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121 Cards in this Set
- Front
- Back
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What subjects relate to earth science? What do geologists try to understand?
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Physics, chem, bio
Understanding seismic risk, climate change, finding natural resources |
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What needs to be considered with traditional and new energy resources?
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Extraction and transport costs, global impacts, local environment
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Look at questions on first lecture before midterm
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YES
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What do all stony planets show? What is evidence of this?
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Meteorite impact scars
Iridium, Platinum, and shocked quartz |
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What is different about Earth with meteorite scars? What specifically happens?
How many times has the ocean floor been replaced? |
Most scars have vanished, constantly resurfaced by geologic processes (faults and volcanoes build mountains, erosion tears them down)
30 times (150 million yrs/surface) |
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Which way is Earth's surface moving? Difference between earthquakes and geodesy?
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Horizontally
Sudden jumps Steady creep |
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What does most change in the earth result from?
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Catastrophes-earthquakes, eruptions, floods, mudslides, dust storms)
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Rock cycle
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Old rocks melted, magma rises-cools to form igneous rock
Weathered and eroded to sediment Transported to basins and becomes sedimentary rock Carried into plate boundaries, metamorphosed under heat and pressure at great depth Melted to magma again |
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Craters: impact velocity is at least...
What happens when craters impact earth, and how big is it? |
11 km/s
Energy of motion converts to heat (4000 deg C) Crater diameter 20x impactor diameter |
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Craters-what has no impact craters?
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Gas giants
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What do low frequency microphone networks run by LANL know about the size/frequency of meteorites?
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2m diameter about once a month
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What example of meteorite hits 1 time per 100 million years? Every million? Every thousand?
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KT
Zhamanshin Meteor crater |
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What's the difference between a meteor and a meteorite?
What is an example in Arizona? |
Meteorite=once it's landed
Meteor=in the air burning Meteor crater, Arizona |
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What is there a spike in during the K/T boundary?
How is it supplied to oceans? |
Iridium
Micro-meteorites from space |
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What is found with the iridium (2)? How?
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Platinum condensed from the vaporized meteorite
Quartz grains created by high pressure shocks |
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Resurfacing occurs by a combination of...
(hides astroid scars) |
Faults and folds
Volcanoes Glaciation Landslides Erosion Dust Sedimentation |
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What does it do?
Faults and folds Volcanoes Glaciation Landslides Erosion Dust Sedimentation |
Lift new mountain ranges
Build new cones and plateaus Grinds away the surface rocks Eat at the sides of mountains and plateaus Slowly erases all surfaces Buries old surfaces |
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How far can earthquakes move?
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10 m/s
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Geodesy
What does it do? |
Accurate measurement of benchmark positions
Repeated to show how things move relative to each other |
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Arrows: what does length and direction show?
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Length=speed
Direction=movement direction |
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Catastrophes cause how much change in how much time
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More than 99% of geologic change in less than 1% of the time
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How do people vs geologists understand catastrophes?
What is the most powerful slow cycle? |
People=arbitrary and unexpected
Geologists=patterns and large-scale slow cycles Plate techtonics |
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What is convection and what does in relate to geologically?
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Spontaneous overturn of a fluid layer caused by cooling at the top
Plate techtonics which moves all continents and replaces ocean floors |
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Is the earth alive or dead?
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Not dead, but a dynamic work in progress
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Isostasy
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Condition of equal mass in all vertical columns
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Arrange earth densities from densest to lightest
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Core, mantle, crust, ocean, atmosphere
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What is the lithosphere?
Asthenosphere? |
Top 1-60 km of the Earth that are cold and stiff enough to resist horizontal flow
Viscous layers that flow horizontally |
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Isostasy needs about 5000 years to be re-established when...
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There is a disturbance like an ice age, due to the viscosity of the asthenosphere
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What is the convective style of our planet? What happens?
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Plate tectonics, continents split and drift apart, leaving new oceans in between
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Witnessing the opening of a new ocean happens by... (4)
Where is this happening? (2) |
High heat flow, volcanoes, thin crust, earthquakes
Gulf of California, Red Sea/Gulf of Aquaba |
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Why is drift possible?
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Because there is a fluid rather than a solid foundation for the plates
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Fluids flow until...
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Surface is level and high density fluid is beneath lower density fluid
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Fluid definition
Physical properties |
Property of matter which deforms viscously over time
Density (m/V) and viscosity |
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Difference between crust and mantle
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Chemically distinct layers of the Earth, different rock types
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Change in pressure is...
Gravity is... What doesn't vary horizontally at equilibrium? |
rho(g)(h)
Approximately constant on the Earth's surface Density (denser on bottom vertically) |
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Diapir
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Salt dome that forms when salt flows underground, rises through the crust, and forms oil and gas traps
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"lithosphere"=?
When will rocks flow like viscous fluids? What depth does it typically happen? Easy to... |
"stony sphere"
At more than 60% of their melting temperatures in K 60km depth Bend |
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Disruption of isostasy corrected example with Hawaii
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Flexure of lithosphere caused by added volcanic load causes a deeper moat around the islands
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Why do continents float higher than the ocean floor?
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Their crust is 30-75 km thick vs 5-10km
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Airy isostasy
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Diff densities/thicknesses of oceanic and continental crust predict an ocean water depth of several km
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What towers 6km above the adjacent ocean floor?
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Continents and continental shelves
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What happened during the ice age?
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Lithosphere slowly bent down as the asthenosphere flowed out of the way due to the weight of the ice caps...sinking continued until a new isostatic balance was created
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What is the lithosphere divided into?
What 3 types of plates are there and how many? |
Rigid plates in constant relative motion
12 major plates, 40 smaller microplates, ambiguous "orogens" |
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What are orogens?
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Mountain forming regions, not plate-like but undergo distributed deformation
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Range of plate movement
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0 to hundreds of mm per year with respect to adjacent plates
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3 boundaries between plates
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Divergent (spreading, ridge)
Area preserving (transform) Convergent (subduction zone) |
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Divergent :
Motion, Effect, Topography, Volcanic activity |
Spreading
Constructive (oceanic lithosphere created) Ridge/rift Yes |
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Convergent
Motion, effect, topography, volcanic activity |
Subduction
Destructive (oceanic lithosphere destroyed), trench, yes |
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Transform:
Motion, effect, topography, volcanic activity |
Lateral sliding
Conservative (oceanic lithosphere neither created or destroyed) No major effect No |
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Difference between continental and oceanic lithosphere
What does it further subdivide? |
Cont=thick crust, oceanic=thin crust
Spreading (rift boundary or spreading ridge) transform (boundary or fault) convergent (boundary or subduction zone) |
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What happens at spreading ridges?
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Submarine volcanism creates new crust of basalt, cooling turns asthenosphere into lithosphere
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Sea floor geologic features
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Pillow basalts, open cracks, hydrothermal vents, axial volcanoes and valleys, little sediment
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Spreading ridges have...
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Faulted central valleys, there are underwater volcanoes overlying a magma chamber
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Pillow basalts
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Seawater chills outside of pillow to make a flexible glassy skin, where continuing eruption inflates the pillow with hot lava
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What are all rocks in ocean ridges?
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Basalt, volcanic
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Basalt: color, grains, texture, minerals, elements
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Black
Tiny Bubbles Feldspar +pyroxene + olivine O+Si+Ca+Fe |
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MORBS
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Mid Ocean Ridge Basalts
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Black smokers
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Hydrothermal vents, hot, metal sulfides, ecosystem based on oxidation of S without sun
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Spreading evidence
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Deep cracks in seafloor
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Lithosphere is what farther from the ridge
What does it do because of isostasy |
Older, cooler, denser, thicker
Floats lower and the ocean is deeper so the ridge is higher |
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Thermal expansion and the coefficient
What increases? |
Expands with heat, shrinks with coolness
1E-5 / degree celsius Shrinking is a larger density |
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Increase in density does what in terms of isostatic balance
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Density increase causes it to sink, pushing out dense asthenosphere, bringing in water above until isostasy is restored
Depth of seafloor increases smoothly in proportion to square root of age |
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Composition
Mechanical definition |
Basalt above, gabbro and peridotite below
Lithosphere is hard and asthenosphere is squishy |
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Sedimentary rock types (5)
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Sandstone, siltstone, claystone, limestone, conglomerate
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Igneous plutonic (3)
Igneous volcanic (4) |
Gabbro, diorite, granite
Basalt, andesite, rhyolite, ignimbrite |
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Metamorphic-recrystalized as solid that didnt melt
(7) |
Slate, phyllite, schist, gneiss, granulite, eclogite, hornfels
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Evidence for seafloor spreading (2)
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Subsidence of volcanic islands to form atolls or guyots
Symmetrical patter of magnetic anomaly bands |
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Transform faults
Subduction |
Active plate boundaries with motion parallel to their length
Consumes old/cold/dense oceanic lithosphere, which is recycled into hot asthenosphere sinking under its own weight |
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Subduction physical evidence (4)
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Trenches, accreted sediment wedges, great earthquakes that cause tsunamis, volcanic arcs
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Volcanism creates...
Volcanism stops |
New seamount (eventually an island)
Rain and waves erode the cone above sea level, coral grows and forms reefs if warm enough |
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Coral
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Important rock forming animal
Needs warm, clean water and sunlight |
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4 Phases of Reefs
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Volcanic island, fringing reef (close to mountain), barrier reef (around a lagoon with a small basaltic mountain in the center), coral atoll (ring of coral around a lagoon with no basalt in sight
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What did Darwin propose? What could he not explain?
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Volcanic cores sinking while reefs growing at the same rate
Sinking, line of islands/seamounts |
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Magnetic anomaly bands process, symmetric
What does it reveal? |
New basalt magnetized by Earth's natural magnetic field, poles switch through time (normal or reversed polarity)
History (spreading apart) and chronology (timing and rate of spreading) |
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Where does Earth's magnetic field originate?
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Outer core of liquid that convects, extends through the Earth and into space
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What creates a parallel universal fabric across the seafloor?
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Fracture zones (inactive former transform traces)
Shows history of spreading directions |
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Conservation of Earth's surface means that...
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Subduction=spreading
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Subduction process
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Cooling of oceanic lithosphere makes it more dense than asthenosphere, falls into interior of mantle under its own weight, helps move the plates
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Surface features of a subduction zone
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Small bulge/outer rise on seafloor caused by bending
Volcanoes possibly! |
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Accretionary wedge
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Made due to subduction, landward wall of trench, site of deformation and burial, leads to metamorphism
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Where do volcanoes appear?
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200km behind the trench, more dangerous and explosive, Island arcs when overriding plate is oceanic and volcanic chains when upper plate is continental
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Classical volcano rocks (3)
Classic subduction volcano behavior |
Rhyolites, andesites, dacites (NOT basalt)
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Eruption types: Describe
Plinean Pelean Strombolian |
Straight up to cloud (greater than 55km high)
Rolling clouds of ash down the side Less explosive than linen, less than 10km high |
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Indirect ways of measuring geologic time (3)
Direct (1) |
Stratigraphy, law of superposition, cross-cutting relationships
Radiometric dating |
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Stress
Strain |
Force exchanged per unit of area (Pressure=perpendicular, shear stress=parallel)
Change in dimension/dimension (volumetric strain, shear strain) |
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Mechanisms of deformation (2/3)
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Elasticity under all conditions and EITHER:
Ductile viscous flow (at high T) or brittle fracture and frictional sliding (at low T and high shear stress) |
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Faults are...
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Surfaces of frictional sliding, extends to the base of the lithosphere and turns into viscous flow in the asthenosphere
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Faults appear in what 3 varieties
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Normal faults (60 degree dip) where crust is stretched (ridges and troughs)
Thrust faults (30) where crust is shortened (subduction zones) Strike slip faults dip vertically and slip horizontally (transforms) |
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What else is a deformation mechanism?
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Solution transfer: water soluble minerals sitting in water for long times deform
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Stress math stuff
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Force/area
Metric units= N/m^2=Pa (100 kPa is equal to the pressure of our atmosphere at sea level |
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What causes high stress? Examples
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A force exchanged across a very small surface
Teeth, claws, knives |
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What is only stress in gasses?
Solids and viscous liquids? |
Pressure (exchanged perpendicular to surface)
Also support shear stress (parallel) |
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Shear strain
What are all strains numerically? |
lateral deflection/length
Dimensionless pure numbers |
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When does frictional sliding occur? When is it eased?
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Material is brittle
Increased fluid pressure or decreased roughness |
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Cohesion
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Glue or welding between particles, holds buildings together, small or absent in faults
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How is a fault recognized?
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Offsets of different rock types
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What happens at shallow depths and the center of faults?
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Shallow: low temp, fault surfaces are scratched and abraded by sliding
Crushed rock at center, thickness indicates the amount of fault slip |
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When are we in the asthenosphere?
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Brittle grinding ends, mineral grains stretch and divide without cracking, viscous flow begins
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Know pictures of faults
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KNOW THEM
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Normal faults
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60 degree dip, most compressive direction is vertical, crust is horizontally stretched
Can become a valley |
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Thrust faults
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30 degree dip, most compressive direction is horizontal and the crust is shortened (reverse fault)
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Strike slip faults
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Most compressive and least compressive directions are both horizontal but 90 degrees apart, don't change surface area of the crust, stright and continuous valleys
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Solution transfer
Elasticity, frictional sliding, and viscous flow |
Water soluble minerals sitting in water for a long time (deformation mechanism)
Always possible, low T and high shear stress (parallel), T greater than 60% of melting |
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What does stress cause for the minerals?
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Minerals dissolve where they press together, this shortens the rock along one axis, but dissolved minerals precipitate out of unstressed surfaces, which expands the rock on a different axis (lintels example)
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What do rocks often do instead of faulting?
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Fold, rich in water soluble minerals, some saturated with water, so many sedimentary rocks are ductile and fold instead of breaking
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Ultimate cause of folds
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Thrust fault (stiff/brittle) metamorphic rocks underneath
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How do centers of tectonic plates move? What does this store?
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Steadily, but edges stick together and bend
Elastic energy |
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What is an earthquake?
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An instability that breaks fault cohesion, allowing plate edges to move quickly to catch up
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How does deep/shallow/center of plates move at all times?
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Continuously glide by viscous flow in asthenosphere (no earthquakes)
Doesn't slide day to day, strained elastically and level of shear stress rises Moves steadily at many mm/year at all times |
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What produces a fault scarp?
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The vertical offset in an earthquake
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What waves to earthquakes radiate? (3)
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Compressional/pressure (P) (push-pull motion)
Shear (S) (slinky) Surface (R-rayleigh) (confined to earth's solid surface) |
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Focus
Epicenter |
The point of initial rupture
Point on the surface vertically above the focus (epi=above in ancient greek) |
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Seismograph
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Records earthquake waves in 3 perpendicular directions, P/S/R, timing/frequency/amplitude
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What is damage to short buildings primarily caused by?
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Peak acceleration and intensity
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What are buildings not well designed to withstand? What does acceleration decline with?
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Horizontal acceleration
Declines with distance from the fault |
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What are casualties in earthquakes from?
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Not waves themselves, but from collapse of buildings not designed for horizontal accelerations
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How are waves detected?
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By the motion of the ground relative to a stationary mass hung on a pendulum or spring
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What is used to compute the distance to the earthquake focus?
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Arrival times of the P and S waves
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What do reflection methods provide?
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Depths of velocity changes layering in sedimentary rocks, core/mantle boundary)
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Refraction methods?
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Determine seismic velocity from the speed of horizontal waves
(refraction=bending of a wave at a boundary where the wave's velocity changes) |
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Tomography
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Measures velocities in 3D within the Earth by measuring travel times with different observation angles
Tracks subducting slabs |
