GLG101: Physical Geology Lecture Outlines for Exam#3:

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G. Calderone- GLG101: Physical Geology Lecture Reviews, Exam#3, August 23, 2011 Page 10 of 20GLG101: Earthquakes Lectures- ReviewsElastic Rebound Theory: Stress can be stored as elastic strain, then suddenly released inpart as seismic waves. The waves travel some distance- vibrating the ground orquaking it as they pass. This action is what we call an earthquake.Basic definitions:Earthquake (EQ) = shaking of ground by passage of seismic waves resulting from the releaseof stress through breakage of rockFocus the point of rupture-= usually occurs below the surface of the Earth.Epicenter = the surface location directly above the point of ruptureAftershocks = smaller Earthquakes representing adjustments of remaining rock to newmotion.Causes of earthquakesFaulting = two masses of rock sliding past one another along fault plane- Elastic reboundtheory. Buildup of strain, release in an earthquake, repeatMagma motion = as magma forces its way to surface, rocks may break causing earthquakesExplosions = Volcanic eruptions or nuclear bombsPossible mineral phase changes for really deep earthquakesSeismic Waves-Body Waves- Waves travel through the "body of rock or body of Earth"p waves- Primary Waves- compressional waves- particle motion is back and forth- veryfast waves- 4-7 km/sec can travel through almost any materials waves - Secondary or Shear waves- particle motion is up/down and sideways(perpendicular do direction of wave travel)- slower than p-waves for the samematerial- 2-5 km/sec. Because waves propagate by shearing particles, s-waves cannottravel through fluids such as gasses and liquidsSurface Waves- waves travel along Surface of the Earth- slower than body wavesLove Waves - particle motion is a horizontal shear wave- cannot travel through fluid.Rayleigh Waves - particle motion is retrograde elliptical- just like ocean waves- althoughslower, Rayleigh waves produce very large ground motion and are responsible for muchof the destructive power of EQs.
G. Calderone- GLG101: Physical Geology Lecture Reviews, Exam#3, August 23, 2011 Page 11 of 20Effects of Earthquakes (see movie "When the Bay Area Quakes")Ground motion- from the passage of seismic wavesThe Mercali Scale: a measure of Earthquake Intensity- Ground shaking “scale”Factors influencing earthquake intensity.Distance from epicenter Rock type Construction TypeLandslides- triggered by passage of seismic wavesLiquefaction- creation of "quicksand" in wet muddy sedimentsSurface rupture- actual ground breakageFires- from rupture and ignition of gas lines etc.Seismic Sea Waves (Tsunamis)- large waves (hurricane sized or larger) caused by landshifts in earthquakesSeiches (pronounced "Say-shays")- rocking motion of water in closed baysAftershocks- "smaller earthquakes" following the main shock. These may further damagestructures weakened by the main shock. Although there will be hundreds or thousands ofaftershocks after a large earthquake, there will usually be 2 or three aftershocks of onemagnitude less than the main shock. If the main shock was a magnitude 8, some of theaftershocks may be magnitude 7- very large aftershocks!Power outages/ Water shortages/ communications out etc.Coping with the Threat of Earthquakes (see attached FEMA what to do list]Earthquake prediction.Long termSeismic frequency- some areas seem to have earthquakes at "regular" intervals of time(Parkfield Experiment)Space-time patterns- patterns in where and when earthquakes occur.Seismic gaps- areas along faults that have not ruptured in a long time. Stress is building.Short term- Parkfield ExperimentForeshocks- smaller earthquakes that may signal onset of larger oneWater level changes- possible changes in groundwater well levels due to shift prior toruptureRadon emissions- possibly due to shifts in Earth prior to ruptureGeodetic changes- shifts in location of areas prior to ruptureLow Frequency Radio Waves- for whatever reason, these may indicate immanent ruptureAnimal behavior
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