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Earthquakes & WavesEarthquakes & Waves
SF 1906
LA 2008
Haiti 2010
Mexico City 1985
Where & how earthquakes occurWhere & how earthquakes occur
Occur at plate boundariesOccur at plate boundaries Caused by the movement of tectonic platesCaused by the movement of tectonic plates Energy is released in Energy is released in seismic wavesseismic waves
Stress builds at plate boundaries Stress builds at plate boundaries until released until released
Raise your hand if you have been on the Earthquake trail in Point Reyes. What happened to the fence?
Where Earthquakes StartWhere Earthquakes Start
They start under ground at the They start under ground at the focus.focus. Waves travel outward from focus in all Waves travel outward from focus in all
directions.directions. The point on the surface, directly above The point on the surface, directly above
the focus is the the focus is the epicenter.epicenter.
Pair share: when have you seen waves moving outward as a circle?
Tsunami Tsunami When an earthquake occurs When an earthquake occurs
in the ocean it can generate in the ocean it can generate enormous waves of water enormous waves of water called called TsunamisTsunamis..
The 2004 Tsunami kill 300,000 people and caused $123 Billion in damage.
About WavesAbout WavesParts of a WaveParts of a Wave
Crests:Crests: highest pointhighest point
TroughsTroughs: : Lowest pointLowest point
AmplitudeAmplitude:: ½ the distance from crest to ½ the distance from crest to troughtrough
Pair share: how many crests will seismo the surfing dog pass over?
Wave termsWave terms
Wavelength:Wavelength: distance from crest to crest distance from crest to crest Period:Period: time it takes for one full wavelength to time it takes for one full wavelength to
to pass byto pass by FrequencyFrequency: the : the numbernumber of waves passing in a of waves passing in a
given given timetime Pair share: how many wavelengths will Echo the surfing dog pass over?
Types of Seismic WavesTypes of Seismic Waves
Longitudinal: Longitudinal: ( P waves) ( P waves)Fastest, travel like a spring Fastest, travel like a spring
through rockthrough rock
TransverseTransverse ( S waves) ( S waves)slower, move like a shaken slower, move like a shaken
roperope
Surface waves:Surface waves: move move out in circles from out in circles from epicenter in a rolling epicenter in a rolling motion, damaging to motion, damaging to structuresstructures
Seismic wave motionSeismic wave motion
P: primary meaning 1st
S: Slower, second
Detecting earthquakes Detecting earthquakes
SeismographsSeismographs: pendulums record motion onto : pendulums record motion onto paperpaper
33 seismographs in different locations can pinpoint seismographs in different locations can pinpoint the epicenter.the epicenter.
EpicenterEpicenter: where P, S, and surface waves meet: where P, S, and surface waves meet
Measuring the magnitudeMeasuring the magnitude Richter scaleRichter scale: rates the : rates the energyenergy
generated by an Earthquake.generated by an Earthquake.
Each level is 10 X greater than Each level is 10 X greater than the nextthe next
Most are very small, not feltMost are very small, not felt
Mercalli indexMercalli index: the amount of : the amount of shaking felt. shaking felt.
ReviewReview
1)1) How is the energy from earthquakes How is the energy from earthquakes transferred? transferred?
2)2) What scale is used to measure the What scale is used to measure the magnitudemagnitude of an earthquake?of an earthquake?
3)3) What kind of wave causes the most damage?What kind of wave causes the most damage?