MODELING THE SEISMIC RESPONSE OF THE CRUST, WESTERN CYCLADES, GREECE

The Cycladic islands of the Aegean Sea, Greece, are a key location to study deep crustal processes since this region experiences the highest levels of seismicity in Europe and Miocene tectonism has exhumed HP rocks through a network of brittle-ductile shear zones. In an attempt to extend our understanding of the origin of seismic anisotropy – the variation of seismic wave speeds with direction of propagation – we model the seismic response of the crust using textural data of deformed rocks. Rocks from three islands (Kea, Kythnos and Sifnos) of the West Cycladic Detachment System (WCDS) were sampled to reflect an idealized vertical profile of the detachment zone. Determining their elastic properties and contribution to seismic anisotropy is crucial to map deformation from seismic velocity profiles. The rocks are part of an exhumed blueschist wedge, including marbles, (calcitic) schists and blueschist-eclogite assemblages. Selected minerals (glaucophane, calcite, quartz and especially micas) were analyzed via SEM-EBSD techniques to measure their crystallographic orientations, and modelled with MTEX to calculate the seismic properties of minerals and polymineralic aggregates. The muscovite in most samples has its (001) plane parallel to foliation and its (010) plane parallel to lineation, and the maximum compressional wave velocity (V_p) has a direction of [100] in the plane of foliation. The most anisotropic rocks are mica schists from the footwall of the detachment (compressional wave anisotropy, AV_p = 45%) and blueschists from the lower footwall (AV_p = 12-26%). Compressional and shear wave velocities have been calculated: V_p ranges from 4.96 km/s (schist) to 8.42 km/s (blueschist). Fast shear wave velocity (V_s1) ranges from 2.87 km/s (schist) to 4.6 km/s (schist and blueschist) and slow shear wave velocity (V_s2) ranges from 2.86 km/s (schist) to 4.42 km/s (blueschist). Calcitic schists and impure quartzites have velocities within these ranges. Simulations of seismic wave propagation through a crustal velocity model based on our data will be compared to recorded seismic data from the Western Cyclades to map the kinematics and geometry of shear zone deformation in the WCDS. This will help resolve details in the seismic data profiles and lead to a comprehensive view on deep seated fault zone processes and anisotropy.