Drilling and monitoring of natural and man-made landslide trigger mechanisms at the Ligurian slope (Mediterranean Sea): the tsunamigenic 1979 Nice Airport landslide, southern France
Abstract
Submarine landslides, occasionally followed by tsunamis, represent a major geohazard and an exciting research target given the wealth of trigger mechanisms and their dynamic interaction. The Ligurian margin, western Mediterranean, is known for its steep topography with numerous landslide scars, however, the cause of these landslides is incompletely understood. Given the geodynamic situation adjacent to the western Alps (with seismicity ranging up to M>6), the lithological variability (coarse sand and conglomerate interbedded with sensitive clay) and different hydrological regimes (coupled to precipitation and seasonal melt-water discharge), as well as the profound human impact on the coast (e.g. collapsed harbour construction site in 1979, followed by a tsunami in the Gulf of Antibes), the French portion of the Riviera is an area where various triggers can be studied in a locally confined region. After a series of seagoing expeditions by MARUM Bremen, Germany and IFREMER Brest, France in recent years, the wealth of geophysical, sedimentological and geochemical evidence as well as long-term data sets support multiple triggers for mass wasting at the shallow Ligurian margin. They include groundwater charging of sand and conglomerate beds, leaching of clay layers, overcompaction by airport construction, seismicity and slope sedimentation processes. To test the associated failure hypotheses, a drilling proposal for a series of holes at the Nice slope where a tsunamigenic landslide occurred after rapid loading by coastal construction 30 yrs ago. Drill sites aim to characterize the metastable slope E and W of the former collapse structure, and the re-deposited material partly occupying the present-day landslide scar. The target depth at each site will provide reconnaissance data in the shallowmost portion (already sampled by gravity coring down to 17 mbsf, and profiled using CPTu devices to up to 60 mbsf) as well as characterization of the underlying strata down to ~150 mbsf. Geotechnical drilling (coring and in situ sonic CPTU) will identify mechanically weak vs. strong layers, hydraulically active horizons, and zones of overpressure owing to groundwater-charging or vertical loading. Long-term objectives include borehole observatory installations and monitoring of the governing physical parameters affecting slope failure (pore pressure, temperature, strain, seismicity) in this densely populated, societally highly relevant part of the French Riviera.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMNH51B1062K
- Keywords:
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- 1810 HYDROLOGY / Debris flow and landslides;
- 1822 HYDROLOGY / Geomechanics;
- 3036 MARINE GEOLOGY AND GEOPHYSICS / Ocean drilling;
- 3070 MARINE GEOLOGY AND GEOPHYSICS / Submarine landslides