Describing and Measuring Earthquakes

10SCIE - Geology

Finn LeSueur

2019

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

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

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

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