Role of African–Eurasian plate setting in the felt areas of intermediate-depth earthquakes: an investigation using crowdsourced data

Abstract

Greek intermediate-depth earthquakes, occurring in the subducted plate of the Hellenic Arc, are felt at greater distances than expected, reaching Italy in some cases. We study in detail macroseismic intensity data from intermediate-depth Italian and Greek earthquakes collected from Internet users who felt the shaking in Italy. The huge amount of data allowed us to outline the felt/not-felt limit and to find a correspondence between attenuation areas and the presence of asthenospheric material at shallow depths. We show that plate boundaries, known to produce the majority of earthquakes, are, in some specific cases, the boundaries of areas in which earthquakes are felt. The Ionian subducted lithosphere propagates seismic waves with low attenuation over large distances, whereas high-attenuation zones in Italy, linked to asthenospheric upwelling, limit the propagation, as evidenced also by PGA values. We identify a typical pattern that can be used to recognize intermediate-depth earthquakes, and to properly locate historical events.