Becel, Anne

Charvis, Philippe

Diaz, Jordi

Flueh, Ernst R.

Hirn, Alfred

Laigle, Mireille

English

OceanRep

Geophysical Research AbstractsVol. 12, EGU2010-PREVIEW, 2010EGU General Assembly 2010© Author(s) 2010Searching for conditions of observation of subduction seismogenic zonetransients on Ocean Bottom Seismometers deployed at the Lesser Antillessubmerged fore-arcAnne Bécel (1), Mireille Laigle (1), Jordi Diaz (2), Alfred Hirn (1), Ernst Flueh (3), and Philippe Charvis (4)(1) IPGP, Dep. Seismology, UMR 7154, Paris, France (becel@ipgp.fr), (2) Institute of Earth Sciences ’Jaume Almera’-CSIC,Barcelona, Spain, (3) IFM-GEOMAR, Leibniz-Institut für Meereswissenschaften, Kiel, Germany, (4) UMR Géoazur,Villefranche-sur-Mer, FranceIn the frame of the European Union « THALES WAS RIGHT » and French ANR CATTELL SUBSISMANTIfunding, an unprecedented array of 80 OBS, Ocean Bottom Seismometers of Géoazur Nice, INSU/IPGP Paris,IfM-GEOMAR Kiel, AWI Bremerhaven could gathered. They have been deployed for continuous recordingover four months on the fore-arc domain of the Lesser Antilles subduction zone offshore Martinique, Dominica,Guadeloupe and Antigua Islands, by scientific cruises of N/O ATALANTE, F/S M. A. MERIAN and N/O ANTEA.One of the aims of this OBS array was the feasibility study of detecting at sea-bottom the seismologicalpart of recently discovered phenomena such as NVT non-volcanic tremors and LP, for Long-Period events. Theability of detecting such transient signals is of importance, since they are possibly related to potential mega-thrustearthquakes and their preparation zone.At the Lesser Antilles subduction zone, the fore-arc domain overlying the seismogenic part of the interplate islocated offshore, covered by as much as 4000 m of water. In this case, transient signals can be accessible onlyfrom OBS observations. Hence, there is a major difference, in the sense of the instrumental and logistical effort,with the subductions under NW US-Canada and under Central Japan where these signals have been discovered.There, the subduction zones have an emerged fore-arc that has allowed the chance discovery of those phenomenaby regular instrument maintained routinely on land.Over 20 of the instruments were BB-OBS, with broadband seismic sensors, possibly the largest such gath-ering at the time of the experiment among the OBS types. Among those broadband OBS designed or used bydifferent Institutions, there were at least three different seismometer brands and acoustical sensors, as well asdifferent mechanical mounting and technical solutions for coupling them to ground. This did not facilitate datarecovery and processing, but on the other hand, as planned by interweaving the different instruments deployments,it provided diverse views, as through different glasses. This ultimately proved valuable to help extract the harderfacts from their diverse appearances when seen through different instruments and in different types of sites.After analyzing the data for spurious and instrument-related peculiarities, and possible interpretation pitfalls, itremains that the noise level shows an overwhelming influence of the marine domain due to both its own sources,hydrosphere motions, and to meteorological-climatological actions. As well, the response of the laterally variablefore-arc basin on top of which measurements have to be made is much adverse to quality recording, with respectto seismological observatories on land which can be buried deep into basement rocks. The study of this noise itselfmay allow us to initiate a discussion of the interactions of the oceanic and atmospheric processes with the SolidEarth.Transients at depth in the subduction zone have been tentatively discussed in terms of its seismogenic evo-lution. If such transient events would indeed have a component over a very broad spectral range from NVT toLP and ULP events as it has been suggested very recently in Japan (Ide et al., 2008), the conditions and the bestobservation windows in which they can be best searched for are now documented for ocean bottom recording inthe case of the Lesser Antilles subduction zone.

Searching for conditions of observation of subduction seismogenic zone transients on Ocean Bottom Seismometers deployed at the Lesser Antilles submerged fore-arc

Searching for conditions of observation of subduction seismogenic zone transients on Ocean Bottom Seismometers deployed at the Lesser Antilles submerged fore-arc

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