Stress Distribution in the Western India-Eurasia Collision Zone: its
Kinematics and Seismotectonic implications.
Abstract
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.