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EarthquakesEarthquakes
I-880, Oakland, CA (October 1989)
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Magnitude 5+ earthquakes Magnitude 5+ earthquakes 1980 - 19901980 - 1990
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Earthquake BasicsEarthquake Basics
The elastic rebound theory is an explanation for how energy is spread during earthquakes.
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Earthquake BasicsEarthquake Basics Elastic Rebound Theory:Elastic Rebound Theory:
– Due to plate motion, rocks on each side of a Due to plate motion, rocks on each side of a fault are moving slowly. If the fault is “locked”, fault are moving slowly. If the fault is “locked”, stress in the rock increases. Once they are stress in the rock increases. Once they are stressed past a certain point, they fracture at stressed past a certain point, they fracture at their weakest point and spring back to their their weakest point and spring back to their original shape (rebound)original shape (rebound)
– AftershocksAftershocks—this release of energy often puts —this release of energy often puts stress on stress on otherother rocks and cause them to break rocks and cause them to break and rebound tooand rebound too
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Earthquake focus Earthquake focus and epicenterand epicenter
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Types of Earthquake WavesTypes of Earthquake Waves
P (primary) wavesP (primary) waves– Compressional (push-pull)Compressional (push-pull)– Fastest waves (first to arrive at seismograph)Fastest waves (first to arrive at seismograph)– Move through all materialsMove through all materials
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Evidence of P-wave motionEvidence of P-wave motion
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Types of Earthquake WavesTypes of Earthquake Waves
S (secondary) wavesS (secondary) waves– Move perpendicular to P Move perpendicular to P
wavewave– Second fastest waves Second fastest waves
(next to arrive at (next to arrive at seismograph)seismograph)
– Move ONLY through Move ONLY through solidssolids
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Types of Earthquake WavesTypes of Earthquake Waves Surface wavesSurface waves
– Rolling motionRolling motion– Slowest waves (arrive last at seismograph)Slowest waves (arrive last at seismograph)– Cause most damageCause most damage
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SeismometerSeismometer
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A seismogram records wave A seismogram records wave amplitude vs. timeamplitude vs. time
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Locating an EpicenterLocating an Epicenter
1.1. View SeismogramsView Seismograms
2.2. Measure P and S Measure P and S wave arrivalswave arrivals
3.3. (cont’d on next (cont’d on next slides)slides)
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PP SS
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Locating an EpicenterLocating an Epicenter
1.1. View SeismogramsView Seismograms
2.2. Measure P and S Measure P and S wave arrivalswave arrivals
3.3. Measure S-wave Measure S-wave “lag” time ( = S - P)“lag” time ( = S - P)
4.4. Use Travel-Time Use Travel-Time graph to correlate graph to correlate distance.distance.
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14.7 Locating an Epicenter14.7 Locating an Epicenter
1.1. View SeismogramsView Seismograms2.2. Measure P and S Measure P and S
wave arrivalswave arrivals3.3. Measure S-wave Measure S-wave
“lag” time ( = S - P)“lag” time ( = S - P)4.4. Use Travel-Time Use Travel-Time
graph to correlate graph to correlate distance.distance.
5.5. Triangulate Triangulate DistancesDistances
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PRACTICE TIME!!PRACTICE TIME!!
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Seismogram
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http://seismo.berkeley.edu/seismo/faq/iup/eq_local.htmlhttp://seismo.berkeley.edu/seismo/faq/iup/eq_local.html
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Shadow ZoneShadow Zone
P-waves P-waves reflectreflect between 0-104between 0-104
P-waves P-waves refractrefract between 104-150between 104-150
S-waves only S-waves only reflectreflect Proves outer core is Proves outer core is
LIQUIDLIQUID!!
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Measuring StrengthMeasuring Strength
Earthquake MagnitudeEarthquake Magnitude• Charles Richter designed first scaleCharles Richter designed first scale• Based on height of the largest seismic Based on height of the largest seismic
wavewave• Every 1 increase in magnitude = 10x Every 1 increase in magnitude = 10x
increase in strengthincrease in strength
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Earthquake Damage: LiquifactionEarthquake Damage: Liquifaction
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Earthquake Damage: LiquifactionEarthquake Damage: Liquifaction
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Earthquake Damage: LiquifactionEarthquake Damage: Liquifaction
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Tsunami FormationTsunami Formation
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Tsunami travel time (hours; simulation)
NOAA
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Dec. 2004 Sumatra Tsunamihttp://staff.aist.go.jp/kenji.satake/animation.gif
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Current Seismic EventsCurrent Seismic Events
EarthquakesEarthquakeshttp://earthquake.usgs.gov/recenteqs/http://earthquake.usgs.gov/recenteqs/
TsunamiTsunamihttp://wcatwc.arh.noaa.gov/tsunami.htmhttp://wcatwc.arh.noaa.gov/tsunami.htm
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References UsedReferences Used
http://science.howstuffworks.com/earthquake6.htmhttp://science.howstuffworks.com/earthquake6.htm http://www.data.scec.org/chrono_index/http://www.data.scec.org/chrono_index/
bigbear.htmlbigbear.html http://pubs.usgs.gov/dds/dds-29/web_pages/http://pubs.usgs.gov/dds/dds-29/web_pages/
los_gatos.htmllos_gatos.html http://earthquake.usgs.gov/bytopic/photos.htmlhttp://earthquake.usgs.gov/bytopic/photos.html http://earthquake.usgs.gov/4teachers/http://earthquake.usgs.gov/4teachers/ http://earthquake.usgs.gov/recenteqs/http://earthquake.usgs.gov/recenteqs/