Paleoearthquakes in the Uimon basin (Gorny Altai)

Abstract

Abstract Paleoseismological studies confirm that the Uimon basin is thrust by its northern mountain border along the active South Terekta fault. The latest motion along the fault in the 7–8th centuries AD induced an earthquake with a magnitude of Mw = 7.4–7.7 and a shaking intensity of I = 9–11 on the MSK-64 scale. The same fault generated another event (M ≥ 7, I = 9–10), possibly, about 16 kyr ago, which triggered gravity sliding. The rockslide dammed the Uimon valley and produced a lake, where lacustrine deposition began about 14 ± 1 kyr ago, and a later M ≥ 7 (I = 9–10) earthquake at ~6 ka caused the dam collapse and the lake drainage. Traces of much older earthquakes that occurred within the Uimon basin are detectable from secondary deformation structures (seismites) in soft sediments deposited during the drainage of a Late Pleistocene ice-dammed lake between 100 and 90 ka and in ~77 ka alluvium. The magnitude and intensity of these paleoearthquakes were at least M ≥ 5.0–5.5 and I ≥ 6–7.