8.2 Measuring Earthquakes

Earthquake Waves

8.2 Measuring Earthquakes

Seismographs are instruments that record earthquake waves.

Seismograms are paper records of recorded ground motion made by seismographs.

Seismographhttp://www.youtube.com/watch?v=DX5VXGmdnAg

Seismogram

Fastest waves Slowest waves and most destructive

8.2 Measuring Earthquakes

3 kinds of waves• P waves

- Have the greatest velocity of all earthquake waves

- Are push-pull waves that push (compress) and pull (expand) in the direction that the waves travel

- Travel through solids, liquids, and gases

http://www.jclahr.com/science/earth_science/tabletop/pslnkmv.html#

“P waves move through the entire earth- crust, mantle, and core) like a slinky”

Earthquake Waves

8.2 Measuring Earthquakes

• S waves- Seismic waves that travel along Earth’s outer layer

- Slower velocity than P waves

- Shake particles at right angles to the direction that they travel

- Travel only through solids

“S waves move through the ground like a rope”

Seismic Waves Paths Through the Earth

S

SS

P

P

Locating an EarthquakeHow far is your location from the epicenter?

8.2 Measuring Earthquakes

• Distance from you to epicenter is found by the measuring difference in the arrival times between P and S waves.

Locating an Earthquake3 seismographs are required to correctly locate the epicenter of an earthquakeEpicenter is located where three circles intersect

Measuring Earthquakes-

8.2 Measuring Earthquakes

Momentum Magnitude• Moment magnitude is the most widely used

measurement for earthquakes • Estimates the energy released by earthquakes.

• Measures very large earthquakes

Earthquake Magnitudes

Some Notable Earthquakes

Modern Earthquakes

• 7.2 Turkey in 2011 572 deaths• 9.0 Japan in 2011 18000 deathshttp://www.youtube.com/watch?v

=fraPBV4kzvI