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Study Guide #1 - Flashcards

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Class:GEOL 240Lxg - Earthquakes
Subject:Geological Sciences
University:University of Southern California
Term:Unknown
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Relative Time -Older vs. Younger -Relative time scale -based on fossil records
Absolute Time -Radioactive age dating -Unstable isotopes break down -some elements can't be used because of half-life -Ex: carbon can't be used to date things millions of years old
Half Life -there won't be enough mineral left to measure after about 4 half lives -Uranium, Potassium: half-lives in billions of year
Age of Earth -4.6 billion years -dating of meteors and other space rocks
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Oldest Continental Rocks -4 billion years old -found at the centers of continents
Oldest Oceanic Rocks -200 million years old -found at plate boundaries
Oldest Fossil Bearing Rocks ~570 years old
Ages of Sun and Other Planets -4.6 billion years -(same as Earth)
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Evolution of the Solar System 1) Dust Cloud 2) Dust cloud collapses -> hydrogen fuses to form helium ->gives off energy -3) Sun lights up-> blows away excess material -terrestrial planets are too light to hold on to hydrogen and helium
Big Bang ~15 billion years ago -Know this by observing the speed that galaxies are moving away from us, we can conclude that they were all in the same place about 15 billion years ago
Fault Plane -A surface along which relative movement between adjacent rock masses takes place -where the Earth's crust is broken along a flat surface; earthquakes occur frequently in this one spot
Fault Trace A fault trace is the intersection of a geological fault with the ground surface, leaving a visible mark.
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Fault Scarp the cliff or escarpment formed by a fault that reaches the earth's surface
Hypocenter (focus) Point where the rupture starts below the surface
Epicenter point on earth's surface directly above the hypocenter
Divergent Plate Boundary -2 plate move apart -Mid-Ocean Ridges
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Convergent Plate Boundary -2 plates move together -Trench/ Island arc structures
Transform Plate Boundary -plates move alongside one another -fracture zones linking sections of mid-ocean ridges
Plate Tectonics Continental Drift+ Sea floor spreading
Lithosphere The solid part of the earth consisting of the crust and outer mantle
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Asthenosphere -located below the lithosphere -part of mantle that lies below the lithosphere
Mantle Convection Mantle convection is the slow creeping motion of Earth's rocky mantle in response to perpetual gravitationally unstable variations in its density.
Hot Spots -Streams of molten rock arise deep inside the Earth and move upward through the crust to erupt on the surface or seafloor. As seafloor spreading moves the crust over these “hot spots” eruptions can create chains of seamounts and islands, such as the Hawaiian Islands
Continental Collision Continental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries when both boundaries are land
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Nature of Seismicity at Each Plate Boundary ????
Deep Focus Earthquakes A deep-focus earthquake is an earthquake that occurs at depths between 300 and 700 km beneath the Earth's surface. -generally occurs at subduction zones and oceanic-continental convergent boundaries
Wegener's Evidence for Continental Drift -Fit of continents -300 million year old southern ice sheet -250 million year old deserts -migration of species from paleontological record
Other Evidence for Continental Drift -Computer fit of continents (includes continental shelf) -Earth's magnetic field -Remnant magnetization -Paleomagnetic polar wander curves -Linear magnetic anomalies parallel to the mid-ocean ridges
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Earth's Magnetic Field -Dipole field -Magnetic field=direction compass needle points at every point in space
Ferromagnetic Materials -can be magnetized -most important material: Magnetite or "loadstone" -In high temperatures, every atom in a ferromagnetic material acts as a magnet, there is not remnant magnetization because each atom cancels each other out -as the material cools, the atoms cluster into magnetic domains when they drop below the Curie temperature (~640 C), From here, it can be magnetized -if you cool a material through its Curie temperature n the presence of a magnetic field, it will assume the same magnetizati
Paleomagnetic Polar Wander Curves formed by figuring out angle to North Pole from rocks collected at various points on the current continental configuration -makes it appear that the North Pole was wandering... actually the continents were -SEE explanation in notes
Linear magnetic anomalies parallel to the mid-ocean ridges -caused by reversals in magnetic direction of Earth's dipole field -at times in the past, Earth's magnetic field would switch polarity for no known reason
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Measurement of Linear magnetic anomalies parallel to the mid-ocean ridges -Everytime a boat would go over a Mid-Ocean ridge with a magnetometer, when it would go over a field that matched the current field, they would add up to a strong magnetic field (darker lines) and when it didn't match, it would subtract from the strength (lighter lines) -This pattern also gives us the rate at which the plates were moving outward -Opening rate =10 cm/yr
Strike -angle between surface trace and North -See picture
Dip -Angle between fault plane and surface -See picture
Strike Slip -motion is horizontal -Left lateral and right lateral
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Dip-Slip motion is in the direction of the dip
Normal Dip-Slip Fault -"Foot wall" -Crustal elongation/ tensioning () -Divergent Boundaries
Reverse (Thrust) Dip-Slip Fault -"hanging wall" -Crustal Shortening (->-
Stress σ=F/A
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Normal Stress -Force is perpendicular to the area
Shear Stress -Force is parallel to the area
Principal Stresses σ1> σ2> σ3
Type of Faulting when σ1 is vertical -Normal -See pic
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Type of Faulting when σ2 is vertical -Strike Slip Fault -See pic
Type of Faulting when σ3 is vertical -Reverse Thrust Fault -See pic
Geodesy and types -The measurement of motion on the Earth's surface -Triangulation-measurement of angles between geodetic markers; measure angles between markers placed along fault, then measure change in angles over time -Trilateration-measurement of distances between geodetic markers -Levelling-measurement of elevation difference between geodetic markers
H.F. Reid -discovered the Elastic Rebound Theory for Earthquakes by making geodetic measurements before and after the 1906 San Francisco Earthquake
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Fault Plane Solution -Beach Ball Solution -SEE NOTES -Be able to tell: -which station is closest/farthest from the earthquake -what is the direction from the earthquake to a station? -What is the strike of the faults? -What is the orientation of the principal stresses?
P waves -motion is parallel to the ray path -propagate in liquids, solids and gases -compression waves
S Waves -motion is perpendicular to the ray path -propagate in solids only
First P motion on a vertical seismometer -Up=away from source -Down=toward source
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San Andreas Fault -Right lateral strike-slip fault -Transform fault linking spreading center beneath the Salton Sea with a spreading center off the Oregon Coast -plate boundary between the Pacific and North American plates -Slip rate=35 mm/year -Age 30 million years (CA coast used to be a subduction zone)
Big Bend -North of LA and compression in the LA basin -Blind-thrust faults
Volcanoes -mostly occur at plate boundaries-exceptions are hot spots
Volcanoes at Convergent Boundaries -andesite magma-contains a lot of silica SiO2 which explains: -gray color -explosive eruptions -steep-sided composite volcanoes
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Volcanoes at Divergent Boundaries (and at hot-spots) -Basalt magma-contains less silica SiO2 which explains: -black color -quiet eruptions -shallow-sloped shield volcanoes
Tsunami -seismic sea wave usually generated by dip-slip faulting on the ocean floor -very long wavelength (~200 km) -very long period (~15 mins) -Velocity=frequency x wavelength, so tsunamis travel about 800 km/hour, the speed of a jet plane
Amplitude increases as wave approaches shore because.. the front of wave slows first when it hits shallow water near shore, then the back of the wave catches up, shortening the wavelength but increasing the amplitude -why ordinary sea waves break when they reach shore
Amplitude -distance above equilibrium
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Wavelength -distance between 2 wave crests
Period length of wave in time
Frequency -cycles per second
Velocity fλ
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Elastic Deformation 1) deformation (strain) disappears when stress is removed 2) deformation (strain) is proportional to the applied stress
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 Relative Time-Older vs. Younger
-Relative time scale
-based on fossil records
 Absolute Time-Radioactive age dating
-Unstable isotopes break down
-some elements can't be used because of half-life
-Ex: carbon can't be used to date things millions of
years old
 Half Life-there won't be enough mineral left to measure after about 4 half lives
-Uranium, Potassium: half-lives in billions of year
 Age of Earth-4.6 billion years
-dating of meteors and other space rocks
 Oldest Continental Rocks-4 billion years old
-found at the centers of continents
 Oldest Oceanic Rocks-200 million years old
-found at plate boundaries
 Oldest Fossil Bearing Rocks~570 years old
 Ages of Sun and Other Planets-4.6 billion years
-(same as Earth)
 Evolution of the Solar System1) Dust Cloud
2) Dust cloud collapses -> hydrogen fuses to form helium
->gives off energy
-3) Sun lights up-> blows away excess material
-terrestrial planets are too light to hold on to
hydrogen and helium
 Big Bang~15 billion years ago
-Know this by observing the speed that galaxies are moving away from us, we can conclude that they were all in the same place about 15 billion years ago
 Fault Plane-A surface along which relative movement between adjacent rock masses takes place
-where the Earth's crust is broken along a flat surface; earthquakes occur frequently in this one spot
 Fault TraceA fault trace is the intersection of a geological fault with the ground surface, leaving a visible mark.
 Fault Scarpthe cliff or escarpment formed by a fault that reaches the earth's surface
 Hypocenter (focus)Point where the rupture starts below the surface
 Epicenterpoint on earth's surface directly above the hypocenter
 Divergent Plate Boundary-2 plate move apart
-Mid-Ocean Ridges
 Convergent Plate Boundary-2 plates move together
-Trench/ Island arc structures
 Transform Plate Boundary-plates move alongside one another
-fracture zones linking sections of mid-ocean ridges
 Plate TectonicsContinental Drift+ Sea floor spreading
 LithosphereThe solid part of the earth consisting of the crust and outer mantle
 Asthenosphere-located below the lithosphere
-part of mantle that lies below the lithosphere
 Mantle ConvectionMantle convection is the slow creeping motion of Earth's rocky mantle in response to perpetual gravitationally unstable variations in its density.
 Hot Spots-Streams of molten rock arise deep inside the Earth and move upward through the crust to erupt on the surface or seafloor. As seafloor spreading moves the crust over these “hot spots” eruptions can create chains of seamounts and islands, such as the Hawaiian Islands
 Continental CollisionContinental collision is a phenomenon of the plate tectonics of Earth that occurs at convergent boundaries when both boundaries are land
 Nature of Seismicity at Each Plate Boundary????
 Deep Focus EarthquakesA deep-focus earthquake is an earthquake that occurs at depths between 300 and 700 km beneath the Earth's surface.
-generally occurs at subduction zones and oceanic-continental convergent boundaries
 Wegener's Evidence for Continental Drift-Fit of continents
-300 million year old southern ice sheet
-250 million year old deserts
-migration of species from paleontological record
 Other Evidence for Continental Drift-Computer fit of continents (includes continental shelf)
-Earth's magnetic field
-Remnant magnetization
-Paleomagnetic polar wander curves
-Linear magnetic anomalies parallel to the mid-ocean ridges
 Earth's Magnetic Field-Dipole field
-Magnetic field=direction compass needle points at
every point in space
 Ferromagnetic Materials-can be magnetized
-most important material: Magnetite or "loadstone"
-In high temperatures, every atom in a ferromagnetic material acts as a magnet, there is not remnant magnetization because each atom cancels each other out
-as the material cools, the atoms cluster into magnetic domains when they drop below the Curie temperature (~640 C), From here, it can be magnetized
-if you cool a material through its Curie temperature n the presence of a magnetic field, it will assume the same magnetizati
 Paleomagnetic Polar Wander Curvesformed by figuring out angle to North Pole from rocks collected at various points on the current continental configuration
-makes it appear that the North Pole was wandering... actually the continents were

-SEE explanation in notes
 Linear magnetic anomalies parallel to the mid-ocean ridges-caused by reversals in magnetic direction of Earth's dipole field
-at times in the past, Earth's magnetic field would switch polarity for no known reason
 Measurement of Linear magnetic anomalies parallel to the mid-ocean ridges-Everytime a boat would go over a Mid-Ocean ridge with a magnetometer, when it would go over a field that matched the current field, they would add up to a strong magnetic field (darker lines) and when it didn't match, it would subtract from the strength (lighter lines)
-This pattern also gives us the rate at which the plates were moving outward
-Opening rate =10 cm/yr
 Strike-angle between surface trace and North
-See picture
 Dip-Angle between fault plane and surface
-See picture
 Strike Slip-motion is horizontal
-Left lateral and right lateral
 Dip-Slipmotion is in the direction of the dip
 Normal Dip-Slip Fault-"Foot wall"
-Crustal elongation/ tensioning ()
-Divergent Boundaries
 Reverse (Thrust) Dip-Slip Fault-"hanging wall"
-Crustal Shortening (->-
 Stressσ=F/A
 Normal Stress-Force is perpendicular to the area
 Shear Stress-Force is parallel to the area
 Principal Stressesσ1> σ2> σ3
 Type of Faulting when σ1 is vertical-Normal
-See pic
 Type of Faulting when σ2 is vertical-Strike Slip Fault
-See pic
 Type of Faulting when σ3 is vertical-Reverse Thrust Fault
-See pic
 Geodesy and types-The measurement of motion on the Earth's surface
-Triangulation-measurement of angles between
geodetic markers; measure angles between
markers placed along fault, then measure change in
angles over time
-Trilateration-measurement of distances between
geodetic markers
-Levelling-measurement of elevation difference
between geodetic markers
 H.F. Reid-discovered the Elastic Rebound Theory for Earthquakes by making geodetic measurements before and after the 1906 San Francisco Earthquake
 Fault Plane Solution-Beach Ball Solution
-SEE NOTES
-Be able to tell:
-which station is closest/farthest from the earthquake
-what is the direction from the earthquake to a
station?
-What is the strike of the faults?
-What is the orientation of the principal stresses?
 P waves-motion is parallel to the ray path
-propagate in liquids, solids and gases
-compression waves
 S Waves-motion is perpendicular to the ray path
-propagate in solids only
 First P motion on a vertical seismometer-Up=away from source
-Down=toward source
 San Andreas Fault-Right lateral strike-slip fault
-Transform fault linking spreading center beneath the Salton Sea with a spreading center off the Oregon Coast
-plate boundary between the Pacific and North American plates
-Slip rate=35 mm/year
-Age 30 million years (CA coast used to be a subduction zone)
 Big Bend-North of LA and compression in the LA basin
-Blind-thrust faults
 Volcanoes-mostly occur at plate boundaries-exceptions are hot spots
 Volcanoes at Convergent Boundaries-andesite magma-contains a lot of silica SiO2 which explains:
-gray color
-explosive eruptions
-steep-sided composite volcanoes
 Volcanoes at Divergent Boundaries (and at hot-spots)-Basalt magma-contains less silica SiO2 which explains:
-black color
-quiet eruptions
-shallow-sloped shield volcanoes
 Tsunami-seismic sea wave usually generated by dip-slip faulting on the ocean floor
-very long wavelength (~200 km)
-very long period (~15 mins)
-Velocity=frequency x wavelength, so tsunamis travel about 800 km/hour, the speed of a jet plane
 Amplitude increases as wave approaches shore because..the front of wave slows first when it hits shallow water near shore, then the back of the wave catches up, shortening the wavelength but increasing the amplitude
-why ordinary sea waves break when they reach shore
 Amplitude-distance above equilibrium
 Wavelength-distance between 2 wave crests
 Periodlength of wave in time
 Frequency-cycles per second
 Velocityfλ
 Elastic Deformation1) deformation (strain) disappears when stress is removed
2) deformation (strain) is proportional to the applied stress
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