Crust and upper mantle S wave velocity structure in eastern Turkey based on ambient noise tomography

Abstract

Eastern Turkey is an ideal location to study continental collision, which is manifested here by the presence of extensive volcanism and rapid tectonic uplift. To better understand the relationship between these surface phenomena and underground structures, we collect continuous waveform data from 121 seismic stations in the region to investigate the S wave velocity structure of the crust and upper mantle using ambient noise tomography. We obtain Rayleigh wave dispersion curves for periods between 5 and 100 s based on frequency-Bessel (F-J) transform dispersion analysis. We then perform quasi-Newton inversion to calculate the S wave velocity structure between 0 and 200 km. The results indicate the presence of two high-velocity anomalies: one in the southern Black Sea that may represent stable and cold lithospheric mantle and another near Lake Van that may represent the subduction remnant of the southern branch of the Neo-Tethys Ocean. In addition, the results demonstrate that the overall velocity in the study area is lower than the global average and reveal extensive upper mantle low-velocity zones (UMLVZs) which represent asthenospheric materials, and mid-crustal low-velocity zones (MCLVZs). In this study, we propose two possible formation mechanisms of the MCLVZs: one is partial melting, and the other is the formation of low-velocity compositional layering due to complex refining and differentiation processes and subsequent continent reworking. Considering that the spatial distribution of the MCLVZs and UMLVZs is well correlated with regional volcanic activity, the MCLVZs and UMLVZs may provide the driving force and are the material sources for volcanism in the area. Furthermore, the extremely thin and weak lithospheric mantle lid and the exceedingly shallow lithosphere asthenosphere boundary (LAB) indicate that the lower part of the lithosphere has delaminated and that the asthenosphere intrudes into a very shallow location, which then supports regional tectonic uplift.