rock deformation deformation chapter 4 earthquakes and ... · chapter 4 earthquakes and tsunamis...
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Geology of the Hawaiian IslandsGeology of the Hawaiian IslandsClass 21Class 21
30 March 200430 March 2004MeanMean
838390909696
4141595983839494100100
54545959676783839494100100
55556161727285859595100100
A B C D F Exam Scores
Mean = 78.5Median = 83
Any Questions?Any Questions?
Chapter 4Chapter 4EarthquakesEarthquakes
and Tsunamisand Tsunamis
Rock DeformationRock Deformation
Large scale deformation of the Large scale deformation of the Earth’s crust = Plate TectonicsEarth’s crust = Plate TectonicsSmaller scale deformation = Smaller scale deformation = structural geologystructural geology
Deformation Deformation
Changes in volume or shape of a rock Changes in volume or shape of a rock bodybody= strain= strain
StressStress
The The forceforce that acts on a rock unit to that acts on a rock unit to change its shape and/or its volumechange its shape and/or its volumeCauses strain or deformationCauses strain or deformation
CompressionCompressionAction of coincident oppositely directed forces acting towards each other
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TensionTensionAction of coincident oppositely directed forces acting away from each other
ShearShearAction of coincident oppositely directed forces acting parallel to each other across a surface in a couple
Kinds of deformationKinds of deformation
Elastic Elastic vsvs Plastic Plastic Brittle Brittle vsvs DuctileDuctile
Factors that affect deformationFactors that affect deformation
TemperatureTemperature
PressurePressure
Strain rateStrain rate
Rock typeRock type
The variation of these factors determines if a rock will fault or fold.
Rocks are:Rocks are:
Elastic and brittle near the earth's Elastic and brittle near the earth's surfacesurfaceMore plastic and ductile deeper in the More plastic and ductile deeper in the crustcrustBecause of the increasing temperature Because of the increasing temperature and pressureand pressure
FoldsFolds
Most common ductile response to Most common ductile response to stress on rocks in the earth's cruststress on rocks in the earth's crust
Folding Due to Compressive Stress
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FractureFracture
Most common brittle response to Most common brittle response to stress stress With With NoNo displacement = displacement = JointJointWith displacement = With displacement = FaultFault
Joints commonly form when the Joints commonly form when the surface of a volcanic rock cools surface of a volcanic rock cools
and contractsand contracts
Faults Faults Occur when large stresses build up in Occur when large stresses build up in the crust, often due to lava movement the crust, often due to lava movement into shallow magma chambers into shallow magma chambers Classified according to the kind of Classified according to the kind of movement that has occurred along movement that has occurred along themthem
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Normal Fault Hanging walldrops down
Tom Bean
Reverse FaultHanging wallmoves up
Strike-slipFault
Faults Faults
Most faults in Hawaii are normal faultsMost faults in Hawaii are normal faultsGrabenGraben are commonare common
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WildroseWildrose GrabenGraben, Southern California, Southern CaliforniaFaults may move several meters in Faults may move several meters in a second or soa second or soThis movement within the earth's This movement within the earth's crust usually generates an crust usually generates an earthquakeearthquake
Tectonic earthquakesTectonic earthquakes
Most common kind Most common kind
Volcanic earthquakesVolcanic earthquakes
Caused by the movement of lava Caused by the movement of lava up toward the surface up toward the surface More common type in Hawaii than More common type in Hawaii than tectonic quakestectonic quakesGenerally much smaller in size than Generally much smaller in size than tectonic quakestectonic quakes
Focus = point where an earthquake originates
Epicenter = location at the surface directly above the focus
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Earthquake energy moves radially away from the focus
Many different kinds of earthquake Many different kinds of earthquake waves waves They travel at different speeds and They travel at different speeds and with different kinds of particle with different kinds of particle motionsmotions
Most common types of Most common types of earthquake waves:earthquake waves:
PP--waveswaves and and SS--waveswavesPPrimaryrimary waves travel the fastest in the waves travel the fastest in the crust and usually are the first waves to crust and usually are the first waves to arrivearriveSSecondaryecondary (or S(or Shearhear) waves are ) waves are slower and therefore take longer to slower and therefore take longer to arrivearrive
P-waves are compressional Waves S-waves are Shear Waves
Seismographs recordearthquakes
P-waves travel faster than S-waves,so they arrive at the recording station sooner
Difference in travel-time for P and S waves tellsus how far away the earthquake is from the recordingstation
We need3 recordingstations todetermine the location of theepicenter
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Earthquake Magnitude Earthquake Magnitude Describes the strength of an Describes the strength of an earthquakeearthquakeMagnitude scale is exponential Magnitude scale is exponential ----magnitude 6 has 10 times greater magnitude 6 has 10 times greater amplitude of ground shaking than amplitude of ground shaking than magnitude 5magnitude 5
Quake magnituderelated tosize ofP and Swaveamplitudeanddistancefrom quake
Earthquake Magnitude Earthquake Magnitude In Hawaii most earthquakes are rather In Hawaii most earthquakes are rather small (M < 3)small (M < 3)Associated with the volcanoes Associated with the volcanoes Small magnitude quakes not very Small magnitude quakes not very destructivedestructive
Earthquake Magnitude Earthquake Magnitude Earthquakes can be very destructive if Earthquakes can be very destructive if they are large enoughthey are large enoughThere have been several historic There have been several historic earthquakes in Hawaii that have earthquakes in Hawaii that have caused destruction due to ground caused destruction due to ground shaking or collapseshaking or collapse
Homework #7Homework #7
Due a week from today, April 6thDue a week from today, April 6thFind it on the web siteFind it on the web site
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TsunamiTsunami
Series of very long-wavelength waves on the ocean
TsunamiTsunami
== "tidal wave" "tidal wave"
Tsunami has nothing to do Tsunami has nothing to do with tideswith tides
Video clip:Video clip:TsunamisTsunamis
Tsunami waves Tsunami waves
Very small out in the open oceanVery small out in the open oceanAmplitude of only ~ 1 meterAmplitude of only ~ 1 meterVery long wavelengths (up to 100 km)Very long wavelengths (up to 100 km)Travel very fast (as much as 500 mph)Travel very fast (as much as 500 mph)
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Tsunami waves Tsunami waves
When waves reach shallow water, they When waves reach shallow water, they "feel" the shallow bottom, just like "feel" the shallow bottom, just like ordinary waves, and they slow down (to ordinary waves, and they slow down (to 2020--30 mph)30 mph)Because of the massive energy, this Because of the massive energy, this slowdown causes them to build up very slowdown causes them to build up very high (up to 50high (up to 50--100 m)100 m)
Tsunami can be generated by any Tsunami can be generated by any process that displaces a large process that displaces a large amount of water: amount of water:
SubSub--sea earthquakessea earthquakesGiant landslides Giant landslides Volcanic eruptionsVolcanic eruptionsMeteorite impactsMeteorite impacts
RunupRunupMaximum height above sea level Maximum height above sea level reached by a tsunami when it reached by a tsunami when it reaches shorereaches shore
Inundation Inundation Horizontal distance from the normal Horizontal distance from the normal water's edge reached by a tsunamiwater's edge reached by a tsunami
Hilo after 1946 tsunami
1952 Tsunamiwave passingunder bridgeat HaleiwaKaiaka Bay
1946 tsunami -- Hilo harbor: 159 fatalities
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Beach in Laie, O`ahu before tsunamigenerated by 1957 quake in Aleutians
1983 Japan tsunami -- water recedes 1983 tsunami in Japan104 people drowned700 boats, 59 houses
destroyed$800 Million property
damage
2000
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Questions? Questions?
S.E. O`ahu Field Trip S.E. O`ahu Field Trip Saturday, April 3rdSaturday, April 3rd9 am 9 am –– 3 pm3 pmMeet Here at 9:00 amMeet Here at 9:00 amWe will see Diamond Head, We will see Diamond Head, HanaumaHanaumaBay, Bay, KokoKoko Crater, Castle JunctionCrater, Castle JunctionBring water, hat, sun screen, walking Bring water, hat, sun screen, walking shoesshoes
ThursdayThursday
Web classWeb classNo formal class meetingNo formal class meeting
Next TuesdayNext Tuesday
Coasts and beachesCoasts and beachesRead Chapter 10Read Chapter 10
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