Earthquake sequences of the last millennium in L'Aquila and surrounding regions (central Italy)

Abstract

We have analysed the history of seismic activity in the region of L'Aquila to compare the 2009 sequence with previous ones. Historical catalogues are exhaustive for large shocks, but not for small earthquakes and swarms. Our original compilation highlights repeated seismic sequences from 1315 ad to present. In the 20th century, at least 23 sequences affected the Abruzzi region, 8 of which were very close to L'Aquila. In previous centuries, we found evidence of at least 13 sequences around L'Aquila, with maximum magnitude ∼4 to ∼5. Only three sequences were followed by stronger shocks (1461, 1703 and 2009). However, many strong events of the region (1349, 1762, 1915, 1950) were not preceded by foreshocks. We describe here the last of these sequences (1985) showing its strong similarity with the 2009 one, except its final evolution (no large event in 1985). Our analysis suggests that seismic sequences alone cannot be considered straight forerunners of incoming strong events.