MODELLIZZAZIONE DI DATI SISMICI A RIFLESSIONE, RIFRAZIONE E TERRA-MARE PER L'ANALISI DEL RISCHIO VULCANICO E SISMICO NELLA SICILIA ORIENTALE

1996/1997X Ciclo1965Versione digitalizzata della tesi di dottorato cartacea. Nell'originale cartaceo manca la pag. 14

Seismic imaging of Late Miocene (Messinian) evaporites from Western Mediterranean back-arc basins

An analysis of multichannel seismic reflection data was conducted focusing on the comparison between the Messinian Salinity Crisis (MSC) and Plio-Quaternary (PQ) evolution of the eastern Sardo-Proven\ue7al and northern Algero- Balearic basins and related margins in the West Mediterranean Sea. Both basins were completely opened during the MSC and their well-defined seismic stratigraphy is very similar in the deep parts. The primary difference between these two basins is due to their different pre-MSC extensional history, including the opening age and the stretching factors. These factors influenced the occurrence of post-MSC salt tectonics on these margins

REGIONAL VERSUS DETAILED VELOCITY ANALYSIS TO QUANTIFY HYDRATE AND FREE GAS IN MARINE SEDIMENTS: THE SOUTH SHETLAND MARGIN CASE STUDY

The presence of gas hydrate and free gas within marine sediments, deposited along the South Shetland margin, offshore the Antarctic Peninsula, was confirmed by low and high resolution geophysical data, acquired during three research cruises. Seismic data analysis has revealed the presence of a bottom simulating reflector that is very strong and continuous in the eastern part of the margin. This area can be considered as a useful site to study the seismic characteristics of sediments containing gas hydrate, with a particular focus on the estimation of gas hydrate and free gas amounts in the pore space. Pre-stack depth migration and tomographic inversion were performed to produce a regional velocity field of gas-phase bearing sediments and to obtain information about the average thickness of gas hydrate and free gas layers. Using these data and theoretical models, the gas hydrate and free gas concentrations can be estimated. Moreover, the common image gather semblance analysis revealed the presence of detailed features, such as layers with small thickness characterised by low velocity alternating with high velocity layers, below and above the bottom simulating reflector. These layers are associated with free gas trapped within the hydrate stability zone and deeper sediments. Thus, the use of the detailed and the regional velocity field analysis is important to give a more reliable estimate of gas content in the marine sediments.Non UBCUnreviewe

Offshore Antarctic Peninsula Gas Hydrate Reservoir Characterization by Geophysical Data Analysis

energie

Analysis of the Seismic Properties for Engineering Purposes of the Shallow Subsurface: Two Case Studies from Italy and Croatia

We present two case studies of the application of seismic surveys to estimate the elastic properties of soil and rock in the shallow subsurface. The two sites present very different geological characteristics. The first test site is a town on the Croatian coast, not far from the city of Split, built on hard rock, where we acquired three seismic lines. The second site is located in the outskirts of the city of Ferrara, in Italy, in an alluvial plain, where two lines were acquired. In both sites, for detailed characterization, we acquired surface-, compressional- and shear-waves, further distinguishing the latter between horizontally (SH) and vertically (SV) polarized wavefields. We processed the data by performing a Multichannel Analysis of Surface Waves to compute a preliminary one-dimensional shear wave velocity profile. Then, we performed first-break tomography to compute P-, SH- and SV-velocity profiles. Such unusual acquisition allowed us to compute not only basic engineering parameters such as the equivalent shear-wave velocity of the first 30 m of subsurface (VS30) from the SH profiles but also other useful parameters such as the VP/VS and estimate the anisotropy of the medium thanks to the VSV/VSH. Given the level of detail of the results and their engineering value, we conclude that the method of investigation we applied in the two test sites is a valuable tool for characterizing the shallow subsurface

Capo Granitola-Sciacca Fault Zone (Sicilian Channel, Central Mediterranean): Structure vs magmatism

Highlights • A structural map of the northern part of the Capo Granitola-Sciacca strike-slip Fault Zone (Sicilian Channel) has been produced. • Numerous magmatic manifestations in addition to those already known in the Graham and Terrible banks, have been recognized. • A relationship between magmatism and structures associated with the Capo Granitola-Sciacca Fault Zone, has been documented. • A mechanism of non-plume origin is proposed for the magmatism observed in the study area. The tectonic framework of the northern sector of the Capo Granitola-Sciacca Fault Zone (CGSFZ), a NNE-oriented lithospheric strike-slip fault zone located in the Sicilian Channel (southern Italy), has been reconstructed with the aim to clarify the relationships between geometry and kinematics of the structures and the occurrence and distribution of the magmatic manifestations observed in the area. This has been achieved by the interpretation of a large dataset composed of 2-D multichannel seismic profiles, Chirp profiles, magnetic data and borehole information. In addition to the volcanic edifices known in the Graham and Terribile banks, this study has allowed to recognize several other magmatic manifestations. The magmatic occurrences consist of small volcanic cones, buried magma ascents and potential igneous sills. The CGSFZ is bounded by two strike-slip fault systems, the Capo Granitola Fault System (CGFS) to the west and the Sciacca Fault System (SFS) to the east, dominated by positive flower structures generated by tectonic inversion of NNE-oriented late Miocene extensional faults. Only the southern part of the CGFS shows the presence of a sub-vertical, N-S oriented strike-slip master fault. The sector between the two fault systems does not show a significant Pliocene-Quaternary tectonic deformation, except for its southern part hosting the Terribile Bank, which is dissected by WNW to NW-trending normal faults developed during late Miocene and later reactivated. This set of faults is currently active at the Terribile Bank, whereas is buried by Pliocene-Quaternary deposits in the central and northern sectors of the CGSFZ. The observed magmatism is driven by a mechanism of non-plume origin. Magmas have used as open paths the faults of the CGFS and SFS, which cut the whole lithosphere reaching the asthenosphere and producing partial melting by simple pressure release. Most of the magmatism develops along the strike-slip master fault associated with the CGFS and the normal faults affecting the Terribile Bank. The magmatic feeding of the Terribile Bank would be related to lateral magma migration coming from the structures of the SFS, which would use the open pathways represented by active normal faults. In the central-northern part of the CGSFZ, magmas migrate upward along lithospheric faults, then move laterally and rise toward the surface through NNE and NW-trending buried normal faults. These late Miocene faults do not reach the surface, and this may have favoured the emplacement of igneous sills, which in turn may explain the observed volcanic centres

Fluid-Related Features in the Offshore Sector of the Sciacca Geothermal Field (SW Sicily): The Role of the Lithospheric Sciacca Fault System

The Sciacca basin extends in the southwestern part of Sicily and hosts an important geothermal field (the Sciacca Geothermal Field) characterized by hot springs containing mantle gasses. Newly acquired high-resolution seismic profiles (Boomer data) integrated with a multichannel seismic reflection profile in close proximity to the Sciacca Geothermal Field have documented the presence of numerous active and shallow fluid-related features (pipes, bright spots, buried and outcropping mud volcanoes, zones of acoustic blanking, and seafloor fluid seeps) in the nearshore sector between Capo San Marco and Sciacca (NW Sicilian Channel) and revealed its deep tectonic structure. The Sciacca Geothermal Field and the diffuse submarine fluid-related features probably form a single onshore–offshore field covering an area of at least 70 km2. This field has developed in a tectonically active zone dominated by a left-lateral transpressive regime associated with the lithospheric, NNE-striking Sciacca Fault System. This structure probably favored the rising of magma and fluids from the mantle in the offshore area, leading to the formation of a geothermal resource hosted in the Triassic carbonate succession that outcrops onshore at Monte San Calogero. This field has been active since the lower Pleistocene, when fluid emissions were likely greater than today and were associated with greater tectonic activity along the Sciacca Fault System