GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 1.1 47 identified by our approach (Fig. 3b). The size of these LF events is evaluated in terms of seismic moment ( M 0 ) calculated according to Havskov and Ottemöller (2010): where Ω 0 is the spectral flat level, ρ is the medium density, ν is the velocity of S wave at source, R is the average radiation pattern effect set to 0.6, Fs is the free surface operator equal to 2 and G is the geometrical spreading term as a function of epicentral distance Δ (m) and hypocentral depth h (m). In this work, the detection procedure has identified about 30 low-frequency events, most of them not contained in the official catalogue, characterized by seismic moment M 0 in the range 10 10 – 10 13 Nm (10 6 – 10 7 Joule in terms of seismic energy). Conclusions. Several neural network approaches are widely adopted to detect and classify the seismicity, especially in active volcanic areas where different types of seismic signals co- exist. In recent years, some methods based on spatial coherence of seismic signals recorded on active volcanoes have been proposed (Permana et al., 2022). The novelty of our methodology consists in combining two complementary techniques: the first one based on the spectral parameters analysis essentially applied to a single seismic station, and the second one based on the coherence analysis that highlights common features of the set of seismic stations used. Preliminary results obtained for Mt. Vesuvius are encouraging as the methodology has allowed to identify low-frequency events not catalogued by commonly used procedures. References Galluzzo, D., Nardone, L., La Rocca, M., Esposito, A.M., Manzo, R., Di Maio, R., 2020: Statistical moments of power spectrum: a fast tool for the classification of seismic events recorded on volcanoes. Advances in Geosciences, 52, 67-74. Havskov, J. and Ottemöller, L., 2010: Routine Data Processing in Earthquake Seismology . Springer. La Rocca, M. and Galluzzo, D., 2016: Volcanic tremor at Mt. Vesuvius associated with low-frequency shear failures . Earth and Planetary Science Letters, 442, 32-38. Permana, T., Nishimura, T., Nakahara, T., Shapiro, N., 2022: Classification of volcanic tremors and earthquakes based on seismic correlation: application at Sakurajima volcano, Japan. Geophysical Journal International, 229, 1077- 1097.