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earth science ch. 6

Restless Earth: Earthquakes, Geologic structures, and mountain building

Terms

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seismology
the study of earthquake and seismic waves
horst
an elongated, uplifted block of crust bounded by faults
moment magnitude
a more precise measure of earthquake magnitude than the richter scale that is derived from the amount of displacement that occurs along a fault zone
anticline
a fold in sedimentary strata that resembles an arch
transform fault
a major strike-slip fault that cuts through the lithosphere and accommodates motion between two plates
accretionary wedge
a large wedge shaped mass of sediment that accumulates in subduction zones. Here sediment is scraped from the subducting oceanic plate and accreted to the over riding crustal block
reverse fault
a fault in which the material above the fault plane moves up in relation to the material below
active continental margin
usually narrow and consisting of highly deformed sediments. they occur where oceanic lithosphere is being subducted beneath the margin of a continent
foreshock
small earthquakes that often precede a major earthquake
earthquake
the vibration of earth produced by the rapid release of energy
lithosphere
the rigid outer layer of earth, including the crust and upper mantle
seismic sea wave (tsunami)
a rapidly moving ocean wave generated by earthquake activity that is capable of inflicting heavy damage in coastal regions
brittle failure or brittle deformation
the loss of strength by a material usually in the form of sudden fracturing
modified Mercalli intensity scale
a 12 point scale developed to evaluate earthquake intensity based on the amount of damage to various structures
ductile deformation
a type of solid-state flow that produces a change in the size and shape of a rock body without fracturing. Occurs at depths where temp. and confining pressures are high
crust
the very thin outermost layer of the earth
normal fault
a fault in which the rock above the fault plane has moved down relative to the rock below
passive continental margin
margin that consists of continental shelf, continental slope, and continental rise. they are not associated with plate boundaries and therefore experence little volcansim and few earthquakes
mantle
the 2900 kilometer (1800 mile) thick layer of earth locate below the crust
outer core
a layer beneath the mantle about 2200 kilometers (1364 miles) thick that has the properties of a liquid
primary (P) wave
a type of seismic wave that involves alternating compression and epansion of the material through which it passes.
elastic rebound
the sudden release of stored strain in rocks that results in movement along a fault
magnitude
the total amount of energy released during an earthquake
aftershock
the adjustments that follow a major earthquake often generate smaller earthquakes
epicenter
the location of earth's surface that lies directly above the forces of an earthquake
fault
fractures in earths crust
syncline
a linear downfold in sedimentary strata; the opposite of anticline
fold
a bent rock layer or series of layers that were originally horizontal and subsequently deformed
dip-slip fault
a fault in which the movement is parallel to the dip of the fault
fault-block mountains
a mountain formed by the displacement of rock along a fault
orogenesis
the processes that collectively result in the formation of mountains
core
the innermost layer of earth based on composition. it is thought to be largely an iron-nickel alloy with minor amounts of oxygen, silicon, and sulfur
richter scale
a scale of earthquake magnitude based on the motion of a seismograph
liquefaction
a phenomenon, sometimes associated with earthquakes, in which soils and other unconsolidated materials containing abundant water are turned into a fluidlike mass that is not capable of supporting buildings
secondary (S) wave
a seismic wave that involves oscillation perpendicular to the direction of propagation
fault scarp
a cliff created by movement along a fault. it represents the exposed surface of the fault prior to modification by weathering and erosion
focus
the zone within earth where rock displacement produces and earthquake
basin
a circular downfolded structure
terrane
a crustal block bounded by faults, whose geologic history is distinct from the histories of adjoining crustal blocks
thrust fault
a low angle reverse fault
strike-slip fault
a fault along which the movement is horizontal
lower mantle (mesosphere)
the part of the mantle that extends from core-mantle boundary to a depth of 660 kilometers. also known as the lower mantle
asthensophere
a subdivision of the mantle situated below that lithosphere; rock within this zone is easily deformed
intensity
a measure of degree of earthquake shaking at a given locale based on the amount of damage
dome
a roughly circular upfolded structure similar to an anticline [ large arched hill ]
surface wave
seismic waves that travel along the outer layer of the earth
seismograph
an instrument that records earthquake waves
graben
a valley formed by the downward displacement of a fault bounded block
inner core
the solid innermost layer of earth, about 1330 kilometers (800 miles) in radius
deformation
the general term for the processes of folding, faulting, shearing, compression or extension of rocks
seismogram
the record made by a seismograph

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