The preparatory phase of the 2009 Mw 6.3 L'Aquila earthquake by improving the detection capability of low-Magnitude foreshocks

We explored the detection capability of low-Magnitude earthquakes before the 6 April 2009 Mw 6.3 L'Aquila event by using a matched filter technique and 512 foreshocks as templates. We analyzed continuous waveforms from 10 broadband seismic stations in a 60 km radius from the epicenter and for ~3 months before the main shock. More than 3000 new events, mostly located on the main shock fault, were detected to define the spatial-Temporal evolution of micro-Seismicity. The foreshock sequence was active northwest of the Mw 6.3 hypocenter in January, then migrated toward it at a speed of ~0.5km/day in middle of February. At that time, in a ~4 km2 patch close to the main shock nucleation point, the cumulative number of earthquakes gradually increased until the Mw 6.3 event. This patch, characterized by a low b-Value, played a key role in controlling the preparation stage to the 2009 L'Aquila main rupture.