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OSP-03 Ocean margin and ocean island sediment mass movements and their consequences: Where? When? Why? - Part 1
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Analysis of triggering mechanisms of the Ana Slide
(Balearic margin of the Eivissa channel, western Mediterranean)
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Sara Lafuerza, GRC Geocičncies Marines (Spain)
Nabil Sultan, Ifremer (France)
Didier Leynaud, Ifremer (France)
Jaume Frigola, GRC Geocičncies Marines (Spain)
Bernard Dennielou, Ifremer (France)
Hong-Viet Nguyen, Ifremer (France)
Antonio Cattaneo, Ifremer (France)
Galderic Lastras, GRC Geocičncies Marines (Spain)
Miquels Canals, GRC Geocičncies Marines (Spain)
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The Ana slide is located in the low sediment rate carbonate continental slope of the Balearic margin of the Eivissa channel (western Mediterranean), where other slides are found with the same slip horizon, indicating a likely simultaneous occurrence under a common triggering mechanism. In the headwall area of the Ana slide, acoustic wipe-out identified from seismic reflection profiles masking the stratified facies beneath the slide could be indicative of the presence of gas. Moreover, the presence of pockmarks located at the headwall areas of the slides suggest that fluid escape processes in the upper Plio-Quaternary sedimentary sequence could be closely linked to its formation.
One of the objectives of the PRISME cruise (October-November 2007 - onboard R/V L'Atalante) was to characterize the physical, mechanical and sedimentological properties of the Ana slide. During the PRISME cruise, in situ measurements using the Penfeld penetrometer (CPTU- with a maximum depth of investigation of 30 mbsf) were carried out at ten different sites between the slide toe and the headwall. Three sediment cores were collected with Kullenberg corers at the slide toe, below and above the headwall, coinciding with CPTU locations. In order to characterize the hydraulic regime of the sliding area, piezometer measurements were run at four sites within and around the headwall scarp. Sedimentary and geotechnical analyses performed onboard and in the UB laboratory include: i) sediment core logging made with the Multi Sensor Core Logging and the Avaatech XRF Core Scanner onboard ii) classification tests (moisture contents, Atterberg limits and grain size analysis) obtained both onboard and in the UB laboratory iii) undrained shear strength acquired using a vane shear and fall-cone devices and iv) P-wave velocity measured with a celerimeter.
The data set gathered during the PRISME cruise and the preliminary results derived from laboratory analyses were used to conduct a slope stability analysis of the Ana slide by using the computer program SAMU3D (Sultan et al., 2007). The numerical analysis aims to identify the triggering mechanism(s) involved in the formation of the Ana slide by evaluating the Factor Of Safety (FOS) of the most critical failure surface under undrained and drained failure conditions.
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