EarthquakesEarthquakes

I-880, Oakland, CA (October 1989)

Magnitude 5+ earthquakes Magnitude 5+ earthquakes 1980 - 19901980 - 1990

Earthquake BasicsEarthquake Basics

The elastic rebound theory is an explanation for how energy is spread during earthquakes.

http://upload.wikimedia.org/wikipedia/en/b/be/ElasticRebound_Thum.png

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

Earthquake focus Earthquake focus and epicenterand epicenter

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

Evidence of P-wave motionEvidence of P-wave motion

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

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

SeismometerSeismometer

A seismogram records wave A seismogram records wave amplitude vs. timeamplitude vs. time

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)

PP SS

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.

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

PRACTICE TIME!!PRACTICE TIME!!

Seismogram

http://seismo.berkeley.edu/seismo/faq/iup/eq_local.htmlhttp://seismo.berkeley.edu/seismo/faq/iup/eq_local.html

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!!

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

Earthquake Damage: LiquifactionEarthquake Damage: Liquifaction

Earthquake Damage: LiquifactionEarthquake Damage: Liquifaction

Earthquake Damage: LiquifactionEarthquake Damage: Liquifaction

Tsunami FormationTsunami Formation

Tsunami travel time (hours; simulation)

NOAA

Dec. 2004 Sumatra Tsunamihttp://staff.aist.go.jp/kenji.satake/animation.gif

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

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/