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136 Cards in this Set
- Front
- Back
angle of dip
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-is measured with in a vertical plane that is perpendicular to both the bedding and the horizontal planes.
-is measured downward from the horizontal plane to the bedding plane |
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anticline
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an upward arching fold in land
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axial plane
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-an imaginary plane containing all of the hinge lines of a fold
-it divides the fold into its two limbs |
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brittle
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a type of behavior that rocks exhibit at stresses higher than their elastic limit (like a rubber band will break if stretched too far)
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compressive stress
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-common along convergent plate boundaries and typically results in rocks being deformed by a shortening strain
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dip-slip fault
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creates movement parallel to the dip of the fault surface
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direction of dip
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the compass direction in which the angle of dip is measured
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ductile
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when a rock acts in a plastic manner and bends while under stress and does not return to its original shape after relaxation of the stress (like silly putty)
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elastic
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when a deformed body recovers its original shape after the stress is reduced or removed
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elastic limit
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the limit a rock can with stand stress before it deforms permanently
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fault
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a fracture in bedrock along which movement has taken place
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fold
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a bend or wavelike feature in layered rock
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footwall
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the underlying surface of an inclined fault plane
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hanging wall
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the overlying surface of an inclined fault
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geologic cross section
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represents a vertical slice through a portion of Earth
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geologic map
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-uses standardized symbols and patterns to represent rock types and geologic structures
-produced from the field map for a given area |
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hinge line
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the axis of a fold
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isoclinal fold
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a fold in which limbs are parallel to one another (implies intense compressive or shear stress
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joint
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a fracture or crack in bedrock that exists when no displacement occurs
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joint set
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where joints are oriented approximately parallel to one another
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left-lateral fault
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a stream or other displaced feature would appear to the left across the fault
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limb
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the type of hill that connects each anticline and adjacent syncline
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normal fault
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when the hanging wall block has moved downward relative to the footwall block
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oblique-slip fault
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has both strike-slip and dip-slip components
(parallel and horizontal motion) |
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open folds
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-have limbs that dip gently
-the more open the fold, the less intense the stress involved |
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overturned fold
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-when the limbs of a fold dip in the same direction
-imply that unequal compressive stresses or even a shearing stress caused the upper limb of the fold to override the lower limb |
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plunging fold
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folds in which the hinge lines are not horizontal
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recumbent fold
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-overturned to such an extent that the limbs are essentially horizontal
-found in the cores of mountain ranges such as the Canadian Rockies |
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reservoir rock
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a rock that contains oil
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reverse fault
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the hanging-wall block has moved upward relative to the footwall block
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right-lateral fault
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when a displaced stream is to the right of a fault
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shear stress
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due to forces parallel to one another, but in opposite directions along a discrete surface such as a fault
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tensional stress
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is caused by forces pulling away from one another in opposite directions
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strain
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the change in size, shape, or both, while an object is undergoing stress
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stress
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a force per unit area
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source rock
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-always a sedimentary rock
-must be present for oil to form |
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strike
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the compass direction of a line formed by the intersection of an inclined plane with a horizontal plane
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strike-slip fault
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a fault where the movement is predominantly horizontal and parallel to the strike of the fault
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structural basin
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when the beds dip toward a central point
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structural dome
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a structure in which the beds dip away from a central point
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syncline
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-troughlike fold
-the bottommost part of the trough of a fold |
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structural geology
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the branch of geology concerned with the shapes, arrangement, and interrelationships of bedrock units and the forces that cause them
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thrust fault
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a reverse fault in which the dip of the fault plane is at a low angle to horizontal
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afershock
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small earthquakes that follow the main shock of an earthquake
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Benioff zones
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zone of inlcined seismic activity
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body waves
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seismic waves that travel through the earth's interior, spreading outward from the focus in all directions
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circum-Pacific belt
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its a belt which encircles the rim of the Pacific Ocean
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depth of focus
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distance between focus and epicenter
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earthquake
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a trembling or shaking of the ground caused by the sudden release of energy stored in rocks benearth earth's surface
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elastic rebound theory
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the classis explanation of why earthquakes take place
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epicenter
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the point on the earth's surface directly above the focus
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focus
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the point within the earth where seismic waves first originate
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intensity
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a measure of an earthquake's effect on people and buildings
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island arc
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when benioff zones slope under a continent or a curved line of islands
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love waves
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most like S waves that have no vertical displacement
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magnitutde
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a measure of the energy released during an earthquake
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mediterranean-Himalayan belt
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the bet which runs through the Mediterranean Sea, crosses the Mideast and the Himalayas, and passes through the East Indies to meet the circum-Pacific belt north of Australia
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modified Mercalli scale
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the scale that determines the intensities of earthquakes
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moment magnitude
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the most objective way of measuring the energy released by a large earthquake
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P wave
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a compressional (or longitudinal) wave in which rock vibrates back and forth parallel to the direction of wave propagation
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Rayleigh waves
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behave like rolling ocean waves but they cause the groud to move in an elliptical path opposite to the direction the wave passes
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Richter scale
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a numerical scale of earthquake magnitudes
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seismic sea wave
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tsunamis - they usually are caused by great earthquakes that disturb the sea floor bu tthey also result from submarine landslides or volcanic explosions
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seismic waves
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the waves of energy produced by an earthquake
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seismogram
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can be used to measure the strength of an earthquake
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seismograph
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a recording device that produces a permanent record of Earth motion detected by a seisometer
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surface wave
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a seismic wave that travels on Earth's surface away from the epicenter, like water waves spreading out from a pebble thrown into a pond
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S wave
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-a type of a body wave
-a slower, transverse wave that travels through near surface rocks at 2 to 5 kilometers per second -it is propagated by a shearing motion much like that in a stretched shaken rope |
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travel-time curve
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plots seismic-wave arrival time against distance
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tsunami
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-a seismic wave
-caused by great earthquakes that disturb the sea floor but also result from submarine landslides or volcanic explosions |
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asthenosphere
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-the zone extending to a depth of perhaps 200 kilometers
-the place where rocks are closest to the melting point |
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convection
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a circulation pattern in which low density material rises and high density material sinks
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core
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-the central zone of Earth
-it is metallic and is the source of Earth's magnetic field |
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crust
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the outer layer of rock which forms a skin on Earth's surface
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crustal rebound
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the rise of the crust after the removal of the ice
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Curie point
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-580 Degrees celcius
-when rocks are cooled below or at this point, they retain their magnetic record |
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geophysics
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the application of physical laws and principles to a study of earth
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geothermal gradient
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the temperture increase with depth into Earth
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gravity meter
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a tool for studying the crust and upper mantle
-measures the gravitational attraction between Earth and a mass with in the instrument |
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heat flow
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the gradual loss of heat through the Earth's surface
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isostasy
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a balance or equilibrium of adjacent blocks or brittle crust "floating" on the upper mantle
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isostatic adjustment
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the concept of vertical movement to reach equilibrium
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lithosphere
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the crust and uppermost mantle
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magnetic field
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a region of magnetic force that surrounds the Earth
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magnetic poles
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-the north and south poles of the magnetic field
-the strength of the magnetic field is greates at the magnetic poles |
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magnetic reversal
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a change in the polarity of the magnetic field when north and south switch in polarity
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magnetometer
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an instrument used to measure the strength of Earth's magnetic field
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mantle
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a thick shell of rock that separates the crust above from the core below
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MOHOrovicic discontinuity
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the boundary that separates the crust from the mantle beneathe it
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negative gravity anomaly
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a gravity reading lower than the normal regional gravity
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negative magnetic anomaly
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a reading of magnetic field strength that is lower than the regional average
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paleomagnetism
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the study of ancient magnetic fields
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positive gravity anomaly
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a gravity reading higher than the normal regional gravity
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positive magnetic anomaly
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a reading of magnetic field strength that is higher than the regional average
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P-wave shadow zone
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the region between 103 degrees and 142 degrees which lakes P waves
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seismic reflection
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the return of some of the energy of seismic waves to Earth's surface after the waves bounce off a rock boundary
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seismic refraction
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the bending of seismic waves as they pass from one material to another (similar to how light waves bend when they pass through the lenses of eyeglasses)
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S-wave shadow zone
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-s-waves are not recorded in the entire region more than 103 degrees away from the epicenter
-indicates that S waves do not travel through the core at all |
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abyssal fans
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-found at the base of many submarine canyons
-made up of land-derived sediment that has moved down the submarine canyons |
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abyssal plains
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very flat regions usually found at the base of the continental rise
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active continental margin
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characterized by earthquakes and by a young mountain belt and volcanoes on land, consists of a continental shelf, a continental slope, and an oceanic trench
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aseismic ridges
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-volcanic chains on the sea floor
-submarine ridges that are not associated with earthquakes |
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atoll
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a circular reef that rims lagoons and is surrounded by deep water
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barrier reefs
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parallel to the shore but are separated from it by wide, deep lagoons
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continental rise
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a wedge of sediment that extends from the lower part of the continental slope to the deep sea floor
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continental slope
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a relatively steep slope that extends from a depth of 100 to 200 meters at the edge of the continental shelf down to oceanic depths
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contour current
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a bottom current that flows parallel to the slopes of the continental margin, along the contour rather than down the slope
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fracture zone
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major lines of weakness in Earth's crust that cross the mid-oceanic ridge at approximately right angles
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fringing reefs
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flat, tablelike reefs attached directly to shore
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guyots
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flat-topped seamounts found mostly in the western Pacific Ocean
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mid-oceanic ridge
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a giant undersea mountain range that extends around the world like the seams on a baseball
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oceanic trench
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a narrow, deep trough parallel to the edge of a continent or an island arc
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ophiolites
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-distinctive rock sequences found in many mountain chains on land
-the top layer consists of marine sedimentary rock and below lies a zone of pillow basalt which is underlain by a sheeted-dike complex that probably served as feeder dikes for the pillowed lava and layers |
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passive continental margin
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includes a continental shelf, continental slope, and continental rise and generally extends down to an abyssal plain at a depth of about 5 kilometers
-it usually develops on geologically quiet coasts that lack earthquakes, volcanoes, and young mountain belts |
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pelagic sediment
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-sediment that settles slowly through the ocean water
-made up of fine-grained clay and the skeletons of microscopic organisms |
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reefs
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-wave-resistant ridges of coral, algae, and other calcareous organisms that form in warm, shallow, sunlit water that is low in suspended sediment
-they stand above the surrounding sea floor |
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rift valley
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a tensional valley bounded by normal faults
-found at diverging plate boundaries on continents and along the crest of the mid-oceanic ridge |
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seamounts
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conical undersea mountains that rise 1,000 meters or more above the sea level
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submarine canyons
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V-shaped valleys that run across continental shelves and down continental slopes
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terrigenous sediment
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land-derived sediment that has found its way to the sea floor
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turbidity currents
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great masses of sediment-laden water that are pulled downhill by gravity
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asthenosphere (2)
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a zone of low seismic-wave velocity that behaves plastically because of increased temperature and pressure
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continental drift
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the idea that continents move freely over Earth's surface, changing their positions relative to one another
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convergent plate boundary
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lies between plates that are moving toward each other
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divergent plate boundary
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a boundary between plates that are moving apart
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island arc
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a curved line of volcanoes that form a string of islands parallel to the oceanic trench
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lithosphere (2)
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plates that make up a relatively rigid outer shell of Earth
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magmatic arc
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a broad term used both for island arcs at sea and for belts of igneous activity on the edges of continents
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mantle plumes
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narrow columns of hot mantle rock that rise through the mantle, much like smoke rising from a chimney
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plate
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a large, mobile slab of rock that is part of Earth's surface
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orogeny
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an episode of intense deformation of rocks in a region
-usually accompanied by metamorphism and igneous activity |
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fold and thrust belts
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characterized by large thrust faults stacked one upon another
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Precambrian shield
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a complex of Precambrian metamorphic and plutonic rocks exposed over a large area
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craton
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the region of a continent that has been structurally stable for a prolonged period of time
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mountain range
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a group of closely spaced mountains or parallel ridges
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major mountain belts
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chains thousands of kilometers long composed of numerous mountain ranges
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