GNGTS 2017 - 36° Convegno Nazionale

402 GNGTS 2017 S essione 2.2 H/V amplitude variations with the azimuth. For the sake of conciseness, only the stations with the major differences are reported in this work. To evaluate the directivity effects we divided the spectral ratios in two groups: local events, for which we have seven azimuth available and regional events, with three azimuth available. For the regional events (Fig. 2a) we observe differences in the frequency peak below 3 Hz for the stations BULG, MIRG and UMSG and a meaningful difference for the station SESG in which we notice all over the frequency range a shift in the amplitude more evident at the peak (~ 4 Hz). For the local events (Fig. 2b), we observe that the spectral ratios have more variability below 4 Hz, with the except of OVDG that shows at high frequency as well differences among the ratios, specifically for the events coming from Potenza (PZ) and Salerno (SA). Fig. 1 - a) Location of the earthquake epicentres. The white square is the area of study. b) the red triangles are the stations of the Mobile Seismic Network installed in the Campi Flegrei area. The red square indicates the presence of a surface station (UMSG) and a 144 m deep station (UMBG). The inset shows the configuration of the underground array “ARF”, installed at a depth of 20 m together with the station CELG.