Limits on earthquake nucleation and other pre-seismic phenomena from continuous strain in the near field of the 2009 L'Aquila earthquake

Two laser strainmeters that operate at 1400-m depth, about 20 km NE of the epicenter of the 2009/04/06 magnitude-6.3 L'Aquila, Italy, earthquake, have produced records of strain since 1995. During the two years before the event, no anomalous signal larger than a few tens of nanostrains is visible, limiting the volume of the possible earthquake preparation zone to less than 100 km(3); moreover, earth tidal response is stable within 0.5% in amplitude and 0.5 in phase. Thus, reality of large-scale precursory phenomena seems unlikely. During the last few days, there is some evidence of dilatancy of satured rock over the earthquake causative fault, maybe related to the foreshocks. Seconds before the event, strain is stable at the 10(-12) level and prerupture nucleation slip in the hypocentral region is constrained to have a moment less than 2 x 10(12) Nm, i. e. 0.00005% of the main shock seismic moment. Citation: Amoruso, A., and L. Crescentini (2010), Limits on earthquake nucleation and other pre-seismic phenomena from continuous strain in the near field of the 2009 L'Aquila earthquake, Geophys. Res. Lett., 37, L10307, doi:10.1029/2010GL043308.