyi Altai. Earthshakes with intensity up to 4 were observed on September 27, 2003, in all the settlements of southern Siberia up to Tomsk and Krasnoyarsk. Previously, only two earthquakes with M ≥ 6.0 had been registered in the northern part of Greater Altai (Gornyi and southern Altai) [1, 2], the Chuya (September 21, 1923; 49.8° N, 87.7° E; M = 6.0) and Zaisan (June 14, 1990; 87.7° N, 85.0° E; M = 6.6) earthquakes [3]. At present, documentary evidence of 36 earthquakes with M ≥ 6.0 is available for the Mongolian and Gobi segments of Altai. In terms of neotectonics, the area of the Chuya earthquake and several subsequent aftershocks is located at the continuation of major dextral NW-trending shear zones, which diverge in a fan-like manner and make up intricate tectonic blocks in the Gornyi Altai region.