Three-dimensional seismic attenuation structure beneath the Aegean region and its tectonic implication

Abstract

The three-dimensional attenuation structure beneath the Aegean Sea and the surrounding regions is determined by inversion of seismic intensity data. A large number of seismic intensity data have been accumulated in a uniform scale in the Aegean region, where the seismic activity is much higher than that of the other Mediterranean regions. Nearly 7000 seismic intensity data from 50 earthquakes that have occurred in these regions are used to determine seismic attenuation structure and source acceleration of the earthquakes. The resultant structure reveals a remarkable contrast of attenuation. In the top layer (depth 0–40 km), low Q is dominant in the Aegean Sea, while high Q is dominant in the surrounding land areas, except for the southwestern Turkey. The low- Q regions correspond to areas of Neogene-Quaternary grabens where the high seismicity of shallow earthquakes appears. In the upper mantle, high- Q zones corresponding to the subducting African Plate dominate along the Hellenic arc. The irregular shape of high- Q zones might reflect the split or disintegration of the African slab. Some low- Q spots corresponding to the distribution of volcanoes exist along the volcanic arc. The low- Q spots might correspond to diapirs causing the subduction volcanism.