Detection of high and moderate crustal strain zones in Uttarakhand Himalaya, India

Abstract

We present geodetically estimated crustal strain rates in Uttarakhand Himalaya, a region which has long been considered as a part of seismic gap. We processed and analyzed the GPS data, acquired from the sites enveloping all the litho-tectonic units from the Sub Himalaya in the south to the Tethys Himalaya in the north together with the major Himalayan thrust/fault systems. On the basis of the obtained dataset, we conclude that the maximum amount of crustal shortening takes place towards the hinterland in the vicinity of Main Central Thrust and Inner Lesser Himalaya which is also in agreement with high seismic activity in these sectors. The GPS velocities of the sites (Indian reference frame) show significant variation from the sub-Himalaya to the Tethys Himalaya. The Sub and Inner Lesser Himalayan parts exhibit low deformation rate in contrast to the maximum amount of deformation in the Inner Lesser and Higher Himalayan segments. The strain analysis reveals lateral variation with high strain zones (HSZ) and moderate strain zones (MSZ) within the compressional regime in the Uttarakhand Himalaya. The strain rate of 0.45 and 0.25 micro-strain/year is observed in the HSZ and MSZ respectively. By comparing the strain rate with the seismicity pattern for the past five decades, we suggest that the earthquakes in the HSZ are related with ramp structure of the MHT, whereas, part of accumulated strain in the MSZ is being released in form of the present day seismic activity.