GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Piezo-Electric Transducers. AEs are then post-processed to derive event rate, amplitude, source mechanism, seismic scattering, average velocity, and their evolution over time. As training parameters for the TDNN, we selected 5 key parameters (Fig. 2): 1) AE event rate, i.e. the number of events obtained during the incremental deformation (strain) of the sample; 2) AE amplitude, i.e. maximum amplitude of S-waves, 3) AE source mechanisms inferred by the source radiation patterns (King et al., 2020; 2021; Kwiatek & Ben-Zion, 2013) to categorize events and obtain source orientations of mixed-mode type mechanisms; 4) Seismic scattering, i.e. the ratio between the low frequency (LF, 50-500 kHz) and high frequency (HF, 500-1000 kHz) peak delay (PD) values for individual AE. LF-PD is a measure of the slowing and broadening of multiple reflections from the sample boundaries, whilst HF-PD highlights the increasing occurrence of trapped waves as the fault zone develops (King et al., 2022) and 5) Bulk elastic S-wave velocity (Benson et al., 2007) measured at intervals throughout the experiment along the ray-paths created by transmitters and receivers. As each parameter investigates a specific mechanical aspect, taken together they provide information on deformation, cracking and the evolving state of the background medium as failure is approached. Discrete parameters are resampled onto a common timeseries and high-pass filtered to simplify the data for the modelling. These timeseries are then classified by the TDNN as variations in stress and strain (target parameters). Figure 2: a) Stress-strain curves (line) and counts of located acoustic emission (AE, histogram) at increasing confinement. b) Source mechanisms type and percentage vs. increasing strain. Compaction and dilatancy dominate phases. c) Scattering ratio and incremental strain. Scattering is defined as the ratio of the peak delay at high frequency vs. low frequency. It provides an