Crustal structure and fault geometries of the Garhwal Himalaya, India: Insight from new high-resolution gravity data modeling and PSO inversion

Abstract

A high-resolution gravity survey from the Indo-Gangetic plain to the MCT zone is carried out across the Garhwal Himalaya, India, which lies in the central seismic gap. The gravity measurements along a ∼205 km transect with dense station interval (<650 m) are modeled using the power spectrum, gravity isolation technique, wavelet analysis, PSO inversion, 2D-forward modeling, and constraints from previous results. The spectral analysis suggests two dominant layer interfaces in the lithosphere at 44 km and 12 km, inferred as the Moho and the Himalayan decollement thrust, respectively. The gravity isolation technique contributes to assessing the previously known geophysical and geological information and separating individual gravity responses despite the complexity of the tectonics of the Himalaya and further deriving the gravity effect of the upper crustal region, including main fault/thrust zones. The computed residual gravity anomaly shows prominent signatures of the main tectonics structures. Wavelet analysis and the Particle Swarm Optimization (PSO) inversion constrain the geometries of the intracrustal fault/thrust zones. Our model shows an increase in the Moho depth towards the north (from ∼40.4 km to 43.5 km). The derived MHT geometry clearly shows the ramp structure and associated Lesser Himalayan Duplex structures towards the north. The proposed detailed density structure discerns the geometries of different crustal structures across the Garhwal Himalaya and gives insight to the upper crustal fault zones.