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Earthquakes. What are Earthquakes?. Earthquakes: the sudden movement of Earth’s Crust!. Where Do Earthquakes Occur?. Mostly occur near tectonic plate A break in the Earth’s crust where movement occurs is called a fault. The Three Types of Faults. Transform Boundary ( shearing ).
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Where Do Earthquakes Occur? • Mostly occur near tectonic plate • A break in the Earth’s crust where movement occurs is called a fault.
The Three Types of Faults Transform Boundary (shearing) Strike Slip Fault Convergent Boundary (compression) Reverse Fault Divergent Boundary (tension) Normal Fault
What Causes Earthquakes? • Deformation of the plates! Rocks that are under stress can eventually break = EQ! • Elastic Rebound = when rocks suddenly break and spring back to their original shape. Check out the DEMO: http://projects.crustal.ucsb.edu/understanding/elastic/rebound.html
How Do Earthquake Waves Travel? There are 3 types of seismic waves: • Primary Waves: P-Waves • Secondary Waves: S-Waves • Surface Waves Click Here for animation!
Primary Waves (P-Waves) • Move the fastest • Move in a straight line • Compress and expand like an accordion • Move through solids, liquids, and gases
Secondary Waves (S-Waves) • 2nd fastest • Vibrate side to side and up and down • Can only move through solids
Surface Waves • Result of P-waves and S-waves when they reach the surface • Only travel in the crust! • Slowest seismic waves • Make the ground roll like ocean waves • Responsible for surface damage and falling buildings.
Surface Waves Notice the top is moving more than the bottom!
How are earthquakes measured? • Seismograph: records ground movements of earthquakes • The pendulum sits still while the ground moves. http://www.wwnorton.com/college/geo/egeo/flash/8_3.swf
What is the seismograph measuring? • Epicenter: Center of earthquake ABOVE GROUND • Focus: Point where rocks break UNDERGROUND
Earthquake Effects - Ground Shaking Loma Prieta, CA 1989 KGO-TV News ABC-7
Earthquake Effects - Ground Shaking Kobe, Japan 1995
Earthquake Effects - Ground Shaking Kobe, Japan 1995
Earthquake Effects - Surface Faulting Landers, CA 1992
Earthquake Effects - Landslides Source: National Geophysical Data Center Turnagain Heights, Alaska,1964 (upper left inset); Santa Cruz Mtns, California , 1989