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Temporal Variation of S-Wave Attenuation During the 2009 L’Aquila, Central Italy, Seismic Sequence

Raul R. Castro, Leonardo Colavitti, Francesca Pacor, Giovanni Lanzano, Sara A. Sgobba, & Daniele Spallarossa

Submitted September 10, 2023, SCEC Contribution #12764, 2023 SCEC Annual Meeting Poster #040

We investigate possible variations of the spectral decay parameter kappa before and after the April 6, 2009, L’Aquila earthquake (Mw 6.1), central Italy. For this purpose, we analyze foreshocks that occurred 10 days before and groups of aftershocks occurring 10 days, and one, three, and six months after the main event. We selected events with magnitudes Mw > 3.2 registered by the dense seismic array of central Italy within a radius of 20 km from the epicenter of the L’Aquila main shock.
We separate the near source, along the path and near site contributions of kappa for each group of events analyzed and we detected significant temporal variations of this S-wave attenuation parameter. Ten days before the main earthquake kappa along the path has the lowest values, probably related to high tectonic stress accumulated, then kappa increased during the main event and remains constant with time up to 40 km; after that distance the attenuation started to decrease during the next three months after the main shock.
Ten days before the principal event the foreshocks that are located to the south show an increase in the near-source attenuation towards the northeast, following the direction to the mainshock epicenter; these spatial variations of kappa are probably related to crustal fluid flows in that direction. The first 10 days of aftershocks concentrate around the main earthquake and show high near-source kappa that tends to decrease towards the southeast. After three months from the mainshock the regional attenuation seems to go back to the original lower near-source kappa.
We conclude that the investigation of temporal variation of the spectral decay parameter kappa provides important clues for the monitoring of the earthquake cycle in central Italy.

Key Words
L'Aquila earthquake, central Italy, temporal variation of Kappa,

Castro, R. R., Colavitti, L., Pacor, F., Lanzano, G., Sgobba, S. A., & Spallarossa, D. (2023, 09). Temporal Variation of S-Wave Attenuation During the 2009 L’Aquila, Central Italy, Seismic Sequence. Poster Presentation at 2023 SCEC Annual Meeting.

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