Earthquakes 5: Earthquake forecasting and survival

Earthquake prediction

• forshocks

• rapid ground deformation

• strange animal behavior etc

how successful are precursors in earthquake prediction??

precursors such as: (foreshocks, rapid ground deformation, rapid changes in water table, unusual animal behaviour)

not accurate. ex. many large earthquakes do not have foreshocks

prediction vs forecast

prediction: vancouver will have an earthquake October 20, 9:30 pm

Forecast: less specific- 10% probability of mag 9 earthquake striking in 90 years

earthquakes occur along

1) plate boundary (subduction interface)

2) subducting plate

3) in the overriding plate

San Andreas Plate

• on the pacific plate

• 1906 sanfrancisco earthquake

Juan de Fuca Plate

• north of san andreas

• january 26 1700 mag 9 earthquake

• caused the “ghost forest” from tsunami

Seismic Gap hypothesis

A gap of seismic activity that occurs before many earthquakes start beggining.

• Lorieta Prieta Gap

• Rupture Zone

  • possible way to forecast earthquakes

  • patches along active fault zone that are seismically quiet

Oral history of Cascadia people

Huu-ay people’s story of mag 9 earthquake matches japan 1700 tsunami oral history

afterschock warning

• expect 3-4 minutes of very strong lateral shaking

• with many aftershocks occurring for months afterward

Real time warning system

alarm goes out when P waves are detected by seismometers near epicentre. Warning time = difference between P and S waves arrival times @ gven location

preaparation

• infrastructure

• communication systems

• emergency evacuation kit

• turn off gas and water

Earthquake Forecasting

Application of statistics

• yield likelihood or risk of earthquake in given location.

• return period/ recurrence intercal

After 3-4 minutes of strong lateral shaking expect __ afterwards

months of aftershocks

Why was March 11 earthquake death toll high?

underestimated size of earthquake and tsunami, communications were down when they tried to send out a second warning