Geology- Lecture 2
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- What happens when rocks fold closer to the surface? deeper in the earth?
- surface: brittle (they fault) deeper: they're hotter so they fold
- Define: Anticlines
- a fold that looks like an A
- Define: Syncline
- a fold that looks like a U
- Define: Symmetrical folds
- the dips are the same
- Define: Asymmetrical fold
- dips are different
- Define: overturned fold
- the top of the layer is facing the bottom
- Define: recumbent fold
- extreme overturn, when the fold is on its side
- Define: plunging anticlines and syncline
- when they get tilted, the strike is pointing into the ground
- What are two ways a rock can break?
- Joints (fractures with no displacement) Faults (fractures with displacement)
- Define: Joints
- fractures with no displacement. Lots of pressure, then pressure is released. The rock fractures a simple crack in the rock
- Define: Faults
- fractures with displacement. rocks slip up and down
- Define: dip-slip fault
- the direction of movement is along the fault
- What are some causes for rocks to respond to stress differently?
- -type -magnitude of stress -pressure and temp -amount of fluid
- Define: stress field
- all the stress is placed on a rock
- Define: Confining Pressure
- a rock experiences pressure equally from all sides (normally at depths)
- Define: Differential Stress
- when one direction of stress is greater in one direction (additional stress comes from outside sources like tectonics)
- Define: Fluid Pressure
- reduces the outside pressure
- How does Continental Crust act at: Shallow levels Increasing depth great depth
- shallow: rocks fracture middle: rocks begin to deform deep: temp is more powerful than pressure so they begin to melt
- What are the three types of stress?
- Compressional (convergent forces) Tensional (divergent) Shear (transform)
- Define: Compression
- push together. shallow: fracture and slip deep: forms an anticline
- Define: Tension
- push away shallow: minerals get caught and make a vein deep: not as common, but still causes veins
- Define: Shear
- sidewise shallow: fault deep: creates a wavy looking rock
- Define: Dip
- if you pored water on the rock, where the water rolls off thats where the dip is
- Define: Strike
- if water floods the area, where the water line makes a horizontal line with the rock, the angle underneath is the strike
- Define: Strike-Slip Fault
- One rock moves left or right relative to the other rock
- Define: Oblique Slip Fault
- One rock moves left/right and up/down to the other rock
- What are the three types of faults
- Normal fault (hanging wall moves down) Reverse Fault (hanging wall moves up) Strike Slip Fault (rock moves side to side)
- Define: Normal Fault
- hanging wall moves down relative to footwall rocks are pulled apart and lengthened
- Define: Reverse Fault
- when the hanging wall moves up relative to the footwall rocks are compressed and shorten rock unit
- Define: Thrust fault
- a reverse fault that has a gentle dip
- Define: Strike Slip Fault
- when the rocks move side to side
- Define: Monocline
- nearly flat layers dip in one direction and then flatten
- Define: hinge/fold axis
- the most sharply curved part
- Define: Plunge
- the direction and amount that the fold points downward
- Define: Axial Surface
- an imaginary plane that cuts through the rock at the hinge. It can either be upright or at an incline
- Define: Asymmetric fold
- when the axial surface is at an incline
- Define: Overturned
- When the left/right limb has been rotated more than 90 degrees
- What are the steps in an earthquake?
- original position --> Deformation --> Rupture and release of energy --> Rocks rebound to original undeformed shape
- Define: Elastic Rebound
- earthquakes build up a lot of stress, then with an earthquake the stress is relieved
- define: liquefaction
- solid material behaves like an liquid (pouring sand)
- Define: Hypocenter
- the place where the earthquake is generated (usually at some depth within the earth)
- Define: Epicenter
- the point on earth's surface directly above where the earthquake occurs (can be the same place as the hypocenter)
- What causes most earthquakes
- plate boundaries
- What are most of the major causes of earthquakes (5)
- -plate boundaries -a volcanic eruption -land slide -nuclear bomb test -meteorite impact
- Where do small earthquakes occur
- at mid ocean rides they are shallow and relatively small
- Where do large earthquakes occur?
- along the entire contact between the subducting plate and the overriding plate
- What kinds of seismic waves do earthquakes generate?
- Body Waves (P and S) and Surface waves
- Define: P waves
- Primary, comes first, can travel through both solid and liquids. Fastest
- Define: S waves
- secondary, can't travel through liquids
- Which wave causes the most damage?
- Surface waves because of the up/down and side/side motion
- How do you determine how far away the earthquake was?
- measure the distance between the P and S wave
- How do we measure the size of an earthquake?
- the max S wave measured on a Richter Scale (Log10 scale)
- Define: Modified Mercalli Intensity Scale
- Based on touch feely science. "are animals acting funny, did you feel it, was there damage"
- What were some major North American Earthquakes?
- -San Francisco 1906 (most of the city destroyed. This is when the US started looking into earthquakes) -Alaska 1964. Magnitude 9.2 (largest earthquake in US history)
- What were some major world earthquakes
- Chile 1960 (mag magnitude 9.5. largest in the world) Turkey 1999 (mag 7.4 killed 17,000 because of poorly built homes) -Sumatra 2004 (mag 9. Tsunami kills 250,000)