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What factors effect the quake damage?
- 1-Magnitude
- 2-distance from epicenter
- 3-ground type
- 4-Duration of shaking
- 5-focusing of seismic waves
- 6-Aftershocks
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Damage caused by what?
- acceleration- how quickly something changes speed—buildings are forced to move quickly therefore cause more damage with faster acceleration, attenuation-how fast waves die off,
- liquefication-quick sand effect (Bay Mud does not liquefy), saturated sediments liquefy
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Ground types
- 1-unconsolidated-sediments, sand, mud gravel, soil (alluvium-river deposits),amplifies shaking-may liquefy, more damage
- 2-Solid Rock-Bedrock, igneous, metamorphic and sedimentary
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Some unconsolidated ground is worse than others what is an example?
- Loma Prieta (1989) San Fran—shaking was highest on Bay mud and it collapsed, least shaking on Bedrock
- -the collapse was built on alluvium
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Isoseismal map
shows level of damage, uses modified mercalli scale
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Why do some areas have higher damage than expected?
based on how buildings are built and the ground type, if the ground liquefies the more damage is caused, how far away its from the epicenter
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Earthquake shaking amplification
Highest to lowest 1-Bay, lake, mud deposits (shake longer) 2-artificial fill 3-sediments 4-shale bedrock 5-poorly cemented sandstones, rock 6-well cemented sandstones 7-crystalline rocks
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Short waves, long waves
- The farther from epicenter you are, the fewer short-period waves arrive b/c they get absorbed by rock.
- LONG-period waves cause more damage—can travel up to a few hundred miles because they are not absorbed
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Resonance
- period of building=period of ground under it…
- EX:building on unconsolidated ground a couple 100 miles away from epicenter (long-period waves arrive) will cause bad resonance EX: Mexico City (1985)-built on lake beds, damage due to resonance
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Modified Mercalli Intensity Scale
- -effects of a quake on earth's surface is called the INTENSITY
- -intensity scale consists of certain key responses (people awakening,furniture movement, total destruction)
- -has 12 increasing levels of intensity, max intensity is near the epicenter
- -magnitude and intensity measure different characteristics of quakes
- -magnitude measures the energy released at the source of the quake
- -Intenstiy measures the strength of the shaking
- -determined by effects on people, human structures, & natural environ.
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