Surface-wave phase-velocity maps of the Anatolia region (Turkey) from ambient noise tomography

摘要

The Anatolian region is an area with very heterogeneous crustal structure accompanied by large velocity contrasts. Despite the complexity of the region, the detailed crustal structure remains to be unraveled. In this study, we first measure the dispersion curves of Rayleigh waves between 1,721 pairs of station and then invert these dispersion curves to obtain high-resolution isotropic and azimuthally anisotropic phase-velocity maps in the period range of 5-25 s. The resulting isotropic phase-velocity patterns display strong correlation with the geological features, while the anisotropic patterns are highly consistent with the GPS-measured surface velocity field in the region. Variations of the isotropic as well as anisotropic patterns indicate the presence of active faulting, especially beneath the East and North Anatolian Faults. Beneath the locations of Holocene volcanoes and crystalline massifs in Cappadocia, high velocities (up to 2.5%) are present, whereas negative velocity anomalies (up to -2%) are found beneath the Menderes Massif in southwestern Anatolia (at periods of 5-20 s), suggesting different origins and tectonic regimes of those massifs. On either side of an active fault, two terranes with different stress patterns are generally found. Active fault can thus be identified by different anisotropy patterns on either sides of the fault. The Central Anatolian Fault do not display strong isotropic velocity contrasts, as well as no noticeable variation in the anisotropic pattern across the fault, suggesting that this fault may not be active in recent times.