Station site characteristics of WWSSN stations in India and southern Asia

Abstract

The continental boundary between the Eurasian and Indian plates is of great geophvsical significance because it is one of the rare instances of presently active continent-continent collision. The region has been instrumented with a relatively large number of WWSSN stations. The crustal structure beneath these stations has been studied by examining their crustal transfer characteristics for incident teleseismic P waves. At those stations well removed from the collision boundary (POO, KOD, NDI, SHI, and MSH), the crustal structure appears to be relatively flat-lying so that long-period body waves are regularly polarized. For these cases, P - to S -converted phases from the Moho have been identified in the records and modeled with synthetic seismograms to measure crustal thickness. The depth to the Moho beneath these stations falls within the usual continental range but shows no systematic variation between the Indian and Eurasian plates. Those stations which lie on or near the collision boundary (QUE, KBL, and NIL) show evidence of strongly dipping structure. Teleseismic P waves recorded there generally contain prominent tangential arrivals. The tangential phases are strong for waves approaching from all azimuths indicating that they are due to complex three-dimensional structures rather than planar layers with a single direction of dip.