The Earth’s Crust Seismic Waves Friday, November 23, 2018Friday, November 23, 2018

There are three kinds of seismic waves produced by an earthquake:

1. P - waves – “primary waves” - the fastest waves (they are compression waves) They can travel through solids, liquids, and gasses.

2. S - waves “secondary waves – these are slower than p waves and occur as a side to side wave. These waves travel only through solids.

3. L- waves – “long waves” or “surface waves”. These waves travel as a double wave along the surface of the earth. They are the slowest waves but they cause the most damage.

Locating Earthquakes The time between the p-wave and the s-wave is used to calculate how far away the earthquake is.

Let’s say station #1 knows the earthquake happened 200 kms away.

Let’s say station #1 knows the earthquake happened 200 kms away.

But 200 kms in what direction?

If a second station reports it as 75 kms away, they can draw a circle and see where it intercepts the first circle.

But that still doesn’t pinpoint the location – it could have happened at either spot where the two circles touch.

But a third station removes all doubt as to where it happened.

But a third station removes all doubt as to where it happened.

Three seismographs are needed to pin- point the source of an earthquake. Seismograph video

Focus – the place deep in the crust where the earthquake begins (source of primary and secondary waves)

Epicentre – the surface location directly above the focus (source of surface waves)

Tsunami – a tidal wave caused by an underwater earthquake subduction tsunami Once and future tsunamis Tsunami Tsunami – open ocean

tsunami

Tsunami devastation

Pacific Tsunami