18: Earthquake Engineering Flashcards
What are the 2 types of earthquake strategies we use?
Empirical Strategies:
- refer to approaches that rely on observation, experimentation, and real-world data to derive conclusions or make predictions.
Early Warning Strategies:
- A variety of methods that identify precursor events (events that occur prior to earthquakes that can be used to provide warning
What are recurrence rates? What are some issues with recurrence rates?
recurrence rates:
- Earthquake recurrence rates are the average number of earthquakes that occur within a given time period
- Utilizing recurrence rates involves prediction of earthquake hazard level based on the probability that an earthquake of a given magnitude will happen at some location over a period of time
recurrence rates assume a uniform distribution of earthquakes over time along the same plate boundary, however, there are “gaps” where plates may be sliding smoothly past each other or storing up a lot of energy to release as a bigger earthquake later.
What are seismic gaps?
Seismic Gap:
- a section of a fault that has produced earthquakes in the past but is now quiet, raising the change that a large quake will occur soon
What are some examples of Empirical Earthquake strategies?
Empirical:
- construction standards based on susceptibility and risk
- Risk-based site selection
- probability analysis
- recurrence rates
What are some examples of Early Warning Earthquake Strategies?
Early Warning Strategies:
- Foreshocks (a mild tremor preceding quakes)
- change in land shape near faults (elevation, tilting, etc.)
- Fluctuations in groundwater levels
- Fluctuations in magnetic field and electrical resistance of the ground
- Radon gas (high levels could indicate cracks in the ground letting it escape)
Can earthquakes be predicted?
No. We cannot predict earthquakes. Early Warning strategies aren’t really trying to predict earthquakes, it’s just trying to look for signs of earthquake hazards rising!
What does HAZARD and RISK mean when we talk about earthquakes?
Hazard:
- involves the likelihood and frequency of earthquakes; the capacity to cause damage
Risk:
- consideration of the consequences of the hazard
- Risk = Hazard x consequence
What are the 7 Earthquake Damage Factors?
- Magnitude and Duration
- Distance from the earthquake’s focus
- Population Density
- Time of day
(higher loss of life during work/school hours) - geology of the affected area
(older crusts more efficient at transmitting seismic energy than younger crusts) - Ground amplification
(like intensity, solid bedrock vs poorly consolidated sediments) - Type of building construction
( some building materials and design are more susceptible to shaking)
What are the 4 main types of earthquake damage?
- Ground motion
- liquefaction
- landslides
- tsunamis & Flooding
What is ground motion? What is ground amplification?
Ground motion:
- shaking structures causes them to collapse
Ground Amplification:
- Unconsolidated rock and soil sediments have a tendency to increase the amplitude and duration of the seismic waves, increasing the potential for damage!
Note:
When amplitude increases, frequency decreases and vice versa. Ground amplification can help earthquake waves match the resonance frequency of taller buildings (as taller buildings have a lower resonance frequency)
What is liquefaction?
liquefaction:
- conversion of formal stable cohesionless solids to a fluid mass, causing damage to structures
In areas where loose soils are saturated with water, seismic shaking can cause water pressure to drastically increase, resulting in liquefaction; the reduction in strength and stiffness of soil.
Think Richmond, Delta Chilliwack, anywhere close to the Fraser river, etc.
How do you avoid liquefaction?
Although avoidance or better building designs are options, most mitigation options work to lessen liquefaction potential by “densifying” poorly consolidated, liquefaction-prone sediments prior to construction
What are the 3 types of compaction?
dynamic compaction:
- a heavy weight is dropped on to the solid surface to compact loose sediments
Compaction grouting:
- the process of injecting a water/sand/cement mixture into the g round to cause compaction of an existing loose soil layer
Vibroflotation:
- the process of inserting a vibrating probe into the ground to cause compaction of sediments
What are tsunamis?
Tsunamis:
- Common misconception that if you’re close to the shore, you will be at threat of tsunamis. Tsunami’s, like all water, follows Q = V * A. Q needs to remain constant, so for tsunamis heavily affect channelized regions like bays and don’t really affect wide, open regions.
