TOMOGRAPHIC STUDY OF NORTH WEST HIMALAYA USING BODY WAVES

Abstract

The aim of this project was to estimate the 1D velocity structure of the North West Himalaya and to determine accurate locations of earthquake hypocenters. Four 1D P wave velocity models from previous work of several researchers were used as initial models. The corresponding S wave velocities were estimated by using the constant Vp/Vs ratio of 1.71 obtained from the Wadati plots. P and S phase data from 971 events recorded at 23 stations was used for performing travel time inversion using VELEST program to obtain 1D velocity models and hypocentral locations. Out of the four models, the final 1D velocity model obtained from Malik (2009) was found to be the best model based on mean rms error and thus it was accepted as the 1D velocity model of the region. Low Vp and Vp/Vs ratio was found in the top 20 km of the crust. Also, majority of the earthquakes were found to originate in this region. This indicated the presence of quartz rich felsic rocks in the region. The earthquakes hypocenters were then relocated with double difference algorithm to further improve their locations. A large number of hypocenters could not be relocated using this method. However the locations of surviving hypocenters were improved significantly.