Transcript Earthquakes and Seismic Waves

Essential Question
 How do earthquakes shape the earth?
Earthquakes and Seismic Waves
Caused by pressures generated
through plate tectonics.
Plates try to move but cannot.
As pressure increases rock breaks along
a fault generating an earthquake.
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Location of Earthquake
 Focus
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The point in the earth’s
interior where the rocks
break and release
energy.
Origin of earthquake.
 Epicenter
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The point on the earth’s
surface directly above
the focus.
Seismic Waves
 Seismic Waves are a release of energy in the
earths crust due to stress.
 All seismic waves leave at the same time.
Seismic Wave Animation
 http://www.classzone.com/books/earth_scien
ce/terc/content/visualizations/es1002/es1002
page01.cfm?chapter_no=visualization
Primary Waves
 Called P-waves
 First to arrive
 Travel through earth’s core
 Travel fastest 6-7 Km/sec
 Cause ground to compress and stretch.
Secondary Waves
 Called S-waves
 Second to arrive
 Cannot travel through earth’s core
 Slightly slower about 3.5 Km/sec
 Cause ground to move up and down.
Surface Waves
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Last to arrive
Only travel on surface/cause the most damage
Slowest about 2.5 Km/sec
Cause ground to move in a rolling motion or sideto-side motion.
See Wave Simulation
Video: Seismic Waves
Locating an Epicenter
 P,S, and L waves do not travel at the same speed.
 As the waves travel the distance between the P and
S waves increases.
 The time interval between the P and S waves is
converted to distance on a graph.
 Doing this in three locations allows you to
triangulate the earthquakes epicenter.
How to find the Epicenter of an
Earthquake
http://quake.wr.usgs.gov/info/eqlocation/index.
html
Measuring Earthquakes
 Magnitude
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A measure of the energy released by an
earthquake.
Richter scale often used
An increase in one is 10 times the ground motion
An increase in one is 32 times the energy
released.
Seismic Activity in our Area
 http://www.ess.washington.edu/SEIS/PNSN/
INFO_GENERAL/eqhazards.html