Curvature of a geometric surface and curvature of gravity and magnetic anomalies

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. G15-G26 ◽  
Author(s):  
Xiong Li
Keyword(s):  
Gravity Data ◽  
Vertical Cylinder ◽  
Equipotential Surface ◽  
Magnetic Anomalies ◽  
Gravity Gradient ◽  
Gravity Gradients ◽  
Theoretical Derivation ◽  
Vertical Gravity Gradient ◽  
Gravity And Magnetic ◽  
Geometric Surface

Curvature describes how much a line deviates from being straight or a surface from being flat. When curvature is used to interpret gravity and magnetic anomalies, we try to delineate geometric information of subsurface structures from an observed nongeometric quantity. In this work, I evaluated curvature attributes of the equipotential surface as functions of gravity gradients and analyzed the differences between the theoretical derivation and a practical application. I computed curvature of a synthetic model that consisted of representative structures (ridge, valley, basin, dome, and vertical cylinder) and curvature of the equipotential surface, gravity, and vertical gravity gradient (which is equivalent to the magnetic reduction-to-the-pole result) due to the same model. A comparison of curvature of such a geometric surface and curvature of different gravity quantities was then made to help understand these curvature differences and an indirect link between curvature of gravity data and actual structures. Finally, I applied curvature analysis to a magnetic anomaly grid in the Gaspé belt of Quebec, Canada, to illustrate its useful property of enhancing subtle features.

Reduction to the pole of the North American magnetic anomalies

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 218-225 ◽  
Author(s):  
J. Arkani‐Hamed ◽  
W. E. S. Urquhart
Keyword(s):  
North America ◽  
Gravity Anomalies ◽  
Magnetic Anomalies ◽  
Gravity Gradient ◽  
Plate Boundaries ◽  
Gravity Gradients ◽  
The North ◽  
Vertical Gravity Gradient ◽  
Regional Tectonic ◽  
Vertical Gravity

Magnetic anomalies of North America are reduced to the pole using a generalized technique which takes into account the variations in the directions of the core field and the magnetization of the crust over North America. The reduced‐to‐the‐pole magnetic anomalies show good correlations with a number of regional tectonic features, such as the Mid‐Continental rift and the collision zones along plate boundaries, which are also apparent in the vertical gravity gradient map of North America. The magnetic anomalies do not, however, show consistent correlation with the vertical gravity gradients, suggesting that magnetic and gravity anomalies do not necessarily arise from common sources.

POSSIBLE APPLICATION OF THE ANOMALOUS FREE‐AIR VERTICAL GRADIENT TO MARINE EXPLORATION

Geophysics ◽  
1966 ◽  
Vol 31 (1) ◽  
pp. 260-263
Author(s):  
Stephen Thyssen‐Bornemisza
Keyword(s):  
Vertical Cylinder ◽  
Vertical Gradient ◽  
Gravity Gradient ◽  
Average Gradient ◽  
Vertical Gravity Gradient ◽  
Free Air ◽  
Vertical Gravity ◽  
Lithologic Unit ◽  
Marine Exploration ◽  
Anomalous Average

Recently it could be shown (Thyssen‐Bornemisza, 1965) that a vertical lithologic unit cylinder generates a relatively strong anomalous free‐air vertical gravity gradient F′ along the cylinder axis. The following simple example may serve as a demonstration. A small vertical cylinder made of gold or tungsten, where radius r and length L are identical, would generate the anomalous average gradient F′∼3,223 Eötvös units over the interval h=r=L going from the cylinders top surface upward. Suppose r=l=1 cm, then an average gradient exceeding the earth’s normal free‐air vertical gradient F is present over the interval h=1 cm.

VARIATIONS OF VERTICAL GRAVITY GRADIENT IN NEW YORK CITY AND ALPINE, NEW JERSEY

Geophysics ◽  
1969 ◽  
Vol 34 (2) ◽  
pp. 235-248 ◽  
Author(s):  
John T. Kuo ◽  
Mario Ottaviani ◽  
Shri K. Singh
Keyword(s):  
New York ◽  
New York City ◽  
New Jersey ◽  
York City ◽  
Gravity Data ◽  
Tall Buildings ◽  
Base Station ◽  
Absolute Gravity ◽  
Gravity Gradient ◽  
Vertical Gravity Gradient

Careful gravity measurements with La Coste‐Romberg geodetic gravimeters were carried out in tall buildings on a floor‐to‐floor basis in New York City and on the Armstrong Tower, Alpine, New Jersey. Corrections for the instrumental drift and tidal gravity variation and for the Bouguer effect, topography, mass of the buildings, and subway and basement excavations have been applied to the gravity data, which are tied to the absolute gravity value of the National Gravity Base Station of Washington, D. C. The observed gravity versus elevation curves are nonlinear, particularly near the surface of the ground; the slope of the observed gravity anomaly versus elevation curves reverses sign at an elevation of about 170 ft for the campus buildings and about 350 ft for the downtown buildings, and is nearly linear without a reversal for the Armstrong Tower. The vertical gradients vary substantially even within short distances. Comparisons of the corrected observed gradients with the theoretical gradients of gravity are made. The anomalous gradient anomalies are positive and are correlated with the positive isostatic surface gravity anomalies. Calibration of gravimeters against the observed vertical gradient of gravity to an accuracy of ±2 μgal is definitely feasible provided the gradient is predetermined to a comparable accuracy by a standard instrument.

Monitoring gas production and C O2 injection at the Sleipner field using time-lapse gravimetry

Geophysics ◽  
2008 ◽  
Vol 73 (6) ◽  
pp. WA155-WA161 ◽  
Author(s):  
Håvard Alnes ◽  
Ola Eiken ◽  
Torkjell Stenvold
Keyword(s):  
Simulation Model ◽  
Gravity Data ◽  
Time Lapse ◽  
Average Density ◽  
Gas Production ◽  
Gravity Gradient ◽  
Water Influx ◽  
Vertical Gravity Gradient ◽  
Plume Geometry ◽  
Best Fit

Thirty seafloor gravity stations have been placed above the carbon dioxide [Formula: see text] injection site and producing gas reservoir at the Sleipner Øst Ty field. Gravity and depth measurements from 2002 and 2005 reveal vertical changes of the permanently deployed benchmarks, probably caused by seafloor erosion and biologic activity (fish). The original gravity data have been reprocessed, resulting in slightly different gravity-change values compared with earlier published results. Observed gravity changes are caused by height variances, gas production and water influx in the Ty Formation, and [Formula: see text] injection in the Utsira Formation. Simultaneous matches to models for these effects have been made. The latest simulation model of the Ty Formation was fitted by permitting a scale factor, and the gravity contribution from the [Formula: see text] plume was determined by using the plume geometry as observed in 4D seismic data and varying the average density. The best-fit vertical gravity gradient is [Formula: see text], and the response from the Ty Formation suggests more water influx than expected in the presurvey simulation model. The best-fit average density of [Formula: see text] is [Formula: see text]. Estimates of the reservoir temperature combined with the equation of state for [Formula: see text] indicate an upper bound on [Formula: see text] density of [Formula: see text]. The gravity data suggest a lower bound of [Formula: see text] at 95% confidence.

scholarly journals Analysis of Groundwater Decline and Land Subsidence by using of Microgravity and Vertical Gravity Gradient Over Time Method

2014 ◽  
Vol 15 (1) ◽  
pp. 7 ◽  
Author(s):  
Suhayat Minardi ◽  
Hiden Hiden ◽  
Daharta Dahrin ◽  
Mahmud Yusuf
Keyword(s):  
Gravity Anomaly ◽  
Land Subsidence ◽  
Gravity Data ◽  
Vertical Gradient ◽  
Time Lapse ◽  
Gravity Gradient ◽  
Vertical Gravity Gradient ◽  
Vertical Gravity ◽  
Groundwater Decline ◽  
Over Time

Studies have been conducted to identify the occurrence of subsidence, a decline of groundwater, and to model the causes of subsidence in areas of Jakarta based on response of microgravity anomaly and vertical gravity gradient over time. Based on the processing and interpretation of gravity data advance of the time concluded that by using a combination of time lapse microgravity and its vertical gradient have been able to localize the source of the gravity anomaly and the results are strongly support the results of filtering to separate the source of the anomaly. The subsidence that occurs predominantly due to resettlement (in West and North Jakarta), caused by the extraction of groundwater and resettlement (in Central and East Jakarta), and dominated due to the extraction of groundwater (in South Jakarta).Keywords : Groundwater, time lapse micogravity, time lapse vertical gradient, resettlement, subsidence

THE VERTICAL GRAVITY GRADIENT IN BOREHOLE EXPLORATION

Geophysics ◽  
1963 ◽  
Vol 28 (6) ◽  
pp. 1072-1073 ◽  
Author(s):  
Stephen Thyssen‐Bornemisza
Keyword(s):  
Point Mass ◽  
Gravity Gradient ◽  
Gravity Gradients ◽  
Vertical Derivative ◽  
Rock Formations ◽  
Vertical Gravity Gradient ◽  
Vertical Gravity ◽  
First Vertical Derivative

In past years vertical gravity‐gradient observations have been repeatedly suggested for the determination of in‐situ densities of rock formations penetrated by a borehole (Smith, 1950; Hammer, 1963). However, calculations made for a point mass to one side of a borehole show that the first vertical derivative of gravity, g, is influenced by this mass to a much greater degree than g itself, or the second vertical derivative. This should be borne in mind if attempts are made to measure vertical gravity gradients in a borehole.

A RAPID METHOD FOR MEASURING THE PROFILE COMPONENTS OF HORIZONTAL AND VERTICAL GRAVITY GRADIENTS

Geophysics ◽  
1943 ◽  
Vol 8 (2) ◽  
pp. 119-133 ◽  
Author(s):  
C. A. Heiland
Keyword(s):  
Thermal Conditions ◽  
Observation Time ◽  
Resolving Power ◽  
Gravity Gradient ◽  
Maximum Effect ◽  
Gravity Gradients ◽  
Optical Sensitivity ◽  
Vertical Gravity Gradient ◽  
Terrain Corrections ◽  
Vertical Gravity

The trend in gravity exploration in the past years indicates the rather remarkable fact that a method of low resolving power (the gravity meter) has replaced one of higher resolving power (the torsion balance). This is entirely due to the superior speed of the former and suggests an instrument and procedure in which observation time is reduced by (1) reduction in number of quantities measured; (2) use of a reference direction near that of the maximum effect; (3) elimination of the torsionless position as unknown; (4) reduction in period, with compensating increase in optical sensitivity; (5) stabilization of thermal conditions. These objectives are attained by (1) measuring the profile components of gradients and curvature values, preferably at right angles to the assumed strike; whereby, for an ideal two‐dimensional feature, also the vertical gravity gradient is obtained, and the vertical and horizontal gravity components may be calculated by integration; (2) by holding the torsionless position constant with temperature control; (3) by decreasing the period and observation time to 3–4 minutes, and (4) by using a beam arrangement which will give the gradient in only one azimuth, and the profile gradient of the horizontal gravity component in a second azimuth if desired. Latitude and terrain corrections are also somewhat simplified by the proposed procedure.

Interval gravity‐gradient determination concepts

Geophysics ◽  
1984 ◽  
Vol 49 (6) ◽  
pp. 828-832 ◽  
Author(s):  
Dwain K. Butler
Keyword(s):  
Finite Difference ◽  
Gravity Data ◽  
Vertical Gradient ◽  
Gravity Gradient ◽  
Gravity Gradients ◽  
Tower Structure ◽  
Gravity Measurements ◽  
Vertical Gradients

Considerable attention has been directed recently to applications of gravity gradients, e.g., Hammer and Anzoleaga (1975), Stanley and Green (1976), Fajklewicz (1976), Butler (1979), Hammer (1979), Ager and Liard (1982), and Butler et al. (1982). Gravity‐gradient interpretive procedures are developed from properties of true or differential gradients, while gradients are determined in an interval or finite‐difference sense from field gravity data. The relations of the interval gravity gradients to the true or differential gravity gradients are examined in this paper. Figure 1 illustrates the concepts of finite‐difference procedures for gravity‐gradient determinations. In Figure 1a, a tower structure is illustrated schematically for determining vertical gradients. Gravity measurements are made at two or more elevations on the tower, and various finite‐difference or interval values of vertical gradient can be determined. For measurements at three elevations on the tower, for example, three interval gradient determinations are possible: [Formula: see text]; [Formula: see text]; [Formula: see text]; where [Formula: see text] and [Formula: see text] etc. For a positive downward z-;axis, these definitions for [Formula: see text] and [Formula: see text] will result in positive values for the vertical gradient. Relations of the interval gradients to each other and to the true or differential gradient are examined in this paper.

scholarly journals 13 million years of seafloor spreading throughout the Red Sea Basin

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nico Augustin ◽  
Froukje M. van der Zwan ◽  
Colin W. Devey ◽  
Bryndís Brandsdóttir
Keyword(s):  
Red Sea ◽  
Gravity Data ◽  
Ocean Basin ◽  
Gravity Gradient ◽  
Ocean Ridges ◽  
Spreading Ridges ◽  
Vertical Gravity Gradient ◽  
Slow Spreading ◽  
Vertical Gravity ◽  
High Resolution Bathymetry

AbstractThe crustal and tectonic structure of the Red Sea and especially the maximum northward extent of the (ultra)slow Red Sea spreading centre has been debated—mainly due to a lack of detailed data. Here, we use a compilation of earthquake and vertical gravity gradient data together with high-resolution bathymetry to show that ocean spreading is occurring throughout the entire basin and is similar in style to that at other (ultra)slow spreading mid-ocean ridges globally, with only one first-order offset along the axis. Off-axis traces of axial volcanic highs, typical features of (ultra)slow-spreading ridges, are clearly visible in gravity data although buried under thick salt and sediments. This allows us to define a minimum off-axis extent of oceanic crust of <55 km off the coast along the complete basin. Hence, the Red Sea is a mature ocean basin in which spreading began along its entire length 13 Ma ago.

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