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Ð The group-velocity distribution beneath the Arabian Plate is investigated using Love and Rayleigh waves. We obtained a balanced path coverage using seismograms generated by earthquakes located along the plate boundaries. We measured Love-and Rayleigh-wave group-velocity dispersion using multiple ®lter analysis and then performed a tomographic inversion using these observations to estimate lateral group velocity variations in the period range of 5±60 s. The Love-and Rayleigh-wave results are consistent and show that the average group velocity across Arabia increases with increasing period. The tomographic results also delineate ®rst-order regional structure heterogeneity as well as the sharp transition between the Arabian shield and the Arabian platform. Systematic dierences are observed in the distribution of the short-period group velocities across the two provinces, which are consistent with surface geology. The slower velocities in the platform reveal the imprint of its thick sedimentary section, while faster velocities correlate well with the exposed volcanic¯ows in the shield. Shear-wave velocity models for the two regions, obtained from the inversion of the group velocities, con®rm results from previous studies of higher S-wave velocity in the upper crust beneath the shield. This may be due to the present remnants of the oceanic crust (ophiolite belts) associated with the island arcs evolutionary model of the Arabian shield.The mapping of the surface-wave group velocity using a large data can be used in constraining the regional structure at existing and planned broadband stations deployed in this tectonically complex region as part of the seismic monitoring under CTBT.

Average frequency-independent Q values have been determined for the upper crust in a 105 × 105 km region centered around the active portion of the New Madrid seismic zone using the spectral decay of P waves from local earthquakes. Q values generally increase with increasing path length, both inside and outside the active region, a result which suggests that Q increases with depth in the upper crust. Q values for paths which are largely confined to the active region are reduced by 1/2 to 1/3 compared to those values for paths outside the active region. The low Q values correlate spatially with regions of low seismic velocity found previously for the New Madrid region (Al-Shukri and Mitchell, 1988), and can be explained by a greater density of fluid-filled cracks in the seismically active region than in the surrounding regions.

Iraq has a rather long well-documented history of seismic activity, where 79 events of major and/or minor effect on the community are documented for the period 1260 B.C. through 1900 A.D. Fourteen of these events are listed and described for the first time from an Arabic manuscript. The historical seismicity follows a well-defined pattern and fits with the boundaries of the major tectonic units of Iraq, as well as with the recent seismicity of the country.

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