Gravity anomalies are often due to unusual concentrations of mass in a region. Conversely, the presence of ocean trenches or even the depression of the landmass that was caused by the presence of glaciers millennia ago can cause negative gravity anomalies.

The gravity method involves measuring the gravitational attraction exerted by the earth at a measurement station on the surface. The strength of the gravitational field is directly proportional to the mass and therefore the density of subsurface materials.

There are two types of gravimeters: absolute and relative. Absolute gravimeters measure the local gravity in absolute units (Gal). Absolute gravimeters are compact (Autograv CG-5 model) and used in the field. They work by directly measuring the acceleration of a mass during freefall in a vacuum.

Gravity station values were collected by using a LaCoste-Romberg gravimeter with modified electronics (an “Aliod” gravimeter) that perform the instrument and Earth-tide corrections internally, so that the gravimeter measurements are output in units of mGal, the standard unit for gravitational measurements.

The term “data gravity” is a metaphor coined by software engineer Dave McCrory in 2010. He was trying to convey the idea that large masses of data exert a form of gravitational pull within IT systems. According to the laws of physics, objects with sufficient mass pull objects with less mass toward them.

Gravity Survey – Measurements of the gravitational field at a series of different locations over an area of interest. The objective in exploration work is to associate variations with differences in the distribution of densities and hence rock types.

1. n. [Geophysics] In gravity surveying, a correction of 0.3086 mGal/m [0.09406 mGal/ft] added to a measurement to compensate for the change in the gravitational field with height above sea level, assuming there is only air between the measurement station and sea level.

The free-air correction adjusts measurements of gravity to what would have been measured at mean sea level, that is, on the geoid. The gravitational attraction of earth below the measurement point and above mean sea level is ignored and it is imagined that the observed gravity is measured in air, hence the name.

isostatic anomaly A gravity anomaly on a scale of more than 100 km that is associated with areas previously loaded, e.g. by ice (see GLACIO-ISOSTASY), lakes, etc., or where recent tectonic activity has loaded the crust, e.g. mountain formation, volcanic loading, etc.

A location with a positive anomaly exhibits more gravity than predicted by the model—suggesting the presence of a sub-surface positive mass anomaly, while a negative anomaly exhibits a lower value than predicted—suggestive of a sub-surface mass deficit.

These negative gravity anomalies are interpreted to mean that the segments of the lithosphere (that is, the crust and upper mantle comprising the rigid, outermost shell of the Earth) that underlie trenches are being forced down against buoyant isostatic forces.

In geodesy and geophysics, the Bouguer anomaly (named after Pierre Bouguer) is a gravity anomaly, corrected for the height at which it is measured and the attraction of terrain. The height correction alone gives a free-air gravity anomaly.

A positive magnetic anomaly is a reading that exceeds the average magnetic field strength and is usually related to more strongly magnetic rocks, such as mafic rocks or magnetite‐bearing rocks, underneath the magnetometer. A negative magnetic anomaly is a reading that is lower than the average magnetic field.

Positive anomalies are defined as intensities that are larger than our simple model the soil effects and basin effects are indistinguishable. A negative anom- intensity increase, this increase will be processed as if it had been created by surface geology.

1 : something different, abnormal, peculiar, or not easily classified : something anomalous They regarded the test results as an anomaly. 2 : deviation from the common rule : irregularity. 3 : the angular distance of a planet from its perihelion as seen from the sun.

The definition of an anomaly is a person or thing that has an abnormality or strays from common rules or methods. A person born with two heads is an example of an anomaly. He is an anomaly among his friends.