Detecting active faults in intramountain basins using electrical resistivity tomography: A focus on Kashmir Basin, NW Himalaya

Abstract

Kashmir basin in the NW Himalaya is surrounded by the main Himalayan boundary faults, has very well documented historical earthquakes and a good instrumental earthquake record. However, the causative faults of these earthquakes except the 8 October 2005 Kashmir earthquake (M7.6) are not known. One of many historical earthquakes that have struck and caused damage and destruction in the Kashmir basin is the 30 May 1885 Kashmir earthquake (~M6.3). The extensive damage due to this earthquake was reported in the NW part of the basin and as usual the causative fault is not known and mapped. As the earthquake related geomorphic features are not preserved due to the high erosion rates in the Kashmir Himalaya, we mapped certain active fault strands using high resolution digital elevation models (DEM) and the Google Earth imagery, later complemented by the field investigation in the NW Kashmir. The Electrical Resistivity Tomography (ERT) was carried out at certain identified sites in the macroseismic epicentral area of the 1885 Kashmir earthquake. The results show a local active normal fault which was named as the NW Kashmir fault. The ERT results were confirmed by excavating a trench and an already existing road cut at the ERT sites. The results show that ERT is a very useful shallow geophysical method to detect faults in the Karewas. Karewas are the Plio-Pleistocene and Holocene (reworked by rivers), fluvio-lacustrine, soft and unconsolidated, sand-clay-conglomerate sediments, deposited as distinct table-land geomorphic features in the Kashmir basin and are significantly water saturated.