Slide 1Created by C. Ippolito May 2009 Updated 5/9/2009 Earthquakes How and where do earthquakes occur? How do scientists locate and measure earthquakes? What types of damage do earthquakes cause?

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 2 Causes of Earthquakes Earthquake –s–shaking of crust by release of energy –s–strain at faults/boundaries break in lithosphere with movement Elastic Rebound Theory –f–friction stop motion increases strain –s–strain deforms plate over comes friction –m–movement/snap back with different orientation Focus –p–point of initial movement Epicenter –p–point on surface directly above focus

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 3 Body Waves Waves –t–travel from focus through earth Primary (P) Waves –c–compressional waves – squeeze and stretch –s–solid rock, magma, ocean water, air Secondary (S) (Shear) Waves –p–perpendicular waves – move at right angle to direction of movement –s–solid materials ONLY

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 4 Surface Waves Love Waves –p–particles move side to side perpendicular to direction of travel Rayleigh Waves –p–particles move up and down in relation to direction of travel

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 5 Locating and Measuring Earthquakes Seismograph –d–detect and record waves Side to Side Motion Up and Down Motion –S–Seismograph Station THREE machines –U–Up and Down –S–Side to Side (N-S) –S–Side to Side (E-W) Seismogram –r–record sheet traces motions

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 6 Interpreting Seismogram P-waves move faster than S-waves –P–P-waves arrive before S-wave –g–greater the difference between P and S waves farther away station is from epicenter

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 7 Measuring Earthquake Magnitude Magnitude –a–amount of energy released by earthquake Richter Scale –C–Charles Richter 1935 based on amplitude of seismic wave relatively easy to calculate quickly each increase of number is 31x energy measures intensity of ground movement inaccurate with large quakes –M–Moment Magnitude measures the total amount of energy released most accurate measure of size good for very large earthquakes requires detailed analysis of seismic waves –M–Modified Mercali Index based on survey of damage I-XII

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 8 Richter Measurement

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 9 Earthquake Hazards Damage –G–Ground Shaking and Foundation Failure Liquefaction – loose soil behaves like a liquid –A–Aftershocks and Fire aftershocks are smaller quakes ruptured gas lines ignited fires –T–Tsumanis fast moving ocean wave from underwater quakes 2004 Indonesia

Updated 5/3/2009Created by C. Ippolito May 2009 Slide 10 Earthquake Prediction Long Term –b–based on seismic gaps places where faults have not moved Short Term –r–relies on recognition of precursors land deformation increased seismic activity geomagnetic and geoelectric changes (affects animal behavior?) groundwater level changes