Earthquakes
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Earthquakes Today’s Journey • 0507.7.1 Create a model to illustrate geologic events responsible for changes in the earth’s crust. • 0507.7.2 Prepare a chart to compare how volcanoes, earthquakes, faulting, and plate movements affect the earth’s surface features. • State Performance Indicators • SPI 0507.7.1 Describe internal forces such as volcanoes, earthquakes, faulting, and plate movements that are responsible for the earth’s major geological features such as mountains, valleys, etc. 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 (Transform Boundaries) • Caused by volcanic or magmatic activity, • Caused by other sudden stress changes in the earth. Three Types of Faults Strike-Slip Thrust Normal What causes earthquakes? • Tectonic plates move past each other causing stress-built up energy on a fault. Stress causes the rock to deform. – The amount of energy released depends on how much rock breaks and how far the blocks of rock move. Focus – point inside the Earth where an earthquake begins; most of these are less than 45 mi below the surface. Epicenter – point on Earth’s surface above focus Where do you think would the intensity be strongest? • The hardest shaking is going to be at the epicenter of an earthquake because the seismic waves at the focus of an earthquake are the strongest and the epicenter is directly above it. – These seismic waves spread out from the focus. As they do, their energy grows weaker. 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 There are two types of Seismic Waves • Body Waves-move through the “body” of the Earth or the inside. – They can pass through rock and liquid. • Surface waves-move along Earth’s surface. Primary Waves (P Waves) • A type of seismic body wave that compresses and expands the ground • The first wave to arrive at an earthquake • When they reach the surface, they cause rock to move back and forth. http://daphne.meccahosting.com/~a0000e89/insideearth2.htm Secondary Waves (S Waves) • A type of seismic body wave that moves the ground up and down or side to side http://daphne.meccahosting.com/~a0000e89/insideearth2.htm Comparing Seismic Waves Make a quick venn diagram to compare the two types of body waves that occur due to an earthquake. Surface Waves • Move along the Earth’s surface • Known as L waves • 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 because they make the ground swell and roll like ocean waves. • Do not travel too far from the epicenter. 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 6: Very Strong 7: Severe 2-4: 8: Violent Moderate- Weak 9: Extreme 5: Strong 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 Bill Nye Earthquake Clip Seismic Waves in the Earth http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Tsunamis http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Formation of a tsunami http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt Today’s Journey • 0507.7.1 Create a model to illustrate geologic events responsible for changes in the earth’s crust. • 0507.7.2 Prepare a chart to compare how volcanoes, earthquakes, faulting, and plate movements affect the earth’s surface features. • State Performance Indicators • SPI 0507.7.1 Describe internal forces such as volcanoes, earthquakes, faulting, and plate movements that are responsible for the earth’s major geological features such as mountains, valleys, etc.
