GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 The AVN sequence was further divided into three-time phases, each one related to a mainshock of AVN: 1) Amatrice sequence, recorded between 24/08/2016 and 25/10/2016; 2) Visso sequence, recorded between 26/10/2016 and 29/10/2016; 3) Norcia sequence, recorded between 30/10/2016 and 05/01/2017. The subdivision of the seismic sequence can highlight changes in scattering attenuation both in space and time, allowing us to interpret the possible patterns of fracture development and fluid migration in the seismogenic zone in 4D. Methods We mapped scattering attenuation (Q s ) measuring the peak delay time, defined as the time difference between the S-wave arrival and the maximum amplitude of the waveform (Takahashi et al., 2007). In an inhomogeneous medium, peak delay provides information about multiple forward scattering in the crust. This technique has already been applied in 2D in volcanic areas (Northeast Japan - Takahashi et al., 2007) and tectonic zones, such as the Pyrenees (Calvet et al., 2013) and the Southern Apennines (Napolitano et al., 2020), where high peak delays values detected highly fractured carbonate successions in the Pollino seismic gap. The peak-delay variation is computed as the difference between the measured peak-delay time of each filtered i-th waveform (t i PD (f)) and the theoretical peak-delay at the related hypocentral distance: (1) ∆ 10 ( ) = 10 ( ) − 10 ( ) Where is the measured peak delay time for the i-th waveform and is the theoretical ( ) ( ) peak delay obtained from: (2) 10 ( ) = ( ) + ( ) · 10 with A(f) and B(f) as the coefficients of the resulting linear fit and R as the hypocentral distance. Positive values of are representative of high scattering and, so, of heterogeneities (e.g., ∆ 10 ( ) fractures and faults) in the crust, while negative values (low scattering) characterize a more compact and rigid crust. To map peak delay, we applied a regionalization approach, associating the averaged value of the to each block of our grid (2.5 × 2.5 km horizontally and 1 km vertically for the depth). ∆ 10 ( ) Results and Discussion