6 August, 2009 (17:00 GMT), 5 Merrion Square, Dublin 2.

Speaker: Brigitte Endrun, University of Potsdam, Germany.
Title: Imaging lithospheric structure in the Aegean region with seismic surface waves and receiver functions.

Abstract:

The Aegean region, with the Hellenic Subduction Zone to the south and the North Anatolian Fault reaching through the Marmara Sea into its northern part, displays the highest earthquake activity in Europe and is also a showcase for other tectonic processes including lithospheric extension, subduction-related volcanism and insipient continental collision. This study deals with information on the current structure of the Aegean region, and implications for its evolution and dynamics, that can be derived from the analysis of teleseismic data. It is focussed on the information on S-wave properties, i.e. velocities, discontinuous changes in velocity, and anisotropy, in the crust and upper-most mantle, using two different methods to isolate this information from seismic recordings: teleseismic receiver functions and dispersion measurements of the Rayleigh wave fundamental mode. A study of Rayleigh wave dispersion covering the whole Aegean region, using measurements along 98 two-station raypaths, leads to one-dimensional models which are discussed in terms of Moho depth, velocity variations, lithospheric thickness and the depth level of the subducting African slab. Building on these measurements, an anisotropic Rayleigh wave tomography of the crust and the upper mantle was carried out. Isotropic anomalies in the phase velocity maps relate to crustal thickness and the low-velocity material at upper-mantle depth along the forearc. Anisotropic contributions reveal layered azimuthal anisotropy indicative of distributed deformation within the lithosphere. In the region of Crete, a combined interpretation of receiver functions and surface waves emphasises structural variations between 20 and 50 km depth. Migrated receiver functions, in agreement with seismicity data from a local network, image the subducting slab down to 180 km depth. The influence of rapid two-dimensional structural variations on receiver functions is investigated by modelling, indicating that pronounced lateral variations cannot be ignored when interpreting the data.