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18 Cards in this Set
- Front
- Back
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Learning Goals |
1) Compare different strategies for dealing with earthquake hazards 2) List and describe factors that contribute to the amount of damage during an earthquake 3) Diagnose which forms of earthquake hazard (direct and indirect) can be mitigated through various engineering designs/planning 4) Recognize how socio-economics factors may limit the extent of mitigation possible through engineering design |
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Mega-thrust earthquakes |
Subducting crust is very young, light, and buoyant and descends at a low angle, exerting an upward force on the base of the obducting plate increasing frictional resistance to subduction |
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Earthquake hazard strategies: empirical |
Establish construction standards, evaluate risk for insurance purposes, risk-based site selection (e.g. for nuclear power plants) |
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Probabilistic approach |
What is likelihood of earthquake of given intensity occurring based on frequency, magnitude, and spatial distribution of past quakes |
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Recurrence rates |
Prediction of earthquake risk based on probability that an earthquake of some magnitude will happen at some location over a given period of time
Problem: assume uniform distribution of earthquakes over time, often not the case |
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Seismic gap |
Section of a fault that has produced earthquakes in the past but is now quiet
Strain is building up in each seismic gap, raising probability that large quake will occur soon |
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Earthquake prediction |
Foreshocks
Change in land shape near faults
Fluctuations in groundwater levels, magnetic field
Radon gas |
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Hazard & Risk |
Hazard: likelihood and frequency of earthquakes; the capacity to cause damage
Risk: consideration of the consequences of the hazard
Risk = hazard x consequences |
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Earthquake Damage Factors |
1) Magnitude & duration (bigger magnitude & longer duration = more deadly quake) 2) Distance from focus (strength of shock waves diminish with distance from the focus) 3) Population density (more people = more chance of injury and death) 4) Time of day (higher loss of life at times when many people are in large buildings because of work or school) 5) Geology of affected area (some rock types transmit seismic energy ore readily) 6) Ground amplification 7) Building construction
Most significant types of damage result from: ground shaking, liquefaction, triggering of mass movements, tsunamis, fires |
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Ground amplification |
Differential settlement: thick soils will settle, increasing potential for damage
Ground shaking: amplitude, duration and damage increases in poorly consolidated soils
Resonance: is more likely to amplify seismic waves of different frequencies through soil vs. rock |
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Bracing |
Adds reinforcement against shearing forces |
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Damping |
absorbs energy caused by moving ground |
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Isolation |
Separating building from moving ground with teflon pads, large rollers, springs, or other devices. Ground moves under foundation without transmitting all of that motion to building |
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Liquefaction |
Conversion of formally stable cohesionless soils to a fluid mass, causing damage to structures
Can be mitigated through densification of poorly consolidated, liquefaction-prone sediments |
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Landslides |
Earthquakes destabilize slopes by inducing shear stresses and weakening internal structure of slope material |
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Tsunamis |
Sea waves caused by displacement of sea floor during an earthquake whose epicenter is located on the ocean floor.
Displace a large mass of water |
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Other consequences |
fire & disease |
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Mitigation of earthquake consequences |
Determining seismic frequency
Earthquake probability maps
Mapping of geological/soil conditions
Following building codes and good engineering practice
Planning and preparedness |
