CEE 1030 1nd Edition Lecture 11: EarthquakesOutline of Last Lecture I. What is structural geology?II. Mapping geological structuresa. Investigating the shallow earthIII. Deformationa. Brittle deformationb. Ductile deformationOutline of Current Lecture I. What is an earthquake?II. SeismologyIII. Distribution of earthquakesIV. Measuring the size of earthquakesV. Earthquake damageVI. Can earthquakes be predicted?VII. ReviewCurrent LectureI. What is an earthquake?a. Sudden release of energy accumulates in deformed rocks, radiates as seismic wavesb. Elastic rebound: sudden brittle failure after slow build up of elastic strain, when stress exceeds fault strength, strained rocks suddenly snap back to original shapeII. Seismologya. Seismology: the study of earthquakes or seismic wavesb. Seismographs: instruments that record seismic activityc. Types of seismic wavesi. Body waves: travel through Earth’s interior (primary and secondary waves)1. P waves: push-pull waves2. S waves: shaking wavesii. Surface waves: travel over Earth’s surface, responsible for most earthquake damage1. Love waves: side to side2. Rayleigh waves: up and downThese 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.d. Locating earthquake sourcei. Focus: place where earthquake waves originateii. Epicenter: location on surface directly above focusiii. Need data from at least three seismograph stations to determine locationof epicentere. Global network of seismic stationsi. Established to monitor international nuclear bomb test ban treatiesIII. Distribution of earthquakesa. Earthquakes focused around plate marginsb. Most earthquakes are shallow because heat weakens rocks and makes them less able to store strain energyIV. Measuring the size of earthquakesa. Intensity: measure of degree of earthquake shaking at a given locale based on the damagei. Scale of I-XIIii. Intensity is influenced by the local geology, building design, and construction1. If you’re on sediments, you’ll notice shaking more than if you’re on solid rockb. Magnitude: estimates amount of energy released at source of earthquakec. Richter scale: based on amplitude of largest seismic wave recorded, adjusted for distance to epicenteri. Each unit of Richter magnitude increase corresponds to tenfold increase in wave amplitude and 32-fold energy increased. Moment magnitude: related to physical properties of fault that caused the earthquake (better estimate of total energy)V. Earthquake damagea. Extent of structural damage depends on:i. Depth of earthquakeii. Intensity and duration of vibrationsiii. Nature of material the structure rests oniv. Design of structurev. Quality of constructionb. Liquefaction: unconsolidated materials saturated with water turn into a mobile fluid, no strength to support buildingsc. Tsunamisi. Destructive ocean waves triggered by movement of surface fault or landslide, appear like a rapidly rising tideVI. Can earthquakes be predicted?a. Short range predictions (days to weeks): monitoring precursors that might precede earthquake, but no reliable method existsb. Long range forecasts (decades to centuries): based on the premise that earthquakes are repetitive or cyclical (use historical records of paleoseismology)c. Most likely places for earthquakes on plate boundary, gaps between earthquake occurrencesVII. Reviewa. San Andreas Fault is a strike-slip
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