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87 Cards in this Set
- Front
- Back
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Define rheology
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the ability of stressed materials to deform or to flow.
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Define Consitutive equation
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Equations that related dynamic and kinematic equations
(EQ: F=ma or Sigma = Ee) |
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Define Yield Stress
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stress at the change from elastic to viscous behavior
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Define Failure Stress
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Stress at fracturing
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Define Isostasy
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When free to move vertically, lithosphere floats at an appropriate level in the asthenosphere so that the pressure at a depth of compensation in the asthenosphere well below the base of the lithosphere is the same.
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Stick-slip mechanism
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One of several mechanisms by which slip occurs on faults. Prior to slip event, rock distorts elastically. In elastic deformation, bonds, bend stretch, but do not break. Elastic deformation stores energy. Stored energy is released during catastrophic slip event
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Elastic rebound Theory
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Apply stress, which creates elastic deformation, friction prevents movement. There's a Slip along fault and the vibration (earthquakes) as rocks "snap back" to the normal spot. Aftershocks are adjustments
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Define Body Waves
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Two kinds of body waves (Compressional and Shear) that travel though earth. P waves are the fastest, and compressional, and travel through solids and liquids. S waves travel slower, are shearing, and they only travel through solids.
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Surface Waves
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Waves that travel on the surface the earth. The slowest in travel speed.
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Define P waves
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Compressional waves, Travel through solids and liquids, travel at the fastest through earth.
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Define S waves
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Shear waves that only travel through only solids. They move the second fastest.
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Define Discontinuities
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A place where seismic waves reflect and refract between a medium where there is one speed to a medium where there is another speed. (Crust, Moho, Mantle)
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Define Moho
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The discontinuity at base of crust
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Define Lithosphere
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The outermost shell of the earth, it includes the crust and cool rigid part of the mantle immediately below it. There is a high seismic velocity, 60~100 KM thick.It's the thinnest (5KM) under the mid ocean ridge, and thickest under the mountain building areas (300KM)
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Define Asthenosphere
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Second zone, below lithosphere above mesosphere. It is the warm relatively ductile layer within the mantel that starts at the low velocity zone and ends ~250 KM thick. It's absent beneath some continental regions
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Define Mesosphere
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The lower portion of the mantle. It is the high seismic velocites and velocity increases with depth. Rock is warm, but high pressure makes melting unlikely and increases strength of rock.
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Low velocity Zone
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It's beneath ocean basins (marks the litosphere/astehnsphere boundary) Abnormally low seismic velocity (may be due to partial melt)
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Wadati-Benioff Zone
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Dipping zone of seismic velocity
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Define Ophiolities
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slices of oceanic crust emplaced on land by thrusting
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Define Wilson Cycle
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Cycle of tetonic activity (ocean basin opens by rifting, grows by seafloor spreading, closes by subduction during collision, and supercontinent forms)
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Define Supercontinent cycle
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The cycle of the creation and destruction of supercontients through the wilson cycle
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DefineFracture
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general term used to refer to any planar or tabular discontinuity within a rock mass
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Define Joint
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A planar discontinuity that lacks measurable offset
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Define Fault
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Is a planar or tabular zone of discontinuity across which this is displacement is parallel to the surface or zone boundaries
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Define extension fracture
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A fracture that's movement is normal to surface and the two block move apart
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Define Stylolitic fracture
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a fracture that's movement is normal to the surface and the two blocks move together through dissolution
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Define shear fracture
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a fault where movement is parallel to the surface.
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Define Plumose structure
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A subtle roughness on the surface of some joints that macroscopically resembles the imprint of a feather
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Define columnar joints
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Joints that break rock into generally hexagonal columns; they form during cooling and contraction in hypabyssal intrusions or lava flows.
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Define vein
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Initiate as joints or fractures adjacent to faults that are often used as conduits for flow of fluids. Usually the are filled with precipitated minerals
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Define en enchlon fractures/veins
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Parallel or subparallel closely spaced, overlapping or step like fractures that are oblique to the overall structural trend
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What happens at a microscopic level when strains reach the elastic limit of a material?
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The bonds of the material have been stretched to the limit. Any more strain on the material will cause the bonds to break.
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What role do hot spots play in the theory of plate tectonics?
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Hot spots are believed to be caused by mantle plums which comes from hot mantle rising from the core mantle boundary. They are believed to be still which shows how the plates move over time
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What process does the wilson cycle describe?
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It describes the super continent cycle. How the plates move apart and together.
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What geologic evidence supports the concept of Wilson cycles?
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There is a single mountain chain across continents that aren't connected that shows the wilson cycle. Also all the oceanic crust has been subducted so there is nothing older than 200 million years.
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How does the Wilson cycle explain the age of oceanic lithosphere?
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Since all of the oceanic crust is more dense than the continental crust, the oceanic crust is pulled under the continental when it collides. All around the world, there is no oceanic crust older than 200 million years.
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Why does the polarity of subduction sometimes switch?
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Once a supercontient forms, there are no longer midocean ridges for the heat from the core/mantle to escape. The mantle keeps heating up under the supercontinent and causes a new area of downwelling to open up in a new area for heat to escape.
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What might explain the wilson cycle?
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The convection cell model, slab pull, ridge push, and basal drag.
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What are the differrent thoughts on the forces that are driving plate motion?
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There are four different models that are though to control plate motion. Convection cell, which is thought to be to have the asthenosphere flow in elliptical paths. There is upwelling at the MOR and downwelling at the subuction zones. However it doesn't work because the geometry doesn't work. The next model was basal drag, which says that there is enough shear stress on the base of a plate to cause it to move. The next one is ridge push force, with the creation of new oceanic crust at the MOR, the crust is pushed around the world and causes the subduction between oceanic and continetal crust. The last one is slab pull force, which says that when the slab starts getting subducted, gravity and desnity takes over and continues to pull it down into the mantle.
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What force controls the supercontinent cycle?
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There is no single force that controls the supercontinent cycle. It is probably a mix of all 4 mentioned, convection cell model, basal drag, slab pull, and ridge push. The last two being more dominante than the first two.
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Discuss the process that takes place at subduction zones
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Once the subduction zone starts, the cool oceanic crust crust starts to sink. As it gets deep, it both heats up and releases water. This causes the rock to release melt and change from basalt to eclogite. Also there are earthquakes along the subduction zones.
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Describe the pattern of earthquakes on earth, consider location, depth, and density.
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Earthquakes can happen anywhere on earth, however most occur on earthquakes occur in discrete zones: MOR, continental rifts, oceanic fracture zones, continental transcurrent faults, and subduction zones. The deeper the earthquakes, the colder the lithosphere is. The deepest earthquakes happen at deep subduction zones of cold lithosphere. Shallow earthquakes occur in axial valleys.
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Compare and contrast the asthenosphere and the lithosphere. What separates them in ocean basins?
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Asthenosphere: Is between 60 and 350 km below the surface. It's about 250 km thick. It is warm and relatively ductile layer within th mantel with a velocity that is higher than lithosphere.
Lithosphere: It is the outermost shell, it's crust and cool, rigid mantle immediately below it. It's usually 60-100 km thick, but can be less than 5 km in MOR axial valley, and more than 300 km thick under mountains. In oceanic basics, there is a low velocity zone that separates the asthenosphere and the lithosphere. |
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Define, compare and contrast P and S waves. What can we learn from P and S waves when they travel through the earth?
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P(rimary) waves are the quickest body waves that can travel through liquids and solids because they compress. S(hear/secondary) waves are the second quickest body waves, they can only travel through the solid rock because liquids can't shear. From both of them we can learn that there is a liquid outer core made of iron and nickel, and that the inner core is a solid mix of iron and nickle.
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What is the source of energy for seismic waves?
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The energy is a build up from the elastic deformation of the rock that gets released in an earthquake.
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What are seismic waves?
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Seismic waves are the released of stored elastic strain energy
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What are the different types of seismic waves? How and why do they behave in different media?
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There are P waves, S waves, and body waves. P waves are compressional so they can go through both liquid and solids. S waves are shear waves so they can only go through solids. Body waves move on the surface.
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What happens when waves cross from one medium to another? What can we learn from that?
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When waves move from one medium to another they refract and reflect. This gives us an inducation that there is a compositional and/or phase change.
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What data have we used to infer the internal structure of the earth and the behaviors of different parts of the earth?
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We have used the seismic energy from earthquakes to define the internal structure of earth and the behaviors of different parts of the earth.
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How do geologists know that the interior of earth is warmer than the exterior?
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By looking at the velocities of the seismic waves geologist can tell that the interior of the earth is warmer than the exterior. The velocities of the body waves decreases as the rock warms up (which decreases density).
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Describe the elastic rebound theory. How was the theory first constructed?
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Stress is applied to the fault, and elastic deformation is caused. However firction prevents movement so the energy builds up until it slips bask and the vibrations are earthquakes as the rock settles back. The theory came from Harry Ried looking at the maps of San Francisco before the 1906 earthquake. He saw that the roads slowly went from straight to curved and broke when the earthquake occurred.
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What types of vein fillings are found and what do they tell you about the formation of the history of the vein?
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There are three types of veins, Vuggy (blocky), Mineral fibers (fibrous), and brecciated fragments.
Vuggy (blocky) shows that the vein was at a shallow depth and the fracture the vein filled was open for some time. Mineral Fibers (fibrous) shows that the fracture was deeper, and that crystals forming did so very slowly as the rock only opened up when the crystals were formed. |
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Why are joints often evenly spaced?
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Formation of a joint relives tensile stress for a critical distance from the joint (Joint stress shadow) and then the next joint usually forms right outside the joint stress shadow.
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What does joint spacing depend on?
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Bed thickness
Lithology Tensile Strength Strain (general rule is that spacing is about the same as bed thickness) |
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What observations would you make in the in the field about joints to learn about the deformation history of the area studied? How would you record that data?
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You take an inventory (choose a representative region and measure every joint) and subjective observation (scan the otcrop and subjectively decide on the dominant sets) to find the best information
You would record that data by creating a map of the strike and dip of joints on a map and/or creating a histogram and rose diagram. |
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How would you recognize a joint in the field?
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There is no deformation of rock associated with adjacent to joint. It's not the bedding surface, it's not cleavage
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What types of markings are often found on joints? What do they reveal about the joints?
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They are plumose structures, the stypib, c type and rhythmic c type.
They indicate the opening direction |
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What is the difference between systematic and non systematic joints?
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Systematic joints are planar or broadly curved in plane view. They form perpendicular or nearly perpendicular to primary layering in host rock and have regular spacing. They also have a narrow range of values for the spacing. Non systematic joints lack all those characteristics
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What type of information do the geometric relationships between two joints provide?
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They give the relative timing of formation of the intersection.
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What determines joint spacing in systematic joints?
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Bed thickness
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What types of joints form in igneous rocks?
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Columnar joints (they are most commonly vertical with a polygonal cross section that has 4-6 sides. It's formed from igneous rocks that cool near/on the surface that causes a network of extension fractures that separate into columns of igneous rock)
Exfliation (sheeting, it's distinctive in subhorizontal) |
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What are outer-arc extension joints? How, why and where do they form?
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Joints that result from the in the rock elastically relaxes to attain a different shape. These joints only occur in areas where the tensile stress has been released
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What are J and S joints, how do they form, and what do they tell us about the deformation history of a region?
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J joints form if sigma 3 is parallel to the walls of older joints.
S(igmodial) joints form if sigma 1 is perpendicular to walls of older joint. The different joints tell us about the relative timing of formation for a joint intersection. |
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What does a plumose structure tell us about the formation of the joint?
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It tells you where the joint originated.
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What are the differences between brittle behavior and ductile behavior?
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Ductile behavior is the general term for the response of a solid material to stress such that the rock appears to flow mesocopially like a viscous fluid. Brittle behavior is the response of a solid material to stress during which the rock loses continuity.
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What temperature, pressure, and deformation rate conditions favor brittle behavior in most solids?
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Low Confining Pressure
Low temperature High e High Pf |
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What temperature pressure and deformation rate conditions favor ductile behavior in most solids?
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High confining pressure
High temperature Low e low pf |
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Rocks are hard and solid, why do we imagine that they exhibit the linearly viscous behavior of a liquid? What are some implication of the notion that rocks may behave in a viscous manner?
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There are so many cracks microspically that the rock moves. This allows the theory of plate tectonics to work.
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Define wall rock
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rock adjacent to a fualt surface
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define fault block
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body of rock that moved as a result of a slip on a fault
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define Hanging wall
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block that is above the fault plane is the hanging wall
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define footwall
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the block that is below the fault plane is the footwall
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Define dip slip fault
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The hanging wall block moves up or down parallel to the dip of the fault plane
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define strike slip fault
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Both blocks move parallel to the strike of the fault wall.
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define oblique slip fault
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the displacement vector of the oblique fault is to both strike and dip.z
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define extensional fault
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A fault that lengths the layer with normal faults at the loss of the stratigrapic section (an example would MOR or basing and range)
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define contractional fault
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A fault that shortens the layers by duplication of the strigraphic section through reverse and thrust faults (eg grand tetons, the applications)
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define exhumed fault
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Exposure of an inactive fault at the surface due to uplift or erosion
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define blind fault
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a fault that dies out in the subsurface without intersecting the surface of the earth
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define fault separation
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distance between the displaced parts of a marker as measured along a specific line on a specific plane
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define net slip
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the distance between two formerly adjacent points that are now on opposite walls of the fault.
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Discuss the significance of faulting to plate tectonics
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faulting is the most significant way in which lithosphereic masses are tectonically transported relative to each other
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What factors influence the location of faulting in the earth?
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Faults common invlove frictional sliding along pre existing joints, veins and other discontinuities, but also initiate and propagate in intact rocks.
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How do you recognize a fault?
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The stratigraphic section does not match.
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On what basis are faults distinguished and described?
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Faults are distingueshed and described by the way footwall/hanging wall moves relative to each other.
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What characterizes a region where the structure is dominated by extensional faults?
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Normal faults with loss of the stratigraphic section
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What characterizes a region where the structure is dominated contractional faults?
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Thrust and reservse faults that duplicate the stratrigraphic section
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