A minimum-curvature gridding algorithm ( Briggs, 1974) is generally used to interpolate scattered gravity data to a regular grid.

Generally, a nonequispaced profile is converted to an equispaced profile using spline interpolation techniques ( Bhattacharyya, 1969).įor similar reasons, gravity data collected at scattered locations need to be organized into a regular grid prior to interpretation. The interpretation of gravity data generally requires multiple anomaly values organized into profiles or grids.Īlthough it is possible to interpret nonequispaced gravity profile data using forward modeling, many profile filtering and interpretation options require equispaced data. Phillips, in Treatise on Geophysics (Second Edition), 2015 11.12.11 Gravity Profiles and GridsĪ gravity anomaly value taken at a single location provides little useful information unless it is combined with anomaly values taken at surrounding locations. (After Smallwood and White (2002) with permission Geological Society of London.) Dotted black line indicates approximate line of Figure 12. Dashed white line shows area of oceanic crust disrupted by fracture zones (FZ) outside this area, oceanic crust was formed at a spreading centre without fracture zones on this scale. These are determined from reconstruction of the magnetic stripes parallel to the fracture zones seen in the gravity data.

Solid white line shows flowlines from present spreading centre indicating direction of paleo-seafloor spreading. Red and white circles show the position of the present-day spreading centre plate boundary. There are also circular gravity highs over igneous centres (IC) and linear anomalies along the continental margins (CM) and ‘V-shaped’ ridges (V) which flank the Reykjanes Ridge and reflect propagating pulses of anomalously hot mantle beneath the spreading centre. There are gravity anomaly highs over topographic highs such as the Reykjanes Ridge (R) and Kolbeinsey Ridge (K) spreading centres, and the extinct Aegir Ridge spreading centre (A). The magnetic stripes form the record of magnetic field reversals during production of oceanic crust at the spreading centre. Free-air gravity anomaly (A) and Magnetic anomaly (B) over the area surrounding Iceland (see Figure 2 for location). These observations have improved the precision of the global gravity field by two orders of magnitude ( Tapley et al., 2005).įigure 8. The data from the Gravity Recovery and Climate Experiment satellites yield a complete measurement of the gravity field to harmonic degree 160 (300 km spatial resolution at the Earth's surface) every 30 days. New satellite measurements of the Earth's gravity field were begun in April 2002.

The largest negative anomalies, indicating a thin lithosphere, are associated with vast Cenozoic regions of plume–lithosphere interaction: the East African Rift and the Basin and Range Province of the western North America. The largest of these positive anomalies over the continents were associated with the Andes, the East European Platform, the Alpine–Mediterranean fold belt, and the central southeastern part of North America. (2003) showed that upper mantle density variations contribute long-wavelength gravity anomalies ranging from − 250 mGal to + 150 mGal. Kane and Godson (1989) demonstrated that long-wavelength gravity highs are correlated with high mantle seismic velocities and gravity lows with low mantle velocities. Short-wavelength (< 250 km) gravity anomalies are usually correlated with crustal structures, while long-wavelength (< 1000 km) gravity anomalies are correlated with lateral variations of mantle densities. Gravity anomalies reveal rock density variations, with the amplitude of the anomaly proportional to the density contrast and thickness of the anomalous body. Mooney, in Treatise on Geophysics (Second Edition), 2015 1.11.4.1 Gravity

Anomaly meaning