3-D structure of the lithosphere in the Aegean region

Abstract

SUMMARY P-wave traveltime residuals from about 300 local and 400 teleseismic earthquakes recorded by the Athens seismological network were used to study the structure of the lithosphere in the Aegean region. Teleseismic data included readings from local stations which do not routinely report to the ISC. The large values of the residuals (up to f3 s) and their variation with azimuth and epicentral distance indicate significant velocity heterogeneity in the upper mantle. P-wave traveltime residuals were inverted simultaneously for both local and teleseismic earthquakes. Tomographic results, which are best resolved at lithospheric depths, reveal a heterogeneous lithosphere down to a depth of 100km or so. A high-velocity anomaly is found dipping at an average of 45 to the NE away from the Hellenic trench, and supports the hypothesis of subduction due to a cooler descending slab of oceanic composition. An area of low velocities is observed at depths less than 80 km in the Aegean back-arc, corresponding well with observed high heat flow values in the area. In contrast, an area of relatively higher velocity anomalies is resolved in the lithosphere underlying the Sea of Crete. The tectonic structure of the crust and upper mantle in the Eastern Mediterranean area results from the complex interaction of several different geodynamic processes, not all of which can be described by simple plate tectonic models. At present, the Eurasian and African plates are converging at a rate of about lcmyr-' in an approximately N-S direction (Minster & Jordan 1978) with the latter descending