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Final Study Guide
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 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. |
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 |
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 |
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 âhot spotsâ 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 |
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 |
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 |
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-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 |
Ï=F/A |
Normal Stress |
-Force is perpendicular to the area |
Shear Stress |
-Force is parallel to the area |
Principal Stresses |
Ï1> Ï2> Ï3 |
Type of Faulting when Ï1 is vertical |
-Normal -See pic |
Type of Faulting when Ï2 is vertical |
-Strike Slip Fault -See pic |
Type of Faulting when Ï3 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 |
Period |
length of wave in time |
Frequency |
-cycles per second |
Velocity |
fλ |
Elastic Deformation |
1) deformation (strain) disappears when stress is removed 2) deformation (strain) is proportional to the applied stress |