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The site-corrected source scaling pattern is estimated for local earthquakes (0.9 ≤ MD ≤ 3.6) at Mt. Vesuvius. The dataset comprises 35 low-to-moderate local earthquakes recorded by 14 three-component seismic stations during 1993, 1996, and 1999. Site-transfer functions in the frequency range 1 Hz-25 Hz are estimated from the spectra of S waves and coda waves and from the horizontal-to-vertical (H/V) spectral ratios. We applied the direct spectral ratios method to S waves, considering as a reference the average spectrum and the inversion method to S waves and coda waves. The site amplification on the coda waves was also compared with that evaluated using the wavelet transform. The standard deviation associated with the experimental results is computed for all of the used methods. Results indicate a general agreement among the methods, and the site-transfer functions show interesting features. The highest amplifications are found for frequencies lower than 12 Hz for sites located at lower altitude. The methods based on coda waves show highest amplification with respect to the methods based on S waves for most of the sites located in the summit part of the volcano. This can be a phenomenon of coda localization, which consists in the trapping inside the upper part of the volcano of scattered waves. The H/V spectral ratios do not show total agreement with the other methods, mostly for the sites located in the summit part of the volcano. The discrepancies among the results obtained in this work are also due to the different normalization applied in the methods of analysis. Generalized inversion method allowed us to estimate the source scaling of the site-corrected source seismic spectrum for the investigated area. The source scaling obtained in terms of seismic moment and source radii shows that the seismicity of Mt. Vesuvius is characterized by stress drop as low as a few bars (10 bars) except for the event of MD 3.6 (Δσ = 100 bars). The scaling pattern shows an apparent linear relationship between source size and seismic moment (for MD ≤ 3.3) but the statistical test shows that the linear trend has low reliability. [ABSTRACT FROM AUTHOR]

Seismicity at Mt. Vesuvius has been relatively weak in the last decades. While the occurrence of shallow volcano-tectonic (VT) events at Mt. Vesuvius is well known, the occurrence of deeper low frequency events (LF) was only recently recognized. Previous source studies only targeted VT events, which were found to have quite heterogeneous focal mechanisms. In this paper, we perform for the first time the source inversion of LF seismicity at Mt. Vesuvius, analysing 27 LF events recorded from 2012 to 2021 with the aim to investigate their source processes. Given the challenges of analysing weak LF earthquakes, we implement a specific moment tensor (MT) inversion approach that combines the fit of displacement seismograms in the time domain and amplitude spectra in the frequency domain. The inversion is simultaneously performed for the source depth and moment tensor components in the 2–7 and 2–5 Hz frequency band, assuming either a full or deviatoric MT representation. Source parameter uncertainties are estimated by using a Bayesian bootstrapping scheme. Our results confirm a larger depth of LF events compared to VTs and show a strong heterogeneity of the LF seismic sources, which present various rupture types, different orientations and heterogeneous, whilst poorly resolved, non-double-couple components. The MT variability is qualitatively confirmed by significant differences among the recorded waveforms. The heterogeneity of both VT and LF source processes is attributed to complex source processes in a highly fractured seismogenic volume submitted to a heterogeneous stress field. • The first moment tensor inversion study of LF seismic events at Mt. Vesuvius. • LF seismic events at Mt. Vesuvius occured at depths between 4 and 8 km b.s.l and have characterized by Mw < 2. • A strong heterogeneity in the fault geometry and the driving stress field characterizes LF seismicity of Mt. Vesuvius in the last 30 years. [ABSTRACT FROM AUTHOR]