Moho Depth Variations and vp/vs Ratio in Northwest of Zagros (Kermanshah Region) using Teleseismic Receiver Functions
N. Afsari1*, F. Sodoudi2, M. R. Gheitanchi3 & A. Kaviani4
Received: 2008 April 19 Accepted: 2008 August 30
Characterization of the detailed structure of the crust and upper mantel is an important continuing goal of geophysical studies. Teleseismic body waveforms have been used to infer crust and upper mantel structure. In this study we use teleseismic receiver function method to determine the crustal thickness and VP/VS ratio under Kermanshah network in north-west of Zagros using teleseismic data (30°<∆<95°, mb≥5.5) which have been recorded at five short-period three component stations (2003-2007). The differential travel time between the incident P wave and P to S converted wave (delay time) is used for computation of crustal thickness. Moho depth is not sensitive to crustal P velocity but there is a trade off between Moho depth and Vp/Vs ratio. The ambiguity can be reduced by incorporating the later multiple converted phases, namely, PpPs and PpSs+ PsPs. We use the method of Zhu and Kanamori (2000). This method performs a grid search through the H and Vp/Vs space and searches for the largest summed amplitudes at the predicted times of direct conversions and multiples. By stacking receiver functions from different distances and directions, effects of lateral structural variation are suppressed and an average crustal thickness is obtained. Applying this method to five short period stations in Kermanshah reveals that the Moho depth is 42 km and varies between 36 and 51.5 km. The thinnest crust was found beneath DHR, whereas the deepest crust was observed beneath VIS. We observed that Moho depth increase from west to east (from DHR to VIS) then decrease to KOM. The average VP/VS ratio as estimated is about 1.76.
Key words: Moho, Teleseismic receiver function, Stacking, Zagros
Corresponding author: N. Afsari; Email: ng email@example.com*
1 Islamic Azad University (IAU), Science & Research Branch, Tehran, Iran.
2 Geo Forschungs Zentrum, Potsdam, Germany.
3 University of Tehran, Institute of Geophysics, Tehran, Iran.
4 Institute for Advanced Studies in Basic Science Zanjan, Geophysics Department, Zanjan, Iran.