Temporal Evolution of Radiated Energy to Seismic Moment Scaling During the Preparatory Phase of the Mw 6.1, 2009 L’Aquila Earthquake (Italy)

Abstract

We investigate the preparatory phase of the 2009, Mw 6.1 L’Aquila earthquake in central Italy by analyzing 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 1 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 energy index (EI) is highest, in agreement with the existing link between energy index (EI) and the mean loading stress.

Detection of Spatial and Temporal Stress Changes During the 2016 Central Italy Seismic Sequence by Monitoring the Evolution of the Energy Index

“…Following Brown and Hudyma (2017) and Picozzi et al. (2022), we compute the differences EI = log(E S ) − log(E St ) between the experimental E S estimates and theoretical E St values derived from the median E S ‐to‐M 0 reference scaling model. Positive EI values indicate that the earthquakes have radiated more energy per unit‐slip and unit‐area (i.e., per seismic moment, M 0 ) than expected according to the reference model.…”

“…Picozzi et al. (2022) investigated the temporal evolution and spatial distribution of the ratio E S to M 0 for microearthquakes that occurred during the preparatory phase of the Mw 6.1, 2009 L’Aquila earthquake, with the aim of testing whether these parameters could capture hints of preparatory processes leading to the mainshock. To this purpose, Picozzi et al.…”

“…To this purpose, Picozzi et al. (2022) studied the deviation of E S for foreshocks from a reference model (calibrated during a period characterized by background seismicity) describing the scaling of E S with respect to M 0 .…”

“…All these recent studies covering a wide range of spatial scales support the idea of McGarr (1999) about the importance of E S , and its scaling with M 0 , for characterizing the crustal stress at which earthquakes occur and for monitoring the evolution of crustal processes leading to earthquakes. Picozzi et al (2022) investigated the temporal evolution and spatial distribution of the ratio E S to M 0 for microearthquakes that occurred during the preparatory phase of the Mw 6.1, 2009 L'Aquila earthquake, with the aim of testing whether these parameters could capture hints of preparatory processes leading to the mainshock. To this purpose, Picozzi et al (2022) studied the deviation of E S for foreshocks from a reference model (calibrated during a period characterized by background seismicity) describing the scaling of E S with respect to M 0 .…”

“…Picozzi et al (2022) investigated the temporal evolution and spatial distribution of the ratio E S to M 0 for microearthquakes that occurred during the preparatory phase of the Mw 6.1, 2009 L'Aquila earthquake, with the aim of testing whether these parameters could capture hints of preparatory processes leading to the mainshock. To this purpose, Picozzi et al (2022) studied the deviation of E S for foreshocks from a reference model (calibrated during a period characterized by background seismicity) describing the scaling of E S with respect to M 0 .…”