Le Suroit SIRENA

Cruise summary report

Cruise Info. 
Ship name (ship code)Le Suroit (35LU)
Cruise identifierSIRENA
Cruise period2002-05-18 — 2002-06-03
Port of departurePonta Delgada, Portugal
Port of returnBrest, France
ObjectivesSix haruphones were deployed in the SOFAR channel in the North Atlantic during the SIRENA cruise (see the general track map in section III for the locations of the mooring sites). At water depths around 1000 metres, acoustic waves generated in the water column by earthquakes - and by marine mammals - propagate to very long distances with a very low signal attenuation. The moorings are located on both flanks of the Mid-Atlantic Ridge (MAR), north of the Azores, between latitudes 40° N and 50.5° N (that is between the Azores Plateau and a major structural discontinuity south of the Gibbs Fracture Zone). An haruphone network, similar to the one which was deployed during the SIRENA cruise, has been deployed south of the Azores by the PMEL/NOAA between latitudes 17° N and 35° N. This network has been operating since February 1999 and will remain active for one more year from now. It should be noted in this respect that the Azores Plateau is globally shallower than the SOFAR channel in the North Atlantic, especially as the apex of the SOFAR channel was found to be unusually deep in the area of survey, exceeding 1000 metres at some of the mooring sites. It therefore acts as a "barrier" to the sound propagation of the acoustic waves generated by earthquakes whose epicenters are located south of the Plateau. The existence of such a barrier explains that the haruphone network which is presently operated by PMEL/NOAA cannot observe any of the events which originate south of the Azores Plateau. This problem is the main reason which warranted the SIRENA experiment.
The SIRENA cruise objectives (two main objectives and an ancillary one) are based on a very accurate determination (better than 2 km) of the epicentres of the earthquakes occurring along the Mid-Atlantic Ridge. Such a precise determination will be made possible by the data recorded by the hydrophone network.
The objectives are the following:
1 - To contribute to the understanding of active processes at the axis of midoceanic ridges.
2 - To get some insight into ridge/hotspot interaction processes in the uppermantle
3 - By observing time-variable along-ridge seismicity north of the Azores and by comparing it to the seismicity observed within the Azores archipelago itself, to contribute to the assessment of the seismic hazard in the Azores archipelago.
Chief scientistJean Goslin (Laboratory of Marine Environmental Science (UMR CNRS 6539))
Coordinating bodyURM6538/CNRS in Brest
Cruise reportLe Suroit SIRENA cruise report ls_sirena_02.pdf (0.42 MB) 
Ocean/sea areas 
GeneralNorth Atlantic Ocean
Track chartsLe Suroit SIRENA cruise track — ls_sirena_02roscop4616trk.pdf (0.16 MB) 
Geology and geophysics 
Multi-beam echosoundingDescription: Topographic survey of the Terceira Ridge
Moorings, landers, buoys 
Geology and geophysics 
Geophysical measurements made at depth42° 43' 1" N  34° 43' 20" W — Deployment of autonomous hydrophone mooring
Geophysical measurements made at depth40° 20' 15" N  25° 2' 13" W — Deployment of autonomous hydrophone mooring (developed by the PMEL/NOAA)
Geophysical measurements made at depth47° 0' 1" N  22° 10' 2" W — Deployment of autonomous hydrophone mooring
Geophysical measurements made at depth50° 34' 31" N  34° 30' 0" W — Deployment of autonomous hydrophone mooring
Geophysical measurements made at depth49° 51' 15" N  24° 34' 26" W — Deployment of autonomous hydrophone mooring
Geophysical measurements made at depth47° 35' 35" N  32° 27' 15" W — Deployment of autonomous hydrophone mooring