gravel
142
depositing medium and the "energy" of the basin of deposition. In general,
coarse sediments are found in high-energy environments and finer sediments in low-energy environments. The availability of grains of various
sizes largely determines the validity of the measure.
gravel -7grain size.
gravity the resultant force on any body of matter due to both the attraction by
the earth and the centrifugal force resulting from the earth's rotation about
its axis. Gravity is defined by the acceleration of a freely falling body. It is
measured by gravimeters (measuring the stretching of a spring). At sea such
measurements were impossible for a long time, because of the motions of
the ship by waves. The first reliable gravity measurements at sea were made
by F.A. Vening Meinesz (1887-1966) with a compensated pendulum apparatus from a submerged submarine. He discovered the belt of negative gravity
anomalies accompanying island arcs. Presently gravimeters can be operated on
surface ships by using servo-mechanisms that keep the instrument well-oriented and by strongly damping the oscillations of the instrument. -7Vening
Meinesz' Submarine Pendulum Surveys and -7geoid.
gravity anomaly any discrepancy between the measured terrestrial gravity and
the theoretical gravity at some reference surface, usually the so-called reference ellipsoid. The theoretical gravity and position of the reference ellipsoid
is calculated as if all masses in the earth's interior were perfectly regularly
distributed, according to a fluid in rotation. Excess observed gravity is called
positive and denotes an surplus of mass, whereas a negative anomaly
denotes a mass deficiency. Free-air anomaly is the anomaly resulting if the
measured gravity is corrected for the elevation of the earth's surface with
respect to some level datum (not necessarily the reference ellipsoid). The
Bouguer anomaly is the anomaly resulting after corrections for elevation and
the attraction of the rock mass between station and level datum.
gravity corer -7corer.
gravity wave in a stratified but nonrotating fluid the only restoring force in case
of a deviation from dynamic equilibrium is the buoyancy force. It causes oscillations within the water around an equilibrium state that are called internal
gravity waves. At the surface the gravity is the restoring force for wavelengths
larger than some cm. For smaller wavelengths gravity waves are replaced by
capillary waves.
gray (Gy) unit of absorbed radiation dose, used to specify the radiation
absorbed by the human body or parts of it, equal to 1 J kg-I. Replaces the old
rad (1 Gy = 100 rad).
142
depositing medium and the "energy" of the basin of deposition. In general,
coarse sediments are found in high-energy environments and finer sediments in low-energy environments. The availability of grains of various
sizes largely determines the validity of the measure.
gravel -7grain size.
gravity the resultant force on any body of matter due to both the attraction by
the earth and the centrifugal force resulting from the earth's rotation about
its axis. Gravity is defined by the acceleration of a freely falling body. It is
measured by gravimeters (measuring the stretching of a spring). At sea such
measurements were impossible for a long time, because of the motions of
the ship by waves. The first reliable gravity measurements at sea were made
by F.A. Vening Meinesz (1887-1966) with a compensated pendulum apparatus from a submerged submarine. He discovered the belt of negative gravity
anomalies accompanying island arcs. Presently gravimeters can be operated on
surface ships by using servo-mechanisms that keep the instrument well-oriented and by strongly damping the oscillations of the instrument. -7Vening
Meinesz' Submarine Pendulum Surveys and -7geoid.
gravity anomaly any discrepancy between the measured terrestrial gravity and
the theoretical gravity at some reference surface, usually the so-called reference ellipsoid. The theoretical gravity and position of the reference ellipsoid
is calculated as if all masses in the earth's interior were perfectly regularly
distributed, according to a fluid in rotation. Excess observed gravity is called
positive and denotes an surplus of mass, whereas a negative anomaly
denotes a mass deficiency. Free-air anomaly is the anomaly resulting if the
measured gravity is corrected for the elevation of the earth's surface with
respect to some level datum (not necessarily the reference ellipsoid). The
Bouguer anomaly is the anomaly resulting after corrections for elevation and
the attraction of the rock mass between station and level datum.
gravity corer -7corer.
gravity wave in a stratified but nonrotating fluid the only restoring force in case
of a deviation from dynamic equilibrium is the buoyancy force. It causes oscillations within the water around an equilibrium state that are called internal
gravity waves. At the surface the gravity is the restoring force for wavelengths
larger than some cm. For smaller wavelengths gravity waves are replaced by
capillary waves.
gray (Gy) unit of absorbed radiation dose, used to specify the radiation
absorbed by the human body or parts of it, equal to 1 J kg-I. Replaces the old
rad (1 Gy = 100 rad).