SEISMIC VELOCITY MODELING OF NORTH AND NORTHEAST IRAQ USING RECEIVER FUNCTIONS Hafidh A. A. Ghalib 1 , Matthew S. Sibol 1 , Youlin Chen 1 , Robert B. Herrmann 2 , Ghassan I. Aleqabi 3 , Hrvoje Tkalcic 1, 4 , Bakir S. Ali 5 , Borhan I. Saleh 5 , Dawood S. Mahmood 6, 7 , Robert A. Wagner 1 , Patrick J. Shore 3 , Omar K. Shaswar 9, 10 , Aras Mahmood 5 , Shaho Abdullah 5 , Fadhil Ibrahim 8 , Rashid Zand 8 , Basoz Ali 5 , Layla Omar 5 , Nokhsha I. Aziz 5 , Nian H. Ahmed 5 , Talal Al-Nasiri 10 , Ali A. Ali 7 , Abdul-Karem A. Taqi 7 , and Samira R. Khalaf 7 Harris Corporation 1 , Saint Louis University 2 , Washington University in Saint Louis 3 , Australian National University 4 , Sulaimaniyah Seismological Observatory 5 , Iraq Meteorological Organization 6 , Baghdad Seismological Observatory 7 , Erbil Seismological Observatory 8 , Sulaimaniyah University 9 , and University of Baghdad 10 Sponsored by Air Force Research Laboratories Contract No. FA8718-04-C-0016 ABSTRACT A primary objective of this project is to estimate the local and regional seismic velocity structures of north and northeastern Iraq, including the northern extension of the Zagros collision zone, using well-established seismological techniques. This is a region where global seismic network coverage is poor and where extrapolated velocity models found in the literature lack sufficient accuracy to permit events to be located with significant precision. Installed in late 2005, ten broadband three-component stations composing the North Iraq Seismographic Network (NISN) provided the unique data that made this phase of the study possible. The results of teleseismic P-wave receiver functions (RF) analysis and velocity structure estimation are presented herein. RF is a time series computed from three-component seismograms that show the relative response of earth structure near a receiver. To date, over 4500 waveforms from about 150 events recorded by NISN stations during the period 30 November 2005 to 31 August 2006 have been scrutinized. Based on the USGS Preliminary Determination of Epicenters (PDE) bulletins, the epicenteral distances of these teleseismic events to NISN stations range from 30º to 90º, and their magnitudes equal or exceed 5.5. Additional data recorded from September 2006 through March 2007 will also be examined. It is anticipated that this will nearly double the amount of data available for reliably estimating the velocity structure of the region. Preliminary results indicate that the depth of the Moho varies considerably beneath NISN. It is relatively shallow (35–45 km) to the northwest and deeper (50–60 km) under the southeastern portion of the network area. Although these initial results correspond well with the tectonic and physiographic framework of the Arabian plate, the values will be further revised and constrained when surface wave dispersion analysis is added to the process. 29th Monitoring Research Review: Ground-Based Nuclear Explosion Monitoring Technologies 54