Recurrence of large paleo-earthquakes in Kashmir Himalaya seismic gap (Riasi area, India)

Abstract

Abstract In Kashmir Himalaya, the Medlicott-Wadia Thrust is a main active fault responsible for the crustal accretionary prism building during the Late Quaternary. Because of the long seismic silence during the last five centuries, it is a key structure to be studied in order to estimate the regional seismic hazard. In the Riasi area, the analysis of two paleoseismological trenches allowed us identifying and measuring several seismic ruptures over the last ~3500 years. We determined that the oldest rupture occurred around 1600–1000 BC, while the youngest occurred after 1470 AD. The latest event is compatible with the great 1555 AD (Mw > 7.5) Kashmir earthquake, whose evidence at the surface had not yet been recognized. Our results show that despite the long-lasting seismic gap, the Medlicott-Wadia Thrust is a main seismogenic structure in the region, able to produce large earthquakes. Their recurrence interval ranges between 500 and 700 years, implying that a main seismic event could occur in the next decades. These seismic ruptures are localized over gently-dipping fault branches associated with decameter-scale scarps. The morphologies observed are due to a significant non-localized component of the deformation in Quaternary sediments.