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CHAPTER 7 EARTHQUAKES 7.1 Notes What are earthquakes? • earthquakes - movements or shaking of the ground when rock (plates) move suddenly and release energy. • aftershock – a release in energy after an earthquake Where do most earthquakes happen? On plate boundaries What causes earthquakes? • Movement of the tectonic plates • When the plates break at a fault located at a boundary How do we know there are different layers of the Earth? • Because of seismic waves from earthquakes • Seismic waves travel through solids faster than liquids • Seismic waves change direction when they change the material they are going through (from a solid to a liquid) • elastic rebound – the sudden return of deformed rock to its normal undeformed shape. (i.e. rubber band) 7.1 Notes • seismic waves – waves of energy that travel through and on the Earth • 2 types of seismic body waves: 1. P-waves (primary waves) – the fastest seismic waves that travel through solids, liquids, and gases • (the P-waves move like a slinky) 2. S-waves (secondary waves) – the second fastest seismic waves that travel through solids • • (the S-waves move like a snake) 1 type of seismic surface waves : 1. L-waves (land & last waves) – the slowest and most destructive seismic waves that travel only on the surface/land • (the L-waves move in big slow circles)