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39 Cards in this Set

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