Over 4.500 "Haisentitoilterremoto" questionnaires filled out by Italian citizens following the earthquakes that affected Greece from 2007 to 2014 with shocks of moment magnitude (Mw) greater than 5.4. To analyze these data, for the study of the territory to seismic stresses, the researchers of the HSIT (Did you hear the earthquake) working group of the National Institute of Geophysics and Volcanology (INGV). Role of African–Eurasian plate setting in the felt areas of intermediate-depth earthquakes: an investigation using crowdsourced data (http://onlinelibrary.wiley.com/doi/10.1111/ter.12245/epdf), published in Terra Nova, analyzes the data provided by citizens to investigate how some recent strong Greek earthquakes of medium depth (50-110km) were felt.
"Earthquakes can be perceived in Italy at greater distances than those normally observed", explains Paola Sbarra, a researcher at INGV and the HSIT group. “In particular, this is observed for citizens located in south-eastern Sicily and Puglia, i.e. on the African side of the boundary of the African and Eurasian plates. While the majority of those on the European side of this border usually do not feel such events. By highlighting the modes of propagation of seismic waves, the study offers significant contributions to the understanding of complex geological areas and has potential implications in the study of seismic hazard".
Even on the occasion of the recent earthquakes that affected Central Italy, the researchers were able to analyze the data of over 45.000 questionnaires filled in by citizens from all over Italy. The preliminary results show an amplification of the earthquake effects in the area north of the epicenters and on the Adriatic coast, and an attenuation on the Tyrrhenian side.
From 2007 to today, 875.390 questionnaires have been completed on the website www.haisentitoilterremoto.it.
Extended
Role of African–Eurasian plate setting in the felt areas of intermediate-depth earthquakes: an investigation using crowdsourced data (Sbarra Paola, Tosi Patrizia and De Rubeis Valerio)
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.
Map of perceptions of an earthquake in Greece. In red the boundary between the African and European plates