Two-Dimensional Attenuation and Velocity Tomography of Iran

Abstract

Seismic bulletin data collected by the Iranian Seismological Center are used to image crust and mantle seismic attenuation, group velocity, and phase velocities for Lg, Pg, Sn, and Pn phases. This is possible because the peak amplitude time is picked, and amplitude measurements can be associated with the phase based on travel time plots. The group velocity is the apparent velocity of the maximum amplitude arrival and represents the combined effect of phase velocity and seismic scattering. Thus, it can be used in combination with the attenuation to identify where scattering attenuation is dominant. The Arabian–Iranian plate boundary separates low-velocity Zagros sediments from central Iran; however, in the mantle, it separates a high-velocity Arabian shield from central Iran. Scattering attenuation is low within the Arabian mantle and crust, and the Zagros sediments do not cause Lg or Pg attenuation. The Eocene Urumieh Dokhtar Magmatic Arc has high attenuation within both the crust and mantle, and while there is no partial melting in the crust, there may be some in the mantle. The northern Eocene Sistan Suture Zone shows particularly high attenuation that is accompanied by high scattering. It represents an incompletely closed ocean basin that has undergone intense alteration. The Alborz Mountains have high attenuation with some scattering.