Description: Boulders are frequently dislodged from rock platforms, transported and deposited along coastal zones by high- magnitude storm waves or tsunamis. Their size and shape are often controlled by the thickness of bedding planes as well as by high-angle to bedding fracture network. We investigate these processes along two coastal areas of Favignana Island by integrating geological data for 81 boulders, 49 rupture surfaces (called sockets) and fracture orientation and spacing with four radiocarbon dates, numerical hydrodynamic analysis, and hindcast numerical simulation data. Boulders are scattered along the carbonate platform as isolated blocks or in small groups, which form, as a whole, a discontinuous berm. Underwater surveys also highlight free boulders with sharp edges and sockets carved out in the rock platform. Boulders are composed of ruditic- to arenitic-size clastic carbonates. Their size ranges from 0.6 to 3.7 m, 0.55 to 2.4 m, and 0.2 to 1 m on the major (A), medium (B), and minor (C) axes, respectively. The highest value of mass estimation is 12.5 t. Almost all of boulders and sockets are char- acterized by a tabular or bladed shape. The comparisons between a) the fractures spacing and the length of A- and B-axes, and b) the frequency peaks of C-axis with the recurrent thickness of beds measured along the coastal zone demonstrate the litho-structural control in the size and shape of joint-bounded boulders. These comparisons, to- gether with the similarity between the shapes of the boulders and those of the sockets as well as between the lithology of boulders and the areas surrounding the sockets, suggest that blocks originate by detachment from the platform edge. Thus, the most common pre-transport setting is the joint-bounded scenario. Hydrodynamic equations estimate that the storm wave heights necessary to initiate the transport of blocks diverge from ~2 m to ~8 m for joint-bounded boulders and from few tens of centimeters up to ~11 m for submerged boulders. The comparison between the wave heights at the breaking point of the coastal zones with the results of hydro- dynamic equations shows that waves approaching the coastline are able to transport all surveyed boulders. Our data suggest that boulders have been transported by several storm events, even in very recent times.

Description: Published

Description: 191-209

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: 2TR. Ricostruzione e modellazione della struttura crostale

Description: JCR Journal

Description: The HVSR method applied to seismic noise can be a very useful technique to map the site effects of the territory, to identify the thickness of the soft covering and so the depth of the seismic bedrock. The case of the urban area of Oliveri is presented. Because of its high seismic hazard this area has been subject of first level seismic microzonation. The town lies on a large coastal plain made of mixed fluvial/marine sediments, overlapping a deformed substrate. In order to identify points on the area probably suffering of relevant site effects and to define a preliminary Vs subsurface model, 23 HVSR measurements were performed. A clustering technique of continuous signals has been used to optimize the calculation of the HVSR curves and 42 reliable peaks, in the frequency range 0.1-20 Hz, have been identified. A second clustering technique has been applied to the set of 42 vectors, containing coordinates, frequency and amplitude of each peak, to identify subsets attributed to the same seismic discontinuities. Three main clusters have been identified. The two characterized by lower frequencies have been considered in the HVSR data inversion, as stratigraphic peaks probably caused by the seismic bedrock. Finally, the morphology of the top of the seismic bedrock has been mapped. The deepening of the seismic bedrock below the mouth of the Elicona Torrent suggests the possible presence of a buried paleo-valley.

Description: Published

Description: SE225

Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica

Description: JCR Journal

Description: This study aims at evaluating the control exerted by fracture stratigraphy and diagenetic processes on oil first migration through an outcropping, mixed carbonate-siliciclastic succession. The present work included results of sedimentological, paleontological, mineralogical, petrographic, structural, and microstructural analyses carried out on organic-rich shales exposed at the Favignana Island of Sicily, Italy. The analyses focus on Upper Triassic yellowish siltstones and greyish laminated dolomitic limestones, which form a 10’s of m-thick succession exposed along the westernmost portion of the Sicilian fold-and-thrust belt. The studied succession deposited in a coastal lagoon associated to a wide carbonate platform, in which anoxic bottom conditions allowed the preservation of the organic matter forming catagenetic patches and veins/fractures infill. In fact, two orthogonal fracture sets perpendicular to bedding are pervaded by organic matter. They are hence interpreted as structural elements that affected the paleofluid circulation and oil migration within the Triassic source rock. These two orthogonal sets form the background fracture network predating the formation of three other sets infilled mainly with calcite cements. The latest fracture set also includes barite cements implying a hydrothermal origin (〈200 ◦C), as supported by the R1 and R3 mixed-layer Illite-Smectite (I–S) stacking. Data are consistent with a burial depth of the sedimentary succession of about 3 ± 0.5 km. In light of these considerations, the study area might represent an outcropping stratigraphic and structural analogue of the source rocks buried in the offshore of western Sicily and northern Tunisia.

Description: Published

Description: 105400

Description: 2T. Deformazione crostale attiva

Description: JCR Journal