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80 Cards in this Set
- Front
- Back
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When rocks are undeformed, they are
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horizontal
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Tectonic forces
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Forces that distort rocks:
1.) Compressive 2.) Tensional 3.) Shearing |
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Compressive Forces
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squeeze and shorten body of rock; causes a shortening strain
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Tensional Forces
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Stretch a body and tend to pull it apart; causes a stretching strain
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Shearing Forces
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Push two sides of a body in opposite directions; causes a shear strain
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Stress
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the push, pull or shear that a material feels when subjected to a force; a force applied per unit area over which the force acts
stress=force/area |
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Strain
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change in shape of a rock in response to deformation, as a result of the application of a stress;
1.) Stretching 2.) Shortening 3.) Shear strain |
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two measurements that are used to describe the orientation of a layer of rock exposed at a given location
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dip and strike
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Dip
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the amount of tilting - angle at which a bed inclines from the horizontal
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Strike
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direction of the intersection of a rock layer with a horizontal surface
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Ductile rocks
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capable of being easily molded or shaped; flexible; smooth and continuous plastic deformation
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Brittle rocks
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likely to break; rigid; undergoes little change until it breaks suddenly
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Whether or not a rock is ductile or brittle depends on:
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Kind of rock
Temperature Surrounding pressure Magnitude of force Speed with which the force is applied ***same material can deform in ductile or brittle way since it depends mostly on temp and pressure (i.e. ice)*** |
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Rocks inside earth experience _______ behavior.
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ductile b/c temperature and pressure are both higher
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Ductile behavior
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folds, bends --> means there were compressive forces
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Brittle behavior
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faults, breaks, fractures
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Types of folds
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Anticlines
Synclines |
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Limbs
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two sides of a fold
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Axial Plane
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imaginary surface that divides a fold as symmetrically as possible, with one limb on either side of the plane
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Fold axis
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line made by the lengthwise intersection of the axial plane with the beds
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Anticlines
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upfolds or arches of layered rocks;
caused by compressional forces; ductile behavior |
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Synclines
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downfolds, or troughs, or layered rocks
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Plunging fold
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if the fold axis isn't horizontal and is tilted instead
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Asymmetrical fold
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one limb is dipping more steeply than the other
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Overturned fold
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one limb is tilted beyond the vertical
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Dome
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Anticlinal structure - broad circular or oval upward bulge of rock layers; beds dip in all directions;
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Basin
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Synclinal structure - bowl shaped depression of rock layers in which the beds dip rapidly toward a central point
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______, ______, and _______ trapped under anticlines
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natural gas, oil, groundwater
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Two kinds of fractures (brittle behavior)
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Joints and faults
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Joints
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fractures in rock caused by regional stress or by the cooling and contraction of the rocks; there is no displacement of the two sides up and down, back or forth, simply opens up
can be caused by all three types of forces (compressive, tensional, shear) |
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Fault
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can be caused by all three forces: compressive, tensional, shearing
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Fault Plane
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surface along which the formation fractures and slips
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Dip Slip Fault
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relative movement up (compression) or down (tension) the fault plane - compressive or tension forces
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Strike-slip fault
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movement is horizontal, paralell to the strike of the fault plane - shearing forces
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Transform fault
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strike-slip fault that forms a plate boundary
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Oblique-slip fault
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movement along the strike and simultaneously up or down the dip - combinations of forces
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Normal Fault
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rocks above the fault plane move down in relation to the rocks below the fault plane causing an EXTENSION of the section; caused by TENSIONAL forces
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Reverse fault
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Rocks above the fault plane move upward in relations to the rock below, causing SHORTENING of the section; caused by COMPRESSIVE forces
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Thrust Fault
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low angle reverse fault, so that the overlying block is pushed mainly horizontally; SHORTENING by breaking and one sheet overrides the other; caused by COMPRESSIVE forces;
i.e. Indonesia - tsunami caused by earthquakes in the ocean, caused by thrust faults in the ocean |
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Right-lateral fault
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facing a strike-slip fault, the block on the other side is displaced to the right
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Left-lateral fault
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facing a strike-slip fault, the block on the other side is displaced to the left
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Earthquake
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earth shaking caused by a rapid release of energy due to tectonic stresses that make rocks break; energy moves outwards
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Seismicity
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earthquake activity
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Seismicity occurs due to:
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Motion along a newly formed crustal fracture (fault);
Motion along an existing fault; A sudden change in mineral structure; Inflation of a magma chamber; Volcanic eruption; giant landslides; meteorite impacts; nuclear detonations |
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Most earthquakes occur along __________.
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Faults (crustal fractures that move rock masses)
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Hypocenter
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focus; the spot within the earth where earthquake waves originate; usually occurs on fault surface
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epicenter
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land surface above the hypocenter
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Footwall
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block below the fault on a sloping fault
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Hanging wall
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block above the fault on a sloping fault
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Most faults display _________ fault character.
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Oblique-slip
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Active faults
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ongoing stresses produce motion
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Inactive faults
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Motion occured in the geologic past
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Fault trace
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a surface tear, crack; sign of displacement
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Fault scarp
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a small cliff; sign of displacement
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blind faults
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invisible faults; don't appear on surface
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Elastic Rebound Theory
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explanation for how energy is spraed during earthquakes - as plates shift on opposite sides of a fault as they are subjected to force, they accumulate energy and slowly deform until their internal strength is exceeded; then, sudden movement occurs along the fault, releasing the accumulated energy (b/c energy's not absorbed) and rocks snap back to their original, respective, undeformed shapes.
Reason for disastrous earthquakes |
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Stick-Slip Behavior
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Faults move in JUMPS; one motion starts, quickly stops due to friction; eventually strain builds up again and fault jumps again
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asperity
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fault protrusion
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Fault creep
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slow, creeping motion without friction, rocks slide easily; uncommon along fault lines, not dangerous
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Fault Motion
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rocks break --> stored elastic strain is released --> energy radiates outward from hypocenter --> energy (waves) generate vibrations --> vibrations cause motion --> often foreshocks and aftershocks
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Compressional/Primary (P) waves
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a body wave - passes through Earth's interior; push-pull (compress and expand) motion; travel through solids, liquids, gases; fastest
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Shear/Secondary (S) Waves
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a body wave - passed through Earth's interior; "shaking" motion; travel only through solids, NOT liquids; slower
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Love Waves
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a surface wave - travel along Earth's surface; S-waves intersecting the surface - move back and forth like a snake
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Rayleigh waves
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Surface wave - travels along Earth's surface; P-waves intersecting the surface - moves like ripples in a pond
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Waves in order from fastest to slowest
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P>S>L>R
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Seismology
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study of earthquake waves; reveals the size and location of earthquakes
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Seismographs
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instruments that record seismicity - measures wave arrival times & magnitude of ground motion
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Order in which waves arrive
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P-waves first, S-waves 2nd, surface waves last
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Locating an epicenter
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P and S waves travel at different velocities;
first arrivals of P and S waves varies with distance; time-travel graph plots distance of each station to epicenter; (S-P) crucial to finding distance between seismograph and epicenter; need 3 stations - triangulation |
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Mercalli Intensity Scale
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measures the INTENSITY of shaking and damage at a specific location; depends on distance to earthquake and strength; create zones of damange; not very scientific
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Richter Magnitude
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measures MAGNITUDE of earthquake; depends on amplitude of the ground movement caused by seismic waves; uses logarithmic scale because size of earthquakes varies vastly
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Two means of describing an earthquake:
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1.) Intensity - degree of shaking based on damage
2.) Magnitude - amount of energy released |
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Seismic-moment magnitude scale
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Based on the measure of an earthquake that indicates what happened at the earthquake source rather than how much the ground shakes at a distance point; depends on product of slip of the fault when it broke, area of the fault break, rigidity or stiffness of rock
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P-wave movement
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rapid up and down movement
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S-wave movement
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back and forth motion which is usually much stronger than P-waves; produce extensive damage
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Severity of shaking and damage of an earthquake depends on:
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Magnitude (energy) of earthquake;
Distance from hypocenter; Intensity and duration of the vibrations; Nature of the subsurface material - bedrock transmits waves quickly --> less damage, sediments bounce waves --> more damage |
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Liquefaction
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when earthquake waves liquefy H2O filled sediments - high pore pressures force grains apart reducing friction --> liquefied sediments flow as slurry --> sand becomes "quicksand" and clay becomes "quickclay" --> sand dikes, sand volcanoes, contorted layering; land slumps and flows, buildings may topple (common near harbor areas)
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To explore interior or earth, geologist do this:
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send seismic body waves through the earth to tell the material - record seismic waves caused by a big earthquake
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Moho
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boundary between crust and mantle
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Velocity of seismic waves in ________ are faster than waves in _________.
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mantle; crust
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