earthquake hazards i. landslides - can be caused by earthquake hundreds of miles away three main...
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Earthquake Hazards
I. Landslides
- can be caused by earthquake hundreds of miles away
Three main types:
1. Fall - usually from a cliff
2. Slip - i.e. slump
3. Flow - i.e. avalanche
* Loess - wind blown sediment deposits
Earthquake Hazards
I. Landslides
- 1995 landslide in La Conchita, California
- 2005 landslide in La Conchita, California
Earthquake Hazards
II. Liquefaction
* the fluidization of fairly solid ground
Three main types:
* 1. Flow - saturated sediments move horizontally (often toward lower elevations)
Earthquake Hazards
II. Liquefaction
*2. Fountaining - geyser of water and sand created by heavy layer of rock on saturated sand.
Earthquake Hazards
II. Liquefaction*3. Flotation - saturated sand on the surface becomes liquefied. Objects could float or sink.
Earthquake Hazards
III. Floods
Four main types:* 1. Impoundment Flood - landslide blocks river’s flow, causing water to rise upstream.
Non-lethal. Plenty of time to evacuate. Mostly property damage.
Quake Lake
Earthquake Hazards
III. Floods
2. Damburst Flood - contents of lake are released downstream due to damage to dam or levee
Very lethal! May result after impoundment flood.
Earthquake Hazards
III. Floods
* 3. Displacement Flood - Water is forced out of a lake or river by a landslide or large-scale surface deformation.
Earthquake Hazards
III. Floods
* 4. Transgression Flood - Coastal land sinks during earthquake and ocean/lake/river water moves in.
This type is permanent.
Earthquake Hazards
IV. Great Waves
* A. Tsunamis - extremely large waves that can travel across entire oceans and cause great destruction.
Earthquake Hazards
IV. Great Waves
A. Tsunamis- What causes a tsunami?
- Violent shaking or surface deformation creates a shallow wave that covers a large area.
- Ships at sea will not feel it.- May move up to a couple hundred miles per hour in open ocean.
- As it nears land, the front edge of the wave slows down, but the back remains fast. Along with a shallow shore, this causes the wave to increase in height.
- Sometimes, hundreds of feet high.
Earthquake Hazards
IV. Great Waves
*B. Seiche - sloshing of water back and forth in a lake or enclosed harbor.
- usually minimal damage / only reaches a few yards high.
Earthquake Hazards
IV. Great Waves
* C. Bore - single crest of water rushing along a river, often upstream.
- can smash or overturn boats
- example - Mississippi River, 1811-1812
Earthquake Hazards
IV. Great Waves* D. Displacement Wave - great wave caused by displacement of water, due to landslide or underwater ground deformation.
- example - Lituya Bay, Alaska - landslide pushed water 1720 ft. up opposite shore.
- occurs in lakes or enclosed harbors.
Earthquake Hazards
V. Structure Failure
- even in recent years, 1000’s killed due to lack of building codes.
- causes the most loss of life
- China, Mexico, Armenia, and Turkey have all lost over 15,000 in single quakes in the past 25 years due to poorly built structures.
- When looking at susceptibility to earthquakes, we need to consider three aspects:
Earthquake Hazards
V. Structure Failure* A. Foundation
- Structures built on solid rock stand up better than structures built on sand or loose sediment.
Earthquake Hazards
V. Structure Failure* B. Materials
- People build with what they have. Historically, it has been adobe, wood, or stone.
- Wood has much more necessary flexibility.
- Which is the most earthquake resistant?
* Which is the least earthquake resistant?
* Adobe - 100,000’s killed in China due to adobe building collapses.
- Today, we use steel. It is extremely strong but will also bend slightly. Often used to reinforce concrete.
Earthquake Hazards
V. Structure Failure* C. Design
- Most buildings constructed to resist vertical forces, not horizontal forces.
* 1. Resonance - If an earthquake shakes the ground at the same frequency of the building, the building itself will amplify the shaking and literally shake itself apart.
- Two big problems?
- Mexico City, 1985 - 98% of all collapsed buildings in the downtown area were between 6 and 18 stories high. Very few of the shorter or taller buildings collapsed.
Earthquake Hazards
V. Structure FailureC. Design
* 2. Outside ornaments or facade can fall off.
- Two big problems?
Earthquake Hazards
VI. Fire- Sometimes an earthquake can cause a fire so enormous that the earthquake itself is the lesser of the two evils.
- Lisbon (1755), San Francisco (1906), Tokyo (1923).
- How does an earthquake cause such disastrous fires?- historically, extensive use of wood in buildings and open flames for cooking.- broken gas lines and electrical lines- destruction of firefighting equipment and water lines- large number of separate fires that grow into one enormous fire- flammability of household items (couches, beds)
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