1. Section 4: Earthquakes and Society
The probability of an earthquake’s occurrence is determined from the history of earthquakes and knowing where and how quickly strain accumulates. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions
What factors affect the amount of damage caused by an earthquake?
What are some of the factors considered in earthquake-probability studies?
How are different types of structures affected by earthquakes?
Earthquakes and Society
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3. Vocabulary Review New geology soil liquefaction tsunami seismic gap
Earthquakes and Society
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4. Earthquake Hazards
Earthquake hazards are factors that determine the severity of damage produced by an earthquake.
Identifying earthquake hazards in an area can sometimes help to prevent some of the damage and loss of life.
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Earthquakes and Society

5. Earthquake Hazards Structural failure
One type of damage caused by earthquakes is called pancaking; shaking causes a building’s supporting walls to collapse and the upper floors to fall one on top of the other like a stack of pancakes.
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Earthquakes and Society

6. Earthquake Hazards Structural failure
If the shaking caused by an earthquake has the same frequency of vibration as the natural sway of buildings of certain heights, those buildings will sway the most during the earthquake. Shorter and taller buildings, however, are less likely to be affected.
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Earthquakes and Society

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8. Earthquake Hazards Land and soil failure
In sloping areas, earthquakes can trigger massive landslides. In areas with sand that is nearly saturated with water, seismic vibrations can cause the ground to behave like a liquid in a phenomenon called soil liquefaction.
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Earthquakes and Society

9. Earthquake Hazards Land and soil failure
Soil liquefaction can cause trees and houses to fall over or to sink into the ground and underground pipes and tanks to rise to the surface.
The type of ground material can affect the severity of an earthquake in an area. Ground motion is amplified in some soft materials, such as unconsolidated sediments. It is muted in more resistant materials, such as granite.
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Earthquakes and Society

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11. Earthquake Hazards Tsunami
Another type of earthquake hazard is a tsunami—a large ocean wave generated by vertical motions of the seafloor during an earthquake.
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Earthquakes and Society

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Tsunami
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13. Earthquake Forecasting
There is currently no completely reliable way to forecast the exact time and location of the next earthquake. Instead, earthquake forecasting is based on calculating the probability of an earthquake.
The probability of an earthquake’s occurrence is based on two factors: the history of earthquakes in an area and the rate at which strain builds up in the rocks.
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Earthquakes and Society

14. Earthquake Forecasting
Seismic risk
The probability of earthquakes in seismic belts is much greater than elsewhere on Earth.
The history of an area’s seismic activity can be used to generate seismic-risk maps.
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Earthquakes and Society

15. Earthquake Forecasting
Recurrence rates
Earthquake-recurrence rates along a fault can indicate whether the fault ruptures at regular intervals to generate similar earthquakes.
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Earthquakes and Society

16. Earthquake Forecasting
Seismic gaps
Seismic gaps are sections located along faults that are known to be active, but which have not experienced significant earthquakes for a long period of time.
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Earthquakes and Society

17. Earthquake Forecasting
Seismic gaps
Earthquakes in 1912 and 1999 happened on either side of Istanbul, Turkey. The earthquakes around the city leave a seismic gap that indicates that an earthquake is likely to occur in that area.
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Earthquakes and Society

18. Earthquake Forecasting
Stress accumulation
The stress accumulated in a particular part of a fault, together with the amount of stress released during the last earthquake in a particular part of the fault, can be used to develop a stress-accumulation map.
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Earthquakes and Society

19. Review Essential Questions Vocabulary
What factors affect the amount of damage caused by an earthquake?
What are some of the factors considered in earthquake-probability studies?
How are different types of structures affected by earthquakes?
Vocabulary
soil liquefaction
tsunami
seismic gap
Earthquakes and Society
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