Scattered wave imaging of the Main Himalayan Thrust and mid-crustal ramp beneath the Arunachal Himalaya and its relation to seismicity

Abstract

Despite numerous seismological experiments in the Himalaya, the Main Himalayan Thrust and the mid-crustal ramp, that is postulated to host major earthquakes in the region, are not precisely imaged. Within the Himalaya, the Arunachal region, which constitutes the eastern most segment, is hitherto less investigated. The current study presents receiver function images of the detachment, mid-crustal ramp and the Moho of the under thrusting Indian plate along four profiles traversing the region, including dense, new data from two of them. The images are constructed by time to depth ray geometry-based migration of ∼31,531 P receiver functions at 62 stations and ∼6187 S receiver functions at 55 stations performed using 3D P and S wave velocity models determined from local earthquake tomography. Results reveal a clear Moho signature in the depth range of 40 to 65 km, with the detachment mapped in the depth range of ∼10 to 20 km. A mid-crustal ramp can be traced in the higher Himalaya especially along one profile. Low seismicity is observed in the central Arunachal region, without any seismicity clustering beneath the higher Himalaya, associated with a ramp on the detachment. These images illuminate a greater detail of the crustal layering compared to those previously constructed using sparser data and simplistic models.