Transcript Earthquakes
Earthquakes! **Adapted from www.middleschoolscience.com 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 volcanic or magma 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. Stress causes the rock to deform, break, and/or move 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 It’s a weighted pen writing on a rolling drum of paper. the pendulum remains fixed as the ground moves beneath it Normally everything would move, but…. …this mass, like the pen, has inertia and so resists motion. Typical Seismogram http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt Primary Waves (P Waves) • PUSH-PULL PATTERN! – A type of seismic wave that pushes & pulls the ground • The FIRST wave to arrive from an earthquake—travels the fastest! • Travels Parallel to the direction the wave travels 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 (perpendicular) to the direction the wave travels • Slower! • More destructive to buildings http://daphne.meccahosting.com/~a0000e89/insideearth2.htm Comparing Seismic Waves **P & S Wave song: http://www.youtube.com/watch?v=w3NLexYxR7g Surface Waves • Move along the Earth’s surface – ROLL OUT! Motion can be up and down, around & back & forth • Travel more slowly than S and P waves – Last to arrive • Most destructive to structures 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 difference between the arrivals of the P waves and the S waves Locating Earthquakes Question: Where could the EQ be? 1. Find the difference in the arrival times, or lag time ( t ), of the P & S waves. r Difference in arrival times 2. Find the distance to the EQ using the lag time and this Time/Distance graph. S-wave Time ( t) P-wave 3. Use the distance from the EQ as the radius (r) for this circle. Answer: Anywhere along the blue line. (not much help) Distance (km) Locating Earthquakes Question: Where could the EQ be, now? **Let’s get someone else that has readings for this EQ to help out… (Same procedure) Difference in arrival time \Arrival diff.\ Answer: Where the green and blue circles cross. (Better, but still a 50-50 change of going to the right place to find the EQ.) Locating Earthquakes So, no more guessing– Question: where is the actual EQ ? **If you get 3 people working on this puzzle, now you can triangulate. Difference in arrival time \Arrival diff.\ \Arrival time diff. \ Answer: Where all 3 circles intersect How are Earthquakes Measured? Richter Scale-measures energy How are Earthquakes Measured? Mercalli Scale-measures damage Click Link for Interactive Demo http://elearning.niu.edu/simulations/images/S_portfolio/Mercalli/Mercalli_Scale.swf Earthquake Waves & Earth’s Interior **See how seismic waves move through the Earth’s layers here (Shadow zone): http://www.classzone.com/books/earth_science/terc/content/visualizations/es1009/es1009page01.cfm 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 Tsunami Warning System http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt