ALBERT

Description: Summary The continental margins of southern Italy are located along converging plate boundaries, which are affected by intense seismicity and volcanic activity. Most of the coastal areas experienced severe earthquakes, landslides, and tsunamis in historical and/or modern times. The most prominent example is the Messina earthquake of Dec. 28, 1908 (Ms=7.3; 80,000 casualties), which was characterized by the worst tsunami Italy experienced in the historical time (~2000 casualties). It is, however, still unclear, whether this tsunami was triggered by a sudden vertical movement along a major fault during the earthquake or as a result of a giant marine slide initiated by the earthquake. The recurrence rates of major landslides and therefore the risk associated with landslides is also unknown. Based on detailed bathymetric data sets collected by Italian colleagues in the frame of the MaGIC Project (Marine Geohazards along the Italian Coast), we collected seismic data (2D and 3D) and gravity cores in three working areas (The Messina Straits, off Eastern Sicily, the Gioia Basin). A dense grid of new 2D-seismic data in the Messina Straits will allow to map fault patterns in great detail. One interesting outcome in this context is the identification of a set of normal faults striking in an EW-direction, which is almost perpendicular to the previously postulated faults. This EW-striking faults seem to be active. The area off eastern Sicily is characterized by numerous landslides and a complex deformation pattern. A 3D-seismic data set has been collected during the cruise using the so called P-cable in order to investigate these deformation patterns in detail. The new data will be the basis for a risk assessment in the working areas.

Description: Cruise MSM34 of R/V MARIA S. MERIAN aimed to investigate a possible test site location for the German SUGAR project. The well sealed gas hydrate deposit should be accessible by the mobile drilling device MeBo 200. During the two legs of cruise MSM34 of R/V MARIA S. MERIAN regional 2D seismic surveying, high resolution 2D and 3D seismic imaging, geo-chemical sampling, heatflow measurements and long-term piezometer installations were undertaken. A grid of 28 2D seismic profiles was collected across the palaeo Danube delta. A number of inactive and partly buried channel systems could be mapped. Most of them were underlain by one or more bottom simulation reflectors (BSR) indicating the existence of gas hydrates. Based on the seismic brute stack images and the limits of the MeBo drilling device a prospective channel system with indications for possible gas hydrate formation at shallow depth (BSR, inverted strong amplitudes) could be identified in about 1500 m water depth. High resolution 2D seismic and 3D P-Cable seismic were used together with OBS deployments in order to allow structural mapping and physical description of the channel infill. Heatflow measurements and geochemical analyses of gravity and multi corer samples accompany these investigations. Neither the multibeam water column images nor Parasound records show any evidence of flares (gas bubbles in the water column) in this working area suggesting a well sealed hydrate reservoir. Active gas expulsion from the seafloor was observed at about 200 m water depth circling around a slump area. The base plane of the failed sediment volume builds the current seafloor at about 600 m to 700 m water depth. On regional 2D seismic profiles a BSR has been mapped underneath the slope failure with unexpectedly strong upward bending. High resolution 2D and 3D P-Cable seismic investigations with complementary OBS deployment will allow imaging the BSR outline. Moreover velocity analyses, heatflow measurements and geo-chemical samples will be available for a detailed description of hydrate distribution and sediment parameters. In a third working area high resolution 2D seismic reflection profiles were acquired across a fully buried channel system. Together with the regional seismic lines slope failure of the channel fill material can be studied across the slope extension of the system. In summary cruise MSM34 achieved all proposed aims. Based on new regional seismic acquisition two working areas were selected for 3D high resolution studies. Investigations of a promising location for a SUGAR pilot site will be supported by a test location for slope stability and analyses of fluid migration pathways in a buried canyon site.