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What are Earthquakes? Where Do Earthquakes Occur? • • Earthquakes occur near tectonic plate edges. A break in the Earth’s crust where plates slide past each other is called a fault. The Three Types of Faults Plate Motion Transform Boundary (shearing) Convergent Boundary (compression) Divergent Boundary (tension) Fault Name Strike Slip Fault Reverse Fault Normal Fault Fault Movement What Causes Earthquakes? • Caused by deformation of the plates. Rocks that are under stress and stretched will eventually break, causing an earthquake. • Elastic Rebound = when rocks suddenly break and spring back to their original shape. How Do Earthquake Waves Travel? There are 3 types of seismic waves: 1. Primary Waves: P-Waves 2. Secondary Waves: S-Waves 3. 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 P-Wave Secondary Waves (S-Waves) • 2nd fastest to P-waves • Vibrate side to side and up and down • Can only move through solids S-Wave 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! Surface Wave Diagram 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 Earthquake Location