A new 1-D velocity structure model is proposed for Microseismic Monitoring system (MSMS) of WAPDA Tarbela Dam Project in Northern Areas of Pakistan. It is expected to serve for routine high accuracy earthquake hypocenter location and to work as a reference model for the tomographic studies. We perform a series of simultaneous inversion of P and S waves’ velocity structure and hypocenter location using VELEST and the arrival time data obtained in site during the period from March 2010 to March 2012.
The new velocity model has the additional boundaries at 23 km and 110 km and higher velocities in the lower crust in comparison with the currently used velocity model and shows a better consistency with the existing studies, although the analysis of hypocenter relocation using these models show that they are equivalent in terms of the residual: its RMS and the distribution throughout the available epicentral range from 0 km to 450 km.
The lack of the shallow events determined within 20 km from any station causes the possibility of a hidden surface layer of low velocity that can be a subject for future study. The new model is expected to improve the accuracy of the routine hypocenter determination and to make it possible to perform 3-D seismic tomography for the Northern Areas of Pakistan in the future.