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International Research
3. Work in progress and future experiments
Interpretation of the signals recovered in August 2008 is presently
in progress. Based on the statistics above, it is expected
that more than 8000 events will be detected and localized by
the MARCHE array during its 3-year deployment period.
Further analysis on the time- and space-distributions of events
over the entire MOMAR area will be conducted as soon as the
three-year catalog is completed and will provide new insights
into active processes along the MOMAR section of the MAR.
Additional work in progress includes a Ph.D. thesis by Abel
Balanche, expected to be completed soon. This work achieved
a 2D finite-element mechanical model of the conversion process
between seismic and acoustic waves at the seafloor interface.
This model shows that a double-couple source mechanism
produces T-waves which can enter the SOFAR channel with
adequate angles to be trapped into this channel. It also confirms
that a source with a high S-wave content is more efficient
in producing T-waves than a simple explosive source that only
generates P-waves (Balanche et al., 2007). This work will allow
a more accurate determination of earthquake magnitudes from
the amplitudes of the acoustic signals recorded by AUHs.
Further development of AUHs is presently underway in Brest.
The prototype was successfully tested in shallow water in July
2008. We plan to test it in real operational conditions offshore
Villefranche-sur-Mer before the end of this year. After this
second test is completed, a first array of four instruments will
be assembled and deployed at the MARCHE sites in 2009,
thus continuing the monitoring of the MOMAR section of the
MAR at a regional scale.
4. Web sites related to the MARCHE experiment
Additional information on MARCHE, including the preliminary
cruise reports related to the first two deployments, can be
accessed through links from the MARCHE web home page:
http://www-sdt.univ-brest.fr/internet/recherche/Chantiers/
marche. Additional information on MOMAR and previous
acoustic monitoring in the region (the SIRENA and South
Azores arrays) can be found at: http://www.momar.org.
5. Acknowledgments
The scientific parties on board R/V Knorr, R/V Arquipélago,
R/V Le Suroit and NRP Alm. Gago Coutinho wish to thank
the ships’ masters, the officers and crews of these four ships for
their efficient seamanship. The French Ministry of Research
funded ship time for the three cruises sailed aboard Arquipélago
and Le Suroit. The Portuguese Estrutura de Missão para a
Extensão da Plataforma Continental (EMEPC) and its Director,
Pr. M. Pinto De Abreu, secured shiptime on NRP Alm.
Gago Coutinho to sail the MARCHE3/2008 cruise. Salaries
and travel costs were provided by the universities and institutions
to the nationals of the three countries involved. The cost
of developing and building the MARCHE hydrophones, the
deployment costs and the freight costs were shared between
the NOAA Ocean Exploration Program, the French CNRS/
INSU (Institut National des Sciences de l'Univers), and the
MOMAR-France Program.
6. References
Balanche, A., Guennou, C., Goslin, J. and Dziak, R.P., Modeling
of conversion of seismic to acoustic waves at the seafloor
interface. AGU Fall Meeting. San Francisco, Dec. 2007.
Dziak, R.P., Fox, C.G., Smith, D., et al., Evidence for a probable
magmatic episode at the Lucky Strike segment of the
MAR. Geophys. Res. Abstr., 5, 01784, 2003.
Dziak, R.P., Haxel, J., Bohnenstiehl, D., Goslin, J., Seismicity
rates of slow, intermediate and fast spreading ridges: Insights
from long-term hydroacoustic monitoring. AGU Fall Meeting.
San Francisco, Dec. 2004.
Goslin, J., Martin, C., Perrot, J., et al., Acoustic monitoring
of the Mid-Atlantic Ridge noth of the Azores: Preliminary
results of the SIRENA experiment. InterRidge News 13, 9-
13, 2004.
Goslin, J., Lourenço, N., Luis, J., et al., Acoustic monitoring of
the Mid-Atlantic Ridge in the MOMAR Area: Preliminary
results of the ''MARCHE'' experiment. AGU Fall Meeting.
San Francisco, Dec. 2008.
Simão, N., Goslin, J., Perrot, J., Haxel, J. and Dziak, R.P.,
Analysis of the spatial and temporal distribution of the seismicity
of the Mid-Atlantic Ridge using the SIRENA and
the South Azores autonomous hydrophone arrays. AGU Fall
Meeting. San Francisco, Dec. 2006.
Simão, N., Haxel, J., Goslin, J., et al., (in prep.) Characterization
and tectonic implications from seismic sequences along
the northern Mid-Atlantic Ridge (12°N - 47°N) using regional
hydrophone arrays.
For more highlights of research activities at MoMAR,
please refer to the cover image and photos, the national news for France,
and the update from the Monitoring and Observatories Working Group.
www.momar.org
InterRidge News 9 Vol. 17, 2008