GEO 101 1st Edition Lecture 12 Outline of Last Lecture 1 Volcanic Eruptions 2 Volcano Types 3 Profiles of Volcanic Landforms 4 Extrusive Materials 5 Other Landforms 6 Hot Spots 7 Plate Tectonics and Igneous Activity Outline of Current Lecture 1 What is an Earthquake 2 Earthquakes 3 Displacement 4 Seismology Current Lecture Chapter 8 Earthquakes What is an Earthquake Vibration of Earth produced by rapid release of energy o Energy waves radiate in all directions from focus o Epicenter directly above focus hypocenter on surface o Instruments around world record energy Earthquakes Earthquakes abbreviated EQ occur when a fault moves Elastic rebound theory o Rocks bend store elastic energy o Resistance holding rocks together at fault overcome at weakest point focus o EQs occur as rock springs back to original shape o Foreshocks aftershocks o Adjustments after major EQ generate smaller EQs aftershocks These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Small EQs before major EQ foreshocks days or several years Displacement Displacement occurs along segments 100 to 200 km long via 3 ways o Slow gradual displacement fault creep o Slip by producing small EQs o Store elastic energy for 100 s of years before rupturing in major EQs Seismology Study of EQ waves seismology Seismographs record seismic waves o Records movement of Earth in relation to a stationary mass on a rotating drum o Records obtained seismograms Types o A Surface waves Travel along outer part of Earth Cause greatest destruction Exhibit greatest amplitude slowest velocity Two Motions for Surface waves Back and forth love wave or L wave Rolling Rayleigh wave or R wave o Body Waves Travel though Earth s interior 2 types Primary P waves o Push through motion o Travel though solids liquids gasses Secondary S waves o Shake motion at right angles o Travel only through solids o Slower velocity than P waves o Greater amplitude than P waves Earthquakes EQ depths o 5 700km o Foci are Shallow 70km Intermediate 70 and 300 km Deep 300 km o Patterns Shallow focus along oceanic ridge system Deep focus EQs occur in circum Pacific belt Why Wadati Bennioff Zone EQs Plate Tectonics Connection of deep focus EQs Oceanic trenches Shallow focus EQs occur along divergent transform fault boundaries Where are EQ s 80 circum pacific 15 Mediterranean Asiatic 5 interiors of plates MORs Every year o 150 000 EQs felt but 900 000 EQs recorded Size of Earthquakes Intensity Scales o Modified Mercalli Intensity Scale destruction may not be true measure of EQs severity Size of EQ described by o Intensity degree of shaking at locality o Magnitude estimates amount of energy released Magnitude Scales o Richter Scale Based on amplitude of largest seismic wave recorded Each unit of Richter magnitude increase corresponds to 10 fold increase in wave amplitude 32 fold energy increase Finding Magnitude of an EQ o Need difference in Arrival time of P S save and amplitude of largest wave Can Earthquakes be Predicted No short range prediction s Long range forecasts o Probability of EQ occurring Gap Theory o Assume EQs cyclical Use paleoseismology o Used to Develop uniform building code Assist in land use planning Where will the next Alaskan earthquake occur The Gap Theory Note Location of Parkfield M 6 0 EQ last year Seismicity Propagated Westward Destruction depends on Magnitude Distance from epicenter type of rock material Would you build your home on bedrock or mud Earthquake Destruction Types o o o o 1 Liquefaction of ground unconsolidated materials saturated with water turn into fluid 2 Fire 3 Landslides and ground failure 4 Tsunami 3 Ground Failure 1964 Alaska 4 Tsunamis Not Tidal Waves Result from motion along fault on ocean floor or undersea landslide In open ocean height 1 m In Shallow Waters 30 m Formation of a tsunami Other Earthquakes Nov 3 2002 Alaskan Earthquake M 7 9 Alaska 1964 M 9 2 131 died Kobe 1995 M 6 5 5000 died Loma Prieta 1989 M 6 9 63 died San Fransisco 1906 M 7 8 1500 died