Building and Testing an a priori Geophysical Model for Western Eurasia and North Africa MICHAEL E. PASYANOS 1 ,WILLIAM R. WALTER 1 ,MEGAN P. FLANAGAN 1 , PETER GOLDSTEIN 1 and JOYDEEP BHATTACHARYYA 1,2 Abstract — We construct and evaluate a new three-dimensional model of crust and upper mantle structure in Western Eurasia and North Africa (WENA) extending to 700 km depth and having 1° parameterization. The model is compiled in an a priori fashion entirely from existing geophysical literature, specifically, combining two regionalized crustal models with a high-resolution global sediment model and a global upper mantle model. The resulting WENA1.0 model consists of 24 layers: water, three sediment layers, upper, middle, and lower crust, uppermost mantle, and 16 additional upper mantle layers. Each of the layers is specified by its depth, compressional and shear velocity, density, and attenuation (quality factors, Q P and Q S ). The model is tested by comparing the model predictions with geophysical observations including: crustal thickness, surface wave group and phase velocities, upper mantle P n velocities, receiver functions, P-wave travel times, waveform characteristics, regional 1-D velocities, and Bouguer gravity. We find generally good agreement between WENA1.0 model predictions and empirical observations for a wide variety of independent data sets. We believe this model is representative of our current knowledge of crust and upper mantle structure in the WENA region and can successfully be used to model the propagation characteristics of regional seismic waveform data. The WENA1.0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified. Eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the Eurasian continent. Key words: 3-D velocity model, crust, upper mantle, Middle East, North Africa, Eurasia. 1. Introduction Accurate modeling of regional seismic data requires thorough knowledge of the three-dimensional velocity heterogeneity of Earth structure at relatively high resolution. Systematic biases caused by inadequately modeled structure are known to cause errors in estimating many geophysical parameters including the arrival time and amplitude of a variety of regional seismic phases. Current 1-D global models are clearly not adequate for modeling regional data, but 3-D global models are of limited 1 Geophysics and Global Security Division, Lawrence Livermore National Laboratory, P.O. Box 808, L-205, Livermore, CA 94551. E-mail: pasyanos1@llnl.gov 2 Now at Science Applications International Corporation, Arlington, VA, U.S.A. Pure appl. geophys. 161 (2004) 235–281 0033 – 4553/04/020235 – 47 DOI 10.1007/s00024-003-2438-5 Ó Birkha ¨ user Verlag, Basel, 2004 Pure and Applied Geophysics