Low-angle subduction of the Indian plate and megathrust geometry below the Eastern Himalayas.

The Eastern Himalayas region represents active intercontinental convergence and tectonic strike-slip extrusion. It frequently produces large earthquakes that devastate population centres for millions of people. However, there is no accepted explanation for how the widespread strike-slip motion and plate convergence deformation cause the frequent earthquakes. Here, we use new data from our recently deployed broadband seismic array in the Eastern Himalayas region to determine the regional stress field and detailed structural information about the converging plates. The stress field obtained from the earthquake focal mechanisms shows dominant north-south horizontal compression. Across the Eastern Himalayas region from south to north, the identified Indian crust exhibits low-angle subduction of the crust-mantle boundary Moho and flat-ramp geometry of the plate interface termed as the Main Himalayan Thrust. We suggest that the generation of megathrust earthquakes and the uplift of the broad mountains beneath the Eastern Himalayas region can be explained by the dominant north-south compression and a gentle underthrusting of the Indian plate.