Earthquakes
Ch. 15 Lesson 1
What are Earthquakes?What are Earthquakes?
•Earthquakes are the vibrations in the groundthat result from the movement along breaksin Earth’s Lithosphere.•Earthquakes are the vibrations in the groundthat result from the movement along breaksin Earth’s Lithosphere.
What are Earthquakes?What are Earthquakes?
•Why do rocks move along a fault?•Why do rocks move along a fault?
•The forces that move tectonic plates also pushand pull on rocks along faults•The forces that move tectonic plates also pushand pull on rocks along faults
–movement of the plate due to convection currents–movement of the plate due to convection currents
What are Earthquakes?What are Earthquakes?
•These forces can move the rock side to side(horizontally) or up and down (vertically)•These forces can move the rock side to side(horizontally) or up and down (vertically)
•The greater the force applied to a fault, thegreater the chance of a large and destructiveearthquake.•The greater the force applied to a fault, thegreater the chance of a large and destructiveearthquake.
Quick QuestionsQuick Questions
•Why are earthquakes much more common inCalifornia?•Why are earthquakes much more common inCalifornia?
•It is near (and in some places on top of) aplate boundary•It is near (and in some places on top of) aplate boundary
Quick QuestionsQuick Questions
•What do you think scientists can learn bystudying the damage caused by anearthquake?•What do you think scientists can learn bystudying the damage caused by anearthquake?
Quick QuestionsQuick Questions
•Are all earthquakes large and destructive?•Are all earthquakes large and destructive?
•No! The destructiveness depends on theamount of force applied to a fault. The greaterthe force, the more energy builds up in a fault•No! The destructiveness depends on theamount of force applied to a fault. The greaterthe force, the more energy builds up in a fault.
Where do Earthquakes Occur?Where do Earthquakes Occur?
The locations of major earthquakes that occurredbetween 2000 - 2008The locations of major earthquakes that occurredbetween 2000 - 2008
Where do Earthquakes Occur?Where do Earthquakes Occur?
•Notice, only a few earthquakes occurred in themiddle of a continent.•Notice, only a few earthquakes occurred in themiddle of a continent.
•Most earthquakes occur where?•Most earthquakes occur where?
Earthquakes and PlateBoundariesEarthquakes and PlateBoundaries
•Some earthquakes occur more than 100 kmbelow Earth’s surface.•Some earthquakes occur more than 100 kmbelow Earth’s surface.
•The deepest earthquakes occur where platescollide along a convergent plate boundarywhere subduction occurs•The deepest earthquakes occur where platescollide along a convergent plate boundarywhere subduction occurs
–Remember, oceanic meets continental crust!–Remember, oceanic meets continental crust!
Where do Earthquakes Occur?Where do Earthquakes Occur?
The locations of major earthquakes that occurredbetween 2000 - 2008The locations of major earthquakes that occurredbetween 2000 - 2008
Shallow EarthquakesShallow Earthquakes
•Shallow earthquakes are common whereplates separate along a divergent plateboundary, like the mid-ocean ridge system.•Shallow earthquakes are common whereplates separate along a divergent plateboundary, like the mid-ocean ridge system.
Shallow EarthquakesShallow Earthquakes
•Shallow earthquakes can also occur alongtransform plate boundaries like the SanAndreas Fault in California.•Shallow earthquakes can also occur alongtransform plate boundaries like the SanAndreas Fault in California.
Continental CollisionsContinental Collisions
•Earthquakes of varying depths occur wherecontinents collide.•Earthquakes of varying depths occur wherecontinents collide.
•Continental collisions result in the formationof large and deformed mountain ranges suchas the Himalayas in Asia.•Continental collisions result in the formationof large and deformed mountain ranges suchas the Himalayas in Asia.
Rock DeformationRock Deformation
•When force is applied to a body of rock,depending on the properties of the rock andthe force applied, the rock might bend orbreak.•When force is applied to a body of rock,depending on the properties of the rock andthe force applied, the rock might bend orbreak.
•When a force such as pressure is applied torock along plate boundaries, the rock canchange shape.•When a force such as pressure is applied torock along plate boundaries, the rock canchange shape.
–This is called rock deformation!–This is called rock deformation!
Rock DeformationRock Deformation
•Eventually the rockscan be deformed somuch that they breakand move.•Eventually the rockscan be deformed somuch that they breakand move.
•The image showshow rockdeformation hasresulted in grounddisplacement•The image showshow rockdeformation hasresulted in grounddisplacement
FaultsFaults
•When stress builds inplaces like a plateboundary rocks canform faults•When stress builds inplaces like a plateboundary rocks canform faults
•A fault is a break inEarth’s lithospherewhere one block ofrock moves toward,away from, or pastanother.•A fault is a break inEarth’s lithospherewhere one block ofrock moves toward,away from, or pastanother.
FaultsFaults
•When rocks move in any direction along a fault, anearthquake occurs.•When rocks move in any direction along a fault, anearthquake occurs.
•The direction that rocks move depends on theforces applied.•The direction that rocks move depends on theforces applied.
FaultsFaults
Quick QuestionsQuick Questions
•What is the relationship between earthquakeslocations and plate boundaries?•What is the relationship between earthquakeslocations and plate boundaries?
•Most earthquakes result from the buildup andrelease of stress along active plate boundaries•Most earthquakes result from the buildup andrelease of stress along active plate boundaries
Quick QuestionsQuick Questions
•Where do most earthquakes occur?•Where do most earthquakes occur?
•Where stress builds up along active plateboundaries•Where stress builds up along active plateboundaries
Quick QuestionsQuick Questions
•Why do earthquakes tend to be deeper andmore disastrous along convergent plateboundaries compared to earthquakes alongdivergent boundaries?•Why do earthquakes tend to be deeper andmore disastrous along convergent plateboundaries compared to earthquakes alongdivergent boundaries?
•More energy is built up and released whereplates move toward each other and where oneplate is pushed below the other (subduction)at convergent boundaries•More energy is built up and released whereplates move toward each other and where oneplate is pushed below the other (subduction)at convergent boundaries
Quick QuestionsQuick Questions
•What is rock deformation?•What is rock deformation?
•Occurs when a rock changes shape•Occurs when a rock changes shape
Quick QuestionsQuick Questions
•How can rock deformation result in grounddisplacement?•How can rock deformation result in grounddisplacement?
•Eventually rocks can become so deformed that theybreak and move. When rocks move, grounddisplacement can occur•Eventually rocks can become so deformed that theybreak and move. When rocks move, grounddisplacement can occur
Earthquake FocusEarthquake Focus
•When rocks movealong a fault, theyrelease energy thattravels as vibrations onand in Earth calledseismic waves.•When rocks movealong a fault, theyrelease energy thattravels as vibrations onand in Earth calledseismic waves.
•These waves originatewhere rocks first movealong the fault, at alocation inside Earthcalled the focus.•These waves originatewhere rocks first movealong the fault, at alocation inside Earthcalled the focus.
Earthquake EpicenterEarthquake Epicenter
•The epicenter isthe location onEarth’s surfacedirectly above theearthquake’s focus•The epicenter isthe location onEarth’s surfacedirectly above theearthquake’s focus
Seismic WavesSeismic Waves
•During an earthquake, a rapid release of energyalong a fault produces seismic waves.•During an earthquake, a rapid release of energyalong a fault produces seismic waves.
•These waves travel outward in all directionsthrough rock.•These waves travel outward in all directionsthrough rock.
–these waves are a transfer of energy–these waves are a transfer of energy
–create motion felt during earthquake–create motion felt during earthquake
–The energy is strongest near the epicenter and lessensas it moves outward–The energy is strongest near the epicenter and lessensas it moves outward
Types of Seismic WavesTypes of Seismic Waves
•Scientists use wave motion, wave speed, andthe type of material that the waves travelthrough to classify seismic waves.•Scientists use wave motion, wave speed, andthe type of material that the waves travelthrough to classify seismic waves.
•The 3 types of waves are•The 3 types of waves are
–Primary waves–Primary waves
–Secondary waves–Secondary waves
–Surface Waves–Surface Waves
Primary WavesPrimary Waves
•Primary Waves (P-waves) cause particlesin the ground to movein a push-pull motionsimilar to a coiledspring.•Primary Waves (P-waves) cause particlesin the ground to movein a push-pull motionsimilar to a coiledspring.
•They are the fastestmoving seismic waves•They are the fastestmoving seismic waves
•The first waves you feelfollowing anearthquake•The first waves you feelfollowing anearthquake
Secondary WavesSecondary Waves
•Secondary Waves (S-waves) are slower than P-waves.•Secondary Waves (S-waves) are slower than P-waves.
•Cause particles to moveup and down at rightangles relative to thedirection the wavetravels.•Cause particles to moveup and down at rightangles relative to thedirection the wavetravels.
–Like shaking a coiledspring side to side and upand down at the sametime–Like shaking a coiledspring side to side and upand down at the sametime
–Can’t move through liquid–Can’t move through liquid
Surface WavesSurface Waves
•Surface Waves cause particles in the ground tomove up and down in a rolling motion•Surface Waves cause particles in the ground tomove up and down in a rolling motion
–Similar to ocean waves–Similar to ocean waves
•Travel only on Earth’s surface closest to theepicenter•Travel only on Earth’s surface closest to theepicenter
–(only P and S waves can travel through Earth’s interior)–(only P and S waves can travel through Earth’s interior)
Seismic WavesSeismic Waves
Quick QuestionsQuick Questions
•What are the 3 types of faults•What are the 3 types of faults
•Strike-slip, normal, reverse•Strike-slip, normal, reverse
Quick QuestionsQuick Questions
•Where do strike-slip faults occur?•Where do strike-slip faults occur?
•Along transform plate boundaries•Along transform plate boundaries
Quick QuestionsQuick Questions
•What are seismic waves?•What are seismic waves?
•They are waves that travel as vibrations onand in Earth•They are waves that travel as vibrations onand in Earth
Quick QuestionsQuick Questions
•Where do theseismic waves ofan earthquakeoriginate?•Where do theseismic waves ofan earthquakeoriginate?
•Where rocksfirst move at anearthquake’sfocus•Where rocksfirst move at anearthquake’sfocus
Quick QuestionsQuick Questions
•Why is locating the epicenter of anearthquake important to scientists?•Why is locating the epicenter of anearthquake important to scientists?
•To observe patterns of movement along afault and to predict the likelihood of futureearthquakes nearby•To observe patterns of movement along afault and to predict the likelihood of futureearthquakes nearby
Quick QuestionsQuick Questions
•What is the difference between surface wavesand primary and secondary waves?•What is the difference between surface wavesand primary and secondary waves?
•Surface waves only travel on Earth’s surface.Primary and secondary waves also travelthrough Earth’s interior•Surface waves only travel on Earth’s surface.Primary and secondary waves also travelthrough Earth’s interior
Mapping Earth’s InteriorMapping Earth’s Interior
•Scientists that studyearthquakes are calledseismologists•Scientists that studyearthquakes are calledseismologists
•They use the properties ofseismic waves to mapEarth’s interior.•They use the properties ofseismic waves to mapEarth’s interior.
Mapping Earth’s InteriorMapping Earth’s Interior
•P-waves and S-waves change speed anddirection depending on the material theytravel through.•P-waves and S-waves change speed anddirection depending on the material theytravel through.
•By comparing these measurements to thedensities of different Earth materials,scientists have determined the composition ofEarth’s layers•By comparing these measurements to thedensities of different Earth materials,scientists have determined the composition ofEarth’s layers
•This figure shows the speed of P-waves and S-wavesat different depths within Earth’s interior.•This figure shows the speed of P-waves and S-wavesat different depths within Earth’s interior.
Remember Me?Remember Me?
Inner and Outer CoreInner and Outer Core
•S-waves cannot travel through the outer core!•S-waves cannot travel through the outer core!
•Why would this be?•Why would this be?
•Because the outer core is liquid unlike the solidinner core•Because the outer core is liquid unlike the solidinner core
•By analyzing the speed of P-weaves travelingthrough the core, seismologists found that theinner and outer cores are composed of mostlyiron and nickle•By analyzing the speed of P-weaves travelingthrough the core, seismologists found that theinner and outer cores are composed of mostlyiron and nickle
The MantleThe Mantle
•Seismic wave studies determined convectioncurrents in the mantle.•Seismic wave studies determined convectioncurrents in the mantle.
•The speeds of seismic waves depend ontemperature, pressure, and chemistry of therocks that the seismic waves travel through•The speeds of seismic waves depend ontemperature, pressure, and chemistry of therocks that the seismic waves travel through
•They slow down through hot material•They slow down through hot material
•Beneath mid-ocean ridges or hotspots•Beneath mid-ocean ridges or hotspots
•Seismic waves are faster in cool areas•Seismic waves are faster in cool areas
•Near subduction zones•Near subduction zones
Locating an Earthquake’s EpicenterLocating an Earthquake’s Epicenter
•A seismometermeasures and recordsground motion and canbe used to determinethe distance seismicwaves travel.•A seismometermeasures and recordsground motion and canbe used to determinethe distance seismicwaves travel.
•Ground motion isrecorded as aseismogram – agraphical illustration ofseismic waves•Ground motion isrecorded as aseismogram – agraphical illustration ofseismic waves
TriangulationTriangulation
•Seismologists use a method calledtriangulation to locate an earthquakesepicenter.•Seismologists use a method calledtriangulation to locate an earthquakesepicenter.
•This method uses the speeds and travel timesof seismic waves to determine the distance tothe earthquake epicenter from at least 3 (likea triangle) different seismomenters•This method uses the speeds and travel timesof seismic waves to determine the distance tothe earthquake epicenter from at least 3 (likea triangle) different seismomenters
Triangulation: Step 1Triangulation: Step 1
1)Find the arrival timedifference1)Find the arrival timedifference
• determine the numberof seconds betweenthe arrival of the first P-wave and the first S-wave on theseismogram.• determine the numberof seconds betweenthe arrival of the first P-wave and the first S-wave on theseismogram.
•This time difference iscalled lag time.•This time difference iscalled lag time.
•Subtract the two times!•Subtract the two times!
Triangulation: Step 2Triangulation: Step 2
2) Find the distance to theepicenter2) Find the distance to theepicenter
•Use a graph showingthe P-wave and S-wavelag time plotted againstdistance.•Use a graph showingthe P-wave and S-wavelag time plotted againstdistance.
•Look at the y-axis andlocate line thatintersects with lag timeyou calculated.•Look at the y-axis andlocate line thatintersects with lag timeyou calculated.
•Red the correspondingdistance from theepicenter on the x-axis•Red the correspondingdistance from theepicenter on the x-axis
Triangulation: Step 3Triangulation: Step 3
3)Plot the distance on a map3)Plot the distance on a map
Quick QuestionsQuick Questions
•How do scientistslearn about Earth’sinterior•How do scientistslearn about Earth’sinterior
•By using theproperties of seismicwaves to mapEarth’s interior•By using theproperties of seismicwaves to mapEarth’s interior
Quick QuestionsQuick Questions
•How did scientists discover that Earth’s outercore is liquid?•How did scientists discover that Earth’s outercore is liquid?
•Because S-waves cannot travel through theouter core•Because S-waves cannot travel through theouter core
Quick QuestionsQuick Questions
•Whathappens to P-waves and S-waves at adepth of2,500 km?•Whathappens to P-waves and S-waves at adepth of2,500 km?
•S-wavedsstop becauseit is the liquidouter core. P-wavesdecrease inspeed•S-wavedsstop becauseit is the liquidouter core. P-wavesdecrease inspeed
Quick QuestionsQuick Questions
•What is the difference between aseismometer and a seismogram?•What is the difference between aseismometer and a seismogram?
•A seismometer is an instrument thatmeasures ground motion. A seismograph is agraphical illustration of earthquake waves•A seismometer is an instrument thatmeasures ground motion. A seismograph is agraphical illustration of earthquake waves
3 Scales3 Scales
•Richter Scale•Richter Scale
•Moment Magnitude Scale•Moment Magnitude Scale
•Modified Mercalli Scale•Modified Mercalli Scale
Determining EarthquakeMagnitudeDetermining EarthquakeMagnitude
•The Richter Magnitude Scale uses the amountof ground motion at a given distance from anearthquake to determine the magnitude.•The Richter Magnitude Scale uses the amountof ground motion at a given distance from anearthquake to determine the magnitude.
–This is used when reporting to the public–This is used when reporting to the public
–It begins at zero, but there is no upper limit.–It begins at zero, but there is no upper limit.
–Each increase of 1 unit represents 10 times theamount of ground motion recorded–Each increase of 1 unit represents 10 times theamount of ground motion recorded
Richter Scale ExampleRichter Scale Example
•A magnitude 8 earthquake produces 10 timesgreater shaking than a magnitude 7earthquake and 100 times greater than amagnitude 6.•A magnitude 8 earthquake produces 10 timesgreater shaking than a magnitude 7earthquake and 100 times greater than amagnitude 6.
Moment of Magnitude ScaleMoment of Magnitude Scale
•A different scale used to measure the totalamount of energy released by the earthquake.•A different scale used to measure the totalamount of energy released by the earthquake.
–The units are exponential–The units are exponential
–For each increase of one unit on the scale, theearthquake releases 21.5 times more energy.–For each increase of one unit on the scale, theearthquake releases 21.5 times more energy.
Moment of Magnitude ScaleExampleMoment of Magnitude ScaleExample
•A magnitude 8 earthquake releases more than992 times the amount of energy than that of amagnitude 6.•A magnitude 8 earthquake releases more than992 times the amount of energy than that of amagnitude 6.
The Modified Mercalli ScaleThe Modified Mercalli Scale
•Measures earthquake intensity based ondescriptions of the earthquake’s effects onpeople and structures.•Measures earthquake intensity based ondescriptions of the earthquake’s effects onpeople and structures.
–Ranges from I – XII–Ranges from I – XII
• (barely noticeable to everything is destroyed)• (barely noticeable to everything is destroyed)
–Places covered in loose sediment will experience agreater intensity of shaking than places on solidbedrock.–Places covered in loose sediment will experience agreater intensity of shaking than places on solidbedrock.
Earthquake RiskEarthquake Risk
•Most earthquakes occur near __________________•Most earthquakes occur near __________________
•The ______________ plate boundary in Californiaand ________________ plate boundaries inOregon, Washington, and Alaska have the highestearthquake risks in the U.S.•The ______________ plate boundary in Californiaand ________________ plate boundaries inOregon, Washington, and Alaska have the highestearthquake risks in the U.S.
Earthquake Risk U.S.Earthquake Risk U.S.
TsunamiTsunami
•https://www.youtube.com/watch?v=3xKMFzKOIfQ