S-P-wave traveltime residuals from earthquakes and lateral inhomogeneity in the upper mantle beneath the Aegean and the Hellenic Trench near Crete

The average S-P-wave traveltime residuals from 29 earthquakes in the Aegean and the Hellenic Trench near Crete imply that there are lateral variations in structure beneath these regions. Average S-P-wave residuals, measured with respect to the Jeffreys-Bullen (J-B) tables (1940), from 14 of 17 earthquakes in the Aegean are greater than +1 s. The largest positive values of residuals in the Aegean imply that the average velocities in the crust and the upper mantle of these parts of the Aegean are lower than those beneath Crete. The existence of volcanoes, heat flow observations, an assumption of relatively low seismic-wave velocities, and variations in S-P-wave residuals from earthquakes in the Aegean provide evidence of lateral variations in uppermost mantle structure beneath the region. Residuals reflect systematic lateral variations that do not correlate well with elevation or with simple aspects of regional geology.