GNGTS 2022 - Atti del 40° Convegno Nazionale

46 GNGTS 2022 Sessione 1.1 background noise, LF seismic signals were idebtified as a result of joint coherence and spectral parameters analyses. The coherence was evaluated at a frequency equal to 4 Hz, which is the main frequency of LF signals (La Rocca and Galluzzo, 2016). All the analyses were performed on 30 s non-overlapping signal windows. In particular, all the time windows characterized by δ between 0.45 and 0.65, Ω between 3 and 6 Hz (Galluzzo et al. , 2020) and coherence ≥ 0.5 (Fig. 2) were selected. Fig. 3a shows an example of a low-frequency signal, initially masked by the high background noise and consequently filtered into the appropriate frequency band and Fig. 3 - Low Frequency seismic event registered on December 01, 2019 at 06:05 am. a) Raw three-component signals recorded by the BKWG broad band station. b) Three-component signals filtered in the 3-6 Hz frequency band recorded by the BKWG broad band station.