Crustal deformation and thickness variation from Zagros to Alborz in Iran: New insights from H-κ-c method

Abstract

The collision between Arabia and Eurasia has had a significant impact on the Iranian plateau, making it a prime location for investigating crustal deformation. The Neotethys Ocean closure and subsequent collision during the Cenozoic era led to extensive deformation in the northern part of the Iranian plateau, in particular development of the Alborz mountain range. In this study, we aim to determine crustal thickness and azimuthal anisotropic parameters in order to gain insights into the patterns of crustal deformation in the region. Using the H-κ-c method (Li et al., 2019), we conducted an investigation into the impact of seismic anisotropy on the estimation of the crustal thickness (H) and Vp/Vs ratio (κ) at 26 seismic stations. Our analysis unveiled significant variations in Moho depth across the studied region. The collisional zones featured a deeper Moho depth when compared to Central Iran. In particular, the Central Iran region demonstrated a relatively thinner crust, characterized by an average Moho depth of 43 km, while the Sanandaj-Sirjan zone showcased a thicker crust, boasting a Moho depth of 59 km. The Alborz mountain ranges demonstrated an average Moho depth of 50 km. Notably, the Central Iran stations exhibited elevated κ values, potentially attributable to fluid contents and thick sedimentary cover. To characterize the anisotropic properties of the crust, we employed curve fitting techniques on the sinusoidal moveouts of the Ps-converted phases originating from the Moho and major intracrustal interfaces. Our analysis identified intracrustal discontinuities at seven stations, indicating the presence of two distinct anisotropic crustal layers. These anisotropic layers displayed maximum delay times of up to 0.6 s. Furthermore, our examination of crustal and mantle anisotropy patterns revealed that the deformation observed in the region cannot be solely attributed to a vertically coherent regime.