Do NowDo Now

Describe the last earthquake you Describe the last earthquake you can remember. (location, strength, can remember. (location, strength, time of day, how it felt, etc.)time of day, how it felt, etc.)

Where do earthquakes occur?Where do earthquakes occur?

Why do earthquakes occur?Why do earthquakes occur?

Earthquakes / Earthquakes / EpicentersEpicenters

Objectives:Objectives:•Define Elastic LimitDefine Elastic Limit•Identify 3 types of fault linesIdentify 3 types of fault lines•Differ between P and S wavesDiffer between P and S waves•Determine shadow zones of P and S wavesDetermine shadow zones of P and S waves

Where do earthquakes Where do earthquakes occur?occur?

Occur at plate boundariesOccur at plate boundaries

ConvergentConvergent: Plates move together: Plates move together DivergentDivergent: Plates move apart: Plates move apart TransformTransform: Plates are sliding : Plates are sliding

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What Causes What Causes EarthquakesEarthquakes

When rock reaches its When rock reaches its elastic limit elastic limit an an earthquake occurs. earthquake occurs.

Elastic Rebound: Elastic Rebound: the sudden “bounce – the sudden “bounce – back” of rock to its original shapeback” of rock to its original shape

During elastic rebound, rock releases energy. During elastic rebound, rock releases energy. Some of this energy travels as seismic waves Some of this energy travels as seismic waves that cause earthquakes.that cause earthquakes.

Fault LinesFault Lines

When rock breaks, they move along When rock breaks, they move along surfaces called surfaces called faultsfaults..

3 Types of faults3 Types of faults NormalNormal ReverseReverse Strike/SlipStrike/Slip

Normal faultNormal fault Force applied = TensionalForce applied = Tensional Movement = Rock above fault moves downward.Movement = Rock above fault moves downward.

BeforeBefore After After

What plate boundary is a normal fault similar to?What plate boundary is a normal fault similar to?

Divergent Divergent

Normal FaultNormal Fault

Hanging wall Hanging wall slides below slides below the foot wall.the foot wall.

Reverse FaultReverse Fault Force applied = CompressionalForce applied = Compressional Movement = Rock above fault moves Movement = Rock above fault moves

Upward.Upward.

BeforeBefore After After

What boundary is a reverse fault What boundary is a reverse fault similar to?similar to?

ConvergentConvergent

Reverse FaultReverse Fault

Hanging Hanging wall slide up wall slide up passed the passed the foot wallfoot wall

Foot Wall

Hanging Wall

Strike/Slip faultStrike/Slip fault Force applied = ShearingForce applied = Shearing Movement = Rocks slide past each other.Movement = Rocks slide past each other.

Energy builds up until elastic limit is reached = Energy builds up until elastic limit is reached = EarthquakeEarthquake

BeforeBefore After After

What boundary is a strike/slip fault similar to?What boundary is a strike/slip fault similar to?

TransformTransform

Strike/Slip FaultStrike/Slip Fault

Strike/Slip fault showStrike/Slip fault show

how the fault line willhow the fault line will

cause the 2 sides to cause the 2 sides to

not line up.not line up.

Do NowDo Now

• Define Elastic LimitDefine Elastic Limit• List and describe the 3 List and describe the 3

types of fault linestypes of fault lines• State which applied force State which applied force

creates each type of faultcreates each type of fault

SEISMIC WAVESSEISMIC WAVES

When earthquakes occur, waves of When earthquakes occur, waves of energy energy SEISMIC WAVESSEISMIC WAVES travel travel outward from the earthquake focus outward from the earthquake focus

3 types of seismic waves are 3 types of seismic waves are produced produced AT THE SAME TIMEAT THE SAME TIME but but each behaves differently within each behaves differently within earth.earth.

Primary waves or compression Primary waves or compression waves waves vibrate parallel to the vibrate parallel to the direction of movement. (slinky)direction of movement. (slinky)

Travel faster than any other wave (6-Travel faster than any other wave (6-8 km/s)8 km/s)

Travel through solids, liquids, and Travel through solids, liquids, and gasesgases

P (Primary) WavesP (Primary) Waves

S (Shear) WAVES (Shear) WAVE Shear wave or secondary waves Shear wave or secondary waves

vibrate back and forth perpendicular vibrate back and forth perpendicular to the direction the wave is movingto the direction the wave is moving

Slower than P waves (4-5 km/s) Slower than P waves (4-5 km/s) TRAVEL THROUGH SOLIDS ONLYTRAVEL THROUGH SOLIDS ONLY

SURFACE OR LONG SURFACE OR LONG WAVESWAVES

Vibrations travel along earth’s Vibrations travel along earth’s surface in a circular motion at surface in a circular motion at relatively slow speeds (2 km/s) like relatively slow speeds (2 km/s) like waves in a pondwaves in a pond

Do more Do more damage damage because they because they produce produce more ground more ground movementmovement

Velocity and seismic Velocity and seismic waveswaves

Velocity depends on the material Velocity depends on the material they are passing throughthey are passing through

a.a. Increase density and pressure – Increase density and pressure – greater the velocity greater the velocity

b.b. Waves are refracted or bent as Waves are refracted or bent as waves pass through material with waves pass through material with different densitiesdifferent densities

Shadow ZoneShadow Zone An area where earthquake waves seem to An area where earthquake waves seem to

disappear.disappear. P-Waves can travel through solid, liquid, and gas.P-Waves can travel through solid, liquid, and gas. S-waves can travel through SOLID ONLY!S-waves can travel through SOLID ONLY!

P-Waves enter liquid outer core = Wave slows P-Waves enter liquid outer core = Wave slows down!down!

S-Waves enter liquid core = Waves disappearS-Waves enter liquid core = Waves disappear. .

Shadow ZoneShadow Zone

S-Waves do not make it through. Cant S-Waves do not make it through. Cant travel through liquid outer core.travel through liquid outer core.

P Wave and S Wave P Wave and S Wave Chart / Locating Chart / Locating

EpicentersEpicentersObjectives:Objectives:•Analyze P and S wave chartAnalyze P and S wave chart•Determine travel times of seismic WavesDetermine travel times of seismic Waves•Analyze seismogramsAnalyze seismograms•Locate epicentersLocate epicenters

Determining distance to Determining distance to EpicenterEpicenter

EpicenterEpicenter – The location of an – The location of an earthquake on the surface of the Earth earthquake on the surface of the Earth above the above the focusfocus..

Focus – Location within the Earth’s Focus – Location within the Earth’s crust where the breaking of rock crust where the breaking of rock occursoccurs

Surface

Seismograph / Seismograph / SeismogramSeismogram

Geologist use an instrument to measure Geologist use an instrument to measure seismic waves called a seismic waves called a seismographseismograph.. Measures the arrival times of the P-Wave, S-Measures the arrival times of the P-Wave, S-

Wave, and Surface Wave.Wave, and Surface Wave.

Which wave will always arrive first???Which wave will always arrive first???

P (Primary) Wave = Faster SpeedP (Primary) Wave = Faster Speed

P – S Wave ChartP – S Wave Chart

Chart can be used Chart can be used to determine to determine arrival times of P arrival times of P and S waves.and S waves.

Can also be used to Can also be used to locate the distance locate the distance to the epicenter to the epicenter from the seismic from the seismic station.station.

Notice the vertical axis

This represents TIME (in minutes!)

Let’s enlarge a small section

Between each minute, we notice that there are 3 segments.

If there are 60 seconds in a minute, each one of these segments must be ________seconds.

What would this time be?

Notice the horizontal axis

This represents DISTANCE (in thousands of Kilometers!)

Let’s enlarge a small section

There are also two curves on this chart that display the way different earthquake waves behave.

This chart can be used for This chart can be used for answering many different answering many different

questions!questions!

How long does it take an S-Wave to travel 5,000km?

The recording station tells us it took 6 minutes and 20 seconds for the P-Wave to reach them. How far away from the epicenter of the earthquake must they be?

I know that there was a 7 minute difference in the arrival of my P and S waves. How far away from the epicenter must I be?

Mark off 7 minutes on scrap paper…

Slide your scrap paper up until the tick marks match up with the curves…

LOCATING THE EPICENTER LOCATING THE EPICENTER OF AN EARTHQUAKEOF AN EARTHQUAKE

The difference in travel time between P and S The difference in travel time between P and S waves can be used to determine the waves can be used to determine the DISTANCEDISTANCE from a station to the epicenterfrom a station to the epicenter

The farther the station , The longer the The farther the station , The longer the travel time.travel time.

TO DETERMINE THE TO DETERMINE THE EXACTEXACT LOCATION OF AN LOCATION OF AN EPICENTER, EPICENTER, you must have 3 seismic you must have 3 seismic stations recording the same earthquakestations recording the same earthquake

Locating an EpicenterLocating an Epicenter

Epicenter

Station A

Station B

Station C

Collecting data from the Collecting data from the recording stations:recording stations:

Station A: San Francisco, CaliforniaStation A: San Francisco, California

P-Wave arrival P-Wave arrival 3:02:203:02:20 S-Wave arrival S-Wave arrival 3:06:303:06:30

Collecting data from the Collecting data from the recording stations:recording stations:

Station B: Denver, ColoradoStation B: Denver, Colorado

P-Wave arrival P-Wave arrival 3:01:403:01:40 S-Wave arrival S-Wave arrival 3:05:003:05:00

What is the time difference between P and S wave arrivals?

Collecting data from the Collecting data from the recording stations:recording stations:

Station C: Missoula, MontanaStation C: Missoula, Montana

P-Wave arrival P-Wave arrival 3:01:003:01:00 S-Wave arrival 3:03S-Wave arrival 3:03:00:00

What is the time difference between P and S wave arrivals?

Find the distance to the Find the distance to the epicenter for each epicenter for each

station.station. Using the P and S wave chart, Find Using the P and S wave chart, Find the distance from each station to the the distance from each station to the epicenter.epicenter.San Francisco: 4:10

Denver, Colorado: 3:20Missoula, Montana 2:00

2,800km

1100km

2,200km

Recording BoardRecording BoardDifference in arrival Difference in arrival

times:times:San Francisco: 41:02,800km

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2,00

0

3,00

0

4,00

0

5,00

0

Open your compass to the EXACT distance on the scale.

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How are earthquakes How are earthquakes measured?measured?

Seismographs measure an Seismographs measure an earthquakes earthquakes MagnitudeMagnitude – The – The amount of energy released.amount of energy released.

The Richter Scale measure local The Richter Scale measure local intensity. Describes how much intensity. Describes how much energy is released.energy is released.

TsunamisTsunamis

Tsunamis – Ocean waves caused by Tsunamis – Ocean waves caused by seismic waves.seismic waves.