Seismogenic Convolutions in Lacustrian Deposits in Issyk-Kul (kyrgyzstan) and Sevan (armenia) Lakes as Indicators of Strong Paleoseismic Events

During recent field investigations we found evidence of sediment deformation structures in one of the most tectonically active areas on the globe: the Tien Shan range in Central Asia and Armenian Highland, Caucasus. We are focused on examining the significance of the deformations as indicators of palaeoseismicity. Soft-sediment deformation structures in the form of balls, pillows, pockets, sharp "waves" and pseudo-nodules are exposed in the Issyk-Kul and Sevan Lakes basins, within interfingering beds of shallow lacustrine, beach and fluviatile origin. Additional deformation structures that were encountered include: a complex and chaotic folded structure, giant balls and a ''pillar'' structure which has not been previously reported, where marl intrudes down into coarse pebbley sand and forms pillar morphology. Liquefaction features and bedforms related to storm and breaking waves were not encountered. Neither was there evidence of turbidites. Seven field criteria for relating soft sediment deformation to palaeoseismic triggering provide strong evidence for a seismic origin of the deformation structures. Empirical relationships between magnitude and the maximum distance from an epicenter to liquefaction sites make the active epicentral zone north of Lake Issyk-Kul and east of the Sevan, with its frequent high magnitude events, the most favorable source for the deformation structures. Luminescence dating of the sediments of the Issyk-Kul lake gives a time window of 26F2.1 to 10.5F0.7 ka BP, indicating latest Pleistocene seismic activity. According to relative geological scheme the Sevan seismites are Pleistocene-Holocene age. The field investigation were supported in frame of NATO project "Caucasus Seismic Emergency Respouse" (CauSER) SfP 983284. Seimogenic convolution in lacustrian deposits of Sevan lake (Armenia) Giant sand "Pillow" in Issyk-Kul lake deposits