Stress distribution in the western India-Eurasia collision zone, its kinematics and seismotectonic implications

Abstract

In this study, we use iterative joint stress inversion technique on a declustered catalogue of 324 focal mechanisms to evaluate the stress distribution in the western India-Eurasia collision zone (IECZ). The stress field has been obtained for different tectonic settings, such as the Himalayan Seismic belt, Karakoram-Tibet region and the individual zones identified based on geology, tectonics and available focal mechanism solutions. The results reveal NE-SW trending principal stress (σ1) with compression for Himalayan seismic belt and strike-slip stress regime for Karakoram-Tibet. We observe that even within the Himalayan region, the western region (75°-77° E latitudes) exhibits arc-oblique compression (NE-SW) in contrast to the arc-normal compression (NNE-SSW) in central Himalaya beyond 77°E; consistent with GPS vectors. The Stress field for the aftershock sequence of 2005 Kashmir earthquake in the Hazara Syntaxis region displays dissimilarity with its adjoining regions (Pamir, Nanga Parbat, Hindukush, etc.), but exhibits similarity with the Central Himalaya. Within the Karakoram-Tibet region, the Karakoram fault exhibits NNE-SSW oriented principal stress with transpressional fault motion, while the Kaurik Chango rift shows N-S oriented principal stress with transtensional motion. The stress ratio in the western IECZ broadly varies between 0.07 and 0.9, suggesting the prominent role of the intermediate stress axis (σ2) in the areas of low-stress ratios. The inferences drawn suggest that the stress distribution in the western IECZ is heterogeneous with variable seismic hazard.