Abstract
Approximately 23,000 well-located earthquakes from 2009 to 2016 are used
as templates to recover seismic activity preceding the 2016 Central
Italy seismic sequence. The resulting spatiotemporal pattern is analyzed
employing ~91,000 newly detected events. In the 8 years
before the sequence onset, microseismicity (Ml minor or equal to 3.7)
develops at the hangingwall of the 2016 fault system and along a
sub-horizontal shear zone. The events, mainly organized in clusters,
represented by foreshock-mainshock and swarm-like sequences, migrate
toward the nucleation area of the first Mw 6.0 mainshock of the sequence
that occurred on the 24th of August in Amatrice. We propose an unlocking
model based on variable temporal clustering of the seismicity, including
repeaters, identifying fault portions with different degree of coupling
and rheology, responding differently to the tectonic loading, and
working to progressively localize the deformation process, increasing
rock damage and weakening the nucleation patch of the Amatrice
mainshock.