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Transcript
Bell Work 12/5/14 On your desk: 1. P.R.I.D.E card 1. How do you get a spaghetti noodle to bend 2. I.N. and not break? 3. Pencil/Pen 2. How do you break a spaghetti noodle? 4. Summary 3. How can you apply this concept to the lithosphere? Earthquakes Earthquakes Earthquake- a movement of Earth’s lithosphere (rigid solid) that occurs when rocks in the lithosphere suddenly shift, releasing stored energy! They’re Caused by a Build-up of STRESS in Earth’s Crust As tectonic plates move, they cause stress in the crust, which in turn produces folds and faults. Stress in Earth’s Crust Stress (in earthquake terms) a force that squeezes rocks together, stretches or pulls them apart, or pushes them in different directions. Does stress occur at… Convergent plate boundaries? Divergent plate boundaries? Transform boundaries? Stress = Folds and Faults! Folds=Plastic Deformation A bend in layers of rock in response to stress Form where rocks are squeezed together, but do not break This doesn’t lead to earthquakes Faults Faults A fracture, or break, in Earth’s lithosphere Blocks of rocks move (scrape) past each other San Andreas Fault Where do earthquakes occur?? Most earthquakes happen along plate boundaries Ring of Fire- belt around the Pacific plate Over 75% of all earthquakes occur here http://www.cleanvide osearch.com/media/ac tion/yt/watch?v=gRlj5 vjp3Ko Why Exactly do Earthquakes Happen? Elastic Rebound-The sudden return of elastically deformed rock to its original shape Elastic rebound occurs when more stress is applied to rock than the rock can withstand. During elastic rebound, energy is released as an earthquake How do we measure earthquakes? 2 different scales Seismic waves vs destruction! Measuring Earthquakes Modified Mercalli scale- Rates earthquakes based on observations of the intensity of ground shaking and damage Modified Mercalli Scale San Francisco earthquake of 1906 was an 11 Measuring Earthquakes Richter scale- Rates earthquakes based on measurements of the times and amplitudes of the seismic waves Created by Charles Richter in the 1930’s How exactly do we Measure earthquakes? To measure earthquakes and pinpoint their epicenters, geologists record seismic waves using seismographs Seismograph a device that can detect and record seismic waves Creates a seismogram What is a Seismogram? Seismogram A tracing of earthquake motion created by a seismograph Seismic Waves – the reason earthquakes are Dangerous! Seismic waves the energy released during an earthquake carried by vibrations 3 main types: P waves S waves Surface waves Seismic Waves P waves (primary waves)- longitudinal waves similar to sound waves Move through solid and liquid material Compress and expand the ground Similar to an accordion or a slinky Seismic Waves S waves (secondary waves)- Transverse waves, like light. They cannot travel through liquids S waves can’t pass through liquid…this is why we know the outer core is a liquid! Seismic Waves Surface Waves- develop when seismic waves reach Earth’s surface Move more slowly than P and S waves Produce larger movements Create greater damage Where do Earthquakes Happen? Earthquakes- occur because stress forces have exceeded the strength of rock. Focus- the location beneath Earth’s surface where an earthquake begins. Epicenter- the location on Earth’s surface directly above the focus. The S-P time method… How it’s used: Collect several seismograms from different seismographs (at different locations) Plot seismograms on a distance-time graph Draw circles around the locations based on the distance-time graph At the point where 3 lines intersect is the earthquake epicenter 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 Adopt a Volcano!!