Neotectonics of western India: evidence from deformed Quaternary fluvial sequences, Mahi River, Gujarat

Abstract

A Quaternary fluvial sequence along the Mahi River, Gujarat, western India, shows evidence for a discrete episode of normal faulting and related surface slumping. Four mapped NW-striking faults have throws ranging from 1 m to over 3 m, and have related growth folds in synchronous sediment units. A slump sheet moved tens of metres northeastward down the 0.7° dip slope of one tilt block during displacement on its bounding fault. The exposed part of the internally folded sheet is probably one side of a lobate slump mass, several hundred metres in width. Fault activity began after deposition of a lower gravel, which regional correlations suggest is about 300 ka old. Faulting ended just before deposition of an upper gravel-sand complex dated by luminescence techniques in correlated sections at no younger than about 60 ka. The Mahi River section shows that neotectonic activity in Peninsular India, exemplified by the 1993 Killari (Latur) earthquake, has a mid- to late Pleistocene component.