chapter 11: earthquakes. introduction earthquake: vibration of the earth produced by rapid release...
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Chapter 11: EarthquakesChapter 11: Earthquakes
IntroductionIntroduction Earthquake:
Vibration of the Earth produced by rapid release of energy
Most often caused by slippage along a fault Energy is in the form of waves
Focus: AKA Hypocenter Source of earthquake from which energy is
released in all directions Epicenter:
Surface location directly above the focus Seismometer:
Instrument sensitive to vibrations Located worldwide & used to measure
earthquakes
Earthquake: Vibration of the Earth produced by rapid
release of energy Most often caused by slippage along a fault Energy is in the form of waves
Focus: AKA Hypocenter Source of earthquake from which energy is
released in all directions Epicenter:
Surface location directly above the focus Seismometer:
Instrument sensitive to vibrations Located worldwide & used to measure
earthquakes
Focus & EpicenterFocus & Epicenter
Elastic ReboundElastic Rebound Stress applied
along pre-existent fault
Stress builds up, straining the rock
Eventually, frictional resistance is overcome
Slippage occurs, releasing the built up strain
Vibrations (earthquake) occur as the rock elastically returns to original shape
Stress applied along pre-existent fault
Stress builds up, straining the rock
Eventually, frictional resistance is overcome
Slippage occurs, releasing the built up strain
Vibrations (earthquake) occur as the rock elastically returns to original shape
Foreshocks & AftershocksForeshocks & Aftershocks
Small earthquakes, called foreshocks, often precede a major earthquake by days or, in some cases, by as much as several years
Adjustments that follow a major earthquake often generate smaller earthquakes called aftershocks
Small earthquakes, called foreshocks, often precede a major earthquake by days or, in some cases, by as much as several years
Adjustments that follow a major earthquake often generate smaller earthquakes called aftershocks
San Andreas FaultSan Andreas Fault Best studied fault system Fault creep:
Slow, gradual displacement
Some segments slip at ~regular intervals Results in small to
moderate quakes Stick-slip motion:
Storing elastic energy for hundreds of years before rupturing in great earthquakes
Quakes every 50 to 200 years
Best studied fault system Fault creep:
Slow, gradual displacement
Some segments slip at ~regular intervals Results in small to
moderate quakes Stick-slip motion:
Storing elastic energy for hundreds of years before rupturing in great earthquakes
Quakes every 50 to 200 years
SeismologySeismology Study of earthquake waves Dates back 2000 years to the
Chinese Seismographs:
Instruments which record earth’s movement relative to stationary mass
Stationary due to high inertia
Study of earthquake waves Dates back 2000 years to the
Chinese Seismographs:
Instruments which record earth’s movement relative to stationary mass
Stationary due to high inertia
Seismographs
Seismographs
Vertical motion
Horizontal motion
Parts of WavesParts of Waves
Frequency = 1/T
Types of seismic waves: P-waves S-waves Surface waves
Frequency = 1/T
Types of seismic waves: P-waves S-waves Surface waves
T
P-wavesP-waves Primary waves Compressional waves ( AKA Push-pull
waves) Travel through liquids & solids
Primary waves Compressional waves ( AKA Push-pull
waves) Travel through liquids & solids
S-wavesS-waves Secondary waves Shake waves Travel only through solids
Secondary waves Shake waves Travel only through solids
Surface WavesSurface Waves Travel along Earth’s surface Greatest amplitude, slowest velocity Cause greatest destruction AKA Long waves or L-waves
Travel along Earth’s surface Greatest amplitude, slowest velocity Cause greatest destruction AKA Long waves or L-waves
Locating the SourceLocating the Source Epicenter located from difference in arrival
time of P-wave and S-wave Requires seismograms from three locations
AKA Triangulation
Epicenter located from difference in arrival time of P-wave and S-wave
Requires seismograms from three locations AKA Triangulation
TriangulationTriangulation
Practice TriangulationPractice TriangulationLocation
Time Interval
Distance (km)
Distance (cm)
Cape Town
13 min 30 sec
Rio de Janeiro
10 min10 sec
Luanda, Angola
7 min45 sec
0
60
120
180
240
300
360
420
480
540
600
660
720
780
840
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance to Epicenter (km)
P-S Interval (seconds)
Practice TriangulationPractice TriangulationLocation
Time Interval
Distance (km)
Distance (cm)
Cape Town
13 min 30 sec
4800
Rio de Janeiro
10 min10 sec
Luanda, Angola
7 min45 sec
0
60
120
180
240
300
360
420
480
540
600
660
720
780
840
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance to Epicenter (km)
P-S Interval (seconds)
Practice TriangulationPractice TriangulationLocation
Time Interval
Distance (km)
Distance (cm)
Cape Town
13 min 30 sec
4800
Rio de Janeiro
10 min10 sec
3700
Luanda, Angola
7 min45 sec
0
60
120
180
240
300
360
420
480
540
600
660
720
780
840
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance to Epicenter (km)
P-S Interval (seconds)
Practice TriangulationPractice TriangulationLocation
Time Interval
Distance (km)
Distance (cm)
Cape Town
13 min 30 sec
4800
Rio de Janeiro
10 min10 sec
3700
Luanda, Angola
7 min45 sec
2900
0
60
120
180
240
300
360
420
480
540
600
660
720
780
840
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Distance to Epicenter (km)
P-S Interval (seconds)
Practice TriangulationPractice Triangulation
Location
Time Interval
Distance (km)
Distance (cm)
Cape Town
13 min 30 sec
4800
Rio de Janeiro
10 min10 sec
3700
Luanda, Angola
7 min45 sec
2900
1.2 cm = 1050 km
1.2 cm = x
1050 km distance
Luanda
Practice TriangulationPractice Triangulation
Location
Time Interval
Distance (km)
Radius (cm)
Cape Town
13 min 30 sec
4800 5.5
Rio de Janeiro
10 min10 sec
3700
Luanda, Angola
7 min45 sec
2900
1.2 cm = 1050 km
1.2 cm = x
1050 km distance
Luanda
Practice TriangulationPractice Triangulation
Location
Time Interval
Distance (km)
Radius (cm)
Cape Town
13 min 30 sec
4800 5.5
Rio de Janeiro
10 min10 sec
3700 4.2
Luanda, Angola
7 min45 sec
2900
1.2 cm = 1050 km
1.2 cm = x
1050 km distance
Luanda
Practice TriangulationPractice Triangulation
Location
Time Interval
Distance (km)
Radius (cm)
Cape Town
13 min 30 sec
4800 5.5
Rio de Janeiro
10 min10 sec
3700 4.2
Luanda, Angola
7 min45 sec
2900 3.3
1.2 cm = 1050 km
1.2 cm = x
1050 km distance
Luanda
Measuring Earthquake SizesMeasuring Earthquake Sizes Intensity Scale
Mercalli Intensity Scale Based on destruction of buildings
Magnitude Scales Richter Magnitude (logarithmic) Based on the Amplitude of the largest
seismic wave recorded on seismogram
Intensity Scale Mercalli Intensity Scale Based on destruction of buildings
Magnitude Scales Richter Magnitude (logarithmic) Based on the Amplitude of the largest
seismic wave recorded on seismogram
Mercalli Intensity Scale
Mercalli Intensity Scale
Richter Magnitude Scale
Richter Magnitude Scale
Earthquake DestructionEarthquake Destruction
Seismic Vibrations Tsunami Landslides & Ground Subsidence Fire
Seismic Vibrations Tsunami Landslides & Ground Subsidence Fire
Formation of TsunamisFormation of Tsunamis
Global Distribution of Earthquakes
Global Distribution of Earthquakes
Evidence for Plate TectonicsEvidence for Plate Tectonics