Seismic Velocities and Crustal Structure Beneath the Shillong Plateau, Mikir Hills and Naga Thrust Zone in Northeastern India

A study of travel times for the P_g, P^* and P_n waves is conducted selecting three traverses over the Shillong Plateau, Mikir Hills and Naga Thrust zone respectively in the Northeast India region. Seismic velocities and thickness of the upper crust, lower crust and depth to the Moho are estimated. These traverses are selected through the location of the maximum number of seismic stations and the epicentres of the earthquakes in the study area. About 136 earthquakes, with magnitude range 2.0-5.0 and depth range 5-30 km, recorded during the period 1986-1999 are used. The P_g, P^* and P_n velocities (km/sec) are estimated to be 6.04-6.21,6.51-6.62 and 8.47-8.65 respectively in the region. The corresponding thickness (km) of the upper crust, lower crust and depth of the Moho are 16-19, 27-30 and 40-50, respectively. The presence of high P_n wave velocity (8.47-8.65 km/sec) in the region is possibly representing a colder and denser lithosphere.