Sediment thickness beneath the Indo-Gangetic Plain and Siwalik Himalaya inferred from receiver function modelling

Abstract

The Indo-Gangetic Plain and the adjoining Siwalik Himalaya are the seismically most vulnerable regions due to high density of human population and presence of thick sediments that amplify the seismic waves due to an earthquake in the region. We investigate the sedimentary structure and crustal thickness of the region through joint inversion of the receiver function time series at 14 broadband seismograph locations and the available Rayleigh velocity data for the region. Results show significant variability of sedimentary layer thicknesses from 1.0 to 2.0 km beneath the Delhi region to 2.0–5.0 km beneath the Indo-Gangetic Plain and the Siwalik Himalaya. As we progress from the Delhi to the Indo-Gangetic Plain, we observe a decrease in the shear velocity in sedimentary layer from ∼2.0 km/s to ∼1.3 km/s while the layer thickness increases progressively from ∼1.0 km in south to 2.0–5.0 km in the north. Average S-velocity in the sedimentary layer beneath the Siwalik Himalaya is ∼2.1 km/s. Crustal thicknesses varies from ∼42 in the Delhi region, ∼48 km in the Indo-Gangetic Plain, ∼50 km in the western part of Siwalik Himalaya to ∼60 km in the Kumaon region of Siwalik Himalaya.