GNGTS 2016 - Atti del 35° Convegno Nazionale

GNGTS 2016 S essione A matrice 65 extensional deformation patterns associated with normal faults with a general NW-SE trend. In addition, oblique and crestal normal faults affect the main anticlines, which represent a later stage of the fold evolution. The normal faults are grouped in several generally SWdipping kilometer long segments with a throw of many hundreds of meters. At the mesoscale, the normal fault structures consist of about 1 m thick cores of fragmented and brecciated carbonate rocks and, sporadically, millimeter and centimeter thick comminuted gauge The damage zone consists of fault rocks and major slip surfaces that separate fault subsets with several meters of offset which bound slivers of rocks having different deformation intensity and dip angles. The internal structures consist of several centimeter thick cemented and uncemented, comminuted cataclasite, flanked by fragmented carbonate rocks a few meters in thickness. In the marly limestone lithology, in the extensional shear zones are prevalent the S/C structures up to 1 m thick (Menichetti, 1982). Mt. Vettore (2,476 m a.s.l.) is the highest peak of the Sibillini mountains chain, where Mesozoic limestones outcrops are arranged in a complex folded structure with a N-S trend axes. The external overturned anticline is thrusted for many km onto the Miocene Laga siliciclastic turbidites. The footwall consists of recumbent synclines and anticlines with NNE-SSW trending axes. The entire Mt. Vettore structure, is crosscut by several SW dipping normal fault systems. The westernmost of these are responsible for the formation of the intramountain basin of Castelluccio di Norcia and dislocates the Lower Jurassic limestone for more than 1000 m. The fault consists of interlinked segments arranged with stepovers in NNW-SSE direction over a distance of over 10 km. Located on the western side of the chain, the fault has a pronounced morphological feature. A continuous limestone scarp is well documented in the upper section of the mountain, together with a few steps located in the piedmont area, where slope deposits of clastic materials buried several splays that distribute the fault throw. In the eastern side of Mt. Vettore, the thrust is crosscut with an offset of a few hundred meters. The fault runs along the Tronto valley and the western side of the Laga Mountains, linking with the Amatrice and Mt. Gorzano faults (Menichetti, 1982; Pizzi and Galadini, 2009; Lavecchia et al. , 2012). Here we present the results of a structural survey of the surface rupture obtained by integrating a direct, classical structural field survey with aerial and remote sensing data. In order to define the topological relationship between faults and fractures, we created a three-dimensional virtual reconstruction of the surface rupture exposed along the Mt. Vettore escarpment. The area covers a surface of about 0.5 km 2 over a distance of about 5 km. A procedure has been developed starting with two kinds of data: classical structural survey data supported by oblique digital georeferenced terrestrial photos and a sequence of more than one thousand georeferenced oblique and zenithal digital photographs acquired from a small quadcopter platform. The camera used for terrestrial acquisition was a hand-held digital Single- Lens Reflex (SLR) Nikon D810 FX equipped with a calibrated Nikon 35 mm f/1.4 lens. The photos have a resolution of 36.3 megapixels (7360 x 4912) in RAW format. Each photo was georeferenced through a standard GPS (GNSS) unit located above the camera body. The camera used for oblique and zenithal acquisition was a single-lens camera equipped with Sony sensor Exmor 1/2 3° with a calibrated Sony FOV 94°, 20 mm f/2.8 lens. The photos have a resolution of 12.76 megapixels (4000x3000) in RAW format. Each photo was georeferenced through a GPS and GLONASS (GNSS) unit located above the camera gimbal. The photo’s geo-location was subsequently verified using several Ground Control Points (GCPs) surveyed with a laser ranger finder telemeter. The average accuracy of the GCP locations obtained by means of GPS was less than 0.05 m. All digital images were processed using Structure from Motion (SfM) algorithms (Lowe, 1999). To take into consideration parameter distortions by the camera and the lens, 3D coordinates of the detected points were extracted and a point cloud was generated. In the surveyed outcrops, clouds of more than 30*10 6 points were obtained. Using the point clouds, a fully rendered 3D geological model of the entire outcrop was generated, making the extraction of the geometries of structural discontinuities possible. The