GNGTS 2013 - Atti del 32° Convegno Nazionale

where Pc is the probability to accept the condition ΔE = E 0 - E 1 , q is an integration constant determined empirically, E min is the objective value of the function of the total minima. In theory E min = 0. Results. From the seismic velocities Vp and Vs estimated at 1 m intervals along the three mechanical drillings we have computed elastic and seismic parameters. The stratigraphy of the study area is characterized by more or less fractured calcareous lithotypes (Fig. 2). Seismic velocity is irregular with depth (Fig. 3). We have identified 4 seismic layers referred to different lithotypes, characterized by the physical parameters listed in Tab. 1. Tab. 1 – Characteristics of the lithotypes. Seismic layer Lithology Vp (m/s) Vs (m/s) γ din (gr/cm 3 ) Coeff. τ Coeff. ξ hFr_C Highly Fractured Calcarenite 1279.49 477.50 1.98 1.20 -0.20 mFr_C Moderately Fractured Calcarenite 1758.18 757.12 2.11 0.83 0.17 lFr_C Little Fractured Calcarenite 2308.98 1092.73 2.22 0.92 0.08 wPr_C Well preserved Calcarenite 3202.42 1572.29 2.36 0.96 0.04 Seismic layer μ (kg/cm 2 ) K (kg/cm 2 ) E (kg/cm 2 ) M (kg/cm 2 ) S.I. (t * m -* s -1 ) σ hFr_C 4771.49 27578.86 13383.85 33940.84 949.62 0.41 mFr_C 12558.74 49709.38 34603.28 66454.37 1599.29 0.39 lFr_C 27345.35 85291.60 73909.50 121752.06 2430.40 0.35 wPr_C 59897.23 167823.70 160397.04 247686.68 3720.13 0.34 The velocity image of the substrate resulting from the tomography survey is characterized by several seismic layers with irregular geometry (Fig. 3). Lateral and vertical velocity changes define three seismic layers. The shallower layer extends from 0 to 2 m from the ground surface with seismic velocities of 500-900 m/s; it corresponds to the altered portion of the substrate; the second layer is characterized by an average P-wave velocity of 1000-2000 m/s and extends from 5.5 m west of S2 to the end of the tomography array; the third layer shows seismic velocity of 2000-3000 m/s. The imaged velocity shows a step-like pattern that can be ascribed to the dislocation along the Ispica fault plane. Conclusion. The study area lies on a calcareous rocky terrain composed of banks of limestones with white-grayish and white-yellowish colors intercalated with soft marly layers. This unit represents the lower portion of the Irminio Member of the Ragusa Formation, of Aquitanian-Burdigalian age. In three mechanical drillings, 30 m deep and aligned along the edge of the cliff, we have carried out down-hole measurements of seismic velocity ( Vs30 ); we have also collected cross- up hole seismic tomography profiles. From the results of these surveys we identified four seismic layers characterized by a different degree of fracturing laterally varying in the NW-SE direction. The fractured portion, that correspond to the fault zone determining the offset of the rocky terrain object of this study, extends in part beneath the Minor Friars Convent. 50 GNGTS 2013 S essione 3.1