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Earthquakes What is an earthquake? • Used to describe both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip • Caused by sudden stress changes in the earth. • Usually occur at or near plate boundaries • Some are strong and can be felt on the surface, some are weak and can only be felt by a seismograph Three Types of Faults Strike-Slip Reverse Normal 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. Elastic Rebound – deformed rock goes back to its original shape http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Focus – point inside the Earth where an earthquake begins Epicenter – point on Earth’s surface above focus 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 Earthquake Vocabulary Seismology – The study of earthquakes Seismograph – An instrument that records vibrations in the ground and determines the location and strength of an earthquake Seismologist – A person who studies earthquakes Seismic Wave – A wave of energy that travels through the Earth and away from an earthquake in all directions Seismogram – a tracing of earthquake motion that is created by a seismograph Primary Waves (P Waves) • A type of seismic wave that compresses and expands the ground • The first wave to arrive at a seismograph 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 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 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 Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM How are Earthquakes Measured? Richter Scale How are Earthquakes Measured? Mercalli Intensity Scale Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf Earthquake Waves & Earth’s Interior Seismic Waves in the Earth http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM
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