Crustal Seismic Anisotropy Beneath the Zagros and Central Iran

Abstract

The study investigates the variation of shear wave anisotropy among the crustal structure of the Zagros and Central Iran. We used the waveforms of 327 tele-seismic earthquakes with magnitude greater than 5.0 (Mb) at epicentral distances between 30° and 90°, recorded by 22 broadband seismic stations in the study area. The radial and transverse components of the receiver functions in the frequency band from 0.05 to 0.5 Hz were calculated using the earthquakes recorded at each station. Considering t₀ as arrival time of the Ps-converted phase on radial receiver functions in the isotropic case, we estimate the effective arrival time for the overlapping phases of the split shear waves as a function of back azimuth. Then we determined the seismic anisotropy parameters of the shear waves (φ, δt). The results show that the average splitting time in the study area varies from 0.24 to 0.65 s, which is a good constraint on the seismic anisotropy compared to the range of crustal seismic anisotropy. Analysis of the fast direction of motion shows that φ changes parallel to the direction of the surface structures and agrees with measurements of the velocity vector GPS that the deformation is rooted in shallower, brittle structures of the crust and active fault zones throughout the environment.