Earthquake Flashcards
Fractures in earth’s surface
Faults
Location where slippage begins
Hypocenter or focus
Point on Earth’s surface directly above the focus or hypocenter
Epicenter
States that large slabs of Earth’s lithosphere are continually grinding past each other
Plate tectonics
Earth’s strongest earthquakes most often occur in
Convergent plate boundaries
Plate boundary between a subducting slab of oceanic lithosphere and an overlying continental plate
Megathrust fault
Faults in which the dominant displacement is horizontal and parallel to the direction of fault trace
Strike-slip faults
Instrument that makes a record of seismic waves
Seismograph or seismometer
Records obtained from seismograph
Seismogram
Earthquakes generate four principal types of elastic waves
- 2
- 2
Body waves - travel within the earth
Surface waves - travel along its surface
Body waves are further divided into
P waves (primary waves) S waves (secondary waves)
*back and forth motion in the direction of the path of propagation, stretching or compressing the medium as the wave passes any point
P waves (compressional or longitudinal)
*move back and forth perpendicular to the direction of propagation
The medium is sheared first in one direction and then in another
S waves (shear waves)
P waves temporarily change the * of material while S waves change the * of the material that transmits them
Volume
Shape
- travel faster and it moves the ground from side to side
Displacement of the medium is entirely perpendicular to the direction of propagation and has no vertical or longitudinal components
Produce entirely horizontal motion
Love waves
Their motion is a combination of longitudinal compression and dilation that results in an elliptical motion of points on the surface
Rolls the ground: moves the ground up and down and side to side
Rayleigh waves
Arrange the waves in order of arrival and increasing amplitude (power/damage)
P - S - Love - Rayleigh
P: 70% faster than S waves
S: 10% faster than surface waves
Zone of greatest seismic activity
Circum-Pacific Belt
Circumpacific belt encompasses the coastal region of
Chile, Central America, Indonesia, Japan, Alaska
Measures the intensity of an earthquake through *
Modified Mercalli Scale
Damage
Measures the magnitude of earthquake through *
Richter scale
Energy released
Tsunamis are generated by displacement along a * fault that suddenly lifts a large slab of sea floor
Megathrust fault
Changes in shape, position, or orientation of a rock mass
Deformation
The chemical bonds of the minerals within a rock are stretched but do not break
*first response
Elastic deformation
Once the elastic limit (strength) is surpassed, it either flows * or fractures *
Ductile deformation
Brittle deformation
Rock near the surface where temperatures and confining pressures are low exhibit…
Brittle deformation
At depth, where temperatures and confining pressures are high, rocks exhibit…
Ductile deformation
Flat-lying sedimentary and volcanic rocks are often bent into a series of wavelike undulations called *
Mostly caused by * that result in the shortening and thickening if thrust
Folds
Compressional forces
Upfold (arrching of sedimentary layers)
Anticlines
Downfolds or troughs
Synclines
In anticline, * is found in Center
In syncline , * is found in center
Oldest strata
Youngest
Structures with approximately circular or slightly elongate, closed outcrop patterns
- convex upward
- concave upward
Domes and basins
Dome convex
Basin concave
Large, step-like folds in otherwise horizontal sedimentary strata
Monoclines
Upper or overlying block
Block below
Hanging wall
Footwall
Dipslip faults where the hanging wall block moves down relative to the footwall block
Normal faults
A block that has dropped relatively downward between two normal faults dipping toward each other
Graben
Block that has been relatively uplifted between two normal faults that dip away from each other
Horst
Dipslip faults in which the hanging wall block moves up relative to the footwall block
Reverse fault
Normal faults occur in * environments, reverse faults result from strong *
Tensional ~ lengthening Of Earth’s crust
Strong compressional forces - shortening or contraction of Earth’s crust
Reverse faults that dip less than 45 degrees
Thrust faults
Thrust faults with very low angle of dip and very large displacement
Overthrust
Fault in which the dominant displacement is horizontal and parallel to the strike of the fault surface
*horizontal compression
Strike-slip fault
Example of strike slip faut
San Andreas Fault
Fractures along which no appreciable displacement has occurred
Joints
Mountain building
*plate boundary
Orogenesis
Convergent
Main driving force of orogenesis
Subduction of oceanic lithosphere
Oceanic lithosphere subducts beneath an oceanic plate
Volcanic island arc
Subduction beneath a continental block
Continental volcanic arc
Chaotic accumulation of sedimentary and metamorphic rocks with occasional scraps of ocean crust
Accretionary wedge
Relatively small crustal fragment which may be accreted to continents when subduction brings them to trench
Terranez
Himalayas and Appalachians were formed by
The collision of landmasses formerly separated by now-subducted ocean basins
