HR: 0800h
AN: T21C-0542 [Abstracts]
TI: Long-Term Seismicity of Northern (15$^\deg$N-60$^\deg$N) Mid-Atlantic Ridge (MAR) Recorded by two
Regional Hydrophone Arrays: a Widespread Along-Ridge Influence of the Azores and Iceland
Hotspots
AU: * Goslin, J
EM: goslin@univ-brest.fr
AF: UMR CNRS 6538 Domaines Oceaniques
Univ. Bretagne Occidentale, IUEM
Technopole Best Iroise, Plouzane, 29280
France
AU: Bazin, S
EM: bazin@ovsg.univ-ag.fr
AF: Laboratoire de Geosciences Marines
Institut de Physique du Globe, 4, place Jussieu, Paris, 75005
France
AU: Dziak, R P
EM: robert.p.dziak@noaa.gov
AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center
2115 SE OSU Drive, Newport, OR 97365
United States
AU: Dziak, R P
EM: robert.p.dziak@noaa.gov
AF: Oregon State University, Hatfield Marine Science Center, Newport, OR 97365
United States
AU: Fox, C
EM: fox@pmel.noaa.gov
AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center
2115 SE OSU Drive, Newport, OR 97365
United States
AU: Fowler, M
EM: matt.fowler@oregonstate.edu
AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center
2115 SE OSU Drive, Newport, OR 97365
United States
AU: Fowler, M
EM: matt.fowler@oregonstate.edu
AF: Oregon State University, Hatfield Marine Science Center, Newport, OR 97365
United States
AU: Haxel, J
EM: joe.haxel@noaa.gov
AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center
2115 SE OSU Drive, Newport, OR 97365
United States
AU: Lourenco, N
EM: nuno.lourenco@fc.ul.pt
AF: Centro de Investigacao Marinha e Ambiantal, Univesidade do Algarve
Campus de Gambelas, Faro, 8005-139
Portugal
AU: Lourenco, N
EM: nuno.lourenco@fc.ul.pt
AF: Centro de Geophysica da Universidade de Lisboa, Campo Grande Ed C8, Lisboa, 1749-016
AU: Luis, J
EM: jluis@ualg.pt
AF: Centro de Investigacao Marinha e Ambiantal, Univesidade do Algarve
Campus de Gambelas, Faro, 8005-139
Portugal
AU: Martin, C
EM: Christophe.Martin@univ-brest.fr
AF: UMR CNRS 6538 Domaines Oceaniques
Univ. Bretagne Occidentale, IUEM
Technopole Best Iroise, Plouzane, 29280
France
AU: Matsumoto, H
EM: Haru.Matsumoto@noaa.gov
AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center
2115 SE OSU Drive, Newport, OR 97365
United States
AU: Perrot, J
EM: Julie.Perrot@univ-brest.fr
AF: UMR CNRS 6538 Domaines Oceaniques
Univ. Bretagne Occidentale, IUEM
Technopole Best Iroise, Plouzane, 29280
France
AU: Royer, J
EM: jyroyer@univ-brest.fr
AF: UMR CNRS 6538 Domaines Oceaniques
Univ. Bretagne Occidentale, IUEM
Technopole Best Iroise, Plouzane, 29280
France
AB:
The seismicity of the North Atlantic was recorded by two networks of hydrophones moored in the SOFAR channel, north and south
of the Azores Plateau. The interpretation of the hydro-acoustic signals recorded during the first six-month common period of
operation of the two networks (June 2002 to Nov. 2002) provides a unique data set on the spatial and time distributions of
the numerous low-magnitude earthquakes which occurred along the Mid-Atlantic Ridge. Close to 2000 events were localized
during this six-month period between latitudes 15$^\deg$N and 63$^\deg$N, 501 of which are localized within the SIRENA
network (40$^\deg$N-51$^\deg$N) and 692 within the wider South Azores network (17$^\deg$N-33$^\deg$N). Using hydrophones to
locate seafloor earthquakes by interpreting T-wave signals lowers the detection threshold of Mid-Atlantic Ridge events to 3.0
mb from the 4.7 mb of global seismic networks. This represents an average thirty-fold increase in the number of events: 62
events were detected by global seismological networks within the same area during the same period.
An along-ridge spatial distribution of the seismicity is obtained by computing the cumulated numbers of events in
1$^\deg$-wide latitudinal bins. When plotted vs. latitude, this first-order distribution shows remarkable long-wavelength
patterns: the seismicity rate is low when approaching the Azores and Iceland (reaching values as low as 10 events/d$^\deg$),
while it peaks to 70 events/d$^\deg$ in the vicinity of the Gibbs FZ. Moreover, the latitudinal distribution of the
seismicity hints at an asymmetric influence of the Azores hotpot on the MAR.
Finally, the spatial distribution of the seismicity anti-correlates well at long wavelengths with the zero-age depths along
the MAR and correlates with the zero-age Mantle Bouguer (MBA) anomaly values and the Vs velocity anomalies at 100 km in the
upper mantle. It is thus proposed that the seismicity level would be partly tied to the rheology and thickness of the brittle
layer and be thus dependant on the thermal regime of the upper mantle. The seismicity distribution could then be used as an
additional tool to characterize the along-ridge influence of the Azores and Iceland hotspots on the MAR slow-spreading
center.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3035 Midocean ridge processes
DE: 3094 Instruments and techniques
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting