GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.3 ______ ___ GNGTS 2023 Figure 1. Representation of the Italian data set. a): Mechanisms of selected earthquakes: the mainshocks of Amatrice, Visso and Norcia, and the seven largest events of Capitignano subsequence (from http://eqinfo.eas.slu.edu/eqc/eqc_mt/MECH.IT/) . Fault traces are represented by colored lines (fault strands with the same color pertain to the same seismogenic fault system, from Gori et al., 2019). Fault systems are matched with the corresponding focal solutions using the same color; stars correspond to the location of the mainshocks, and green squares represent the main cities of the area. b) and c): Locations and magnitudes of the 13,980 earthquakes used in this study (1.1 < M < 6.0) occurred in the time window between 01/01/2012 and 23/08/2016 (b)) and between 24/08/2016 and 05/05/2022 (c)); orange triangles in b) and c) indicate the positions of the 21 seismic stations used. 3D visualization of the seismic attenuation parameter . d): During the most energetic part of the −1 ,( ) Amatrice-Visso-Norcia seismic sequence. It is very clear that the main events produce a sharp coseismic drop in seismic attenuation at relatively high frequencies (only frequencies Hz are plotted here) due to crack closing (Muir-Wood ≥1 and King, 1993), followed by a more gentle rise, probably due to fluid displacement through diffusion, and a wide trough that is probably due to the cumulative effects of coseismic crack closure produced by the aftershocks. The pattern is reproduced after each main event. Patterns of colors relative to “damage” and “negative dilatation” are indicated.