J Seismol (2010) 14:823–836 DOI 10.1007/s10950-010-9199-2 ORIGINAL ARTICLE Lithospheric structure of NW Iran from P and S receiver functions Fataneh Taghizadeh-Farahmand · Forough Sodoudi · Narges Afsari · Mohammad R. Ghassemi Received: 7 January 2010 / Accepted: 6 June 2010 / Published online: 25 June 2010 © Springer Science+Business Media B.V. 2010 Abstract We computed P and S receiver functions to investigate the lithospheric structure beneath the northwest Iran and compute the Vp/Vs ra- tio within the crust of this seismologically active area. Our results enabled us to map the lateral variations of the Moho as well as those of the lithosphere–asthenosphere boundary (LAB) be- neath this region. We selected data from teleseis- mic events (M b > 5.5, epicentral distance between Electronic supplementary material The online version of this article (doi:10.1007/s10950-010-9199-2) contains supplementary material, which is available to authorized users. F. Taghizadeh-Farahmand (B ) Department of Physics, Qom Branch, Islamic Azad University, Qom, Iran e-mail: f_farahmand@Qom-iau.ac.ir F. Sodoudi Helmholtz Center Potsdam, GFZ Research Center for Geosciences, Telegrafenberg 14473, Potsdam, Germany N. Afsari Department of Physics, Islamshahr Branch, Islamic Azad University, Tehran, Iran M. R. Ghassemi Research Institute for Earth Sciences, Geological Survey of Iran, Azadi Sq., Meraj Ave., P.O.Box: 13185-1494, Tehran, Iran 30 ◦ and 95 ◦ for P receiver functions and M b > 5.7, epicentral distance between 60 ◦ and 85 ◦ for S receiver functions) recorded from 1995 to 2008 at 8 three-component short-period stations of Tabriz Telemetry Seismic Network. Our results obtained from P receiver functions indicate clear conver- sions at the Moho boundary. The Moho depth was firstly estimated from the delay time of the Moho converted phase relative to the direct P wave. Then we used the H-Vp/Vs stacking algo- rithm of Zhu and Kanamori to estimate the crustal thickness and Vp/Vs ratio underneath the stations with clear Moho multiples. We found an average Moho depth of 48 km, which varies between 38.5 and 53 km. The Moho boundary showed a sig- nificant deepening towards east and north. This may reveal a crustal thickening towards northeast possibly due to the collision between the Central Iran and South Caspian plates. The obtained av- erage Vp/Vs ratio was estimated to be 1.76, which varies between 1.73 and 1.82. The crustal structure was also determined by modeling of P receiver functions. We obtained a three-layered model for the crust beneath this area. The thickness of the layers is estimated to be 6–11, 18–35, and 38– 53 km, respectively. The average of the shear wave velocity was calculated to be 3.4 km/s in the crust and reaches 4.3 km/s below the Moho dis- continuity. The crustal thickness values obtained from P receiver functions are in good agreement with those derived by S receiver functions. In