CEE 1030 1nd Edition Lecture 11 Earthquakes Outline of Last Lecture I What is structural geology II Mapping geological structures a Investigating the shallow earth III Deformation a Brittle deformation b Ductile deformation Outline of Current Lecture I What is an earthquake II Seismology III Distribution of earthquakes IV Measuring the size of earthquakes V Earthquake damage VI Can earthquakes be predicted VII Review Current Lecture I II What is an earthquake a Sudden release of energy accumulates in deformed rocks radiates as seismic waves b Elastic rebound sudden brittle failure after slow build up of elastic strain when stress exceeds fault strength strained rocks suddenly snap back to original shape Seismology a Seismology the study of earthquakes or seismic waves b Seismographs instruments that record seismic activity c Types of seismic waves i Body waves travel through Earth s interior primary and secondary waves 1 P waves push pull waves 2 S waves shaking waves ii Surface waves travel over Earth s surface responsible for most earthquake damage 1 Love waves side to side 2 Rayleigh waves up and down 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 III IV V VI d Locating earthquake source i Focus place where earthquake waves originate ii Epicenter location on surface directly above focus iii Need data from at least three seismograph stations to determine location of epicenter e Global network of seismic stations i Established to monitor international nuclear bomb test ban treaties Distribution of earthquakes a Earthquakes focused around plate margins b Most earthquakes are shallow because heat weakens rocks and makes them less able to store strain energy Measuring the size of earthquakes a Intensity measure of degree of earthquake shaking at a given locale based on the damage i Scale of I XII ii Intensity is influenced by the local geology building design and construction 1 If you re on sediments you ll notice shaking more than if you re on solid rock b Magnitude estimates amount of energy released at source of earthquake c Richter scale based on amplitude of largest seismic wave recorded adjusted for distance to epicenter i Each unit of Richter magnitude increase corresponds to tenfold increase in wave amplitude and 32 fold energy increase d Moment magnitude related to physical properties of fault that caused the earthquake better estimate of total energy Earthquake damage a Extent of structural damage depends on i Depth of earthquake ii Intensity and duration of vibrations iii Nature of material the structure rests on iv Design of structure v Quality of construction b Liquefaction unconsolidated materials saturated with water turn into a mobile fluid no strength to support buildings c Tsunamis i Destructive ocean waves triggered by movement of surface fault or landslide appear like a rapidly rising tide Can earthquakes be predicted a Short range predictions days to weeks monitoring precursors that might precede earthquake but no reliable method exists VII b 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 occurrences Review a San Andreas Fault is a strike slip fault
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