Tectonic setting and geological manifestations of the 2003 Altai earthquake

Geological and geomorphic manifestations of the source of the earthquake that occurred in the southern Gorny Altai on September 27, 2003, are described. This earthquake, the strongest over the entire history of seismological observations, caused damage to buildings and structures in the Chuya and Kurai basins and was accompanied by exposure of its source at the surface with formation of a system of seismic ruptures trending in the northwestern direction. The linear zone of seismic rupture was traced for more than 70 km on the northern slopes of the North Chuya and South Chuya ranges, and a developed network of related splays was found. The secondary (gravitational and vibrational) seismic dislocations were expressed as downfalls, landslides, and gryphons in the pleistoseist zone. These dislocations occur over an area of approximately 90 x 25 km(2) that broadly coincides with the region of quakes having intensities of IX-VII. The paleoseismogeological investigations performed in the source region of the 2003 earthquake have shown that seven seismic events with M = 7.0-8.0 occurred in its source over the last 5000 years with a 500-to 900-year recurrence period. The study of the tectonic setting of the earthquake source in the Gorny Altai has allowed northward tracing of the main seismically active zones of the Mongolian and Gobi Altai, where earthquakes with a magnitude M > 7.0 occurred repeatedly, in particular, during the 20th century, and combination of all mountain systems of the Greater Altai into a common high-magnitude seismotectonic province.