The potential of satellite gravity and gravity gradiometry in deciphering structural setting of the Himalayan Collision Zone

Abstract

During the last decade, three dedicated satellite gravity missions (CHAMP, GRACE and GOCE) have greatly improved the knowledge of the static and dynamic gravity field of the Earth. Bouguer gravity anomalies (BGA) derived from global gravity models (e.g. EGM2008), which consist of GRACE satellite observations and terrestrial gravity data, are analysed to demonstrate through selected applications, their potential use in studying large scale geological features of the Himalaya, where little or no terrestrial data are available. A constrained 3D lithospheric density model over a part of the Eastern Himalayan region is constructed from modelling of BGA and utilized to calculate forward responses of selected gravity gradient (GG) tensors, highlighting certain aspects of the structural features of the Himalayan Collision Zone (HCZ). In addition, GG are also computed directly from BGA by Fourier transformation to study the additional information content they may provide. This exercise may demonstrate the extra advantages of modelling gravity gradiometry measurements, which is of high contemporary relevance in view of the fact that satellite gravity gradient data from the ongoing GOCE mission will be available shortly. We find that structural features like Main Boundary Thrust, Main Central Thrust are sharply reflected in GG and combined interpretation of BGA and GG can better resolve the locations and possibly the depth extent of the density anomalies. BGA is also utilized to constrain crustal thickness variation and used along with topography to estimate variation of effective elastic thickness across the Eastern Himalayan region.