COSTA cruise IMANICE2 (Nice, France)
Mapping of Holocene sediments
evidencing detailed morphology of slope failure area
S. Delandsheer, Y. Thomas, T. Marsset, B. Marsset, S. Didailler, P. Cochonat (IFREMER Brest, BP70 29280 Plouzané)
One of the objectives of the COSTA project being the understanding of seafloor failure dynamics through 3D imaging of sediment architecture, the Nice area
was selected, due to the existence of previous slope failures (1979) during the construction of a new harbour.
The 3D seismic acquisition system was designed for optimal coverage of sites of limited extent (2 km * 1 km) in water depths up to 100 m and a target vertical
resolution of a meter.
The analysis of the 3D seismic data is conducted in two steps:
1) a first conventional 2D multichannel analysis was applied on the whole area in order to image the general architecture of sediments and to select the
targets of key geotechnical importance,
2) the 3D analysis will be performed on the selected targets implying the extraction of depth slices and horizon slices.
This poster presents results of the 2D analysis by pseudo 3D mapping of the superficial units. A 3D volume, extracted from the Northern area, is proposed as
an example of 3D processing sequence.
3D VHR METHODOLOGY
10 m10 m
• 4 streamers of 6 traces:
! distance between streamers: 5 m
! distance between traces: 2 m
! distance between sailed l ines: 10 m
• Sparker: firing rate 0.5s
• av erage speed: 3.5 nds
B) Seimic interpretation:
1) Unit U1 :
• wide variations of thickness (0 to 35 m) on the shelf and on the
• seismic facies characterised by internal parallel reflectors of low
amplitude draping the underlying unit U2.
• interpreted as made of fine sediments (muds).
• seismic reflectors terminations characterised by truncations
along the sea-bottom (unconformity surface) suggesting post-
depositional (erosional?) effect.
• erosional axes often superimposed (or wit