Abstract

Passive Seismic Tomography (PST) is increasingly recognized as a powerful technique for subsurface imaging in hydrocarbon exploration, particularly in tectonically active and geologically complex regions. Unlike active seismic methods that rely on artificial sources, PST utilizes naturally occurring seismic waves— primarily from local and regional earthquakes— to construct velocity models of the subsurface. This method is especially advantageous in areas where conventional seismic surveys are limited by terrain, environmental restrictions, or logistical challenges. In the context of the West Tripura region, part of the tectonically active Indo-Burmese Arc, a dense temporary seismological network was established to record microseismic events across a wide frequency range. The primary objective was to derive high-resolution 3D velocity models of Pwave (Vp), S-wave (Vs), and the Vp/Vs ratio, which are critical parameters for understanding lithological variations, fluid content, and crustal structure. Arrival times of P- and S-waves from numerous local seismic events were used in tomographic inversion to generate these models. The results of the PST study enabled accurate earthquake location, focal mechanism solutions, and detailed imaging of subsurface velocity variations. Importantly, the inversion revealed two major décollement zones associated with thrust faulting and crustal shortening, characteristic of collisional foreland systems. Additionally, the tomographic models delineated significant stratigraphic boundaries, including the unconformity between Neogene and Paleogene sedimentary sequences, and the interface between Paleogene sediments and the underlying crystalline basement. These structural insights contribute to improved understanding of trap configuration, stress regime, and potential hydrocarbon migration pathways in the region.