Seismicity

What is, by definition, an earthquake?

a violent shaking of the Earth's crust

Where do 90% of earthquakes occur?

at plate boundaries

What is the main primary hazard of earthquakes?

shock waves

What are some secondary hazards of earthquakes?

• tsunamis

• liquefaction

• landslides

What are shock waves (seismic waves)?

movements of energy that travel out from the focus of an earthquake

What are the two types of shock waves (seismic waves)?

• body waves

• surface waves

What are the characteristics of body waves?

• travel through the Earth

• P (primary) waves - 3-5km/s

• S (secondary) waves - 2-3km/s

What are the characteristics of surface waves?

• travel along the Earth's surface

• Rayleigh waves - up and down

• Love waves - sideways

What are the characteristics of tsunamis?

• large, displaced volumes of water

• triggered by underwater earthquakes

• often hit without much warning, which can cause high death tolls

• the waves travel very fast in deep water

• can have heights of up to 30m

• very long wavelength out at sea

• very high speed (640 - 960km/h)

• long wave period (10 - 60 minutes betweeen each wave)

• destructive waves

What is liquefaction?

The space between the grains of soil contains air and water. During an earthquake, the shaking causes particles of soil to clump together, which forces water to quickly rise upwards. As the water breaks through to the surface, it floods large areas with wet, sticky sludge.

What are the characteristics of landslides?

• rock dislodged by the shaking of the ground

• falling rocks that can destroy buildings and cause injuries

• move downslope quickly

• cause approx. $3.5 billion of damage per year in the US