Crustal structure of the Gujarat region, India: New constraints from the analysis of teleseismic receiver functions

In this study, receiver function analysis is carried out at 32 broadband stations spread all over the Gujarat region, located in the western part of India to image the sedimentary structure and investigate the crustal composition for the entire region. The powerful Genetic Algorithm technique is applied to the receiver functions to derive S-velocity structure beneath each site. A detail image in terms of basement depths and Moho thickness for the entire Gujarat region is obtained for the first time. Gujarat comprises of three distinct regions: Kachchh, Saurashtra and Mainland. In Kachchh region, depth of the basement varies from around 1.5 km in the eastern part to 6 km in the western part and around 2-3 km in the northern part to 4-5 km in the southern part. In the Saurashtra region, there is not much variation in the depth of the basement and is between 3 km and 4 km. In Gujarat mainland part, the basement depth is 5-8 km in the Cambay basin and western edge of Narmada basin. In other parts of the mainland, it is 3-4 km. The depth of Moho beneath each site is obtained using stacking algorithm approach. The Moho is at shallower depth (26-30 km) in the western part of Kachchh region. In the eastern part and epicentral zone of the 2001 Bhuj earthquake, large variation in the Moho depths is noticed (36-46 km). In the Saurashtra region, the crust is more thick in the northern part. It varies from 36-38 km in the southern part to 42-44 km in the northern part. In the mainland region, the crust is more thick (40-44 km) in the northern and southern part and is shallow in Cambay and Narmada basins (32-36 km). The large variations of Poisson's ratio across Gujarat region may be interpreted as heterogeneity in crustal composition. High values of σ (∼0.30) at many sites in Kachchh and few sites in Saurashtra and Mainland regions may be related to the existence of high-velocity lower crust with a mafic/ultramafic composition and, locally, to the presence of partial melt. The existing tectono-sedimentary models proposed by various researchers were also examined.