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UA GEO 101 - Earthquakes
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GEO 101 1st Edition Lecture 12 Outline of Last Lecture 1. Volcanic Eruptions 2. Volcano Types3. Profiles of Volcanic Landforms4. Extrusive Materials 5. Other Landforms 6. Hot Spots7. Plate Tectonics and Igneous Activity Outline of Current Lecture 1. What is an Earthquake 2. Earthquakes 3. Displacement4. Seismology Current LectureChapter 8: Earthquakes What is an Earthquake?- Vibration of Earth produced by rapid release of energyo Energy waves radiate in all directions from focus o Epicenter directly above focus (hypocenter) on surfaceo Instruments around world record energy Earthquakes- Earthquakes (abbreviated EQ) occur when a fault moves - Elastic rebound theoryo 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 shapeo- Foreshocks & aftershockso 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 wayso 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 drumo 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) waveso Push-through motion o Travel though solids, liquids & gasses- Secondary (S) waveso “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 EQo Need difference in Arrival time of P & S save and amplitude of largest waveCan Earthquakes be Predicted? - No short-range prediction s- Long range forecastso 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 1. Liquefaction of ground – unconsolidated materials saturated with water turn into fluido 2. Fireo 3. Landslides and ground failureo 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 tsunamiOther Earthquakes Nov 3 2002 Alaskan Earthquake M 7.9Alaska 1964 M 9.2 131 died Kobe 1995 M 6.5 5000+ diedLoma Prieta 1989 M 6.9 63 died San Fransisco 1906 M 7.8 1500


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UA GEO 101 - Earthquakes

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