## 3 Results
Visual inspection and examination of seismic catalogues revealed that the selected signal did not correspond to a local LF event. The third window selected from the automatic detection is summarized in Figure 7. Seismograms of some stations of the monitoring network are shown in Figure 7a. There appears to be no signal with a signal-to-noise ratio clearly observable in the seismic records. However, after filtering the seismograms in the frequency band of interest (2-8 Hz), a low-amplitude seismic event is visible at all the stations of the monitoring network. This is the case of a very low amplitude event, with spectral characteristics typical of LF events and recorded by the whole seismic network. It is not possible to identify any particular phases in these seismograms due to the emergent onset and the low amplitude of the signals and, for these reasons, the source of this event cannot be localized. Considering the spectral and shape characteristics, this event has been classified as an LF volcanic tremor. Figure 4: Central frequency, shape factor, coherence and average spectral amplitude versus time for the signals recorded on 2 May 2020. Central frequency and shape factor (blue circles) are shown only for BKWG station. Coherence and average spectral amplitude (black circles) were evaluated and focused at 4 Hz for the signals recorded at BKWG, BKSG and SVAG. The yellow circles identify the signal windows that satisfy the features of LF events. Small yellow circles mark windows for which only one condition between spectral features (yellow and blue circles) and coherence threshold (yellow and black circles) is satisfied. Larger yellow circles with red border show the windows that satisfy all the characteristics (spectral features and coherence) of LF events. Figure 5: (**a**) Three low-frequency events characterized by low amplitude as recorded at BKSG and BKWG sites. (**b**) Seismograms filtered between 2 Hz and 6 Hz of the first LF earthquake visible in plot (**a**), where it is identified by vertical blue lines. Figure 6: Regional earthquake (20200502 12:51:05 UTC, latitude 34.14\({}^{\circ}\) N, longitude 25.70\({}^{\circ}\) E, depth 10 km, Mw6.6 Crete, Greece) recorded by BKSG, BKWG and SVAG stations. Further examples of LF events detected by our procedure are shown in Figures 8-10. The two events shown in Figures 8 and 9 are recognizable by visual inspection of the seismograms, but those of Figure 9 are not easily identifiable and classifiable through a simple visualization because of their very low signal-to-noise ratio. In Figure 10, we show the spectrogram of LF event 202009071932. Most of the frequency content is included in the 2-6 Hz band for both the small initial event and the subsequent larger one. In both cases, the spectral and coherence analysis provides parameters fully compatible with LF earthquakes. Specifically, our analysis applied to the selected dataset (years 2019, 2020 and part of 2021) highlighted the presence of 80 seismic signals potentially classifiable as LF events. Visual inspection of the seismograms and catalogue examination allowed us to recognize at least 12 LF earthquakes, a few LF tremors and 62 events not clearly classifiable in the LF category because they have extremely small amplitudes, almost undistinguishable from the background noise even in the filtered signals. The 12 LF events discovered by our analysis and shown in Table 1 do not appear in the catalog of Vesuvius seismicity. Figure 7: (a) Seismic waveforms (vertical components in red lines, no filtered data) recorded from eight seismic stations installed at the top of the volcano (Figure 1). At first sight, these seismograms show only seismic noise. (b) The same seismograms after filtering in the 2–8 Hz frequency band (in blue lines) show a very small amplitude signal with onset just before 30 s, visible at all stations of the monitoring network. Figure 8: Two low-frequency earthquakes recorded at stations BKSG and BKWG.