Geol 140 Exam 2
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Explain how earthquakes occur using elastic rebound theory.
- Energy is stored in rocks
- The stored stress exceeds the strength of the friction or the strength of the rock on the fault
- The rocks break to release the energy
- Plates snap to new low-stress position
- The snap produces the seismic waves of an earthquake
Compare the magnitude and intensity of an earthquake. For each, be sure to include a definition, how it is measured, and what factors affect it.
- Magnitude: amount of energy released in an earthquake
- Only one magnitude per earthquake
- Estimated by amplitude of seismogram
- Measured on moment magnitude scale
- Intensity: degree of shaking
- Many intensities per earthquake
- Measured on modified Mercalli scale
- Depends on distance from epicenter & geological material
Describe five ways in which earthquakes do damage.
- Ground motion: physical shaking can damage buildings and structures, depending on intensity
- Liquefaction: water-soaked sediment sinks, can cause structural collapse and subsidence
- Landslides: physical loss of ground support
- Fire: broken gas pipes and sparks can lead to fires and further damage
- Tsunami: earthquakes that occur under offshore produce a large wave that can cause a large amount of damage
What is the discharge of a stream? If the discharge of the stream changes, what else about the stream might change?
- Discharge: volume of water per unit of time
- The width, depth, and/or velocity of the stream may change discharge
Describe at least five ways people increase the risk from flooding.
- Alter flow patterns
- Remove vegetation
- Pave watershed
- Decrease channel volume
- Decrease floodplain capacity
Explain two methods of controlling damage from floods by managing development.
- Flood zoning to manage land use
- Flood insurance
Describe three kinds of flood control structure, and describe the advantages and disadvantages of each.
- Levees: wall designed to keep river channel under control
- can be eroded
- encourage development next to the river
- height gives water more energy when it breaches
- bypass: area designed to flood
- diverts flood to low risk area
- takes up area that can be used for other productive means
- dams: structure built to contain water for flooding and drinking purposes
- regulates amount of water in streams
- provides hydroelectricity
- can create major flood if breached or broken
You have been hired to write a public service brochure on earthquake preparedness. Write a list of the most important things to do to prepare for an earthquake. Include details on what people should do BEFORE, DURING and AFTER an earthquake to be safe.
- Plan evacuation route
- Adapt buildings and structures
- Have an emergency kit (water, food, money, radio, etc)
- Secure cabinets
- Keep a gas wrench next to the gas valve
- Choose an out of state contact
- Take shelter under a table or in an area with frames, such as a closet
- Get away from glass
- Do not run outside
- Stay in an open area
- Stay in your car if driving
- Go outside and stay there until building is deemed safe
- Check for gas leaks
- Use radio
- Check for fires
- Get emergency kit
- Call out of state contact to report in
You are an earthquake safety consultant writing a brochure on safe and unsafe structures. Provide an annotated list of unsafe and safe building types, and a brief description of how to retrofit an older house to be earthquake-resistant.
- Wood frame buildings, flexible, will bend with motion
- Steel frame buildings, somewhat flexible, bend with shock
- Shear walls & crossbracing, provide extra support and stabilization
- Base isolators, allow independent movement
- Buildings on piers, add shear walls & cross bracing
- Unreinforced brick structures, reinforce with steel structure
- Structures not bolted to foundation, bolt or add base isolators
- Porches, reinforce with shear walls
- Poured concrete, reinforce with steel structure
- Soft-story buildings, reinforce with shear walls & cross bracing
Describe how people and property are at risk from that natural hazard. Be specific, and be sure you include the information you learned in class about that hazard.
Describe how people make the hazard worse with at least one example of where this has happened.
Describe some methods for lowering the risk from that hazard, and give at least one example of where this has happened
- ground motion
- MORE RISK
- settling on fault zones
- unsafe buildings
- LESS RISK
- evac & safety drills
- take necessary precautions
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