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Earthquakes:

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Earthquakes:

How to find where they originate…

- 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

- 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

- P waves
- 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)

- Seismograph data (seismograms) will tell us distance from an earthquake epicenter
- We need 3 seismograph readings to find an epicenter

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

- Lag time between P wave and S wave tells us distance
- Fast Runners and Slow Runners...

- http://www.sciencecourseware.com/VirtualEarthquake/VQuakeExecute.html