Frequency-domain reduction of potential field measurements to a horizontal plane

Guspí, Fernando

doi:10.1016/0016-7142(87)90083-4

Cited by 59 publications

(61 citation statements)

References 8 publications

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“…The magnetic data were corrected for the regional geomagnetic field determined from the 1995 International Geomagnetic Reference Field (IGRF) calculated at each measurement location [International Association of Geomagnetism and Aeronomy, 1996]. The total field anomaly profiles were first upward continued using the Fourier-based method of Guspi [1987] to a level plane at 2000 m below sea level. We acknowledge that the high-cut filtering and the upward continuation process induce a loss in resolution, mainly for the deepest (and older) parts of the profiles, and for those of high topographic contrast (i.e., in the axial valley ).…”

Section: Near-bottom Data Processingmentioning

confidence: 99%

A geomagnetic record over the last 3.5 million years from deep‐tow magnetic anomaly profiles across the Central Indian Ridge

Pouliquen¹,

Gallet²,

Patriat³

et al. 2001

J. Geophys. Res.

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Abstract. High-resolution records of the geomagnetic field intensity over the last 4 Myr provided by paleomagnetic analyses of marine sediments have shown the occurrence of shortlived low field intensity features associated with excursions or short polarity intervals. In order to evaluate the ability of marine magnetic anomalies to record the same geomagnetic events, we have collected six deep-tow (-500 m above the seafloor) and several sea surface magnetic anomaly profiles from the Central Indian Ridge across the Brunhes, Matuyama, and Gauss chrons (i.e., from the ridge axis to anomaly 2A). After removal of topography, latitude, and azimuth effects, we converted distances into time sequences using well-dated polarity reversal anomalies as tie points. We calculated the average signal to test the robustness of the short-wavelength anomalies. The resulting stacked profile is very similar to stacked sea surface and downward continued profiles from the Central Indian Ridge, the East Pacific Rise, and the Pacific-Antarctic Ridge. Our results suggest that in addition to polarity reversals, to previously suggested geomagnetic events (subchrons or excursions) within the Brunhes and Matuyama chrons. A new small-scale magnetic anomaly, likely generated by several closely spaced geomagnetic field intensity variations represent the major contributor to the detailed shape of recent marine magnetic anomalies in investigated areas. We observe a dense succession of microanomalies that are correlated excursions (Ontong Java 1 and 2, and Gilsa), is found after the Olduvai chron. The near-bottom results support the existence of three geomagnetic features between the Gauss-Matuyama boundary and Olduvai. They also suggest three geomagnetic events during the C2A. I n subchron within the Gauss chron. This study emphasizes the potential of deep-tow magnetic surveys in detecting fluctuations in geomagnetic field intensity and, in particular, short-lived excursions, a poorly constrained part of the geomagnetic field temporal variation spectrum.

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Section: Near-bottom Data Processingmentioning

confidence: 99%

A geomagnetic record over the last 3.5 million years from deep‐tow magnetic anomaly profiles across the Central Indian Ridge

Pouliquen¹,

Gallet²,

Patriat³

et al. 2001

J. Geophys. Res.

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“…We use an iterative Fast Fourier Transform approach to obtain this upward continued field [Guspi, 1987;Pilkington and Urquhart, 1990]. Figure 5-8 shows the geometry necessary to reduce the magnetic measurements made on an uneven surface to a level plane.…”

Section: Data Processing and Resultsmentioning

confidence: 99%

“…The choice of this water-depth leads to better convergence of the Fourier transform method [Guspi, 1987]. Finally, the magnetic field data were upward continued to another constant water-depth that is also referred to as guspi level, since all bathymetry of the survey lies below this water depth.…”

Section: Data Processing and Resultsmentioning

confidence: 99%

“…The resultant upward continued magnetic profiles are shown in Figure 5-9, and all the profiles, in general, exhibit clear variations up the scarp. A cartoon shows the guspi-upcon transform procedure to reduce magnetic measurements made on an uneven surface to a level plane [Guspi, 1987]. First of all, the observed level is rotated clockwise to a horizontal plane, i.e., with an average scarp angle 23° in this paper.…”

Section: Data Processing and Resultsmentioning

confidence: 99%

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Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings

Xu¹

2012

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The structure of the oceanic lithosphere results from magmatic and extensional processes taking place at mid-ocean ridges (MORs). The temporal and spatial scales of the variability of these two processes control the degree of heterogeneity of the oceanic lithosphere, represented by two end-member models: the classical Penrose Model exemplified by layered magmatic crust formed along fast-spreading MORs, e.g., East Pacific Rise (EPR); and the recently defined Chapman Model describing heterogeneous mafic and ultramafic lithosphere formed in settings of oceanic detachment faulting common along slow-spreading MORs, e.g., Mid-Atlantic Ridge (MAR). This thesis is using advanced marine geophysical methods (including finite-difference wave propagation modeling, 3D multi-channel seismic reflection imaging, waveform inversion, streamer tomography, and near-bottom magnetics) to study lithospheric accretion processes in MORs characterized by contrasting tectono-magmatic settings: the magmatically dominated EPR axis between 9°30'-10°00'N, and the Kane Oceanic Core Complex (KOCC), a section of MAR lithosphere (23°20'-23°38'N) formed by detachment faulting. At the EPR study area, I found that the axial magma chamber (AMC) melt sill is segmented into four prominent 2-4-km-long sections spaced every ~5-10 km along the ridge axis characterized by high melt content (>95%). In contrast, within the intervening sections, the AMC sill has a lower melt content (41-46%). The total magma volume extracted from the AMC sill was estimated of ~46 × 10 6 m 3 , with ~24 × 10 6 m 3 left unerupted in the upper crust as dikes after 2005-06 eruption. At the KOCC, I used streamer tomography to constrain the shallow seismic velocity structure. Lithological interpretation of the seismic tomographic models provides insights into the temporal and spatial evolution of the melt supply at the spreading axis as the KOCC formed and evolved. Investigation of a magnetic polarity reversal boundary in crosssection at the northern boundary of KOCC suggests that the boundary (representing both a frozen isotherm and an isochron) dips away from the ridge axis along the Kane transform fault scarp, with a west-dipping angle of ~45° in the shallow (<1 km) crust and <20° in the deeper crust. Many thanks to my project advisors and cooperators, Brian Tucholke, RalphStephen, and Maurice Tivey, who have worked with me during the past five and a half years. These research experiences have greatly broadened my horizons on marine geology and geophysics, synthetic seismology, and geomagnetism. Brian introduced me into the geological world of detachment fault system, and his patience and insightful comments on our scientific paper on Kane oceanic core complex are greatly appreciated.I am very thankful for Ralph who introduced me to the world of time-domain finite difference (TDFD) synthetic seismology and Tom Bolmer for setting up the workstation for my TDFD calculations. Ralph's encouragement, enthusiasm, and interactions with me have inspired me to dig out more intere...

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“…In geophysical applications, the planar approximation of Poisson integral is frequently used to reduce the observed gravity on the Earth's surface to a lower level inside the Earth (Grant and West, 1965;Roy, 1966;Meyer, 1974;Fogarty, 1981;Guspí, 1987;Morgan and Blackman, 1993;Blakely, 1995;Cooper, 2004;Fedi, et al, 2005; * E-mail: meh goli@yahoo.com † E-mail: mnajalm@yahoo.com Hwang, et al, 2006;Xu, et al, 2007;Prutkin and Saleh, 2009). …”

Section: Introductionmentioning

confidence: 99%

Planar, spherical and ellipsoidal approximations of Poisson's integral in near zone

Goli

Najafi-Alamdari

2011

Journal of Geodetic Science

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Abstract:Planar, spherical, and ellipsoidal approximations of Poisson's integral for downward continuation (DWC) of gravity anomalies are discussed in this study. The planar approximation of Poisson integral is assessed versus the spherical and ellipsoidal approximations by examining the outcomes of DWC and finally the geoidal heights. We present the analytical solution of Poisson's kernel in the point-mean discretization model that speed up computation time 500 times faster than spherical Poisson kernel while preserving a good numerical accuracy. The new formulas are very simple and stable even for regions with very low height. It is shown that the maximum differences between spherical and planar DWC as well as planar and ellipsoidal DWC are about 6 mm and 18 mm respectively in the geoidal heights for a rough mountainous area such as Iran.

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Frequency-domain reduction of potential field measurements to a horizontal plane

Cited by 59 publications

References 8 publications

A geomagnetic record over the last 3.5 million years from deep‐tow magnetic anomaly profiles across the Central Indian Ridge

A geomagnetic record over the last 3.5 million years from deep‐tow magnetic anomaly profiles across the Central Indian Ridge

Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings

Planar, spherical and ellipsoidal approximations of Poisson's integral in near zone

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