Geoid lineations of 1000 km wavelength over the central Pacific

Cazenave, Anny; Parsons, B.; Calcagno, Philippe

doi:10.1029/94gl02858

Cited by 25 publications

(12 citation statements)

References 11 publications

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“…Its use has increased rapidly in communications, image processing and optical engineering applications as an alternative to the Fourier transform in preserving local, non-periodic, multiscaled phenomena. Recently, wavelet analysis has been applied to a variety of geophysical signals, including a bathymetric pro®le near Hawaii (Little et al, 1993), time-series of the Earth's length of day (Gambis, 1992;Chao and Naito, 1995) and solar irradiance (Kiang et al, 1994), spatial and temporal variations in sea surface temperatures (Meyers and O'Brien, 1994) and radar altimeter pro®les used for computation of a geoid surface model (Cazenave et al, 1995). Wavelet transformations of meteorological time-series have revealed structures in boundary layer turbulence (Hagelburg and Gamage, 1994;Hayashi, 1994;Turner et al, 1994;Katul and Parlange, 1995), winter thunderclouds (Takeuchi et al, 1994), atmospheric gravity waves (Sato and Yamada, 1994) and the scale of¯uctuations in spatial rainfall ®elds (Kumar and Foufoula-Georgiou, 1993).…”

Section: Introductionmentioning

confidence: 99%

Stream flow characterization and feature detection using a discrete wavelet transform

1998

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Abstract:An exploration of the wavelet transform as applied to daily river discharge records demonstrates its strong potential for quantifying stream¯ow variability. Both periodic and non-periodic features are detected equally, and their locations in time preserved. Wavelet scalograms often reveal structures that are obscure in raw discharge data. Integration of transform magnitude vectors over time yields wavelet spectra that re¯ect the characteristic time-scales of a river's¯ow, which in turn are controlled by the hydroclimatic regime. For example, snowmelt rivers in Colorado possess maximum wavelet spectral energy at time-scales on the order of 4 months owing to sustained high summer¯ows; Hawaiian streams display high energies at time-scales of a few days, re¯ecting the domination of brief rainstorm events. Wavelet spectral analyses of daily discharge records for 91 rivers in the US and on tropical islands indicate that this is a simple and robust way to characterize stream¯ow variability. Wavelet spectral shape is controlled by the distribution of event time-scales, which in turn re¯ects the timing, variability and often the mechanism of water delivery to the river. Five hydroclimatic regions, listed here in order of decreasing seasonality and increasing pulsatory nature, are described from the wavelet spectral analysis: (a) western snowmelt, (b) north-eastern snowmelt, (c) mid-central humid, (d) southwestern arid and (e)`rainstorm island'. Spectral shape is qualitatively diagnostic for three of these regions. While more work is needed to establish the use of wavelets for hydrograph analysis, our results suggest that river¯ows may be eectively classi®ed into distinct hydroclimatic categories using this approach. # 1998 John

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Section: Introductionmentioning

confidence: 99%

Stream flow characterization and feature detection using a discrete wavelet transform

1998

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“…Satellite altimetry revealed a series of free‐air anomaly gravity lineaments in the South Pacific beginning a few hundred kilometers from the East Pacific Rise (EPR) and extending westward in the direction of absolute plate motion (APM) of the Pacific plate in the hot spot coordinate frame [ Haxby and Weissel , 1986]. The lineaments have a peak‐to‐peak amplitude of 5 to 20 mGal and an initial dominant wavelength on the order of 170–200 km that increases somewhat to the west (Figure 1), although a range of wavelengths is present in all ages of seafloor [ Moriceau and Fleitout , 1989; Baudry and Kroenke , 1991; Maia and Diament , 1991; Cazenave et al , 1992; Fleitout and Moriceau , 1992; Wessel et al , 1994; Cazenave et al , 1995; Wessel et al , 1996; Marquart et al , 1999]. Bathymetric surveying and higher resolution altimetry identified sets of narrow, en echelon, volcanic ridges also trending in the direction of absolute plate motion, coincident with the lows of some of the gravity lineaments [ Winterer and Sandwell , 1987; McAdoo and Sandwell , 1989; Shen et al , 1993; Sandwell et al , 1995; Scheirer et al , 1996, 1998].…”

Section: Introductionmentioning

confidence: 99%

Analysis of gravity and topography in the GLIMPSE study region: Isostatic compensation and uplift of the Sojourn and Hotu Matua Ridge systems

2006

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[1] The Gravity Lineations Intraplate Melting Petrologic and Seismic Expedition (GLIMPSE) Experiment investigated the formation of a series of non-hot spot, intraplate volcanic ridges in the South Pacific and their relationship to cross-grain gravity lineaments detected by satellite altimetry. Using shipboard gravity measurements and a simple model of surface loading of a thin elastic plate, we estimate effective elastic thicknesses ranging from $2 km beneath the Sojourn Ridge to a maximum of 10 km beneath the Southern Cross Seamount. These elastic thicknesses are lower than predicted for the 3-9 Ma seafloor on which the volcanoes lie, perhaps due to reheating and thinning of the plate during emplacement. Anomalously low apparent densities estimated for the Matua and Southern Cross seamounts of 2050 and 2250 kg m À3 , respectively, probably are artifacts caused by the assumption of only surface loading, ignoring the presence of subsurface loading in the form of underplated crust and/or low-density mantle. Using satellite free-air gravity and shipboard bathymetry, we calculate the age-detrended, residual mantle Bouguer anomaly (rMBA). The rMBA corrects the free-air anomaly for the direct effects of topography, including the thickening of the crust beneath the seamounts and volcanic ridges due to surface loading of the volcanic edifices. There are broad, negative rMBA anomalies along the Sojourn and Brown ridges and the Hotu Matua seamount chain that extend nearly to the East Pacific Rise. These negative rMBA anomalies connect to negative free-air anomalies in the western part of the study area that have been recognized previously as the beginnings of the cross-grain gravity lineaments. Subtracting the topographic effects of surface loading by the ridges and seamounts from the observed topography reveals that the ridges are built on broad bands of anomalously elevated seafloor. This swell topography and the negative rMBA anomalies contradict the predictions of lithospheric cracking models for the origin of gravity lineaments and associated volcanic ridges, favoring models with a dynamic mantle component such as small-scale convection or channelized asthenospheric return flow.

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“…In spite of the fact that upper mantle convection is questionable for the Earth, it should be mentioned that these upper‐mantle‐wide rolls with wavelengths of about 800 km, which appear after some tens of millions of years of constant plate drift, may provide an explanation for the large‐wavelength gravity anomalies observed for the Pacific plate by Cazenave et al . (1992, 1995).…”

Section: Discussionmentioning

confidence: 99%

“…Investigations of sea‐surface height data obtained from SEASAT altimetry (Maia & Diament 1991) and of geoid data in different wavebands (Cazenave et al . 1992, 1995) provided evidence for E–W‐trending anomalies on the entire Pacific Plate of even greater wavelengths of 400–1000 km. While some authors (Haxby & Weissel 1986; Marquart et al .…”

Section: Introductionmentioning

confidence: 99%

On the geometry of mantle flow beneath drifting lithospheric plates

Marquart

2001

Geophysical Journal International

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Summary The convective flow pattern beneath the oceanic lithosphere is strongly influenced by the movement of the lithospheric plate on top. Assuming upper mantle convection, the wavelengths, geometric structure and time of onset for ridge‐perpendicular rolls as functions of the Rayleigh number and the plate velocity have been investigated by numerical modelling. The related gravity anomalies have been estimated and compared to observations from the SE Pacific, which show ridge‐perpendicular anomalies with wavelengths of 150–220 km and amplitudes of about 10 mGal. For constant viscosity, the type of secondary circulation perpendicular to the diverging ridge depends on the relation between imposed plate velocity, vs, and maximum velocity in the free‐convection case, vHfree. If vs is less than vHfree the flow is dominated by off‐ridge up‐ and downwellings; if vs is about 10 times larger than vHfree the flow remains 2‐D. If vs is between these extrema, a chain of ridge plumes develops from the lower thermal boundary layer with adjacent ridge‐perpendicular walls that lead to roll‐like circulation (‘Richter rolls’) throughout the model box. The wavelength of these rolls is a function of the Rayleigh number and the plate velocity. For parameters realistic for the Earth, rolls with considerable amplitude first develop after more than 50 Myr with wavelengths of at least 250 km. For temperature‐ and pressure‐ (depth‐) dependent viscosity, the wavelengths of the evolving rolls are determined by the Rayleigh number related to the maximum viscosity in the interior of the convecting system (and not to the average viscosity). For models with a strong decrease in viscosity to values of about 1019 Pa s in a 100‐km‐wide asthenospheric channel below the lithosphere, ridge‐perpendicular rolls, which only fill the low‐viscosity layer, appear after a few million years. After a transitional stage of some tens of millions of years rolls in the whole upper mantle also evolve. The asthenospheric rolls develop from instabilities of the upper thermal boundary layer and have wavelengths of about 220–280 km. The time needed for alignment of these rolls to the direction of plate movement is a few million years and the distance from the ridge to the point of onset of the rolls is about 200–500 km; both are functions of the plate velocity. While the formation time for rolls in the whole upper mantle is quite large and their existence is related largely to two‐layered convection, this type of flow might not be very relevant for the Earth, although it has been used to account for 3‐D structures at oceanic ridges. To explain the observed gravity anomalies in the SE Pacific, roll‐like circulation in a low‐viscosity asthenospheric layer is the preferred candidate, where the modelled amplitudes and wavelengths of gravity anomalies fit the observations.

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Geoid lineations of 1000 km wavelength over the central Pacific

Cited by 25 publications

References 11 publications

Stream flow characterization and feature detection using a discrete wavelet transform

Stream flow characterization and feature detection using a discrete wavelet transform

Analysis of gravity and topography in the GLIMPSE study region: Isostatic compensation and uplift of the Sojourn and Hotu Matua Ridge systems

On the geometry of mantle flow beneath drifting lithospheric plates

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