Monitoring the Pollino Earthquake Swarm (Italy)

Abstract:

The Mercure Basin (MB) and the Castrovillari Fault (CF) in the Pollino range (southern Apennines, Italy) represent
one of the most prominent seismic gaps in the Italian seismic catalog, with no M>6 earthquakes during the last
centuries. In recent times, the MB has been repeatedly interested by seismic swarms.
The most energetic swarm started in 2010 and still active in 2014.
The seismicity culminated in autumn 2012 with a M=5 event on October 25.
In contrast, the CF appears aseismic. Only the northern part of the CF has experienced microseismicity.
The range host a number of additional sub-parallel faults.
Their rheology is unclear. Current debates include the potential of the MB and the CF to host large
earthquakes and the level and the style of deformation.
Understanding the seismicity and the behaviour of the faults
is therefore necessary to assess the seismic hazard.

The GFZ German Research Centre for Geosciences and INGV, Italy, have been jointly monitoring the ongoing seismicity using a small-aperture seismic array, integrated in a temporary seismic network.

Using the array, we automatically detect about ten times more earthquakes than currently included in
local catalogues corresponding to completeness above M~0.5.
In the course of the swarm, seismicity has mainly migrated within the Mercure Basin.
However, the eastward spread towards the northern tio of the CF in 2013 marks
a phase with seismicity located outside of the Mercure Basin.
The event locations indicate spatially distinct clusters with different mechanisms across the E-W trending Pollino Fault.
The clusters differ in strike and dip.
Calibration of the local magnitude scale confirms earlier studies further north in the Apennines.
The station corrections show N-S variation indicating that the Pollino Fault forms an important structural boundary.