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Earthquakes:. How to find where they originate…. 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. Graph vs Gram.

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Earthquakes

Earthquakes:

How to find where they originate…


Terminology
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


Graph vs gram
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


S waves vs p waves
S waves vs P waves

  • 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)


How do we locate earthquakes
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


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


How do we determine distance
How do we determine distance?

  • Lag time between P wave and S wave tells us distance

  • Fast Runners and Slow Runners...




Try the activity
Try the activity:

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


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