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Chapter 6 Lesson 1 Plate Boundaries & Earthquakes Type of Boundary Description of Movement Description of Earthquake Divergent Pulling apart of stretching Shallow; relatively small in size Convergent Pushing Together Deep; largest earthquakes ; historically they have been the most destructive earthquakes Transform Scrape past one another Shallow; major earthquakes on continents shallow focus produces severe shaking- that is what causes dangerous earthquakes to occur Earthquakes Away from Plate Boundaries • • Some earthquakes occur away from plate boundaries So, they will unexpectedly happen in the middle of continents & they can be dangerous Chapter 6 Lesson 2 What are Seismic Waves? • These are the waves of energy that are produced at the focus of an earthquake How do they travel? • • seismic waves move outward from the focus in all directions an earthquake epicenter is the point on Earth’s surface directly above the earthquake focus Types of Seismic Waves 1.P-Waves • compressional waves that move rock parallel to the direction the wave is moving • fastest seismic waves 2.S-Waves • shearing waves that move rock back and forth perpendicular to the direction the wave is moving • about 60% as fast as P-waves 3.Surface Waves •energy (from the p- and s-waves) that get trapped in the upper areas of Earth's crust •slowest type of seismic wave •usually cause stronger shaking than p-and s-waves (often most destructive type of wave) Using Seismic Wave Data • Speed of Seismic Waves • • S-wave is always behind P-wave Surface wave arrives last • Path of Seismic Waves the different paths each wave takes, causes them to come reach us faster or slower • • Mapping Earth’s internal surface the densities of rock increase with depth as pressure increases. This makes the paths of the waves change as they pass through Earth • •