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International Research
It was therefore decided to achieve a three-year monitoring
of the MOMAR area by deploying and turning
over an array of four AUHs, deployed west and south
of the Azores, on both flanks of the MAR. Table 2
summarizes the various operations conducted within
the framework of the MARCHE experiment.
2. Some earthquake statistics derived from
the MARCHE hydro-acoustic data
The first two deployments (Goslin et al., 2008) allowed
localization of a total of 4445 events. A total of 149 of
these events occurred in a 1°-square area approximately
centered on the Lucky Strike (LS) hydrothermal site
(see white frame on Fig. 1). Only two events are listed
in the catalog compiled by the National Earthquake
Information Center of the U.S. Geological Survey for
the same area and period. Among the events localized
within the 1°-square area, 26 were localized with errors
smaller than 2.5 km in both latitude and longitude by
the four MARCHE AUHs.
The distributions of AUH-detected events vs. time show
both long- (~one year) and short-period variations. For
the short-term variations, activity is separated by periods
of quiescence lasting up to several weeks, during
which no event was detected in the area (Fig. 2).
Table 2: Operations conducted within the framework of the MARCHE
experiment.
1 st deployment
(July 2005
- April 2006)
2 nd deployment
(April 2006
- August 2007)
3 rd deployment
(August 2007
- August 2008)
Final recovery of
the MARCHE
array
Deployment (D),
turn-over (TO), or
recovery (R) cruises
KNORR 182 Leg 3 (D)
(R/V Knorr)
Hydro-MOMAR-05 (D)
(R/V Arquipélago)
MARCHE
(R/V Le Suroit) (TO)
MARCHE 2
(R/V Le Suroit) (TO)
MARCHE 3 (NRP Alm.
Gago Coutinho) (R)
Mooring operations
& data recovered
M6 & M7 moored
M2 & M8 moored
4 instruments
turned-over, 2375
events localized
3 instruments
recovered, 2070
events localized;
4 instruments
moored
4 instruments
recovered
Finally, Fig. 2 indicates that no event cluster has been
detected in the vicinity of the Lucky Strike site during
the first two years of deployment of the MARCHE array.
One seismic sequence was observed by the MARCHE
array on 13 February 2007. It included 55 events and
its mean location was 36.085ºN, 33.942ºW.
Figure 1: (upper) Black dots show the epicenters of
earthquakes localized by interpreting acoustic signals recorded
by the MARCHE array during its first two deployments
(26 Jul. 2005 - 12 Apr. 2006 and 17 Apr. 2006 - 1 Aug.
2007). Epicenters localized by all four instruments of the first
deployment are shown as blue dots. Among these, the subset
of events located with an error