R. Arun Prasath

and 2 more

To evaluate stress distribution of the western India-Eurasia collision zone (IECZ), an iterative joint stress inversion technique has been applied to a declustered catalogue of 324 focal mechanisms for the first time. The results are then used to understand fault kinematics, seismogenesis and seismotectonics of the region. The inversion results reveal an NNE-SSW trending principal stress (σ1) with compression for the Himalayan seismic belt and an NNE-SSW trending σ1 with strike-slip stress regime for the Karakoram-Tibet, consistent with plate motion of the Indian plate. Within the Himalaya region, the western Himalaya (75°-77°; E) exhibits arc-oblique compression (NE-SW) in contrast to arc-normal compression (NNE-SSW) in central Himalaya beyond 77°E; consistent with GPS vectors. Stress field for the aftershock sequence of the 2005 Kashmir earthquake in the Hazara Syntaxis region show dissimilarity with its surrounding regions (Pamir, Nanga Parbat, Hindukush, etc.), however, exhibits similarity with that of the Central Himalaya; therefore, we suggest this earthquake be Himalayan-type. Within the Karakoram-Tibet region, the Karakoram fault exhibits transpression oriented towards NNE-SSW, while the transverse structure i.e., the Kaurik Chango rift (KCR) located south of the Karakoram Fault shows transtensional motion with N-S oriented principal stress. The stress ratio in the western IECZ largely varies between 0.07 and 0.9, thus supports the significant role of the intermediate stress axis (σ2) in the areas of low-stress ratios. Besides, the low-stress ratios for Hazara Syntaxis, Karakoram-Tibet and KCR reveal the role of local structural variability and multiple tectonic forces suggesting heterogeneous stress field in the western IECZ.

R. Arun Prasath

and 2 more

The western India-Eurasia collision zone (IECZ) has experienced devastating earthquakes in the past century and continues to be seismically active. However, the Stress regime and Seismotectonics of the region remains poorly understood. In view of this, we carried out iterative, joint stress inversions of 245 well-constrained earthquake focal mechanisms to constrain the stress regime and its spatial variability in the region and dwell upon their implications for earthquake generation. Salient new findings from the study are, (i) the Kangra-Chamba-Kishtwar region shows arc-oblique horizontal maximum compressive stress (sigma 1, WSW-ENE) in contrast to arc-normal (NNE-SSW) in other regions of the Himalaya, (ii) the Kashmir earthquake sequence (in 2005) and its epicentral region i.e. the Hazara Syntaxis show similar stress patterns with that of the Central Himalaya, (iii) Nanga Parbat Syntaxis experiences pure extension, and (iv) Kaurik Chango Rift, with N-S trending sigma 1, probably extends deep into the Karakoram fault. Based on these findings, we categorize the region into six state of stress fields consistent with geology and plate motion models. The magnitudes for these stress fields show a decreasing trend from 0.90 in the southeast (Garhwal-Kumaun-Shimla) to 0.46 in the northwest (Hazara Syntaxis) and 0.39 in the northeast (Karakoram) suggesting multiple tectonic forces in northwestern and northeastern regions. The study reveals heterogeneity in the stress field within the western IECZ, induced by tectonic forces and structural variability.