Crustal thickness and Poisson's ratio variations in the northeast India-Asia collision zone: Insight into the Tuting-Tidding Suture zone, eastern Himalaya

摘要

Crustal thickness and Poisson's ratio were estimated at 11 broadband seismic stations established in a profile along the Lohit river valley of Arunachal Himalaya passing across the Tuting-Tidding Suture Zone (TTSZ). The average crustal thickness (H) and Poisson's ratio were estimated with the help of H-k stacking analysis of receiver functions at each station. The study reveals a thickening of crust from similar to 46 km beneath the Brahmaputra valley in the west to similar to 55 km in the western part of the Lohit Plutonic Complex (LPC). Marginal uplifts of Moho depths (similar to 50-52 km) are observed at some stations to the eastern part of the profile (LTL, HWI and SDL stations). The estimated Poisson's ratio in the Brahmaputra valley is low (0.23), suggesting the felsic composition of the crust. The Poisson's ratio is intermediate in the Mishmi Thrust zone (0.249-0.261) and in some parts of the LPC. High Poisson's ratio (0.277-0.293) is observed beneath the TTSZ and western part of the LPC, indicating the effect of aqueous fluid/partial melt present in the crust. The seismicity in the study area has been investigated based on data recorded by our network and data obtained from the reviewed catalogue of the International Seismological Center (ISC) bulletin. Seismicity is observed to be distributed mainly at a shallow depth range similar to 1-15 km. However, earthquakes of M > 4.0 are primarily concentrated at similar to 25-35 km depths. This bimodal distribution of seismicity has a significant role in understanding subsurface configuration beneath the profile.