## 3 Results  
### Seismological Results  
We carefully picked the P- and, when possible, the S-phases, and marked the polarities of the P-phases. Then we performed a 3D non-linear probabilistic location [35], which takesinto account topography and lateral heterogeneities of the medium. In Figure 1 we show the epicenter positions. The sources' depths are reported in Table 1. The average error for the 3D locations is 0.03 km for both the epicentral distance (ERH) and depth (ERZ). The output files containing P-polarity, takeoff angles, azimuths, and distances obtained from the 3D location served as input to FPFIT. We used data showing at least six reliable P-wave polarities. In Table 1 we reported the obtained strike, dip and rake for each earthquake. Two examples of the estimated focal mechanisms (beachballs) are shown in the first column of Figure 2, where the uncertainties of the calculated mechanisms are also reported. To estimate the source dimensions and the net slip on the fault, we used the signals recorded by BKWB and BKSG mobile digital stations (Figure 1). These two stations have had a very stable operation over the studied time period, except during the earthquake MD = 2.2 of 16/08/2018, when both were not operative. Moreover, their site responses are well known [22]. For each earthquake, the displacement amplitude spectra for the direct S-waves were estimated in the frequency domain after Fast Fourier Transform of seismic time series. We selected three s-windows of signals, starting 0.2 s before the S-onset, with 5% Hanning tapering, which allowed us to calculate stable S-wave spectra, in agreement with [14, 22]. The source spectrum of the S-wave is obtained as the mean value of the spectra of the two horizontal components (NS and EW). The distance between the stations and the hypocenters of the most considered VTs fall in the range 0.8-3.8 km, producing a negligible anelastic attenuation effect on the recorded spectra. Even the deeper event (2019/05/18 21:11) with a station-source distance of about 5.6 km shows an incidence of the attenuation effects of about 5% on the source spectra estimated parameters and, hence, we did not consider the attenuation effect in the following. To estimate the source spectra parameters, we considered the values for velocities and densities inferred from the tomographic study of [PERSON] et al. [35], a 2D layered medium, with a P-wave velocity \(\alpha=2\) km/s for the topography, \(\alpha=3\) km/s from the sea level to 2 km of depth b.s.l. and \(\alpha=6\) km/s below 2 km of depth [36]. The S-wave velocity values were estimated from the relation \(\alpha/\beta=1.9\). Similarly to [21, 22], we found homogeneous spectra in the 1-4/6 Hz frequency band (Figure 3). Figure 3: Examples of source spectra, in loglog plots. For BKWB station, the spectra are shown in black, the linear interpolations of the low-frequency level are reported in dark blue, and the high-frequency pattern interpolations (–17-27 Hz) are in red. For BKSG, the spectra are gray, the low-frequency levels are light blue, and the high-frequency patterns are magenta. (**a,b**) show the temporal indication and the MD value. The fc values are calculated from the intersection of the low- and high-frequency asymptotes (shown by a gold oval). Most of the located earthquakes are shallow, with a depth less than 2 km. For these VTs we set \(\rho\) = 2400 kg/m\({}^{3}\), while \(\rho\) = 2700 kg/m\({}^{3}\) for the few deeper earthquakes. \(\Omega_{0}\) was estimated from the spectra (Figure 3) by interpolating the low frequency level, in the range 1-4/6 Hz, and averaging, when possible, the estimation for BKWB and BKSG. In general, the two stations show comparable source spectra (Figure 3). The corner frequency, fc, was calculated as the intersection of the low-frequency and the high-frequency asymptote of the spectral envelope in a loglog plot (Figure 3). We found fc values in the interval 5-17 Hz, in good accordance with [14,21,22].