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)

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

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)

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)

Seismograph Detects Earthquake waves

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

Richter Scale

Mercalli Scale

Seismogram