Pg Attenuation Tomography within the Northern Middle East

A seismic attenuation map of regional phase Pg is constructed for the northern Middle East using two-station frequency-dependent Q measurements and seismic attenuation tomography. Pg is widely used in source discrimination, but its attenuation behavior is not well understood. We investigate the functional form of the geometrical spreading of Pg for both uniform and more complex seismic velocity structures. We find that there is significant trade-off between attenuation and geometrical spreading of Pg, and we quantify this trade-off to interpret the observed Pg attenuation in the Middle East. The northern Middle East attenuation tomographic images show significant lateral Q(Pg) variations, which may be caused by lateral variations of crustal rheology if intrinsic attenuation dominates the seismic attenuation mechanism of this region. We observe very large variations in the Q(Pg) model, such as low Q(Pg) within the Anatolian plate and high Q(Pg) within much of the stable Arabian plate. The low Q(Pg) anomalies generally coincide with active fault systems or Quaternary volcanisms. In order to perform a systematic comparison with Lg propagation, we have also updated the Q(Lg) map of Zor et al. (2007). These two new maps provide estimates for crustal Q(alpha) (Pg) and Q(beta)(Lg) for the northern Middle East.