Seismic evidence of crustal low velocity beneath Eastern Ghat Mobile Belt, India

Abstract

The Eastern Ghat Mobile Belt (EGMB), a tectonically active area extends along the eastern margin of Peninsular India, is divided into three provinces, namely, Eastern Ghat Province, the Jeypore Province, and the Krishna Province. The Ongole domain of Krishna Province is a seismically active region that has experienced four moderate earthquakes of magnitude ⩾5.0, of which largest one is of magnitude 5.4 occurred on 27th March 1967. The crustal shear wave velocity structure in the Eastern Ghat Mobile Belt has been investigated using joint inversion of receiver functions and Rayleigh wave group velocity at 5 locations in the study region. The results show crustal thickness variation from 37 to 42km and average shear velocity variation from 3.67 to 3.78km/s in the study region. A low velocity layer of variable thickness and velocities 3.54–3.7km/s) is also observed in the region. The low velocity layer in most of the stations is observed at a depth of ∼20km. This low velocity layer may be due to the presence of fluid in the crust, which also be one of the causes of the intraplate earthquakes in the study region.