GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.3 ______ ___ GNGTS 2023 Figure 2. Conceptual model of fluid behavior. Scaling the attenuation vs. time curves from after the Amatrice, Norcia, and Capitignano earthquakes, we note a consistent shape. Each mainshock that initiates a sequence is associated with a sharp increase in , followed by a comparatively steep drop. This happens during periods −1 ,( ), = 2. 2 where potential diffusion is also observed. A subsequent gradual recovery in , persists up until −1 , ( ), = 2. 2 the next mainshock. We hypothesize that this recovery is associated with the redistribution of fluids into newly damaged faults and into the shallow crust. Figure 3. a) representation of the Ridgecrest dataset, made of ~15,450 earthquakes and ~ 370,000 waveforms, selected based on epicentral distance. No events from the Coso volcanic area were allowed, and, differently from the Central Apennines, no quality control was performed on waveforms, with the exception of the year 2019, before and after the mainshock. Results, in terms of the seismic attenuation parameter , were obtained after performing a −1 ,( ) set of 6,800,000 regressions (ten regressions per each one of the 44 frequencies and each one of the 15,450 time steps). b) fluctuations of the attenuation parameter at Ridgecrest , with respect to an average value computed between 01/01/2000 and 03/07/2019 (the day before the Ridgecrest earthquake). The frequency band shown in the plot is: 0.4 – 30 Hz. Note that anomalies have much lesser amplitudes than in the Central Apennines. Also, the effect of damage, after the mainshocks and during the sequence, seems to be very limited, almost absent. References Barbosa, N.D., J. Hunziker, S. Lissa, E.H Saenger, and M. Lupi (2019). Fracture unclogging: A numerical study of seismically induced viscous shear stresses in fluid-saturated fractured rocks, J. Geophys. Res., 124, 11, pp 11705-11727, https://doi.org/10.1029/2019JB017984. Gori, S., I. Munafò, E. Falcucci, M. Moro, M. Saroli, L. Malagnini, and F. Galadini (2019). Active faulting and seismotectonics in central Italy: lesson learned from the past 20 years of seismicity.