1

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

2

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

3

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

4

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

5

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

6

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

7

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

8

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)

9

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

10

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

11

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