Transcript Earthquakes
Earthquakes What Is An Earthquake? Click here to find out 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 plate activity, http://eqseis.geosc.psu.edu The map above shows the distribution of earthquakes with magnitudes greater than 5.0 that occurred between 1965 and 1995. Three Types of Faults Strike-Slip Animation of fault movement Reverse Normal Normal fault Pulls on the crust stretching rock so that it becomes thinner (like pulling on bubble gum) = Occurs when plates are moving apart Hanging wall Foot wall Results in hanging wall slipping downward animation What type of fault? normal Hanging wall Foot wall http://www.bgs.ac.uk/eqr/GeoD_Structures.htm What causes earthquakes? • Tectonic plates move past each other causing stress. Stress causes the rock to deform – What type of fault boundary is this? transform – What type of stress is shown? shearing Strike – slip fault Rocks on either side of fault slip past each other sideways with little up or down motion What type of stress is produced? Occurs at a transform plate boundary Animation of strike-slip motion Fault rupture across road in western Kaynasli, right-lateral strike slip displacement was about 4.0 m (13 feet) at this location http://www.geerassociation.org/GEER_Post%20EQ%2 0Reports/Duzce_1999/kaynasli1.htm Reverse fault Pushes on the crust squeezing rock until it folds or breaks (like a trash compactor) = Occurs when plates are moving together Hanging wall Foot wall Results in hanging wall slipping upward animation What type of fault? reverse Hanging wall Foot wall http://geologicalintroduction.baffl.co.uk What type of fault? http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Focus – 1. point inside the Earth where an earthquake begins Epicenter – 2. point on Earth’s surface above focus where earthquake is FELT most strongly 2 1 How Seismographs Work A seismograph is an instrument used for recording the intensity and duration of an earthquake. the pendulum remains fixed as the ground moves beneath it http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Earthquakes • How are earthquakes measured? Seismogram – seismic wave display record Seismograph machine Seismic Waves 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 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 Animation of wave types 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 Typical Seismogram How much time elapsed between the arrival of the P wave (start) and the arrival of the S wave (finish)? start http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt finish Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Locating Earthquakes http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Now you are going to be seismologists and locate an Earthquake http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Go to: http://tinyurl.com/11quake13 Click here to go to virtual earthquake site National Geographic earthquake information How are Earthquakes Measured? Richter Scale A logarithmic scale used to express the total amount of energy released magnitude of an ___________ earthquake. Its values typically fall between 0 and 9, with each increase of 1 representing a _________ increase 10-fold in energy. How are Earthquakes Measured? Mercalli Intensity Scale A scale of earthquake intensity based on ___________ observed effects and ranging from I (detectable only with instruments) to XII (causing almost total destruction). Click for Interactive Demo Go to http://tinyurl.com/13quake13 Earthquake Waves & Earth’s Interior Seismic wave animation Seismic Waves in the Earth Click here for animation http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Tsunamis Click here for explanation of a tsunami http://www.uwgb.edu/dutchs/EarthSC-102VisualsIndex.HTM Formation of a tsunami a large ocean wave usually caused by an underwater earthquake or a volcanic explosion. PBS –tsunami animation http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt With typical waves, water flows in circles, but with a tsunami, water flows straight. This is why tsunamis cause so much damage! Click here for Japan helicopter view of tsunami Tsunami Warning System http://isu.indstate.edu/jspeer/Earth&Sky/EarthCh11.ppt Review Questions 1. A large ocean wave usually caused by an underwater earthquake or a volcanic explosion. tsunami 2. Used to describe both a sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip earthquake How are Earthquakes Measured? 3. Which one uses a logarithmic scale to express the total amount of energy released or magnitude of an earthquake. Richter Scale 4. Which uses a scale of earthquake intensity based on observed effects and ranging from I (detectable only with instruments) to XII (causing almost total destruction). Modified Mercalli Scale What type of fault is shown by each picture? 1. 2. Normal Reverse 3. Transverse or strike-slip S-wave Surface or Love waves What type of fault? Source: indiana.edu http://geologicalintroduction.baffl.co.uk A Hanging wall has moved upward Reverse fault B Strike –slip or transverse fault Focus – 1. point inside the Earth where an earthquake begins Epicenter – 2. point on Earth’s surface above focus where earthquake is FELT most strongly 2 1 People walk along a damaged road in the province of Bohol on Tuesday, October 15, 2013. Do you think this was a major earthquake? Why or why not? Yes, it was a major quake. It crumbled a number of buildings Such as this church 7.1 magnitude earthquake hit the Philippines Earthquakes 3. Surface 1. P-wave 2. S-wave Seismogram 4. ____________ seismic wave display record 5. Seismograph __________ machine