Along-track gravity anomalies from Geostat and Seasat altimetry: GEBCO overlays

Sandwell, David T.; Ruiz, Miguel B.

doi:10.1007/bf01270629

Cited by 10 publications

(4 citation statements)

References 9 publications

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“…Similarly, we have also compared the final free-air anomaly with that derived from a stacked Geosat ascending track which crosses the study area (Figure 7, top). The free-air anomaly derived from the Geosat altimetry data assumes that the source of the anomaly is twodimensional in a direction normal to the track [Sandwell and Ruiz, 1992…”

Section: Fortunately Most Surveys (Or Set Of Surveys) Extend Across mentioning

confidence: 99%

A three‐dimensional gravity analysis of the East Pacific Rise from 18° to 21°30′S

Cormier¹,

Macdonald²,

Wilson³

1995

J. Geophys. Res.

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Multibeam bathymetry and gravity coverage of the East Pacific Rise (EPR) between 18 ø and 21 ø30'S is used to investigate the relation between melt supply and tectonic segmentation at ultrafast spreading rates. The long-wavelength features in the residual anomaly show a good correlation with those in the bathymetry. The highest residual anomaly values occur over the broad discordant zone of the 20ø40'S overlapping spreading center (OSC), for seafloor ages of 0 Ma to at least 1.5 Ma. We interpret the deepening of the bathymetry and the increase of the residual anomaly toward that discordant zone as due to a decrease of 500 + 200 m of the crustal thickness. Hence the 20ø40'S OSC has been associated with a reduced magmatic budget for at least the past 1.5 m.y. and represents a persistent segmentation of the EPR. This is consistent with models in which mantle upwelling, even at the fastest spreading centers, is enhanced between large discontinuities rather than evenly distributed along axis. However, this decrease of the crustal thickness toward an axial discontinuity is several times smaller than that typically documented for slow spreading ridges, which suggests that mantle upwelling is less focused at fast spreading ridges, or that along-axis transport of crustal material is more efficient, or both. Across the study area, the residual anomaly decreases toward the NW by 15-20 mGal. This regional gradient can be modeled with lateral temperature variations in the upper mantle of up to 60øC, increasing toward the NW. This interpretation is consistent with the numerous seamounts present to the NW and the robust magmatic budget of the ridge between 17 ø and 18øS, and it could also explain why the ridge segments defined by the smaller OSCs between 18 ø and 19øS propagate very rapidly away from the robust area. Similar patterns of ridge propagation away from the shallowest section of a ridge have been documented near the Galapagos and Easter Island hot spots. Hence these shorter ridge segments may not be associated with significant individual melt sources. Rather, they may represent a superficial segmentation due to the interaction between the EPR and a mantle heterogeneity located between 17 ø and 18øS. Macdonald et al., 1984; Schouten et al., 1985; Crane, 1985; Macdonald et al., 1988a]. An implication of focused mantle upwelling models is that the magma supply should decrease toward large discontinuities. Indeed, at slow spreading ridges, seismic refraction data have shown that the crust accreted near •Now at Lamont-Doherty Earth Paper number 95JB00243. 0148-0227/95/95JB-00243505 .00 transform zones can have as little as half the typical oceanic crustal thickness [e.g., White et al., 1984]. At fast spreading ridges, detailed analyses of multibeam bathymetry data show that the deepening of the axial high toward large overlapping spreading centers (OSCs) and transform faults correlates with a narrowing of its cross section and, often, with the disappearance of the seismic reflector interpreted as the top of an axial magma...

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Section: Fortunately Most Surveys (Or Set Of Surveys) Extend Across mentioning

confidence: 99%

A three‐dimensional gravity analysis of the East Pacific Rise from 18° to 21°30′S

Cormier¹,

Macdonald²,

Wilson³

1995

J. Geophys. Res.

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“…Abbreviations of ship or expedition names are ELT, Eltanin; CON, Conrad; OC, Oceanographer; S'TOW and M'THON,Scripps expeditions SOUTHTOW and MARATHON. Distribution of seamounts and pattern of normal and oblique fracture zones are based on satellite altimetry [Sandwell and Ruiz, 1992;Sandwell and Smith, 1992]…”

Section: Objectivesmentioning

confidence: 99%

Geomorphology and structural segmentation of the crest of the southern (Pacific‐Antarctic) East Pacific Rise

Lonsdale¹

1994

J. Geophys. Res.

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Geomorphology of the boundary between Pacific and Antarctic plates was mapped with a Sea Beam multibeam echosounder and a SeaMARC II bathymetric side scan sonar, from the southern end of Juan Fernandez microplate at 35°S to Heezen transform at 56°S. There are six spreading center systems separated by two large, left‐stepping nontransform offsets (at 36.5°S and 41.5°S), two right‐stepping transform‐fault systems, and a left‐stepping hybrid structure with equally long strike‐slip and nontransform offsets. Axial rift zones (spreading axes) are generally within 1° of normal to the relative motion predicted by current plate rotation models. Most axial rift zones crop out along the crests of typical East Pacific Rise (EPR) axial ridges which commonly have flat rather than humped long profiles. About 2% of this fast‐spreading (84–100 mm/yr) rise crest has an axial rift valley instead of an axial ridge. The longest rift‐valley segment is midway between Menard and Vacquier transforms near 51°S, where an anomalously deep rise crest may mark a zone of below‐average mantle upwelling. Nontransform offsets structurally similar to those on the tropical EPR, but mostly formed by differential asymmetric spreading, subdivide the four longest spreading center systems. On the northern, transform‐free two thirds of the rise, net rift propagation at migrating offsets has been into the faster Pacific plate. This causes right steps to migrate north, left steps to migrate south, and crust to be transferred to the east flank. This pattern has prevailed for several million years, judging from the oblique fracture zones (pseudofaults) mapped on the rise flanks with older marine data and Geosat altimetry. On this rise crest, the difference in stress on two plates with very different velocities may control the direction of offset migration.

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“…In geophysics they are used to locate uncharted features for planning detailed shipboard surveys (Baudry et al, 1987). In geodesy, it is used to determine sea surface height and geoid and to detect sea floor features (Sandwell and Miguel, 1992). It is also used to collect gravity anomalies in areas where shipborne or airborne data are not available.…”

Section: Introductionmentioning

confidence: 99%

Recovery of marine gravity anomalies from ERS1, ERS2 and ENVISAT satellite altimetry data for geoid computations over Norway

2007

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Free-Air Anomalies (FAA) for the Norwegian marine area including some parts of theNorth Sea, the Norwegian Sea and the Barents Sea are computed from satellite altimetry data. A total of 84 cycles of ERS2 along-track data, 25 cycles of ENVISAT along-track data and high density ERS1 data during its geodetic mission are used. The new geopotential model from the Gravity Recovery and Climate Experiment (GRACE) mission, GGM02S (Tapely et al., 2005) is used to compute the long wavelength contributions of the geoid and the FAA. To correct data for mean dynamic topography, the available Levitus climatology model (Levitus and Boyer, 1994) is used. Corrected data are then used to compute along-track gradients in each cycle-pass to suppress the orbital and the atmospheric errors below the noise level of the altimeter. Resulted gradients are then stacked and the east-west and the north-south components of the deflection of verticals are computed where ascending and descending tracks meet each other. Finally, the inverse Vening-Meinesz formula is implemented on the gridded deflections to compute FAA. Results are then compared with available marine and airborne data. Standard deviations of ± 4.301 and ± 6.159 mGal in comparison with airborne and marine FAA were achieved. Thereafter, the derived anomalies are combined with marine and airborne FAA together with the land FAA to compute a fine resolution geoid for Norway and the surrounding marine areas. This geoid is evaluated over sea and land with the synthetic geoid (the geoid derived from the mean sea surface by subtracting the mean dynamic topography) and Global Positioning System (GPS)-levelling and the standard deviations of the differences are ± 20.9 and ± 12.8 cm respectively.

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Along-track gravity anomalies from Geostat and Seasat altimetry: GEBCO overlays

Cited by 10 publications

References 9 publications

A three‐dimensional gravity analysis of the East Pacific Rise from 18° to 21°30′S

A three‐dimensional gravity analysis of the East Pacific Rise from 18° to 21°30′S

Geomorphology and structural segmentation of the crest of the southern (Pacific‐Antarctic) East Pacific Rise

Recovery of marine gravity anomalies from ERS1, ERS2 and ENVISAT satellite altimetry data for geoid computations over Norway

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