Source analysis of low frequency seismicity at Mt. Vesuvius by a hybrid moment tensor inversion

Seismicity at Mt. Vesuvius has been relatively weak in the last decades. While the occurrence of shallow volcanotectonic (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