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Topic: Gravity anomalies

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	Pan-American Center for Earth and Environmental Studies
		A good example of the utility of gravity anomalies is their use to delineate the geometry and lateral extent of basins that contain ground water resources.
		Gravity modeling is used to provide quantitative estimates of the depth of the basin and thus the extent of the water resource.
		In most applications of gravity techniques, the data processing and qualitative interpretation of maps is followed by a quantitative interpretation in which a profile (or grid) of anomaly values is modeled by constructing an earth model whose calculated gravitational and/or magnetic effect closely approximates the observed profile (or grid).
	paces.geo.utep.edu /gravity/getstart.htm (6798 words)

	Gravity (Site not responding. Last check: 2007-11-05)
		This section is to present the view that the gravity perturbations are caused by planetary gravitational shielding as described with this radiation and shadowing model of gravity.
		The anomaly variations for the Moon and Mars are in the range of 1000+ milli gals (1 gal = 1cm/s/s).
		This delta measurement of 1000+ milli gals is approximately equal to one tenth of one percent of the earths surface gravity.
	home.netcom.com /~sbyers11/grav11d.htm (2721 words)

	Integrated Geophysics Corporation - Gravity/Magnetic Glossary
		The gravity anomalies observed in the Bouguer field are caused by lateral density contrasts within the sedimentary section, crust and sub-crust of the earth.
		The relationship is important in gravity modeling because a gravity anomaly may be caused by a gradational change in density rather than a relatively abrupt density contrast, such as that which may occur at a fault, contact, or unconformity.
		For 2-dimensional modeling, the density and susceptibility models of the geology and the observed gravity and magnetic anomalies for the model are assumed to be semi-infinite.
	www.igcworld.com /gm_glos.html (2687 words)

	Gravity Diamonds Limited - December 2004 Quarterly Report (Site not responding. Last check: 2007-11-05)
		Gravity Diamonds planned extensive follow-up sampling programmes on these anomalies commencing in June 2004, however, programme approvals by the Northern Land Council were delayed until late November 2004 and no effective sampling programmes could be carried out prior to the completion of the 2004 field season.
		Gravity Diamonds is pleased with the proportion of positive results from the FALCON® gravity anomalies tested in this programme and, with Striker Resources, will assess the importance and significance of these results and plan conclusive exploration programmes for early in 2005.
		Gravity Diamonds is encouraged by the incidence of artisanal workings in many of the drainages that were sampled and by the number of diamonds being recovered from the area.
	www.gravitydiamonds.com.au /Dec04quarter.html (1921 words)

	Untitled
		Gravity is usually measured in units of acceleration, as gals (or in mapping, as milligals) with a standard value (which has varied slightly as better measurments refine it) at 981.275 centimeters per second per second.
		Instead, gravity variations can be calculated from changes in the position (shifts in orbital height) of a satellite as it orbits - these are caused by the varying force of gravity from both the transient nadir points and surrounding areas near the path trace.
		Here is a gravity anomaly map of a region in the southwest Pacific in which one of the major ocean trenches (Tonga-Kermadee, on the left) is easily recognized, as are a series of small ocean floor volcanoes making up seamounts.
	rst.gsfc.nasa.gov /Intro/Part2_1b.html (2648 words)

	Gravity Prospecting for Massive Sulphide Deposits: Intermediate-Size Gravity Anomalies
		Gravity anomalies as large as the Brunswick No. 6 example are exceptional, and anomalies of more moderate magnitude are more common.
		The similarity in the amplitudes of the two anomalies (over Armstrong 'A' and Murray Brook) is surprising, given the large difference in ore reserves and even in the widths of the two deposits.
		They are, apparently, of relatively uniform density, since the gravity anomaly over the deposit, which is superposed on a gentle gradient and attains an amplitude of ~ 0.9 mGal, stands out from the background field and there are no indications of disturbing (dense) masses nearby.
	gdcinfo.agg.nrcan.gc.ca /app/bathgrav/intermediate_e.html (693 words)

	Michael Studinger's Homepage Gravity Anomalies of Sedimentary Basins and their mechanical implications
		Process-oriented gravity modeling indicates that magmatic underplating and crustal intrusions are inconsistent with the observed gravity and basement geometry of the Ross Sea basins.
		Positive gravity anomalies over extensional basins can be a consequence of a relatively low flexural strength of the lithosphere during rifting being contrasted by higher flexural strengths later during sedimentation.
		The narrow width of the Terror Rift precludes it from having a positive gravity anomaly while the opposite is true for the large Ross Sea basins.
	www.ldeo.columbia.edu /~mstuding/gravity_basins.html (787 words)

	Gravity Variations Predict Earthquake Behavior
		A gravity anomaly occurs when gravity is stronger or weaker than the regional average.
		Comparing variations in gravity along the trenches with earthquake data from two different catalogs going back 100 years, the team found that, within a given subduction zone, areas with negative gravity anomalies correlated with increased large earthquake activity.
		Because topography and gravity variations persist over periods of time much longer than the typical time between earthquakes, 100 to 1,000 years, large earthquakes should be consistently absent from areas with large positive gravity anomalies, say Song and Simons.
	www.physlink.com /News/080603GravityEarthquake.cfm (848 words)

	Gravity and antigravity (1)
		Her equation for ‘circular’ force (including gravity) is F = aA, where a is the acceleration and A is the area of a circle with a radius equal to the mean distance of the orbiting body from the central body.
		Spolter believes that her gravity equation solves the mystery of Kepler’s third law of planetary motion: this law states that the ratio of the cube of the mean distance (r) of each planet from the sun to the square of its period of revolution (T) is always the same number (r³/T² = constant).
		Various conventional explanations have been put forward to explain gravity anomalies during eclipses, such as instrument errors, gravity effects of denser air due to cooling of the upper atmosphere, seismic disturbances caused by sightseers moving into and out of a place where an eclipse is visible, and tilting of the ground due to cooling.
	ourworld.compuserve.com /homepages/dp5/gravity.htm (10737 words)

	USGS Fact Sheet 078-95 -- Geophysical Data Grids for the Conterminous United States
		The magnetic anomaly and gamma-ray data sets are gridded at a 2- kilometer grid interval; the gravity anomaly and topographic-bathymetric data sets are gridded at a 4-kilometer grid interval.
		Gravity anomalies are produced by density variations within the rocks of the Earth's crust and upper mantle.
		Topographic and bathymetric data are used in the reduction and interpretation of magnetic anomaly and gravity anomaly data and in the construction of geologic and topographic maps.
	pubs.usgs.gov /fs/fs-0078-95/FS078-95.html (634 words)

	Physical geodesy - Wikipedia, the free encyclopedia
		Physical geodesy is the study of the physical properties of the gravity field of the Earth, the geopotential, with a view to their application in geodesy.
		Traditional geodetic instruments such as theodolites rely on the gravity field for orienting their vertical axis along the local plumb line or local vertical direction with the aid of a spirit level.
		In this formula, Δg stands for gravity anomalies, differences between true and normal (reference) gravity, and S is the Stokes function, a kernel function derived by Stokes in closed analytical form.
	en.wikipedia.org /wiki/Physical_geodesy (1242 words)

	DNAG Gravity Data
		These data, representing Bouguer gravity anomalies on land and free air gravity anomalies over the oceans, were produced under the direction of the Committee for the Gravity Anomaly Map of North America.
		For continental areas, anomalies have been computed from measurements made with static gravimeters operated on dry land, sea and lake bottoms, and the frozen surfaces of the sea or lakes.
		Bouguer gravity anomalies were calculated using a standard crustal density of 2670 kg/m3.
	www.ngdc.noaa.gov /seg/gravity/document/html/dnaggrav.shtml (1373 words)

	Gravity anomaly - Wikipedia, the free encyclopedia
		A gravity anomaly is the difference between the observed gravity and a value predicted from a model.
		Bouguer anomalies are ideal for geophysics because they show the effects of different rock densities of the subsurface.
		The Bouguer anomalies usually are negative in the mountains because of isostasy: the rock density of their roots is lower, compared with the surrounding earth's mantle.
	en.wikipedia.org /wiki/Gravity_anomaly (535 words)

	Gravity Diamonds Limited - Announcements (Site not responding. Last check: 2007-11-05)
		gravity anomaly can be only partially attributed to increases in density associated with the intersected mineralisation and significant potential remains for more massive mineralisation within the area of the anomaly.
		Gravity Capital Limited ("Gravity") is to commence drilling its priority drill targets in the Broken Hill project area in early November.
		With the aim of determining the cause of the gravity anomaly, one or more lines of drill holes to a maximum hole depth of 150 metres are planned for each target,.
	www.gravitydiamonds.com.au /Announcements2003.html (6838 words)

	GRACE - Gravity Recovery and Climate Experiment
		Subduction zones, for example, were previously only observed in space-based gravity models as a broad area of high gravity due to the combined mass of the subducting slab beneath a volcanic arc.
		As we look from east to west across this region (starting from right-center of the left panel) we observe in the gravity anomaly map a high (yellow), a low (blue/green), a high (red), and drop to a smaller high (yellow).
		a drop to a lower gravity anomaly magnitude in the Lau Basin as the Australian Plate is 'pulled' towards the Pacific Plate, forming a back-arc basin.
	www.csr.utexas.edu /grace/gravity/solid_earth.html (406 words)

	Creating Observed Gravity Anomalies from raw field data (Site not responding. Last check: 2007-11-05)
		The milligal is the primary unit of gravity exploration, and is equivalent to one thousandth of a gal (Galileo), the geophysical unit of gravity.
		The gravity has increased by drifting upward 60 microgals over a four hour span, at a rate of 15 microgals per hour, or 0.25 microgals per minute (this is actually a rather high drift rate).
		The gravity differences for the stations are then added algebraically to the absolute value to obtain absolute values at each station (used in the most common type of reduction scheme to Bouguer anomaly values).
	seis.natsci.csulb.edu /grannell/gravity1.html (2557 words)

	GRACE Gravity Model- Gravity Recovery and Climate Experiment Gravity Model
		This global Earth gravity model is a significant improvement upon, and supersedes, the previously released model GGM01.
		Consequently the accuracy and resolution of the Earth gravity field models were limited, with most of the satellite contributions limited to wavelengths of 700 km or longer.
		As a result, improvements to the Earth gravity models at medium & short wavelengths had to come from the use of measurements of terrestrial or marine gravity - also of varying vintage, quality and geographic coverage.
	www.csr.utexas.edu /grace/gravity (600 words)

	GRAVITY DATA OF NEVADA
		Data were processed to complete Bouguer and isostatic gravity anomalies by applying standard gravity corrections including terrain corrections to a radial distance of 167 km and isostatic corrections based on an Airy-Heiskanen model of local compensation (Heiskanen and Moritz, 1967).
		Gravity data were reduced using the Geodetic Reference System of 1967 (International Union of Geodesy and Geophysics, 1971) and adjusted to the International Gravity Standardization Net 1971 (IGSN 71) gravity datum (Morelli, 1974).
		Gravity data were reduced to complete Bouguer and isostatic anomalies using a reduction density of 2.67 g/cm^3.
	www.ngdc.noaa.gov /seg/gravity/document/html/nev97a.shtml (3226 words)

	Mongolia gravity
		Synthetic Bouguer gravity produced by the two modelled density anomalies and localised fault flexure (north and south of the dome).
		Gravity and topographic data, combined with other constraints on crustal and mantle structure such as seismic tomography and analyses of mantle xenoliths, do not provide evidence for a high-flux plume (or “hot spot”) beneath Mongolia.
		This is in agreement with the petrology and geochemistry of the basalts which suggest a low-flux thermal anomaly located in the lower lithosphere or upper asthenosphere, as suggested by Barry et al.
	www.mantleplumes.org /MongoliaGravity.html (1761 words)

	Gravity and Inertia via Radiation Pressure (Site not responding. Last check: 2007-11-05)
		A surface gravity and/or radiation pressure limit are shown to exist when the radiation flow is totally shielded by large planets.
		The cause for the inverse square laws of physics is shown to be a natural result of shadowing geometry with distance.
		A multitude of combinations of the electrostatic, magnetic and inertial forces may be tried, with the objective of shielding or focusing the radiation to modify the local effects of gravity and inertia upon an object.
	home.netcom.com /~sbyers11 (685 words)

	Gravity Anomalies
		The gravity anomaly, defined as a scalar quantitiy, is merely the difference in magnitude.
		What can be seen in these maps, when compared with those found on the geoid page, is that gravity anomalies are a higher frequency phenomena.
		In this formula, we see that a gravity anomaly is given as a sum of the negative change in the disturbing potential taken with respect to height (the first term) and the product of the corresponding geoid height with the change in normal gravity taken with respect to height.
	www.geocities.com /geodsci/GravAnom.htm (199 words)

	Gravity Prospecting for Massive Sulphide Deposits: Large Gravity Anomalies
		The Brunswick No. 6 deposit, mined out after producing about 12 million tonnes, gave rise to probably the largest gravity anomaly associated with a sulphide deposit in the Bathurst camp (shown to the left).
		Densities of similar rocks elsewhere in the immediate area fall within a fairly narrow range, and hence the sulphide anomaly is reasonably symmetrical.
		The only interference to the signature is caused by iron formation, but since the sulphide contribution is so strong, it would not have posed a problem for exploration.
	gdcinfo.agg.nrcan.gc.ca /app/bathgrav/large_e.html (329 words)

	Gravity anomalies and crustal structure at the southeast Greenland margin
		Gravity anomalies and crustal structure at the southeast Greenland margin
		Free-air gravity anomalies across the southeast Greenland margin are investigated in conjunction with a well-constrained seismic velocity model to provide a constraint on subsurface density structure.
		If most of the residual gravity anomaly has a crustal origin, applying a conversion law with a denser upper crust in the continent-ocean transition zone seems to be the only plausible option to resolve this difficulty.
	www.agu.org /pubs/crossref/2001/2000JB900416.shtml (395 words)

	Bouguer Gravity Anomalies of New Jersey (1 milligal interval)
		Bouguer Anomalies of New Jersey is a GIS shapefile of bouguer gravity contours (lines) at 1 milligal intervals.
		Sugarman, P. J., 1981, The geological interpretation of gravity anomalies in the vicinity of Raritan Bay, New Jersey and New York: unpublished M.S. Thesis University of Delaware.
		Gravity data for New Jersey and vicinity obtained from the National Imagery and Mapping Agency, US Dept. of Defense and the New Jersey Geological Survey were reduced to obtain Bouguer gravity anomalies.
	www.state.nj.us /dep/njgs/geodata/nj_grav1md.htm (1555 words)

	Gravity Anomalies! - Unexplained Mysteries Discussion Forums
		The big regional gravity anomalies have been accommodated to some degree for many decades, but the failure to identify "local" gravity anomalies has brought into doubt the accuracy of many so-called precision surveys.
		It is now known that "deviations of the vertical" and the direction of the gravity vector can cause systematic errors that are well in excess of the surveying instruments precision, thus effectively negating the stated accuracy of surveyed values.
		The mascons on the moon present very intense gravity anomalies and disturbed the orbits of the various moon orbiters.
	www.unexplained-mysteries.com /forum/index.php?showtopic=5501 (1590 words)

	UFORCE: TST, UFOs and Gravity Anomalies (Site not responding. Last check: 2007-11-05)
		Gravity research, especially how it relates to mountainous regions, was in its infancy and remains so to this day.
		Mass warps gravity, and it is within these areas of high gravity distortion, that UFO activity is the highest.
		This is evident from gravity readings taken around specific mountain chains, which will show and do demonstrate that this is indeed the case, drawing from the evidence which is available, namely gravity anomaly readings.
	www.angelfire.com /journal2/UFORCE/page8.html (1887 words)

	Gravity CD-ROM (Site not responding. Last check: 2007-11-05)
		The 1994 edition of the Gravity CD-ROM has been significantly enhanced and improved by several new and important contributions consisting of observed and derived gravity measurements.
		Approximately 25 percent of the data are observed values -- regional station data collections (separated primarily by contributors) and absolute gravity measurements.
		Gridded data include U.S. and North America Bouguer and free-air anomalies, isostatic gravity, Canada gravity geoid and gridded gravity anomalies for the southern ocean.
	gcmd.nasa.gov /records/GCMD_FE01018.html (270 words)

	Bouguer Gravity Anomalies of New Jersey (5 milligal interval)
		Bouguer Gravity Anomalies of New Jersey (5 milligal interval)
		Bouguer Anomalies of New Jersey is a GIS shapefile of bouguer gravity contours (polygons) at 5 milligal intervals.
		The New Jersey contours were clipped at the state outline.The bouguer anomalies in New Jersey have lows ranging from -55 to -60 milligals and highs ranging from +35 to +40 milligals.
	www.state.nj.us /dep/njgs/geodata/nj_grav5md.htm (1553 words)

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