1. 19.4 – Earthquakes & Society

2. Damages Death and injuries Collapse of buildings Landslides Fires
Explosions
Flood waters

3. Earthquake Hazards
Identifying hazards can prevent some damage and loss of life
Design of building can affect damage
Unreinforced buildings made of concrete crumble
Wood structures are more resilient

4. Structural Failure Buildings are destroyed as ground shakes
Ground floor walls fail and cause upper floors to fall and collapse as they hit the lower floors
Pancaking

5. Height also impacts building strength
If frequency of vibration is close to natural sway = sways most violently
Ground vibrations
Too rapid = do not impact tall buildings
Too slow = do not impact shorter buildings

6. Land & Soil Failure Sloping areas create landslides
Soil liquefaction = sand is nearly saturated with water
Vibration cause ground to behave like liquid
Surface waves are amplified in soft materials
Muted in more resistant (granite)

7. Tsunami
Large ocean wave generated by vertical motions of seafloor during Earthquake
Caused by faulting and underwater landslides
Faulting causes a sudden drop or rise in ocean floor and the mass of water changes
Violent water movements create long, low waves
In shallow water, waves become high breakers larger than 30 meters in height

9. Earthquake Forecasting
Based on calculating probability of earthquake
Uses history of earthquakes and rate strain builds up
Seismic risk
Probability is greater along Seismic Belt
Pattern of past activity is reliable indicator

10. Earthquake Forecasting
Recurrence risk
Indicate whether fault ruptures at regular intervals
San Andreas
6 earthquakes every 22 years between
1987, 90% probability of an earthquake occurring
6.6 Magnitude earthquake occurred November 1987

11. Earthquake Forecasting
Seismic gaps
Sections along faults that are known to be active but have not experienced significant earthquakes
Stress Accumulation
Rate at which stress builds up in rocks

12. In-Class Assignment/Homework
Pg. 555 #1-10 and 17-26
Work with a partner put both names on paper and turn into tray when finished