T21C0542 TI: LongTerm Seismicity of Northern (15°N60°N) MidAtlantic Ridge (MAR) Recorded by two Regional Hydrophone Arrays: a Widespread AlongRidge Influence of the Azores and Iceland Hotspots AU: * Goslin, J EM: goslin@univbrest.fr AF: UMR CNRS 6538 Domaines Oceaniques Univ. Bretagne Occidentale, IUEM Technopole Best Iroise, Plouzane, 29280 France AU: Bazin, S EM:
[email protected]ag.fr AF: Laboratoire de Geosciences Marines Institut de Physique du Globe, 4, place Jussieu, Paris, 75005 France AU: Dziak, R P EM:
[email protected] AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center 2115 SE OSU Drive, Newport, OR 97365 United States AU: Dziak, R P EM:
[email protected] AF: Oregon State University, Hatfield Marine Science Center, Newport, OR 97365 United States AU: Fox, C EM:
[email protected] AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center 2115 SE OSU Drive, Newport, OR 97365 United States AU: Fowler, M EM:
[email protected] AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center 2115 SE OSU Drive, Newport, OR 97365 United States AU: Fowler, M EM:
[email protected] AF: Oregon State University, Hatfield Marine Science Center, Newport, OR 97365 United States AU: Haxel, J EM:
[email protected] AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center 2115 SE OSU Drive, Newport, OR 97365 United States AU: Lourenco, N EM:
[email protected] AF: Centro de Investigacao Marinha e Ambiantal, Univesidade do Algarve Campus de Gambelas, Faro, 8005139 Portugal AU: Lourenco, N EM:
[email protected] AF: Centro de Geophysica da Universidade de Lisboa, Campo Grande Ed C8, Lisboa, 1749016 AU: Luis, J EM:
[email protected] AF: Centro de Investigacao Marinha e Ambiantal, Univesidade do Algarve Campus de Gambelas, Faro, 8005139 Portugal AU: Martin, C EM: Christophe.Martin@univbrest.fr AF: UMR CNRS 6538 Domaines Oceaniques Univ. Bretagne Occidentale, IUEM Technopole Best Iroise, Plouzane, 29280 France AU: Matsumoto, H EM:
[email protected] AF: Pacific Marine Environmental Lab, Hatfield Marine Science Center 2115 SE OSU Drive, Newport, OR 97365 United States AU: Perrot, J EM: Julie.Perrot@univbrest.fr AF: UMR CNRS 6538 Domaines Oceaniques Univ. Bretagne Occidentale, IUEM Technopole Best Iroise, Plouzane, 29280 France
AU: Royer, J EM: jyroyer@univbrest.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 hydroacoustic signals recorded during the first sixmonth 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 lowmagnitude earthquakes which occurred along the MidAtlantic Ridge. Close to 2000 events were localized during this sixmonth period between latitudes 15°N and 63°N, 501 of which are localized within the SIRENA network (40°N51°N) and 692 within the wider South Azores network (17°N33°N). Using hydrophones to locate seafloor earthquakes by interpreting Twave signals lowers the detection threshold of MidAtlantic Ridge events to 3.0 mb from the 4.7 mb of global seismic networks. This represents an average thirtyfold increase in the number of events: 62 events were detected by global seismological networks within the same area during the same period. An alongridge spatial distribution of the seismicity is obtained by computing the cumulated numbers of events in 1°wide latitudinal bins. When plotted vs. latitude, this firstorder 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°), while it peaks to 70 events/d° 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 anticorrelates well at long wavelengths with the zeroage depths along the MAR and correlates with the zeroage 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 alongridge influence of the Azores and Iceland hotspots on the MAR slowspreading 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