Table T1. Marine geophysical data used for this proposal.
|
Aguadomar 1999 |
Caraval 2002 |
Gwadaseis 2009 |
JC45/46 2010 |
|
|---|---|---|---|---|
| Research vessel | R/V L’Atalante | R/V L’Atalante | R/V Le Suroit | R/V James Cook |
| Swath bathymetry | ||||
| Multibeam echosounder | Simrad EM12D | Simrad EM12D | Simrad EM 300 | Simrad EM120 |
| Predicted depth accuracy |
0.1–0.3% of depth (1–3m in water depth of 1000m) |
0.1–0.3% of depth | 0.1–0.3% of depth | 0.1–0.3% of depth |
| Cell size (m) | 50 | 50 | 50 | 50 |
| GPS | Starfix differential GPS | GPS | GPS | GPS |
| Ship positioning accuracy | Few meters | Few meters | Few meters | Few meters |
| Seismic reflection | ||||
| Sources (Cu/in) | GI 45/45 and 105/105 | GI 45/45 | GI 35/35 and 45/45 | GI 105/45 |
| Number of guns | 2 | 2 | 4 | 2 |
| Gun depth (m) | 7 | 1.5 | 3 | 3 |
| Number of recording channels | 6 | 24 | 72 | 60 |
| Channel spacing (m) | 50 | 12.5 | 6.25 | 1 |
| Streamer depth (m) | 5 | 3 | 3 | 1 |
| Streamer length (m) | 530 | ~500 | 358 | 100 |
| Vertical resolution (m) | ~20 | ~10 | 3 | 4 |
Notes: The swath bathymetry was processed using the Caraïbes software developed by IFREMER. The multichannel seismic reflection data were filtered, stacked and migrated using the Seismic Unix software for the 1999, 2002 and 2009 data, with Landmark’s ProMAX software for the 2010 data. The AGUADOMAR and CARAVAL data were migrated at a seawater velocity of 1450 m/s, a NMO correction was applied for the GWADASEIS data, and the JC45/46 data were migrated at a linearly increasing velocity of 1450–2500 m/s. Recently, to estimate the average thickness of debris avalanche deposits, we selected as our best value the seismic velocity of 2150 m/s, derived from JC45/46 seismic data analysis (common-reflection point NMO velocity picking). This value is slightly higher than some assumed velocity values used previously in similar deposits [e.g., 1800 m/s; Urgeles et al., 1997; Collot et al., 2001; Le Friant et al., 2004, 2000 m/s Bull et al., 2009] and in the proposal 681-Full2. Consequently, to consider uncertainties related to seismic velocity used, the depth of drilling have been recalculated using a maximum seismic velocity of 2200 m/s.
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