Imaging the crustal structure at the northeast corner of the indenting Indian Plate in the Eastern Himalayan Syntaxis

Abstract

SUMMARY Crustal configuration beneath the indenting northeast corner of the Indian Plate in the Eastern Himalayan Syntaxis has been investigated with the help of receiver function (RF) analysis of teleseismic earthquakes recorded by 19 broad-band seismological stations. The common conversion point stacking of RFs and 1-D velocity models obtained through inversion provide new information on the intracrustal structure. The study reveals the signature of the Main Himalayan Thrust (MHT) beneath the Lohit Valley at ∼22–26 km depth. The MHT is not prominent in the Siang window plausibly due to large-scale crustal deformation related to the formation of the window and antiform folding. Unlike in the western and central Himalaya, the MHT does not play a major role in seismogenesis in the Lohit Valley and Siang Window, where seismicity is active up to the crustal depth of ∼40 km. The crustal thickness increases from ∼38 km at Pasighat in the south to ∼50 km at the northernmost station (Gelling) in the Siang window. In Lohit Valley, the crustal thickness increases from ∼40 km at Mahadevpur in the west to ∼54 km in the Tidding–Tuting suture zone, which again shallows to ∼51 km in the eastern Lohit Plutonic Complex (Walong station). The thinner crust beneath the Tidding–Tuting suture compared to the Indus Tsangpo Suture Zone of northwest Himalaya is caused due to the differences in convergence rate, higher exhumation rate and mechanisms to accommodate collision and rotational tectonics.