Earthquakesand

Earth’s Interior

Earthquakesand

Earth’s Interior

33

QuestionsQuestions::• How many have felt an earthquake?How many have felt an earthquake?

• What is an earthquake (EQ)?What is an earthquake (EQ)?

Earthquake StatisticsEarthquake Statistics• 30,000 EQ’s strong enough to feel annually30,000 EQ’s strong enough to feel annually

• 75 significant EQ’s each year75 significant EQ’s each year

• 1960 Southern Chile, M 9.51960 Southern Chile, M 9.5

• 1964 Alaska, M 9.21964 Alaska, M 9.2

• 2004, Sumatra-Andaman, M 9.12004, Sumatra-Andaman, M 9.1

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(M 9.2), Alaska-1964(M 9.2), Alaska-1964(M 9.2), Alaska-1964(M 9.2), Alaska-1964

(M 9.5), So. Chile-1960(M 9.5), So. Chile-1960(M 9.5), So. Chile-1960(M 9.5), So. Chile-1960

(M 9.1), Sumatra-Andaman-2004(M 9.1), Sumatra-Andaman-2004(M 9.1), Sumatra-Andaman-2004(M 9.1), Sumatra-Andaman-2004

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How are earthquake vibrations similar to a How are earthquake vibrations similar to a rock rock entering water?entering water?

How are earthquake vibrations similar to a How are earthquake vibrations similar to a rock rock entering water?entering water?

EarthquakeEarthquake – vibrations within the earth that – vibrations within the earth that produce rapid release of energyproduce rapid release of energy in the form of seismic wavesin the form of seismic waves

EarthquakeEarthquake – vibrations within the earth that – vibrations within the earth that produce rapid release of energyproduce rapid release of energy in the form of seismic wavesin the form of seismic waves

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Is there evidence for earthquakes?Is there evidence for earthquakes?San Francisco, 1906San Francisco, 1906Is there evidence for earthquakes?Is there evidence for earthquakes?San Francisco, 1906San Francisco, 1906

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23 mi south of Bakersfield23 mi south of Bakersfield23 mi south of Bakersfield23 mi south of Bakersfield

1919thth street, Bakersfield street, Bakersfield1919thth street, Bakersfield street, Bakersfield

1919thth st and Chester st and Chester1919thth st and Chester st and Chester

July 21, 1952 Bakersfield EQJuly 21, 1952 Bakersfield EQJuly 21, 1952 Bakersfield EQJuly 21, 1952 Bakersfield EQ

Earthquake TerminologyEarthquake TerminologyEarthquake TerminologyEarthquake Terminology

EpicenterEpicenter rupture point directlyrupture point directly

above the focusabove the focus

EpicenterEpicenter rupture point directlyrupture point directly

above the focusabove the focus

FocusFocus actual rupture takes actual rupture takes

placeplace

FocusFocus actual rupture takes actual rupture takes

placeplace

Seismic WavesSeismic Waves vibrations released from vibrations released from

an actual rupturean actual rupture

Seismic WavesSeismic Waves vibrations released from vibrations released from

an actual rupturean actual rupture

1010

I I I I a good earthquake. a good earthquake. a good earthquake. a good earthquake.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:

1.1.How would you define an earthquake?How would you define an earthquake?

2. About how many significant EQ’s 2. About how many significant EQ’s take place per year?take place per year?

3. Define the following:3. Define the following:epicenterepicenter seismic wavesseismic wavesfocusfocus

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What is taking place?What is taking place?

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How do EQ’s occur?How do EQ’s occur?How do EQ’s occur?How do EQ’s occur?

The Elastic Rebound Theory:The Elastic Rebound Theory:

•Stresses begin to build and strain the crust.Stresses begin to build and strain the crust.

•Continued stress stores energy and begins toContinued stress stores energy and begins to reach the “elastic” limits of the rock. reach the “elastic” limits of the rock.

•The rock SNAPS, releasing stored energyThe rock SNAPS, releasing stored energy in the form of seismic waves. in the form of seismic waves.

•Rock begins to reposition back into place,Rock begins to reposition back into place, producing aftershocks.producing aftershocks.

The Elastic Rebound Theory:The Elastic Rebound Theory:

•Stresses begin to build and strain the crust.Stresses begin to build and strain the crust.

•Continued stress stores energy and begins toContinued stress stores energy and begins to reach the “elastic” limits of the rock. reach the “elastic” limits of the rock.

•The rock SNAPS, releasing stored energyThe rock SNAPS, releasing stored energy in the form of seismic waves. in the form of seismic waves.

•Rock begins to reposition back into place,Rock begins to reposition back into place, producing aftershocks.producing aftershocks.

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““Good Vibrations” – released seismic wavesGood Vibrations” – released seismic waves““Good Vibrations” – released seismic wavesGood Vibrations” – released seismic wavesThree major seismic waves are released:Three major seismic waves are released:

•The P-waveThe P-wave•The S-waveThe S-wave•The L-wave (surface wave)The L-wave (surface wave)

Three major seismic waves are released:Three major seismic waves are released:

•The P-waveThe P-wave•The S-waveThe S-wave•The L-wave (surface wave)The L-wave (surface wave)

What measures the incoming seismic waves?What measures the incoming seismic waves?•The SeismographThe Seismograph

What measures the incoming seismic waves?What measures the incoming seismic waves?•The SeismographThe Seismograph

The inertia of the suspended mass keeps the seismographmotionless while the seismicwaves vibrate the recording drum anchored to thebedrock – produces a seismogram.

The inertia of the suspended mass keeps the seismographmotionless while the seismicwaves vibrate the recording drum anchored to thebedrock – produces a seismogram.

The SeismographThe SeismographThe SeismographThe Seismograph

body wavesbody wavesbody wavesbody waves

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The P-waveThe P-waveThe P-waveThe P-waveThe P-wave (the primary wave)The P-wave (the primary wave)

•compressional wavecompressional wave•compresses and expands rock materialcompresses and expands rock material

•fastest of the 3 seismic wavesfastest of the 3 seismic waves• typically 6 km/s in the upper crusttypically 6 km/s in the upper crust

•travels through both solids and liquidstravels through both solids and liquids

The P-wave (the primary wave)The P-wave (the primary wave)

•compressional wavecompressional wave•compresses and expands rock materialcompresses and expands rock material

•fastest of the 3 seismic wavesfastest of the 3 seismic waves• typically 6 km/s in the upper crusttypically 6 km/s in the upper crust

•travels through both solids and liquidstravels through both solids and liquids

1515

The S-waveThe S-waveThe S-waveThe S-wave

The S-wave (secondary wave)The S-wave (secondary wave)

•the shearing wavethe shearing wave•moves particles up and down (right angles moves particles up and down (right angles to to each other)each other)

•travels 2/3 the speed of the P-wavetravels 2/3 the speed of the P-wave• typically moves about 3.5 km/s in typically moves about 3.5 km/s in thethe upper crustupper crust

•travels through solids travels through solids ONLYONLY

The S-wave (secondary wave)The S-wave (secondary wave)

•the shearing wavethe shearing wave•moves particles up and down (right angles moves particles up and down (right angles to to each other)each other)

•travels 2/3 the speed of the P-wavetravels 2/3 the speed of the P-wave• typically moves about 3.5 km/s in typically moves about 3.5 km/s in thethe upper crustupper crust

•travels through solids travels through solids ONLYONLY

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The The L-waveL-wave and and RayleighRayleigh wave (Surface Waves) wave (Surface Waves)The The L-waveL-wave and and RayleighRayleigh wave (Surface Waves) wave (Surface Waves)

The L-wave (Love Wave)The L-wave (Love Wave)

•exhibits horizontal motion (like an S-wave)exhibits horizontal motion (like an S-wave)

•travels the slowest travels the slowest

•travels along the surface – producing horizontaltravels along the surface – producing horizontal motionmotion

The L-wave (Love Wave)The L-wave (Love Wave)

•exhibits horizontal motion (like an S-wave)exhibits horizontal motion (like an S-wave)

•travels the slowest travels the slowest

•travels along the surface – producing horizontaltravels along the surface – producing horizontal motionmotion

The Rayleigh waveThe Rayleigh wave•travels similar to an ocean wavetravels similar to an ocean wave

•the slowest wave the slowest wave

•travels along the surface – producing atravels along the surface – producing a rolling motionrolling motion

The Rayleigh waveThe Rayleigh wave•travels similar to an ocean wavetravels similar to an ocean wave

•the slowest wave the slowest wave

•travels along the surface – producing atravels along the surface – producing a rolling motionrolling motion

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Surface WavesSurface Waves

1818

Delano - BakoDelano - BakoDelano - BakoDelano - Bako

SAFSAFSAFSAF

1919

Seismogram

2020

I I I I a good earthquake.a good earthquake.a good earthquake.a good earthquake.

I will get an A on my exams and quizzes.I will get an A on my exams and quizzes.

Discuss with a friend:Discuss with a friend:

1. Explain the elastic rebound theory.1. Explain the elastic rebound theory.

2. Describe the motions of P, S, and surface2. Describe the motions of P, S, and surface waves.waves.

3.Give three characteristics of each wave.3.Give three characteristics of each wave.

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What’s the difference between an 8 magnitude and What’s the difference between an 8 magnitude and a 6.5 magnitude?a 6.5 magnitude?What’s the difference between an 8 magnitude and What’s the difference between an 8 magnitude and a 6.5 magnitude?a 6.5 magnitude?

Did you feel the earthquake? – Measuring an EQDid you feel the earthquake? – Measuring an EQDid you feel the earthquake? – Measuring an EQDid you feel the earthquake? – Measuring an EQ

Three ways to measure EQ’s:Three ways to measure EQ’s:

MercalliMercalli Intensity ScaleIntensity Scale

Richter Scale Richter Scale

Moment Magnitude ScaleMoment Magnitude Scale

Three ways to measure EQ’s:Three ways to measure EQ’s:

MercalliMercalli Intensity ScaleIntensity Scale

Richter Scale Richter Scale

Moment Magnitude ScaleMoment Magnitude Scale

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Modified Modified Mercalli Intensity ScaleMercalli Intensity Scale• measures the intensity of the EQ – how much measures the intensity of the EQ – how much damage occurs damage occurs

•closer to the epicenter-- more damagecloser to the epicenter-- more damage•farther from the epicenter -- less damage farther from the epicenter -- less damage

• people report the damagepeople report the damage

• destruction is assigned a Roman Numeral (I – XII)destruction is assigned a Roman Numeral (I – XII)•I – least intensityI – least intensity•XII – greatest intensityXII – greatest intensity

Modified Modified Mercalli Intensity ScaleMercalli Intensity Scale• measures the intensity of the EQ – how much measures the intensity of the EQ – how much damage occurs damage occurs

•closer to the epicenter-- more damagecloser to the epicenter-- more damage•farther from the epicenter -- less damage farther from the epicenter -- less damage

• people report the damagepeople report the damage

• destruction is assigned a Roman Numeral (I – XII)destruction is assigned a Roman Numeral (I – XII)•I – least intensityI – least intensity•XII – greatest intensityXII – greatest intensity

Less intenseLess intenseLess intenseLess intense

More intenseMore intenseMore intenseMore intense2323

Richter ScaleRichter Scale (Charles Richter – 1935) (Charles Richter – 1935)• measures the intensity of an EQ using a measures the intensity of an EQ using a seismogramseismogram

• maximum intensity = largest amplitude maximum intensity = largest amplitude recorded recorded

• EQ intensity is based on the logarithmic scale. EQ intensity is based on the logarithmic scale.

• each step each step (M1…M2…M3..)(M1…M2…M3..) increases the increases the amplitude X10 amplitude X10 • M5 has an amplitude 10 times larger than an M5 has an amplitude 10 times larger than an M4 M4 • M5 has an amplitude 100 times larger than M5 has an amplitude 100 times larger than an M3 an M3

• What about the energy released?What about the energy released?•Each increase in Richter amplitude (by 10) increases Each increase in Richter amplitude (by 10) increases energy energy 32 times 32 times so,so,

•An M6 releases An M6 releases 3232 more times energy than an M5. more times energy than an M5.

•An M6 releases _____ more times energy than an An M6 releases _____ more times energy than an M4.M4.

•An M6 releases _____ more times energy than an An M6 releases _____ more times energy than an M3.M3.

•An M6 releases ________ more times energy than an An M6 releases ________ more times energy than an M2.M2.

Richter ScaleRichter Scale (Charles Richter – 1935) (Charles Richter – 1935)• measures the intensity of an EQ using a measures the intensity of an EQ using a seismogramseismogram

• maximum intensity = largest amplitude maximum intensity = largest amplitude recorded recorded

• EQ intensity is based on the logarithmic scale. EQ intensity is based on the logarithmic scale.

• each step each step (M1…M2…M3..)(M1…M2…M3..) increases the increases the amplitude X10 amplitude X10 • M5 has an amplitude 10 times larger than an M5 has an amplitude 10 times larger than an M4 M4 • M5 has an amplitude 100 times larger than M5 has an amplitude 100 times larger than an M3 an M3

• What about the energy released?What about the energy released?•Each increase in Richter amplitude (by 10) increases Each increase in Richter amplitude (by 10) increases energy energy 32 times 32 times so,so,

•An M6 releases An M6 releases 3232 more times energy than an M5. more times energy than an M5.

•An M6 releases _____ more times energy than an An M6 releases _____ more times energy than an M4.M4.

•An M6 releases _____ more times energy than an An M6 releases _____ more times energy than an M3.M3.

•An M6 releases ________ more times energy than an An M6 releases ________ more times energy than an M2.M2.

32,76832,76832,76832,768

1,0241,0241,0241,024

1,048,5761,048,5761,048,5761,048,576

What observations can you make about the increasing energyWhat observations can you make about the increasing energy

release from one magnitude to the next?release from one magnitude to the next? What observations can you make about the increasing energyWhat observations can you make about the increasing energy

release from one magnitude to the next?release from one magnitude to the next? 2424

largest amplitudelargest amplitudelargest amplitudelargest amplitude

Richter MagnitudesRichter MagnitudesRichter MagnitudesRichter Magnitudes

< 2.0< 2.0 generally not felt, but recordedgenerally not felt, but recorded 600,000600,000

2.0 -2.92.0 -2.9 potentially perceptiblepotentially perceptible 300,000300,000

3.0 -3.93.0 -3.9 felt by somefelt by some 49,00049,000

4.0-4.94.0-4.9 felt by mostfelt by most 6,2006,200

5.0 – 5.95.0 – 5.9 damaging shocksdamaging shocks 800800

6.0 – 6.96.0 – 6.9 destructive in populous regionsdestructive in populous regions 266266

7.0 – 7.97.0 – 7.9 major EQ – inflicts serious damagemajor EQ – inflicts serious damage 1818

8.08.0 great EQ – destroys communities great EQ – destroys communities near epicenternear epicenter 1.41.4

< 2.0< 2.0 generally not felt, but recordedgenerally not felt, but recorded 600,000600,000

2.0 -2.92.0 -2.9 potentially perceptiblepotentially perceptible 300,000300,000

3.0 -3.93.0 -3.9 felt by somefelt by some 49,00049,000

4.0-4.94.0-4.9 felt by mostfelt by most 6,2006,200

5.0 – 5.95.0 – 5.9 damaging shocksdamaging shocks 800800

6.0 – 6.96.0 – 6.9 destructive in populous regionsdestructive in populous regions 266266

7.0 – 7.97.0 – 7.9 major EQ – inflicts serious damagemajor EQ – inflicts serious damage 1818

8.08.0 great EQ – destroys communities great EQ – destroys communities near epicenternear epicenter 1.41.4

Per/yearPer/yearPer/yearPer/year

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M 7.8M 7.8M 7.8M 7.8

M 5.6M 5.6M 5.6M 5.6M 6.6M 6.6M 6.6M 6.6

M 7.6M 7.6M 7.6M 7.6

M 4.2M 4.2M 4.2M 4.2

M 8.0M 8.0M 8.0M 8.0

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The Moment Magnitude Scale (MMS or MThe Moment Magnitude Scale (MMS or Mww))The Moment Magnitude Scale (MMS or MThe Moment Magnitude Scale (MMS or Mww))

•based on “work” done (Mbased on “work” done (Mww))•measures the energy releasedmeasures the energy released•based on the moment of the earthquakebased on the moment of the earthquake

•based on “work” done (Mbased on “work” done (Mww))•measures the energy releasedmeasures the energy released•based on the moment of the earthquakebased on the moment of the earthquake

Moment = Moment = Moment = Moment = Rigidity ofRigidity ofthe earththe earthRigidity ofRigidity ofthe earththe earth XXXX

Average amt. of slipAverage amt. of slipandand

size of the area that slippedsize of the area that slipped

Average amt. of slipAverage amt. of slipandand

size of the area that slippedsize of the area that slipped

• developed in the 1970’s – replaces the developed in the 1970’s – replaces the Richter ScaleRichter Scale

• uses magnitude values defined by the uses magnitude values defined by the Richter ScaleRichter Scale

• used by the USGS folksused by the USGS folks

• developed in the 1970’s – replaces the developed in the 1970’s – replaces the Richter ScaleRichter Scale

• uses magnitude values defined by the uses magnitude values defined by the Richter ScaleRichter Scale

• used by the USGS folksused by the USGS folks

(rock properties)(rock properties)(rock properties)(rock properties)

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Richter scale vs. Moment magnitude usingRichter scale vs. Moment magnitude usingdifferent starting assumptions:different starting assumptions:Richter scale vs. Moment magnitude usingRichter scale vs. Moment magnitude usingdifferent starting assumptions:different starting assumptions:

Richter ScaleRichter Scale::• assumes EQ focus is a pointassumes EQ focus is a point• best suited for EQ energy release from a best suited for EQ energy release from a small areasmall area• EQ intensity is based on amplitudeEQ intensity is based on amplitude measurements.measurements.

Richter ScaleRichter Scale::• assumes EQ focus is a pointassumes EQ focus is a point• best suited for EQ energy release from a best suited for EQ energy release from a small areasmall area• EQ intensity is based on amplitudeEQ intensity is based on amplitude measurements.measurements.

Moment Magnitude Scale:Moment Magnitude Scale:• assumes energy is released over a large areaassumes energy is released over a large area• measures the actual energy released and measures the actual energy released and considers the various rock types that waves considers the various rock types that waves move throughmove through

Moment Magnitude Scale:Moment Magnitude Scale:• assumes energy is released over a large areaassumes energy is released over a large area• measures the actual energy released and measures the actual energy released and considers the various rock types that waves considers the various rock types that waves move throughmove through

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I I I I a good earthquake. a good earthquake. a good earthquake. a good earthquake.

I will get an A on my exams and quizzesI will get an A on my exams and quizzes

Discuss with a friend:Discuss with a friend:

1.1.Explain the differences between theExplain the differences between the Mercalli Intensity scale, RichterMercalli Intensity scale, Richter scale and Moment scale.scale and Moment scale.

2. What’s wrong with the Mercalli Scale2. What’s wrong with the Mercalli Scale when compared to the Richter scale?when compared to the Richter scale?

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How do EQ’s provide scientists a look into the How do EQ’s provide scientists a look into the earth’s interior?earth’s interior?

Seismic waves propagate through the earth’sSeismic waves propagate through the earth’sinterior encountering different rock types.interior encountering different rock types.

• Seismic waves behave differently depending on the materialsSeismic waves behave differently depending on the materials they pass through. they pass through.

• Seismic discontinuitySeismic discontinuity::• A boundary inside the earth where the velocities andA boundary inside the earth where the velocities and directions of seismic waves change abruptly.directions of seismic waves change abruptly. refractedrefracted::

waves are bent as they pass from one materialwaves are bent as they pass from one material to anotherto another

reflectedreflected::waves are bounced backwaves are bounced back

absorbed:absorbed:waves are blocked or impededwaves are blocked or impeded

Seismic waves propagate through the earth’sSeismic waves propagate through the earth’sinterior encountering different rock types.interior encountering different rock types.

• Seismic waves behave differently depending on the materialsSeismic waves behave differently depending on the materials they pass through. they pass through.

• Seismic discontinuitySeismic discontinuity::• A boundary inside the earth where the velocities andA boundary inside the earth where the velocities and directions of seismic waves change abruptly.directions of seismic waves change abruptly. refractedrefracted::

waves are bent as they pass from one materialwaves are bent as they pass from one material to anotherto another

reflectedreflected::waves are bounced backwaves are bounced back

absorbed:absorbed:waves are blocked or impededwaves are blocked or impeded3030

Seismic discontinuitiesSeismic discontinuities

The Mohorovicic The Mohorovicic discontinuitydiscontinuity(the moho) and (the moho) and asthenosphereasthenosphereRocks are ductile with littleRocks are ductile with littlestrength (upper mantle) – strength (upper mantle) – lowlowvelocity zonevelocity zone

The Mohorovicic The Mohorovicic discontinuitydiscontinuity(the moho) and (the moho) and asthenosphereasthenosphereRocks are ductile with littleRocks are ductile with littlestrength (upper mantle) – strength (upper mantle) – lowlowvelocity zonevelocity zone

The mantle:The mantle:MesosphereMesosphere: 350km to the: 350km to thecore mantle boundary iscore mantle boundary ishighly compressed rock highly compressed rock (more dense) increasing (more dense) increasing seismic wave velocities.seismic wave velocities.

The mantle:The mantle:MesosphereMesosphere: 350km to the: 350km to thecore mantle boundary iscore mantle boundary ishighly compressed rock highly compressed rock (more dense) increasing (more dense) increasing seismic wave velocities.seismic wave velocities.

Seismic waves are refracted,Seismic waves are refracted,or reflected changing the waveor reflected changing the wavevelocity within the materialvelocity within the materialthey pass through.they pass through.

The earth’s mantle has severalThe earth’s mantle has severalseismic boundariesseismic boundaries

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How do geologists understand the “layering” of ourHow do geologists understand the “layering” of ourearth??earth??How do geologists understand the “layering” of ourHow do geologists understand the “layering” of ourearth??earth??

An earthquake takes place.An earthquake takes place.An earthquake takes place.An earthquake takes place.

P-waves ONLYP-waves ONLYP-waves ONLYP-waves ONLY

The absence of both P and SThe absence of both P and Swaves – NO WAVESwaves – NO WAVESThe Shadow ZoneThe Shadow Zone

The absence of both P and SThe absence of both P and Swaves – NO WAVESwaves – NO WAVESThe Shadow ZoneThe Shadow Zone

4040oo4040oo

P and S waves measuredP and S waves measuredat seismic stationsat seismic stationsP and S waves measuredP and S waves measuredat seismic stationsat seismic stations

3333

I I I I a good earthquake. a good earthquake. a good earthquake. a good earthquake.

I will get an A on my exams and quizzesI will get an A on my exams and quizzes

Discuss with a friend:Discuss with a friend:1.1.What is a seismic discontinuity?What is a seismic discontinuity?2.2. Explain the differences between refraction, Explain the differences between refraction, reflection and absorbsion of seismicreflection and absorbsion of seismic waves.waves.3. What seismic evidence suggests a low-3. What seismic evidence suggests a low- velocity zone within the upper mantle?velocity zone within the upper mantle?4. What is the shadow zone?4. What is the shadow zone?

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1.01.02.02.0

3.03.0

4.04.0

5.05.0

6.06.07.07.0

What is a tsunamiWhat is a tsunami? ? an enormous ocean wave created an enormous ocean wave created from an earthquakefrom an earthquake

or an undersea volcanic eruptionor an undersea volcanic eruption

What is a tsunamiWhat is a tsunami? ? an enormous ocean wave created an enormous ocean wave created from an earthquakefrom an earthquake

or an undersea volcanic eruptionor an undersea volcanic eruption

Sea floor shifts,Sea floor shifts,displacing water anddisplacing water andcreating tsunami.creating tsunami.

3535

I I I I A good earthquake A good earthquake A good earthquake A good earthquake

I will get an A on my exams and quizzesI will get an A on my exams and quizzesDiscuss with a friendDiscuss with a friend

1.1.Explain why the shadow zone existsExplain why the shadow zone exists

2. Why do P-waves occur on the other side2. Why do P-waves occur on the other side of the earth and S-waves do not?of the earth and S-waves do not?

3. How is the earth’s interior layering3. How is the earth’s interior layering understood --- if a person has not beenunderstood --- if a person has not been there??????there??????

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At this time – EQ’s cannot successfully be At this time – EQ’s cannot successfully be predicted.predicted.

In order to predict an EQ – science folks mustIn order to predict an EQ – science folks must predict a small range of predict a small range of uncertaintyuncertainty as to the as to the locationlocation and and timing.timing.

Predictions must be able to produce few failuresPredictions must be able to produce few failures and no false alarms.and no false alarms.

At this time – EQ’s cannot successfully be At this time – EQ’s cannot successfully be predicted.predicted.

In order to predict an EQ – science folks mustIn order to predict an EQ – science folks must predict a small range of predict a small range of uncertaintyuncertainty as to the as to the locationlocation and and timing.timing.

Predictions must be able to produce few failuresPredictions must be able to produce few failures and no false alarms.and no false alarms.

Can earthquakes be predicted???????????Can earthquakes be predicted???????????Can earthquakes be predicted???????????Can earthquakes be predicted???????????

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Can earthquakes be predicted along the SAF??Can earthquakes be predicted along the SAF??Can earthquakes be predicted along the SAF??Can earthquakes be predicted along the SAF??

Seismologists warn that Seismologists warn that an EQ larger than 6.5 an EQ larger than 6.5

will occur along the San will occur along the San Andreas Fault.Andreas Fault.

Seismologists warn that Seismologists warn that an EQ larger than 6.5 an EQ larger than 6.5

will occur along the San will occur along the San Andreas Fault.Andreas Fault.

BakersfieldHow do seismologistsHow do seismologistspredict this warning?predict this warning?How do seismologistsHow do seismologistspredict this warning?predict this warning?

3939

How geologists predict EQ’s How geologists predict EQ’s How geologists predict EQ’s How geologists predict EQ’s

Long Range EQ-Prediction – Seismic gap methodLong Range EQ-Prediction – Seismic gap methodLong Range EQ-Prediction – Seismic gap methodLong Range EQ-Prediction – Seismic gap method• Prediction of an EQ is based on Prediction of an EQ is based on probabilityprobability – What is the probability – What is the probability of an EQ?of an EQ?

•Statistical estimation when EQ’s take place over a given timeStatistical estimation when EQ’s take place over a given time span (the frequency of EQ’s)span (the frequency of EQ’s)

•Assumption that EQ’s are cyclic -- repetitiveAssumption that EQ’s are cyclic -- repetitive

Based on studies of the San Andreas Fault,Based on studies of the San Andreas Fault,the probability of an EQ is:the probability of an EQ is:Based on studies of the San Andreas Fault,Based on studies of the San Andreas Fault,the probability of an EQ is:the probability of an EQ is:

•Less than 10% in Northern CALess than 10% in Northern CA

•Parkfield (central CA) = 90%Parkfield (central CA) = 90%

•Southern CA = 30%Southern CA = 30%

•Less than 10% in Northern CALess than 10% in Northern CA

•Parkfield (central CA) = 90%Parkfield (central CA) = 90%

•Southern CA = 30%Southern CA = 30%

Seismic gap methodSeismic gap method - SAF - SAFSeismic gap methodSeismic gap method - SAF - SAF

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Use of the seismic gapUse of the seismic gapmethod along the SAF method along the SAF Use of the seismic gapUse of the seismic gapmethod along the SAF method along the SAF

Cyclic EQ’s in Parkfield,CACyclic EQ’s in Parkfield,CACyclic EQ’s in Parkfield,CACyclic EQ’s in Parkfield,CA

ParkfieldParkfieldParkfieldParkfield

BakersfieldBakersfield

185718571881188119011901192219221934193419661966

185718571881188119011901192219221934193419661966

Cyclic EQ M6 or greaterCyclic EQ M6 or greaterrupturing in the samerupturing in the samearea of the fault zonearea of the fault zone

Cyclic EQ M6 or greaterCyclic EQ M6 or greaterrupturing in the samerupturing in the samearea of the fault zonearea of the fault zone

1 EQ about 1 EQ about every 22 yearsevery 22 years1 EQ about 1 EQ about every 22 yearsevery 22 years

The next predicted EQThe next predicted EQbefore 1993before 1993

DID NOT HAPPEN!DID NOT HAPPEN!

The next predicted EQThe next predicted EQbefore 1993before 1993

DID NOT HAPPEN!DID NOT HAPPEN!

90%90%

90% chance of a major EQ90% chance of a major EQ90% chance of a major EQ90% chance of a major EQ4141

EC – Did the EQ on 9/28 reduce theEC – Did the EQ on 9/28 reduce theprobability of 90%?probability of 90%?EC – Did the EQ on 9/28 reduce theEC – Did the EQ on 9/28 reduce theprobability of 90%?probability of 90%?

September 28, 2004September 28, 2004M6 at ParkfieldM6 at Parkfield

September 28, 2004September 28, 2004M6 at ParkfieldM6 at Parkfield

www.quake.usgs.gov/recenteqs/www.quake.usgs.gov/recenteqs/

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I I I I a good earthquake a good earthquake a good earthquake a good earthquake

I will get an A on my exams and quizzesI will get an A on my exams and quizzes

Discuss with a friend:Discuss with a friend:

1.1.Can EQ’s be predicted? – Why or Why not?Can EQ’s be predicted? – Why or Why not?

2. Draw a picture of CA and show where2. Draw a picture of CA and show where the San Andreas fault is located.the San Andreas fault is located.

3. Explain how the seismic-gap method 3. Explain how the seismic-gap method works when predicting earthquakes.works when predicting earthquakes.

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Structural GeologyStructural GeologyFaults Faults

Structural GeologyStructural GeologyFaults Faults

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Structural Geology – Earth DeformationStructural Geology – Earth DeformationStructural Geology – Earth DeformationStructural Geology – Earth Deformation

FoldsFoldsFoldsFolds

Fault Fault

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How is rock deformed?How is rock deformed?How is rock deformed?How is rock deformed?(stress and strain relationships)(stress and strain relationships)

StressStress• force (pressure) acting on the rock surfaceforce (pressure) acting on the rock surface

StressStress• force (pressure) acting on the rock surfaceforce (pressure) acting on the rock surface

StrainStrain• a change in the shape (deformation) to thea change in the shape (deformation) to the response of stressresponse of stress

StrainStrain• a change in the shape (deformation) to thea change in the shape (deformation) to the response of stressresponse of stress

CompressionCompressionCompressionCompression

ShearShearShearShearundisturbed undisturbed cubecube

ExtensionExtensionExtensionExtension

JointJoint – fracture within a rock body – fracture within a rock bodyFault Fault – movement along a fracture or joint– movement along a fracture or jointJointJoint – fracture within a rock body – fracture within a rock bodyFault Fault – movement along a fracture or joint– movement along a fracture or joint

FaultsFaultsFaultsFaults

JointJoint

faultfault

AA

BB

BA

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DisplacementDisplacement

I I I I A good earthquake A good earthquake A good earthquake A good earthquake

I will get an A on my exams and quizzesI will get an A on my exams and quizzesDiscuss with a friendDiscuss with a friend

1.1.Describe the differences between stressDescribe the differences between stress and strainand strain2. Describe the stress types 2. Describe the stress types compressioncompression tensionaltensional, and , and shearshear 3.3.Draw a fault block and label:Draw a fault block and label:

1.1. hanging/footwallshanging/footwalls2.2. fault planefault plane

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FWFWHWHW

Normal FaultNormal Fault• HW HW downdown relative to FW relative to FW

Normal FaultNormal Fault• HW HW downdown relative to FW relative to FW

FWFW

HWHW

HWHW

FWFW

Reverse FaultReverse Fault• HW HW upup relative to FW relative to FW

Reverse FaultReverse Fault• HW HW upup relative to FW relative to FW

• Tensional stress• extension of crust• Tensional stress• extension of crust

• Compression stress• shorting of crust• Compression stress• shorting of crust

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FWFW

HWHW

HWHW

FWFW

HW

FW HWHW

FWFW

Normal faultingNormal faulting(extension of crust)(extension of crust) Normal faultingNormal faulting(extension of crust)(extension of crust)

Reverse faultingReverse faulting(compression of crust)(compression of crust) Reverse faultingReverse faulting(compression of crust)(compression of crust)

Vertical type faultsVertical type faultsVertical type faultsVertical type faults

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Strike-slip faulting: two blocks sliding past one anotherStrike-slip faulting: two blocks sliding past one anotherStrike-slip faulting: two blocks sliding past one anotherStrike-slip faulting: two blocks sliding past one another

Map ViewMap ViewMap ViewMap View

Turned to RightTurned to Right

Turned to LeftTurned to Left

What is the type of strike-slip fault?What is the type of strike-slip fault?

Right-Lateral – strike slipRight-Lateral – strike slipRight-Lateral – strike slipRight-Lateral – strike slip

San Andreas Fault – Wallace Creek, San Andreas Fault – Wallace Creek, Carrizo PlaneCarrizo PlaneSan Andreas Fault – Wallace Creek, San Andreas Fault – Wallace Creek, Carrizo PlaneCarrizo Plane

Right-LateralRight-LateralStrike slipStrike slip

Right-LateralRight-LateralStrike slipStrike slip

Wallace CreekWallace CreekWallace CreekWallace Creek

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What type of fault ?What type of fault ?What type of fault ?What type of fault ?

Normal faultNormal faultNormal faultNormal fault

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I I I I a good earthquake a good earthquake a good earthquake a good earthquake

I will get an A on my exams and quizzesI will get an A on my exams and quizzes

Discuss with a friend:Discuss with a friend:1.1.Draw a diagram showing the differencesDraw a diagram showing the differences between a between a normalnormal and and reversereverse fault. fault.

2. Explain the differences between the 2. Explain the differences between the cross-sectional fault views of a normal,cross-sectional fault views of a normal, reverse, and strike-slip faultreverse, and strike-slip fault

3.3.Describe the type of stresses that produceDescribe the type of stresses that produce both normal and reverse faults. both normal and reverse faults.

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