A surface wave dispersion study of the Middle East and North Africa for monitoring the comprehensive nuclear-test-ban treaty

We present results from a large-scale study of surface-wave group velocity dispersion across the Middle East, North Africa, southern Eurasia and the M editerranean. Our database for the region is populated with seismic data fr om regional events recorded at permanent and portable broadband, three-comp onent digital stations. We have measured the group velocity using a multipl e narrow-band filter on deconvolved displacement data. Overall, we have exa mined more than 13,500 seismograms and made good quality dispersion measure ments for 6817 Rayleigh- and 3806 Love-wave paths. We use a conjugate gradi ent method to perform a group-velocity tomography, Our current results incl ude both Love- and Rayleigh-wave inversions across the region for periods f rom 10 to 60 seconds. Our findings indicate that short-period structure is sensitive to slow velocities associated with large sedimentary features suc h as the Mediterranean Sea and Persian Gulf. We find our long-period Raylei gh-wave inversion is sensitive to crustal thickness, such as fast velocitie s under the oceans and slow along the relatively thick Zagros Mts. and Turk ish-Iranian Plateau. We also find slow upper mantle velocities along known rift systems. Accurate group velocity maps can be used to construct phase-m atched filters along any given path. The filters can improve weak surface w ave signals by compressing the dispersed signal. The signals can then be us ed to calculate regionally determined M-S measurements, which we hope can b e used to extend the threshold of m(b):M-S discriminants down to lower magn itude levels. Other applications include using the group velocities in the creation of a suitable background model for forming station calibration map s, and using the group velocities to model the velocity structure of the cr ust and upper mantle.