Wilson [1963] et Morgan [1971, 1972] ont propose d'expliquer l'origine des rides et bombe... more Wilson [1963] et Morgan [1971, 1972] ont propose d'expliquer l'origine des rides et bombements situes dans les bassins oceaniques par le passage des plaques au-dessus de panaches chauds montant depuis le manteau profond. Ce modele etait base sur la localisation et la geometrie de ces anomalies de topographie, sur une progression des âges du volcanisme le long des chaines volcaniques - supposee reguliere, en interpretant les donnees alors disponibles - et sur une signature geochimique differente de celle des basaltes des centres d'accretion oceaniques. L'interpretation de donnees nouvelles, provenant essentiellement de la geochronologie, de l'altimetrie satellitaire et de la tomographie sismique conduisent a reviser de facon substantielle le modele initial, dont la simplicite n'etait pas le moindre atout. Les resultats recemment publies sont passes en revue
The different segments along the Mid-Atlantic Ridge would reflect different phases in segment evo... more The different segments along the Mid-Atlantic Ridge would reflect different phases in segment evolution, a given segment evolving progressively from a "colder" to a "hotter" so to a "colder" state. Such a thermal evolution could explain the rhomb - shaped areas observed off-axis in the Mid-Atlantic Ridge (20°-24°N) and interpreted as the trace of segment lengthening then shortening through time
The Mid-atlantic Ridge comprehensive Hydrophone experiment (MaRcHe) completed a long-term acousti... more The Mid-atlantic Ridge comprehensive Hydrophone experiment (MaRcHe) completed a long-term acoustic monitoring effort on the seismic activity of the MoMaR area and several segments of the Mid-atlantic Ridge (MaR), southwest of the azores archipelago . The monitoring was achieved over a threeyear period, which extended from July 2005 to mid-august 2008, by the deployment of the “MaRcHe array” of four autonomous hydrophones (aUHs) moored in the sofaR channel . The deployment, turn-over, and recovery of the array required five cruises . The MaRcHe3 cruise, which sailed from 13-20 august 2008, was the final recovery cruise of the array . based on the statistics derived from the data recorded during the first two years of the deployment of the MaRcHe array, we anticipate that ~8000 events will be detected and localized during the total deployment period . Preliminary interpretations of the spatial and temporal distributions derived from this catalog provide major insights on the processes...
Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate... more Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate long-term volcano-tectonic seismicity levels from segments of the fast-spreading rate East Pacific Rise (EPR) from 20° S-20° N, intermediate-spreading rate Juan de Fuca Ridge (JdFR) from 39° -52° N and Galapagos Rift (GR) from 90° -103° W, and the slow-spreading northern Mid-Atlantic Ridge (MAR) from 5° -60° N. The hydrophones record the acoustic energy of seafloor earthquakes that propagate along the ocean sound channel with little attenuation over large distances. Frequency-magnitude relationships (Bohnenstiehl et al., 2002; Dziak et al., 2004) indicate the hydrophone catalogs are complete in these regions to body-wave magnitude ˜2.5 (EPR and GR), 2.5 (JdFR), and 3.0 (MAR), an improvement of 1.5 to 2 units over the land-based seismic catalogs for mid-ocean ridge systems. Using the hydrophone earthquake catalog, we will compare seismicity rates of the JdFR (12 years of data), to seismicity rates along the GR (6 years) and EPR (6 years) and MAR (4 years of data from 5° -39° N; 16 months from 39° -60° N). During these monitoring periods, five confirmed seafloor spreading events (four of which were associated with magmatic activity) were recorded on discrete JdFR segments, while 6 possible magmatic events were observed on the EPR, one on the GR, and one on the MAR. Empirical orthogonal functions will be used to elucidate the space-time patterns of seismicity and compare between the various spreading rates ridges, as well as to investigate the recurrence rate of seafloor spreading events present. In addition, single-link cluster analysis (SLC; Frolich and Davis, 1990) will be used to de-cluster the earthquake databases to reduce the effects of aftershock sequences and magmatic swarms, allowing us to evaluate how overall plate motion and changes in spreading rate effect levels of seismicity between ridge segments and different ridge systems. Preliminary results indicate the distribution of seismicity at the JdFR "super"-segments (between transforms) are positively skewed, indicating there are significant, yet brief periods of time (1-2 months) when seismic activity is well above the mean. Transforms along the JdFR, however, exhibit a random distribution.
Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate... more Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate long-term volcano-tectonic seismicity levels from segments of the fast-spreading rate East Pacific Rise (EPR) from 20° S-20° N, intermediate-spreading rate Juan de Fuca Ridge (JdFR) from 39° -52° N and Galapagos Rift (GR) from 90° -103° W, and the slow-spreading northern Mid-Atlantic Ridge (MAR) from 5° -60° N. The hydrophones record the acoustic energy of seafloor earthquakes that propagate along the ocean sound channel with little attenuation over large distances. Frequency-magnitude relationships (Bohnenstiehl et al., 2002; Dziak et al., 2004) indicate the hydrophone catalogs are complete in these regions to body-wave magnitude ˜2.5 (EPR and GR), 2.5 (JdFR), and 3.0 (MAR), an improvement of 1.5 to 2 units over the land-based seismic catalogs for mid-ocean ridge systems. Using the hydrophone earthquake catalog, we will compare seismicity rates of the JdFR (12 years of data), to seismicity rates along the GR (6 years) and EPR (6 years) and MAR (4 years of data from 5° -39° N; 16 months from 39° -60° N). During these monitoring periods, five confirmed seafloor spreading events (four of which were associated with magmatic activity) were recorded on discrete JdFR segments, while 6 possible magmatic events were observed on the EPR, one on the GR, and one on the MAR. Empirical orthogonal functions will be used to elucidate the space-time patterns of seismicity and compare between the various spreading rates ridges, as well as to investigate the recurrence rate of seafloor spreading events present. In addition, single-link cluster analysis (SLC; Frolich and Davis, 1990) will be used to de-cluster the earthquake databases to reduce the effects of aftershock sequences and magmatic swarms, allowing us to evaluate how overall plate motion and changes in spreading rate effect levels of seismicity between ridge segments and different ridge systems. Preliminary results indicate the distribution of seismicity at the JdFR "super"-segments (between transforms) are positively skewed, indicating there are significant, yet brief periods of time (1-2 months) when seismic activity is well above the mean. Transforms along the JdFR, however, exhibit a random distribution.
Along-axis magnetic observations show that the amplitude of the axial magnetic anomaly is twice a... more Along-axis magnetic observations show that the amplitude of the axial magnetic anomaly is twice as high at segment ends than at segment centers. In a previous work we have modeled numerically this variation in the case of aligned segments and shown that it results from the thermal structure of the segments which, in turn, bears a direct influence on the
The seismicity of the North Atlantic Ocean was recorded by the SIRENA array of 6 autonomous under... more The seismicity of the North Atlantic Ocean was recorded by the SIRENA array of 6 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed north of the Azores Plateau between 40° and 50°N from June 2002 to September 2003. The low attenuation properties of the SOFAR channel for
The intraplate seismicity that affects the ocean seafloor is poorly! known, while! it is of criti... more The intraplate seismicity that affects the ocean seafloor is poorly! known, while! it is of critical importance to understand the thermal structure of the! oceanic! lithosphere and assess the pecularities - if any - of the earthquake! generation! processes in submarine environments.! T-waves generated by submarine earthquakes can propagate almost without! attenuation in the SOFAR (Sound Fixing And Ranging) channel,
A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during... more A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during the NOFI cruise by the R/V l'Atalante in August-September, 1994. The two ridges inside the study area, the South Pandora Ridge and the Tripartite Ridge, present different structures and states of isostatic equilibrium in terms of gravity anomaly and its tectonic implications.
Wilson [1963] et Morgan [1971, 1972] ont propose d'expliquer l'origine des rides et bombe... more Wilson [1963] et Morgan [1971, 1972] ont propose d'expliquer l'origine des rides et bombements situes dans les bassins oceaniques par le passage des plaques au-dessus de panaches chauds montant depuis le manteau profond. Ce modele etait base sur la localisation et la geometrie de ces anomalies de topographie, sur une progression des âges du volcanisme le long des chaines volcaniques - supposee reguliere, en interpretant les donnees alors disponibles - et sur une signature geochimique differente de celle des basaltes des centres d'accretion oceaniques. L'interpretation de donnees nouvelles, provenant essentiellement de la geochronologie, de l'altimetrie satellitaire et de la tomographie sismique conduisent a reviser de facon substantielle le modele initial, dont la simplicite n'etait pas le moindre atout. Les resultats recemment publies sont passes en revue
The different segments along the Mid-Atlantic Ridge would reflect different phases in segment evo... more The different segments along the Mid-Atlantic Ridge would reflect different phases in segment evolution, a given segment evolving progressively from a "colder" to a "hotter" so to a "colder" state. Such a thermal evolution could explain the rhomb - shaped areas observed off-axis in the Mid-Atlantic Ridge (20°-24°N) and interpreted as the trace of segment lengthening then shortening through time
The Mid-atlantic Ridge comprehensive Hydrophone experiment (MaRcHe) completed a long-term acousti... more The Mid-atlantic Ridge comprehensive Hydrophone experiment (MaRcHe) completed a long-term acoustic monitoring effort on the seismic activity of the MoMaR area and several segments of the Mid-atlantic Ridge (MaR), southwest of the azores archipelago . The monitoring was achieved over a threeyear period, which extended from July 2005 to mid-august 2008, by the deployment of the “MaRcHe array” of four autonomous hydrophones (aUHs) moored in the sofaR channel . The deployment, turn-over, and recovery of the array required five cruises . The MaRcHe3 cruise, which sailed from 13-20 august 2008, was the final recovery cruise of the array . based on the statistics derived from the data recorded during the first two years of the deployment of the MaRcHe array, we anticipate that ~8000 events will be detected and localized during the total deployment period . Preliminary interpretations of the spatial and temporal distributions derived from this catalog provide major insights on the processes...
Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate... more Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate long-term volcano-tectonic seismicity levels from segments of the fast-spreading rate East Pacific Rise (EPR) from 20° S-20° N, intermediate-spreading rate Juan de Fuca Ridge (JdFR) from 39° -52° N and Galapagos Rift (GR) from 90° -103° W, and the slow-spreading northern Mid-Atlantic Ridge (MAR) from 5° -60° N. The hydrophones record the acoustic energy of seafloor earthquakes that propagate along the ocean sound channel with little attenuation over large distances. Frequency-magnitude relationships (Bohnenstiehl et al., 2002; Dziak et al., 2004) indicate the hydrophone catalogs are complete in these regions to body-wave magnitude ˜2.5 (EPR and GR), 2.5 (JdFR), and 3.0 (MAR), an improvement of 1.5 to 2 units over the land-based seismic catalogs for mid-ocean ridge systems. Using the hydrophone earthquake catalog, we will compare seismicity rates of the JdFR (12 years of data), to seismicity rates along the GR (6 years) and EPR (6 years) and MAR (4 years of data from 5° -39° N; 16 months from 39° -60° N). During these monitoring periods, five confirmed seafloor spreading events (four of which were associated with magmatic activity) were recorded on discrete JdFR segments, while 6 possible magmatic events were observed on the EPR, one on the GR, and one on the MAR. Empirical orthogonal functions will be used to elucidate the space-time patterns of seismicity and compare between the various spreading rates ridges, as well as to investigate the recurrence rate of seafloor spreading events present. In addition, single-link cluster analysis (SLC; Frolich and Davis, 1990) will be used to de-cluster the earthquake databases to reduce the effects of aftershock sequences and magmatic swarms, allowing us to evaluate how overall plate motion and changes in spreading rate effect levels of seismicity between ridge segments and different ridge systems. Preliminary results indicate the distribution of seismicity at the JdFR "super"-segments (between transforms) are positively skewed, indicating there are significant, yet brief periods of time (1-2 months) when seismic activity is well above the mean. Transforms along the JdFR, however, exhibit a random distribution.
Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate... more Ocean basin earthquakes recorded on NOAA/OSU and U.S. Navy hydrophone arrays are used to evaluate long-term volcano-tectonic seismicity levels from segments of the fast-spreading rate East Pacific Rise (EPR) from 20° S-20° N, intermediate-spreading rate Juan de Fuca Ridge (JdFR) from 39° -52° N and Galapagos Rift (GR) from 90° -103° W, and the slow-spreading northern Mid-Atlantic Ridge (MAR) from 5° -60° N. The hydrophones record the acoustic energy of seafloor earthquakes that propagate along the ocean sound channel with little attenuation over large distances. Frequency-magnitude relationships (Bohnenstiehl et al., 2002; Dziak et al., 2004) indicate the hydrophone catalogs are complete in these regions to body-wave magnitude ˜2.5 (EPR and GR), 2.5 (JdFR), and 3.0 (MAR), an improvement of 1.5 to 2 units over the land-based seismic catalogs for mid-ocean ridge systems. Using the hydrophone earthquake catalog, we will compare seismicity rates of the JdFR (12 years of data), to seismicity rates along the GR (6 years) and EPR (6 years) and MAR (4 years of data from 5° -39° N; 16 months from 39° -60° N). During these monitoring periods, five confirmed seafloor spreading events (four of which were associated with magmatic activity) were recorded on discrete JdFR segments, while 6 possible magmatic events were observed on the EPR, one on the GR, and one on the MAR. Empirical orthogonal functions will be used to elucidate the space-time patterns of seismicity and compare between the various spreading rates ridges, as well as to investigate the recurrence rate of seafloor spreading events present. In addition, single-link cluster analysis (SLC; Frolich and Davis, 1990) will be used to de-cluster the earthquake databases to reduce the effects of aftershock sequences and magmatic swarms, allowing us to evaluate how overall plate motion and changes in spreading rate effect levels of seismicity between ridge segments and different ridge systems. Preliminary results indicate the distribution of seismicity at the JdFR "super"-segments (between transforms) are positively skewed, indicating there are significant, yet brief periods of time (1-2 months) when seismic activity is well above the mean. Transforms along the JdFR, however, exhibit a random distribution.
Along-axis magnetic observations show that the amplitude of the axial magnetic anomaly is twice a... more Along-axis magnetic observations show that the amplitude of the axial magnetic anomaly is twice as high at segment ends than at segment centers. In a previous work we have modeled numerically this variation in the case of aligned segments and shown that it results from the thermal structure of the segments which, in turn, bears a direct influence on the
The seismicity of the North Atlantic Ocean was recorded by the SIRENA array of 6 autonomous under... more The seismicity of the North Atlantic Ocean was recorded by the SIRENA array of 6 autonomous underwater hydrophones (AUH) moored within the SOFAR channel on the flanks of the Mid-Atlantic Ridge (MAR). The instruments were deployed north of the Azores Plateau between 40° and 50°N from June 2002 to September 2003. The low attenuation properties of the SOFAR channel for
The intraplate seismicity that affects the ocean seafloor is poorly! known, while! it is of criti... more The intraplate seismicity that affects the ocean seafloor is poorly! known, while! it is of critical importance to understand the thermal structure of the! oceanic! lithosphere and assess the pecularities - if any - of the earthquake! generation! processes in submarine environments.! T-waves generated by submarine earthquakes can propagate almost without! attenuation in the SOFAR (Sound Fixing And Ranging) channel,
A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during... more A surface ship gravity survey was carried out in the northern part of the North Fiji Basin during the NOFI cruise by the R/V l'Atalante in August-September, 1994. The two ridges inside the study area, the South Pandora Ridge and the Tripartite Ridge, present different structures and states of isostatic equilibrium in terms of gravity anomaly and its tectonic implications.
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Papers by J. Goslin