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Abstract:
We investigate the preparatory phase of the 2009, Mw 6.1 L’Aquila earthquake in central Italy by analysing the temporal evolution and spatial distribution of the seismic moment, M0, to radiated energy, ES. Our approach focuses on monitoring the deviations of the scaling between M0 and ES with respect to a model calibrated for the background seismicity. The temporal evolution of these deviations, defined as Energy Index, EI, identifies the onset of the activation phase one week before the mainshock. We show that foreshocks are characterized by a progressive increase in slip per unit stress, in agreement with the diffusion of highly pressurized fluids before the L’Aquila earthquake proposed by previous studies. Our results suggest that the largest events occur where EI is highest, in agreement with the existing link between EI and the mean loading stress.
