1. Earthquake factoids 95% of earthquakes occur on plate boundaries
Over 1 million occur on Earth each year. That’s about one every 30 seconds.
They tell us a lot about the interior of the earth.
. epicenter
(the place on the surface above the focus)
. focus
(the spot inside the earth where the earthquake
Actually occurs)

2. P Waves AKA “primary” or “compressional” waves
The fastest wave (so first to arrive)
like a slinky or ten-car pile up
can travel through solids, liquids or gases
the denser the medium, the faster they travel

3. S Waves AKA “shear” or “secondary” The second to arrive
Side to side motion
Travel only through solids
The denser the medium, the faster they go.
*****How we know the outer core is liquid! (S waves are stopped)

4. What they’ve taught us The outer core is liquid (S waves stop dead)
The Earth’s density increases with depth (all waves go faster and faster with increasing depth)
We can find the distance to and location of an epicenter because P and S waves travel at different velocities (P wave is constantly gaining..the bigger the “lead” the greater the distance)

5. Seismograph
Detects Earthquake waves

6. How Earthquakes are Measured
Richter Scale: measures strength or magnitude
Mercalli: Measure INTENSITY, or what people saw, heard and felt

7. Richter Scale

8. Mercalli Scale

9. Seismogram