Seismic velocity and Q structure of the middle eastern crust and upper mantle from surface-wave dispersion and attenuation

Observed velocities and attenuation of fundamental-mode Rayleigh waves in t he period range 7-82 sec were inverted for shear-wave velocity and shear-wa ve Q structure in the Middle East using a two-station method. Additional in formation on Q structure variation within each region was obtained by study ing amplitude spectra of fundamental-mode and higher-made Rayleigh waves. W e obtained models for the Turkish and Iranian Plateaus (Region 1), areas su rrounding and including the Black and Caspian Seas (Region 2), and the Arab ian Peninsula (Region 3). The effect of continent-ocean boundaries and mixe d paths in Region 2 may lead to unrealistic features in the models obtained there. At lower crustal and upper-mantle depths, shear velocities are simi lar in all three regions. Shear velocities vary significantly in the upperm ost 10 km of the crust, being 3.21, 2.85, and 3.39 km/s for Regions 1, 2, a nd 3, respectively. Q models obtained from an inversion of interstation att enuation data show that crustal shear-wave e is highest in Region 3 and low est in Region 1. e's for the upper 10 km of the crust are 63, 71, and 201 f or Regions 1, 2, and 3, respectively. Crustal e's at 30 km depth for the th ree regions are about 51, 71, and 134. The lower crustal Q values contrast sharply with results from stable continental regions where shear-wave e may reach one thousand or more. These low values may indicate that fluids resi de in faults, cracks, and permeable rock at lower crustal, as well as upper crustal depths due to convergence and intense deformation at all depths in the Middle Eastern crust.