Scattering and absorption imaging of a highly fractured fluid-filled
seismogenetic volume in a region of slow deformation
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Abstract
Regions of slow strain often produce swarm-like sequences, characterized by the lack of a clear mainshockaftershock
pattern. The comprehension of their underlying physical mechanisms is challenging and still
debated. We used seismic recordings from the last Pollino swarm (2010–2014) and nearby to separate and map
seismic scattering (from P peak-delays) and absorption (from late-time coda-wave attenuation) at different frequencies
in the Pollino range and surroundings. High-scattering and high-absorption anomalies are markers of a
fluid-filled fracture volume extending from SE to NW (1.5–6 Hz) across the range. With increasing frequency,
these anomalies approximately cover the area where the strongest earthquakes occurred from the sixteenth
century until 1998. In our interpretation, the NW fracture propagation ends where carbonates of the Lucanian
Apennines begin, as marked by a high-scattering and low-absorption area. At the highest frequency (12 Hz) the
anomalies widen southward in the middle of the range, consistently marking the faults active during the recent
Pollino swarm. Our results suggest that fracture healing has closed small-scale fractures across the SE faults that
were active in the past centuries, and that the propagation of fluids may have played a crucial role in triggering
the 2010–2014 Pollino swarm. Assuming that the fluid propagation ended at the carbonates barrier in the NW
direction, fractures opened new paths to the South, favoring the nucleation of the last Pollino swarm. Indeed, the
recently active faults in the middle of the seismogenic volume are marked by a high-scattering and highabsorption
footprints. Our work provides evidence that attenuation parameters may track shape and dynamics
of fluid-filled fracture networks in fault areas.
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