Crustal velocity structure has a very important role in precise locating of seismic events. In this study attempt has been made to investigate the velocity structure of the crust and the upper mantle in the Ghir-Karzin region of the central Zagros using local earthquakes recorded by a temporary network of 30 seismological stations operated for two months. The geometry of the Moho discontinuity is planned to be investigated using all readings of Pn phases and applying relative time-distance method. Therefore, first using arrival times of refracted Pg from different layer interfaces, a P-wave velocity of 5.9 and 6.45 km/s was obtained for second and third layer respectively.
Relative time-distance curves of Pn arrival time for 3 regional earthquakes located enough away from our network reveal an apparent velocity of 8.0 km/s for the upper mantle beneath the seismic network. Using same method, we demonstrated that the crustal thickness increases toward NE. A dip of (2 ± 1) degree was estimated for the Moho beneath our seismological network.