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  • 1
    Online Resource
    Online Resource
    Ocean Gravity Models From Future Satellite Missions
    American Geophysical Union (AGU) ; 2010
    In:  Eos, Transactions American Geophysical Union Vol. 91, No. 3 ( 2010-01-19), p. 21-22
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 91, No. 3 ( 2010-01-19), p. 21-22
    Abstract: Over the past 3 decades, satellite altimetry has been a key tool for dynamic ocean studies and for accurately estimating sea surface heights. The geodetic reference surface—the “geoid”—can be approximated as the mean sea surface height of an ocean corrected for dynamic terms such as tides and currents. It is an equipotential surface of the gravity field; and variations of this field are quantified as free‐air anomalies, from which density heterogeneities of the oceanic basement can be inferred. Using such data in combination with other geophysical data, scientists have improved their knowledge of the nature of submarine relief and underlying structures. In solid Earth geophysics, major breakthroughs came from the development of high‐resolution marine gravity models based on closely spaced altimetry profiles collected during the U.S. Navy's Geosat satellite geodetic mission (launched in 1985) and the first version of the European Remote Sensing satellite geodetic mission (ERS 1, launched in 1991). These were combined with other repetitive profiles from the international TOPEX/ POSEIDON satellite (launched in 1992); ERS 1; TOPEX/POSEIDON's successor, Jason (launched in 2001); and the European Space Agency's (ESA) Envisat missions (ERS's successors [see, e.g., Sandwell and Smith, 1997; Andersen and Knudsen, 1998]).
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/2010EO030001
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2010
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  • 2
    Online Resource
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    Deep structure of the West African continental margin (Congo, Zaïre, Angola), between 5°S and 8°S, from reflection/refraction seismics and gravity data
    Oxford University Press (OUP) ; 2004
    In:  Geophysical Journal International Vol. 158, No. 2 ( 2004-08), p. 529-553
    Details
    In: Geophysical Journal International, Oxford University Press (OUP), Vol. 158, No. 2 ( 2004-08), p. 529-553
    Type of Medium: Online Resource
    ISSN: 0956-540X , 1365-246X
    URL: Issue
    URL: Article
    DOI: 10.1111/gji.2004.158.issue-2
    DOI: 10.1111/j.1365-246X.2004.02303.x
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2004
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  • 3
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    Location of Louisville hotspot and origin of Hollister Ridge: geophysical constraints
    Elsevier BV ; 1998
    In:  Earth and Planetary Science Letters Vol. 164, No. 1-2 ( 1998-12), p. 31-40
    Details
    In: Earth and Planetary Science Letters, Elsevier BV, Vol. 164, No. 1-2 ( 1998-12), p. 31-40
    Type of Medium: Online Resource
    ISSN: 0012-821X
    URL: Article
    DOI: 10.1016/S0012-821X(98)00217-9
    RVK:
    TE 1000
    Language: English
    Publisher: Elsevier BV
    Publication Date: 1998
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  • 4
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    Evolution of the Pacific-Antarctic Ridge South of the Udintsev Fracture Zone
    American Association for the Advancement of Science (AAAS) ; 1997
    In:  Science Vol. 278, No. 5341 ( 1997-11-14), p. 1281-1284
    Details
    In: Science, American Association for the Advancement of Science (AAAS), Vol. 278, No. 5341 ( 1997-11-14), p. 1281-1284
    Abstract: Because of the proximity of the Euler poles of rotation of the Pacific and Antarctic plates, small variations in plate kinematics are fully recorded in the axial morphology and in the geometry of the Pacific-Antarctic Ridge south of the Udintsev fracture zone. Swath bathymetry and magnetic data show that clockwise rotations of the relative motion between the Pacific and Antarctic plates over the last 6 million years resulted in rift propagation or in the linkage of ridge segments, with transitions from transform faults to giant overlapping spreading centers. This bimodal axial rearrangement has propagated southward for the last 30 to 35 million years, leaving trails on the sea floor along a 1000-kilometer-long V-shaped structure south of the Udintsev fracture zone.
    Type of Medium: Online Resource
    ISSN: 0036-8075 , 1095-9203
    URL: Article
    DOI: 10.1126/science.278.5341.1281
    RVK:
    TA 1000
    RVK:
    WA 15000
    Language: English
    Publisher: American Association for the Advancement of Science (AAAS)
    Publication Date: 1997
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  • 5
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    Geological constraints on the evolution of the Angolan margin based on reflection and refraction seismic data (ZaïAngo project)
    Oxford University Press (OUP) ; 2005
    In:  Geophysical Journal International Vol. 162, No. 3 ( 2005-09), p. 793-810
    Details
    In: Geophysical Journal International, Oxford University Press (OUP), Vol. 162, No. 3 ( 2005-09), p. 793-810
    Type of Medium: Online Resource
    ISSN: 0956-540X , 1365-246X
    URL: Issue
    URL: Article
    DOI: 10.1111/gji.2005.162.issue-3
    DOI: 10.1111/j.1365-246X.2005.02668.x
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2005
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  • 6
    Online Resource
    Online Resource
    Morphological reorganization within the Pacific-Antarctic Discordance
    Elsevier BV ; 1996
    In:  Earth and Planetary Science Letters Vol. 137, No. 1-4 ( 1996-1), p. 157-173
    Details
    In: Earth and Planetary Science Letters, Elsevier BV, Vol. 137, No. 1-4 ( 1996-1), p. 157-173
    Type of Medium: Online Resource
    ISSN: 0012-821X
    URL: Article
    DOI: 10.1016/0012-821X(95)01185-K
    RVK:
    TE 1000
    Language: English
    Publisher: Elsevier BV
    Publication Date: 1996
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  • 7
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    Deep‐penetration heat flow probes raise questions about interpretations from shorter probes
    American Geophysical Union (AGU) ; 2001
    In:  Eos, Transactions American Geophysical Union Vol. 82, No. 29 ( 2001-07-17), p. 317-320
    Details
    In: Eos, Transactions American Geophysical Union, American Geophysical Union (AGU), Vol. 82, No. 29 ( 2001-07-17), p. 317-320
    Abstract: More than 40% of the marine heat flow data collected since the early experiments of Sir Edward Bullard in 1949 were obtained using shallow penetration probes less than 5 m long [ Louden and Wright, 1989]. The common belief that these data are reliable enough to model deep‐seated thermal processes is supported by a few experiments in which heat flow measurements made in the Deep Sea Drilling Program (DSDP) and the Ocean Drilling Program (ODP) were compared to nearby surface heat flow measurements [e.g., Hyndman et al., 1984]. However, thermal measurements made with 18‐m penetrations recently collected on the northern flank of the South‐East Indian Ridge (SEIR) bring a new perspective to this belief. In the study area, measurements of heat flow taken at the surface ( 0–5 m) and measurements taken at greater depths (3–18 m) did not always concur. Investigating this lack of agreement will help address difficult questions about the interpretation of shallow penetration ( 〈 5 m) marine heat flow measurements.
    Type of Medium: Online Resource
    ISSN: 0096-3941 , 2324-9250
    URL: Article
    DOI: 10.1029/01EO00186
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2001
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  • 8
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    Variations in axial morphology, segmentation, and seafloor roughness along the Pacific‐Antarctic Ridge between 56°S and 66°S
    American Geophysical Union (AGU) ; 2001
    In:  Journal of Geophysical Research: Solid Earth Vol. 106, No. B5 ( 2001-05-10), p. 8521-8546
    Details
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 106, No. B5 ( 2001-05-10), p. 8521-8546
    Abstract: The spreading rate at the Pacific‐Antarctic Ridge (PAR) increases rapidly from 54 mm/yr near Pitman Fracture Zone (FZ) up to 76 mm/yr near Udintsev FZ, resulting in three domains of axial morphology: an axial valley south of Pitman FZ, an axial high north of Saint Exupéry FZ, and in between, the transitional domain extends over 650 km. It comprises sections of ridge with an axial valley or an axial high and generally displays a very low cross‐sectional relief. It is also characterized by two propagating rifts. Two domains of different seafloor roughness appear south of Udintsev FZ: east of 157°W these two domains are separated by a 1000‐km V‐shaped boundary. West of 157°W, the boundary approximately coincides with Chron 3a or Chron 4. The southward migration of the transitional area during the last 35 Myr explains the V‐shaped boundary: (1) increases in spreading rate above a threshold value produced changes in axial morphology; and (2) in the transition zone, rotations of the spreading direction were accommodated by the plate boundary, either by rift propagation or by transitions from fracture zones to non transform discontinuities, leaving trails on the seafloor that presently delineate the V. Seafloor roughness variations are not controlled by exactly the same spreading rate dependence as changes in axial morphology. The transition from rough to smooth seems to have occurred everywhere for spreading rates greater than 50 mm/yr, except in a domain presently centered on Saint‐Exupéry FZ, where it occurred for spreading rates 〉 60 to 65 mm/yr. Independent results from melting model calculations of major elements [ Vlastelic et al. , 2000] indicate that the upper mantle temperature is likely to be cooler between Antipodes and La Rose FZs. The combination of these two results reveals the existence of a 700‐km‐long segmentation of the upper mantle, with a “cool” area centered on Saint‐Exupéry FZ.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2000JB900394
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2001
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  • 9
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    Chemical systematics of an intermediate spreading ridge: The Pacific‐Antarctic Ridge between 56°S and 66°S
    American Geophysical Union (AGU) ; 2000
    In:  Journal of Geophysical Research: Solid Earth Vol. 105, No. B2 ( 2000-02-10), p. 2915-2936
    Details
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 105, No. B2 ( 2000-02-10), p. 2915-2936
    Abstract: Axial bathymetry, major/trace elements, and isotopes suggest that the Pacific‐Antarctic Ridge (PAR) between 56°S and 66°S is devoid of any hotspot influence. PAR (56–66°S) samples have in average lower 87 Sr/ 86 Sr and 143 Nd/ 144 Nd and higher 206 Pb/ 204 Pb than northern Pacific mid‐ocean ridge basalts (MORB), and also than MORB from the other oceans. The high variability of Pb isotopic ratios (compared to Sr and Nd) can be due to either a general high μ (HIMU) (high U/Pb) affinity of the southern Pacific upper mantle or to a mantle event first recorded in time by Pb isotopes. Compiling the results of this study with those from the PAR between 53°S and 57°S gives a continuous view of mantle characteristics from south Pitman Fracture Zone (FZ) to Vacquier FZ, representing about 3000 km of spreading axis. The latitude of Udintsev FZ (56°S) is a limit between, to the north, a domain with large geochemical variations and, to the south, one with small variations. The spreading rate has intermediate values (54 mm/yr at 66°S to 74 mm/yr at 56°S) which increase along the PAR, while the axial morphology changes from valley to dome. The morphological transition is not recorded by the chemical properties of the ridge basalts nor by the inferred mantle temperature which displays few variations (30–40°C) along the PAR. Contrary to what is observed along the South‐East Indian Ridge, PAR morphology appears to be controlled more by spreading rate rather than by mantle temperature. Much of the major and trace element variability results from segmentation control on the shallowest thermal structure of the mantle. The cold edge of a fracture zone seems to be more efficient when occurring in an axial dome context. It is expressed as an increase of the magnitude of the Transform Fault Effect along the valley‐dome transition, resulting in a clear increase of trace element ratio variability (such as Nb/Zr). There is no strong evidence for the previously proposed southwestward asthenospheric flow in the area. However, this flow model could explain the intrasegment asymmetric patterns.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/1999JB900234
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2000
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  • 10
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    Seismic wave propagation in a very permeable water‐saturated surface layer
    American Geophysical Union (AGU) ; 1987
    In:  Journal of Geophysical Research: Solid Earth Vol. 92, No. B8 ( 1987-07-10), p. 7931-7944
    Details
    In: Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 92, No. B8 ( 1987-07-10), p. 7931-7944
    Abstract: According to Biot's (1956 a , b ) model, the presence of water plays an important role in the propagation of seismic waves in at least three different ways: (1) in an infinite medium, water saturation induces an attenuation that can be accounted for by a complex formulation of wave velocities, as in viscoelastic media; (2) at the boundaries of the saturated medium, pore pressure and water flux determine specific continuity conditions; and (3) there is a second compressional wave, called the P 2 wave. In this paper, we discuss the latter two effects. Biot's model is presented first, with homogenization theory used to provide the numerical values of the different coefficients used in the model. In an infinite medium, the model is of practical interest when the frequency ƒ is about the same order of magnitude as a characteristic frequency noted ƒ c , which depends on the properties of the constituents. This limits the application of Biot's model to a few particular fields in geophysics. In a layered medium, Biot's model has a wider scope in that it provides a tool for modeling fluid‐solid interaction at the boundaries of the saturated medium. This is illustrated in our paper for the case of a very permeable water‐saturated surface layer over an elastic half‐space. Two examples are given; in the first example (rigid sands) we discuss the physics of the strongly attenuated P 2 wave predicted by Biot, the amplitude of which becomes significant when the ƒ/ƒ c ratio is about equal to or greater than 0.1. In the second example (soft unconsolidated sediments) the P 2 wave is negligible, but the calculation of the complete wave field is required when the ƒ/ƒ c ratio is about 0.01. There is no adequate equivalent single phase model that gives a correct estimation of the amplitude of the ground motion. In this case, we argue that the P 2 wave is not important in itself, but Biot's model allows the description of the fluid‐solid interaction at the water table; continuity of effective stress and pore pressure can be explicitly formulated.
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/JB092iB08p07931
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 1987
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