Seismites in the Pleistocene succession and recurrence period of large earthquakes in the Kathmandu Valley, Nepal

Abstract

Background: Kathmandu Valley, which is a rapidly growing place in Nepal, was largely damaged by the earthquakes of April 25 (Mw 7.8) and May 12 (Mw 7.3). For taking measures against future large earthquakes, knowledge of the long-term earthquake history is crucial for future disaster prevention or disaster reduction. Results: Twelve seismites thicker than 0.2 m were identified from the Tokha Formation, the major part of which was deposited at about 20 – 17 ka (calibrated 14 C ages). Some seismites show evidence of sliding occurred on the delta plain. Conclusions: The reconstructed earthquake recurrence period is ca. 0.25 ka or shorter. Six of the seismites show evidence of sliding when deformation structures were formed. This was probably due to the tilting of the surface in the studied site, where a buried flexure was discovered nearby. The discovery of the seismites with sliding in the delta plain deposit suggests the possibility of sliding by future large earthquakes and requirement of risk management for the plain area of the Kathmandu Valley.