Variation in Moho topography and Poisson's ratio in the Eastern Himalayan arc

Abstract

The eastern Himalaya comprised of Sikkim, Bhutan, and Arunachal Himalaya possess unique seismicity, which experienced small to great earthquakes due to the Indo-Eurasia collision tectonics along the Himalayan arc. Knowing the structure and composition of the crust is a vital way to a better understanding of crustal deformation and seismicity in this region. In this study, we present the results of teleseismic receiver functions to investigate the crustal thickness and VP/VS(k) ratio beneath the eastern Himalaya region. A total of 585 receiver functions were analyzed using teleseismic events recorded from 23 broadband seismograph stations distributed in the Brahmaputra valley plain to higher-Himalaya. We observed a wide range of variations with respect to crustal thickness among the seismic stations, owing to geographical regimes. The crustal thicknesses of high-altitude stations are thicker, mostly reaching 55–59 km in Bhutan High-Himalaya, and 35–39 km in the foredeep Brahmaputra valley. The high velocity lower crust exhibited in the Sikkim Himalaya to the Bhutan Himalaya agrees with previous geophysical studies. The Moho depths and average Poisson ratio were determined at each station using H-k stacking technique reveal higher Poisson's ratio near the major thrust belt region, and low to medium near the foredeep valley region.