Upper mantle seismic anisotropy in the eastern Mediterranean and seismicity in Cyprus

Abstract

This thesis concerns the tectonics and geodynamics of the eastern Mediterranean, a zone of terminal-stage ocean basin closure between Eurasia and Africa, through two seismological investigations. First, large-scale mantle deformation related to the tectonics of Anatolia and complex subduction dynamics is investigated. Some have suggested the westward tectonic motion of Anatolia is linked to a similar deep flow in the asthenospheric mantle; however, several smaller-scale geodynamic processes may instead dominate the asthenospheric flow field, including slab break-off, slab tearing, and lithospheric delamination. I investigate the relative importance of these processes through measuring upper mantle seismic anisotropy via SKS shear-wave splitting analysis. Spatial variations in direction and strength of anisotropy attest to the influence of the complex slab architecture and multiple geodynamic processes on mantle flow. Additionally, lithospheric anisotropy in a mantle shear zone beneath the North Anatolian Fault is revealed for the first time. Subsequently, I study seismicity in Cyprus associated with proposed incipient continental collision and the uplift of the Troodos ophiolite. I combine manual and automated techniques to identify and pick P- and S-phase arrivals for local earthquakes during a 2-year period and present a method to remove quarry blasts from the catalogue. I constrain 1-D seismic velocity models for earthquake location and present a new local magnitude scale. I interpret the earthquake locations with new and existing focal mechanisms in terms of the tectonic setting. There is evidence for active subduction of the Eratosthenes seamount beneath Cyprus, with earthquakes associated with the dehydration of the downgoing plate and with intra- slab deformation. A lack of seismicity in a 20 km-wide zone at the peak of the seamount is likely associated with fluid focusing that causes high-degree serpentinisation of the overlying Troodos mantle, providing the first seismological evidence of a deep root to the Mt. Olympus serpentinite diapir.