Seismic Imaging of the Crust Beneath Arunachal Himalaya

摘要

We present the first high-resolution seismic images of the crust beneath the Arunachal Himalaya, using 22,525 high quality teleseismic receiver functions (RFs). Data from 32 broadband seismic stations deployed in the Arunachal Himalaya during 2010-2016 is used for this purpose. In addition, data from the HIMNT, SIKKIM, Hi-CLIMB, and Geodynamics ANd Seismic Structure of the Eastern-Himalaya Region networks are used to investigate along strike variations in the crustal architecture of the Eastern Himalayan mountain belt. Common Conversions Point stacks constructed using RFs from 203 seismic stations along various S-N profiles reveal lateral variations in the crustal structure. We observe, (a) a less complex crust beneath the Arunachal Himalaya compared to that in the Nepal and Sikkim Himalaya (b) a highly deformed layer running parallel to the Main Himalayan Thrust (c) intermittent anisotropic low velocity layer in the middle crust (d) that the crustal thickness estimates are in close agreement with those in other segments of the Eastern Himalaya (40-60 kms) (e) no prominent signatures of a mid-crustal ramp as observed in the Nepal Himalaya. The geometry of the crust in the Eastern Himalayan segments appears less complex compared to the Central Himalayan segments. The presence of strong anisotropy associated with the low velocity layer at depths of 20-30 km suggests a mechanically weak middle crust beneath Arunachal Himalaya. Attributing these anisotropic signatures to the channel flow model appears contentious.