GNGTS 2016 - Atti del 35° Convegno Nazionale

362 GNGTS 2016 S essione 2.2 (most of the slicken lines on fault surfaces has pitch values>160° or <25°) and a related fracture network producing centimetre-to-decimetre along-fault offsets. Fault surfaces have general high dip values (>60°), dipping both to NE and SW. We identified a composite fault architecture consisting of a central 8 m-width core zone (including cohesive breccias with pronounced grain size reduction from fine crush breccia to cataclasite) and two lateral damage zones (including fault breccias and variable-spaced fracture network). Progressive fracturing is responsible for anisotropy-controlled shape of rock lithons, changing from orthorombic (within the damage zone) to sigmoidal and isometric (within the core zone). Geomechanical analysis. For the selected geological-structural sectors, we performed in- situ geomechanical measurements by using a Schmidt hammer (an engineering tool providing a hardness index that can be translate to the uniaxial strength of the rock mass). The Schmidt hammer have been applied on vertical portions of the rock mass in order to test the variation of the rock geomechanical parameters in the surroundings of the major fault/fracture. Fracture density. The fracture density (expressed in cm-1) is the summed length of all fractures within a properly drawn inventory circle, divided by the area of the circle. In the same sectors where we measured their geomechanical properties, we estimated the fracture density by the circle-inventory method (Davis and Reynolds, 1996). Discussion and implications. Our preliminary results highlights the variability of seismic waves polarization and amplification within the different fault domains, making possible to recognize probable bidimensional and tridimensional site effects. In detail our work shows that most of the amplification occurs within the damage/core zone (T1, T4, L5, T3); indeed no amplification have been detected out of the fault zone (T10, T11). Wave polarization occurs both parallel (T3, T4, T1) and transversal (T2, L5, L8) to the fault strike. Dispersion of polarisation angle could be related to different physical phenomen (trapped waves in the core zone, athypical topographic effects, ...). This work has implication for local seismic response andmicrozonation studies of urban areas located on rocky landforms, which are widespread in Italy and the Mediterranean region.  References Centamore E., Fumanti F., Nisio S.; 2002: The Central NorthernApenninesgeologicalevolution from Triassic to Neogene time. Boll. Soc. Geol. It., Special volume 1, 181–197. Davis G.H., Reynolds S.J.; 1996: Structuralgeology of rocks and regions (2nd ed.) . John Wiley&Sons, 776 pp. Martino S., Minutolo A., Paciello A., Rovelli A., ScarasciaMugnozza G. andVerrubbi V.; 2006: Evidence of amplificationeffects in fault zone related to mass jointing. NatHazards, 39:419–449. Pagliaroli A., Avalle A., Falcucci E., Gori S., Galadini F.; 2015: Numerical and experimentalevaluation of site effectsatridgescharacterized by complexgeologicalsetting. Bull. EarthquakeEng. DOI 10.1007/s10518-015- 9753-y. Pagliaroli A., Lanzo G., D’Elia B.; 2011: Numericalevaluation of topographiceffectsat the Nicastro ridge in Southern Italy . J. Earthq. Eng. 15(3), 404-432. Rovelli A., Caserta A., Marra F., Ruggiero V.; 2002: Can seismicwaves be trapped inside an inactive fault zone? The case study of Nocera Umbra, Central Italy. Bull. Seism. Soc. Am., 92, 2217-2232. Saroli M., Biasini A., Cavinato G.P., Di Luzio E.; 2003: Geologicalsetting of the southernsector of the Roveto Valley (Central Apennines, Italy) . Boll. Soc. Geol. It., 122 , 467-481. Wise D.U., Funiciello R., Parotto M., Salvini F.; 1985: Topographiclineamentswarms: clues to theirorigin from domain analysis of Italy. Geol. Soc. Am. Bull., 96, 952–967.