GNGTS 2014 - Atti del 33° Convegno Nazionale

module (Quality Positioning Services B.V.). This tool shows water column data with their exact position in space and time, preserving relevant information, such as time-based navigation and attitude (roll, pitch and heave corrections). The time series were sub-sampled during format conversion, yet preserving the full resolution of the water column features. Preliminary results and conclusions. Due to the optimal compromise solution of penetration/resolution, it was possible to achieve two main results: 1) to map the sedimentary sequence down to the M reflector, which is generally interpreted to be the top of the Messinian evaporites (about 1-1.5 TWT seconds deep, Fig. 3) in the Mediterranean area; 2) and to keep the highest resolution in the shallower part of the sub seafloor, where free gas accumulations and seep conduits were the primary target of the investigation. It has been thus confirmed that gas emissions at the seafloor occurred exclusively in the areas of highest backscatter. Only one point of high backscatter was not associated with gas venting at the seafloor. The sampling of sediment over this high backscatter spot revealed that the high reflectivity was due to the presence of a steep slope and hardground at the seafloor. Free gas is visible in the seismics close to the seafloor (Fig. 3) and almost everywhere coincides with the gas flares. This setting is very similar to theHikurangiMargin, NewZealand, where seepage is associated with the gas hydrate system (Crutchley et al. , 2010). Very suspicious and anomalous signals, that are present in the seismic data, can be related to bright spots or to the presence of a deep BSR, but this must be analyzed in more detail with a specific processing sequence. Mud diapirs (not depicted here) lie directly on top of convex bending of the Messinian reflectors; this occurs also, even if geometries are questionable there, in the mud volcanoes (Fig. 3). The mud diapirs develop along deep-rooted normal faults, which are now fully imaged by seismic data, and are covered by at least 200 TWT ms of sediment which appear to lie directly on top of the M reflector. The relationships between the supposed salt diapirs and the pockmark-related mud structures must be constrained in more detail. A new fault segment was imaged in the sedimentary sequence of the southern Propeller basin, this fault does not reach the seafloor and has no bathymetry morphology, but it can be interpreted as the prolongation of the fault dissecting diapir D2 (Fig. 1a). This fault is also the theoretical prolongation of the fracture zone SDFZ (Fig. 1a) on land, and this finding seems to confirm the main fault axes that were already hypothesized to be responsible for the geometry of the Propeller Basin (Fig. 1a). Further lines were shot on the very southern end of the Paola Ridge to cross the possible offshore part of the SLFZ fault zone (Fig. 1a), where also some earthquakes show a faint alignment, but preliminary interpretation of the stacked sections did not image any active fault, with faults ending their activity probably at the base of the Plio-Quaternary reflector. Another interesting goal achieved with the new seismic data is in fact the possibility to clearly differentiate between active and buried faults. Most of the faults that appear not being Fig. 3 – Stacked section of BP14_003 seismic profile. Location in Fig. 1. GNGTS 2014 S essione 1.2 173