1. Earthquakes

2. What Causes Earthquakes?
The sudden formation of a new fault
Sudden slip on an already existing fault (#1 cause of)
Movement of magma in, or explosion of, a volcano
Plus more! – giant landslides
Meteorite impact
Underground nuclear-bomb test!

3. The place within the Earth where rock ruptures and slips, is the focus of the earthquake.
The point on the surface of the Earth that lies directly above the focus is the epicenter.

4. Seismic Waves
Seismologists distinguish different types of seismic waves:
1. Compressional waves (P-waves): waves that cause particles of material to move back and forth parallel to the direction of the wave itself – push and pull

5. 2. Shear waves (S-waves): waves that cause particles of material to move back and forth perpendicular to the direction of the wave itself

7. Different waves travel at different velocities:
P-waves travel the fastest (arriving first)
S-waves travel 60% the speed of P-waves
Friction absorbs energy as waves pass through a material, so the amount of energy carried by seismic waves decreases the farther they travel

8. How to measure Earthquakes
Researchers use an instrument, called a seismometer, to systemically measure the ground motion from an earthquake
They measure the vertical and horizontal ground motion

9. An earthquake record produced is called a seismogram
The horizontal axis represents time and the vertical axis represents the amplitude of the seismic waves.

10. To determine the location of a epicenter, seismologists calculate the distance between the epicenter and the seismometer station – using the difference in time between the P and S waves (using time vs. distance graphs!! Yay Grade 10 Science!)
Vertical axis time – horizontal axis distance

11. Using triangulation, seismologists take the distance from THREE stations!
The epicenter lies at the intersection of the three circles!

12. Earthquake Magnitude Scales
The magnitude of an earthquake is a number that represents the maximum amplitude of ground motion that is measured by a seismometer.
The Richter scale (1935!) is based on the maximum amplitude of motion that is recorded at a station about 100 km from the epicenter.
These days, seismologists actually use several different scales! (moment magnitude scale) Because the original scale only works well for shallow quakes

13. All magnitude scales are logarithmic, meaning that an increase of one unit of magnitude represents a tenfold increase in max. amplitude!
Example: an 8 magnitude earthquake results in ground motion that is 10 times greater than a 7 magnitude
Largest recorded quake: 9.5 Mw In 1960 Chile

16. Hyperlink to US geological survey! Maps! Latest Earthquakes