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39 Cards in this Set
- Front
- Back
P Waves
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Slinky "push"
Fastest Compressional |
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S Waves
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Slinky "waved"
Slower Side-to-side, Up and down More damage than P waves |
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Fault ruptures occurr how deep?
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Fault ruptures occurr 5 -100 km deep
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Point of rupture?
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Hypocenter (focus)
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Surface above rupture?
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Epicenter
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Measure earthquake effects in ____
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Measure earthquake effects in G (gravity)
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Recognizing fault in the field—5 Ways
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1. Offset of strata
2. Offset of streams 3. Topography 4. Offset of manmade features 5. Surface water |
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Strike-slip movement occurs which way (primarily)?
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side-to-side, not up-down
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1 g is equal to ________
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Free-fall acceleration at 32ft/sec^2
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humans can sense ~_____ g?
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~0.001g
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Non resistant building crumble at ~___?
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~.1g
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What soil resists earthquakes best?
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bedrock
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What soil resists earthquakes least?
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landfill
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What soil amplifies shaking?
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Wet, unconsolidated soil
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What is a fault?
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Any crack offsetting rock
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What is a joint?
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A crack without offset
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A large offset is measured in ______
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Km
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A small offset is measured in ______
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mm
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3 types of faults
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1. Strike-slip
2. Normal 3. Reverse |
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Reverse fault hanging wall moves up or down?
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hanging wall moves up
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Are thrust faults obvious?
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No, they hide themselves
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What are thrust faults?
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Very low angle reverse fault
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How to identify offset strata?
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Different rock types, weird juxtapositions
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How to topographically identify fault?
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scarp: cliff formed on fault plane
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en echelon shears
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tiny parallel cracks
shears “step”to left or right |
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\\\\\\\\\\\\
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scarp =L SS = left-stepping EE shears
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////////////
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LL SS = right-stepping EE shears
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How to recognize fault via surface water/springs (2 ways)
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1. fault “grinding”produces clay
-> clay blocks water (aquitard) 2. Sag ponds –torn apart by fault mvt |
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How to locate earthquake?
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P-S wave difference = distance from quake
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2 ways to measure earthquake size
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Modified Mercalli
Richter |
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Modified Mercalli: What is it good for?
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Measuring old earthquakes through journals, etc., because it is subjective (windows breaking, trees shaking)
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Modified Mercalli uses what symbol to measure?
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Roman numeral
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Richter uses what scale (not richter scale)
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Logarithmic scale
(M4 ten times larger than M3 M5 one hundred times larger than M3 ) |
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How to measure using Richter Magnitude?
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1. Start with seismographic record
2. Measure time btwn P & S wave arrivals 3. Measure height at highest mark |
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Problems with Richter Scale (3)
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1. Amplitude varies by material
2. Richter Scale doesn’t consider damage 3. Moment Magnitude Scale (Mw) |
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Explain "Amplitude varies by material"
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weak mud = higher amplitude= bigger M
bedrock = lower amplitude= smaller M |
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How to calculate using Moment Magnitude
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Considers length of fault rupture x distance moved
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Advantages of Moment Magnitude Scale (2)
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More consistent #’s
Better for bigger quakes (Richter inconsistent >7.5) |
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Disadvantages of Moment Magnitude Scale (2)
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Not every quake ruptures ground or
displaces big subduction quakes Takes much longer to calculate |