Geomorphic and paleoseismological evidence of active Kachchh Mainland Fault, Kachchh, India

Abstract

The present work pertains to the stratigraphic evidences found during paleoseismic investigations on the trench walls opened across the Kachchh Mainland Fault (KMF). High-resolution satellite (CARTOSAT-1 DEM) data is used for mapping fault traces and carried out paleoseismic studies to identify paleo-earthquakes. We undertook geomorphological and paleoseismological investigations along the central segment of the KMF zone with the aim of estimating long-term slip rate and recurrence interval of strong earthquakes. Two N-S trenches were excavated across the E-W striking branches of the KMF, named as KMF-1 and KMF-2, revealing that the KMF is dipping towards the north. Detailed studies of the trench walls and optical dating of event horizons have confirmed four earthquakes occurred in the KMF zone between 5600 and 1000 years. The earthquake event I occurred between 5000 and 5500 years; event II occurred between 4000 and 4600 years. The event III occurred between 2000 and 2900 years, and the event IV occurred between 1023 and 1259 AD and 02 BC to 427 AD. Our studies further indicate that the central KMF zone is probably undergoing a quiescent period of ~ 1000 years accumulating the stress in the system to generate a large earthquake. The uplifted and truncated fluvial strath terrace deposits resulting from the Holocene displacements are preserved along the hanging wall block of the KMF. Dividing the elevation of the bedrock strath by their ages yields estimates of the vertical uplift rate of 0.37 to 1.48 mm/year of the hanging wall block of central KMF. With the help of displaced sedimentary units and optical ages, we estimated an average slip rate of 0.28 mm/year and uplift rate of 0.13 mm/year along KMF-1 over an interval of 1800–4000 years. However, the estimated slip rate along KMF-2 is 0.30 mm/year and the observed uplift rate is 0.17 mm/year. The results obtained from the trench investigations along the KMF not only help in understanding the dynamics of KMF but also aid seismic hazard evaluation in the Western Peninsular India.