1. How to find where they originate…
Earthquakes:
How to find where they originate…

2. Terminology: Epicenter vs. Focus
Focus is the point beneath Earth's surface where rock breaks under stress (or plates shift) and causes an earthquake.
Epicenter is the point on land, directly above the focus

4. Graph vs Gram
Seismograph are instruments that measure and record motions of the ground, including seismic waves generated by earthquakes, nuclear explosions, and other seismic sources
Seismogram is a graph output by a seismograph. It is a record of the ground motion at a measuring station as a function of time.
How Seismograph Works

6. S waves vs P waves P waves S waves S wave P wave Animation (slinky)
Primary Waves
Named that because they leave the focus first
Travel faster than S waves
Compression Waves
S waves
Secondary Waves
Named that because they leave the focus second
Travel slower than P waves
Transverse Waves
S wave P wave Animation
(slinky)

7. How do we locate earthquakes?
Seismograph data (seismograms) will tell us distance from an earthquake epicenter
We need 3 seismograph readings to find an epicenter

8. 1400 km from Denver, 2600 km from Houston, 4000 km from Miami

9. How do we determine distance?
Lag time between P wave and S wave tells us distance
Fast Runners and Slow Runners...

11. How to read a Seismogram

12. Use lag time to figure out distance traveled

14. Try the activity: