Transcript Earthquakes
Earthquakes Lesson 4.8 What is an earthquake? • Tectonic plates move past each other causing stress. Stress causes the rock to deform – When the stress is too great, the rock will rupture and cause and earthquake – Released as seismic wave Focus – point inside the Earth along a fault where an earthquake begins Epicenter – point on Earth’s surface above focus What causes earthquakes? • Tectonic plates move past each other causing stress. Stress causes the rock to deform – Plastic deformation – does not cause earthquakes – Elastic deformation – rock stretches then reaches a breaking point, releasing energy. • Rock returns to nearly the same shape after the stress is removed- Elastic Rebound Elastic Rebound – deformed rock goes back to its original shape http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Where do earthquakes happen? • At divergent boundaries, tension stress causes normal faults to form. Earthquakes tend to be shallow because the crust is thin. Copyright © Houghton Mifflin Harcourt Publishing Company Where do earthquakes happen? • At convergent boundaries, rock is squeezed, causing reverse faults to form. Earthquakes can be very strong and deep. Copyright © Houghton Mifflin Harcourt Publishing Company Where do earthquakes happen? • At transform boundaries, shear stress pushes tectonic plates in opposite directions. Earthquakes tend to be relatively shallow. Copyright © Houghton Mifflin Harcourt Publishing Company Primary Waves (P Waves) • A type of seismic wave that compresses and expands the ground • The first wave to arrive at an earthquake http://daphne.meccahosting.com/~a0000e89/insideearth2.htm Secondary Waves (S Waves) • A type of seismic wave that moves the ground up and down or side to side http://daphne.meccahosting.com/~a0000e89/insideearth2.htm Comparing Seismic Waves Earthquake Waves & Earth’s Interior How are Earthquakes Measured? Richter Scale Surface Waves • Move along the Earth’s surface • Produces motion in the upper crust – Motion can be up and down – Motion can be around – Motion can be back and forth • Travel more slowly than S and P waves • More destructive How Seismographs Work the pendulum remains fixed as the ground moves beneath it http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Typical Seismogram http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt How do scientists calculate how far a location is from the epicenter of an earthquake? • Scientists calculate the difference between arrival times of the P waves and S waves • The further away an earthquake is, the greater the time between the arrival of the P waves and the S waves Tsunamis http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Tsunami • An earthquake under the water cause vertical movement of the sea floor – Moves an enormous amount of water • May cause a tsunami • Tsunami- a series of extremely long waves that travel quickly across the ocean – Travel outwards in all direction from point where earthquake occurred Tsunami Approach • As the wave approaches the shoreline, it increases in size – Can be taller than 30 M – Destroy anything in their path • Can cause: – Floods – Polluted water supplies – Large amounts of debris Formation of a tsunami Tsunami Animation http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt Tsunami Warning System http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt