Basement configuration of on-land Kutch basin from seismic refraction studies and modeling of first arrival travel time skips

Abstract

The Kutch basin is one of the three (Narmada, Cambay and Kutch) major marginal rift basins that are close to each other in mid-western part of the Indian subcontinent. The seismic refraction and wide-angle reflection data were acquired and a first order velocity structure of the Kutch sedimentary basin along Jakhau–Mandvi, Mandvi–Mundra, Mundra–Adesar and Hamirpur–Halvad profiles is derived. The travel time skip phenomenon has been noticed in the travel time plots and record sections indicating presence of low velocity sediments. Derived two-dimensional velocity–depth models revealed a Mesozoic sedimentary sequence sandwiched between Trap and Limestone layers, in some of the profiles. Two thick low velocity layers (that corresponds early to late Mesozoic era) have been identified. These are dipping towards Mandvi along Jakhau–Mandvi profile. The early Mesozoic layer that is thinning towards southeast is completely missing in Mandvi–Mundra profile. It is also noticed that the early Mesozoic Bhuj formation exists in the northern parts of the Mundra–Adesar and Hamirpur–Halvad profiles, where it directly overlies the granitic basement. The derived velocity–depth model suggests that the basement is about 3 km deep near Jakhau and reaches a depth of about 6 km near Mandvi. The layered structure may correspond to the Tertiary, Trap, Late Mesozoic sediments and Mesozoic limestone. The velocity–depth model obtained in Kutch is very similar to earlier derived model for Jamnagar and Dwarka sub-basins of northwestern Saurashtra peninsula suggesting probable continuity/linkage between southern on-land Kutch and, across the Gulf of Kutch to Saurashtra peninunsula. We also conclude that the evolution of Kutch basin, as a peri-cratonic rift basin, is essentially controlled by the four (F1–F4) faults inferred from obvious abrupt changes in layer thickness/velocity along the seismic refraction profiles.