Fast Changes in Seismic Attenuation of the Upper Crust due to Fracturing and Fluid Migration: The 2016–2017 Central Italy Seismic Sequence

The Amatrice–Visso–Norcia seismic sequence struck Central Italy across the Apenninic normal fault system in 2016. Fluids likely triggered and reduced stability of network following first earthquake (Amatrice, M w 6.0), with their migration nucleating Visso (M 5.9) Norcia 6.5) mainshocks. However, both spatial extent mechanisms fluid diffusion through remain unclear. High content, enhanced permeability, pervasive microcracking increase attenuation, but different processes contribute to attenuation mechanisms. Here, we measured mapped peak delay time coda using them as proxies scattering absorption before during sequence. We observed that structural discontinuities lithology control losses at all frequencies, highest delineating carbonate formations within Gran Sasso massif. Monti Sibillini thrust marks strongest contrasts scattering, indicating a barrier for northward fracture propagation. Absorption does not show any sensitivity presence these main geological structures. Before sequence, low-frequency high-absorption anomalies distribute around NW-SE-oriented Apennine Mountain chain. During anomaly develops from SSE NNW seismogenic zone remains bounded north by thrust. attribute this expansion deep CO 2 -bearing fluids strike source trapped close Amatrice earthquake. expand SSE-NNW primarily then diffuse zones