Abstract
AbstractCentral Asia is highly vulnerable to large earthquakes, yet existing records of past seismic activity in this area are still insufficient to reliably assess regional earthquake hazard on longer timescales. Within this study, the sediments of Sary Chelek, a mountain lake in the western Kyrgyz Tian Shan, were investigated to explore its potential as a natural paleoseismic archive. The lacustrine deposits are characterized by a succession of annually laminated (varved) sediments overlying event deposits that consist of large-scale turbidites and distorted lake sediments, similar to earthquake-related deposits described from other lake sediment records. Microscopic sediment analysis furthermore revealed distorted varves in the laminated sequence that closely resemble earthquake-related soft-sediment deformation structures. Varve counting and radiometric dating determine the formation of the distorted varves and the emplacement of the large-scale event deposits to the early 1990s and mid-1940s, respectively. This is in good temporal agreement with the occurrence of two large earthquakes that struck western Kyrgyzstan in AD 1992 and AD 1946. These results and particularly the precise age control of the Sary Chelek sediment record highlight its potential for establishing a long and precisely dated record of regional earthquake activity.
Highlights
Large earthquakes represent a major threat for modern societies and economies
It is concluded that the large-scale turbidites below the varved sediments are related to mass-transport events that most likely represent the subaquatic continuation of landslides/rockfalls or slope failures that were caused by a common and simultaneous trigger
Considering the documented seismic activity of the nearby Talas-Fergana Fault, which is the largest strike-slip fault in Central Asia, it is very likely that the emplacement of the event deposits in the Sary Chelek lake basin was triggered by multiple landslides, slope failures, and/or rockfalls that were caused by an MLH = 7.5 earthquake, which occurred on November 2, 1946, within a distance of only 20 km from the lake
Summary
Large earthquakes represent a major threat for modern societies and economies. This is true for Kyrgyzstan and the other emerging countries of post-Soviet Central Asia, where a high, tectonically induced seismic hazard (Giardini et al, 1999; Ullah et al, 2015) concurs with a high vulnerability related to still existing infrastructural and economic deficiencies. Instrumental data on past seismicity in Kyrgyzstan only reach back to AD 1927 (Kalmetieva et al, 2009), and documentary sources, though usually covering a few hundred years, are generally considered incomplete As this is insufficient to reliably assess the long-term recurrence pattern of large earthquakes and the seismic hazard, there is a large need for exploring natural archives to date and reconstruct past seismic activity in the region.
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