3D Scattering and Absorption model during the 2016-2017 Central Italy Seismic Sequence

Abstract

<p>The Amatrice-Visso-Norcia seismic sequence struck the Central Apennine (Italy) in 2016. Previous works brought to light how fluid movements likely triggered the sequence and reduced the stability of the normal fault network following the first earthquake (Amatrice, M<sub>w</sub>6.0), and the subsequent events of Visso (M<sub>w</sub>5.9) and Norcia (M<sub>w</sub>6.5) mainshocks.<br>Seismic attenuation has the potential to<em> </em>visualize fluids presence and fractures in a seismic sequence and to image the effect of fluid migration in the events nucleation.</p><p>This work aims to provide 3D images of scattering and absorption at different frequency bands for two datasets, one before the sequence (March 2013-August 2016) and a second from the Amatrice-Visso-Norcia sequence (August 2016-January 2017). To measure scattering and absorption we used peak delay mapping and coda-attenuation tomography, respectively.<br>Previous 2D imaging of scattering and absorption showed a difference between the pre-sequence and the singular sequences at different frequency bands. Structural discontinuities and lithology control scattering losses at all frequencies, while a single high-absorption anomaly developed NNW-SSE across the seismogenic zone during the seismic sequence, probably related to the migration of deep-CO<sub>2</sub> fluids from a deep source of trapped CO<sub>2</sub> near the Amatrice earth.<br>The 3D preliminary results<em> </em>are in agreement with the 2D mapping, with high-scattering anomalies following the main structural and lithological elements of the Central Apennines (e.g. Monti Sibillini thrust), both during the pre-sequence and the sequence, also in depth. As for the 2D, the high absorption anomaly is widespread in the area before the Amatrice event, while it is mainly focused on the seismogenic zone during the sequence. This spatial expansion can be related to the deep migration of CO<sub>2</sub>-bearing fluids across the fault network also at seismogenic depths.</p>