An investigation on the crustal structure using coda wave attenuation and surface wave tomography in Western part of Iran

Abstract

We interpret coda wave attenuation and Rayleigh wave group velocity to investigate the processes controlling the crustal structure beneath the western part of Iranian plateau and to determine the relevance of the Sahand and Sabalan to shallow crustal hot spot-like structures. Given that seismic wave attenuation is more sensitive to the thermal structure than the velocity, it provides additional information on the seismic velocity and helps identify compositional and thermal structures.

A total of 370 events recorded at 24 broadband seismic stations were used to create Rayleigh wave tomographic maps for six periods: 5, 10, 15, 20, 25, and 30 s. Moreover, more than 9800 local events were investigated to estimate lateral variations of the coda wave attenuation using multiple-scattering method. After examining different lapse times from the origin time with a fixed window length of 20 s, the results showed that a lapse time of 70 s provides stable QC indices, which were independent of the distance to the epicenter. After estimating the velocity and attenuation within the area, it was figured out that the low-velocity (high-attenuation) region underlying the Sahand Mountain (detected with a 5-s period) is related to the magma chamber beneath the crust resulting from the Anatolian and Arabian plates' collision. A shallow low-velocity region in the eastern part of the study area (detected with a 5-s period and disappeared for longer periods) might be associated with the Quaternary near-surface magma accumulations and/or upper crustal warm-ups.