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?