Ngā Whāinga Ako

• Describe how earthquakes travel through the Earth’s rust
• Describe the characteristics of P, S and L seismic waves

Types of Earthquake Waves

• 3 different types of waves move through the Earth’s crust during an earthquake
• P, S and L waves

P Waves

• They are the first to reach the surface
• They travel the fastest (approx. $8\frac{km}{s}$)
• They squeeze and stretch the rock

S Waves

• They are the second wave to hit the surface
• They move at around $5\frac{km}{s}$
• They make the ground move up and down (and side to side)

L Waves

• Also called surface waves
• They are the last waves to hit the surface
• They do the most damage as they travel near the surface
• They move at around $4\frac{km}{s}$

Whakakite: Slinky

• Use a slink to demonstrate P and S type waves

Ngā Whāinga Ako

• How do we measure earthquakes?

Measuring Earthquakes

• To measure earthquakes we use a seismograph
• The inertia of the mass keeps the pen still as the ground moves below it, creating graph

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The energy ________ travels outwards as _____. The point in the Earth’s crust where this happens is called the _____, the point directly above the focus on the Earth’s surface is called the _________. Seismologists use ___________ to determine the magnitude and ________ of earthquakes.

Words: seismographs, focus, location, waves, epicentre, released

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• Hypocenter (focus): The point where the earthquake starts
• Epicenter: The point on the surface directly above the hypocenter

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We can see that the epicenter is the closest place on the surface to the focus. This is why the s waves get there first.

Richter Scale

• Uses numbers from 1 to 10
• Each number has 32x more energy than the previous
• It doesn’t really work because it was designed for use in Southern California for their particular geology

Mercalli Intensity Scale

• This scale uses the impact of the earthquake on the surface, rather than measuring the energy specifically