Download • Introduction • Seismic Waves • Effects of Earthquakes • Earthquake

• Introduction
• Seismic Waves
– Locating Earthquakes
– Probing Earth’s interior
• Effects of Earthquakes
• Earthquake Risks and Predictions
• Waiting for the BIG ONE
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San Francisco CA - San Andreas Strike Slip Fault
M=7.0 Loma Prieta EQ, 1989 Bay Bridge collapse
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M=8.3 San Francisco, April 18, 1906
3,000 casualties
http://earthquake.usgs.gov/recenteqsww/Quakes/uscvad.htm
Bam, Iran
Mw = 6.6
December 26, 2003
30,000 casualties/30,000 injured
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Introduction
• An earthquake is a trembling of Earth caused by
sudden release of stored energy, usually along faults.
San Andreas fault, CA
Introduction
• Earthquakes are also associated with
volcanic activity
Eruption of Mt. St. Helens
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Introduction
• Earthquakes confined to a few narrow belts
Introduction
• The focus of an earthquake is the location within
the earth where the earthquake originates.
• The epicenter is the point on the earth’s surface
directly above the focus.
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• Introduction
• Seismic Waves
– Location and size of Earthquakes
– Probing Earth’s Interior
• Effects of Earthquakes
• Earthquake Risks and Predictions
• Waiting for the BIG ONE
Seismic Waves
• Seismic Waves are the waves of
energy produced by an earthquake.
• Seismograms reveal two main groups
of seismic waves
• Seismometer
– Suspended weight that
detects wave motion
• Seismograph
– Drum/computer that
records wave motion
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Seismic Waves
• Body waves
• P-waves - travel through solids and fluids
• S-waves - only travel through solids
– Slower than P waves
–Surface waves
• Slowest
• Most damaging
Body Waves
Surface Waves
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Seismogram
1906 San Franscico Earthquake
First P wave
First S wave
Seismic Waves
Seismic waves are useful for:
1. determining size & location of
earthquakes
2. monitoring volcanic activity
3. monitoring nuclear explosions
4. probing interior of the Earth
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• Introduction
• Seismic Waves
– Location and size of Earthquakes
– Probing Earth’s Interior
• Effects of Earthquakes
• Earthquake Risks and Predictions
• Waiting for the BIG ONE
Locating an Earthquake
• The difference between P and S wave velocity
provides method to locate epicenter
– Travel time curves
First P wave First S wave
10 min. time difference
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Locating an Earthquake
• Epicenter located using seismograms from 3 stations
Measuring the Size of Earthquakes
Magnitude - measure of the amount of energy
released during an earthquake
– Modified Mercalli scale
• observed damage
– Richter scale (M)
• calculate energy released from amplitude of waves
– Moment magnitude scale (Mw)
• energy from rock strength, surface rupture area,
displacement along fault
• logarithmic scale--each unit corresponds to roughly a
10-fold increase in released energy
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M = 7.0
M = 8.3
First P wave
First S wave
Richter magnitude / EQ frequency / Energy released
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• Introduction
• Seismic Waves
– Location and size of Earthquakes
– Probing Earth’s Interior
• Effects of Earthquakes
• Earthquake Risks and Predictions
• Waiting for the BIG ONE
Earth’s Internal Structure
• The Core
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P-wave Shadow Zones
S-wave Shadow Zone
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• Introduction
• Seismic Waves
– Location and size of Earthquakes
– Probing Earth’s Interior
• Effects of Earthquakes
• Earthquake Risks and Predictions
• Waiting for the BIG ONE
Effects of Earthquakes
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Ground motion
Landslides
Ground displacement
Liquefaction
Tsunamis
Aftershocks
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Effects of Earthquakes
• Ground motion
• Landslides
• Permanent ground displacement
Effects of Earthquakes
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Ground motion
Landslides
Ground displacement
Liquefaction
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Effects of Earthquakes
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Ground motion
Landslides
Ground displacement
Liquefaction
• Tsunamis - seismic sea waves
Effects of Earthquakes
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Ground motion
Landslides
Ground displacement
Liquefaction
Tsunamis
Aftershocks
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• Introduction
• Seismic Waves
– Location and size of Earthquakes
– Probing Earth’s Interior
• Effects of Earthquakes
• Earthquake Risks and Predictions
• Waiting for the BIG ONE
Earthquake Prediction and Risk
Scientific techniques being explored
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Microseisms, small strains near fault
Changes in properties of rock near fault
Water levels, Radon in wells
Surface tilt and changes of elevation
Patterns of past Earthquakes
– In space and time
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Earthquake Prediction and Risk
• Microseisms, small strains near fault
• Example: Parkfield, California
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San Andreas fault
Earthquake Prediction and Risk
• Microseisms, small strains near fault
• Changes in properties of rock near fault
• Water levels in wells
Water well
monitoring
along the San
Andreas fault
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Earthquake Prediction
• Surface tilt and elevation changes
Lasers measure very small changes in distance and angles
Earthquake Prediction and Risk
• Microseisms, small strains near fault
• Example: Parkfield, California
Global
Positioning
System (GPS)
measurements
of motion via
satellite
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Earthquake Prediction
• Animal behavior
• Foreshocks
• Patterns of earthquakes in time and space
– Seismic Gaps
Seismic Risk Map
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Waiting for the
BIG ONE
The San Andreas fault
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1906 San Francisco M 8.3
1857 Fort Tejon M=7.6
1994 Northridge M=6.4
1989 Loma Prieta M=7.0
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With respect to great EQs,
EQs,
southern section has been
inactive longer—
longer—
– Is this region due for a
great earthquake?
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M 8 quake releases 32 times
the energy of M 7 quake !
Earthquake distribution
• narrow belts reflect plate boundary behavior
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Earthquakes at Plate Boundaries
• Divergent
– depth: shallow
• Transform
• depth: shallow-intermediate < 20 km
• Convergent
• depth: shallow - intermediate - very
deep (< 670 km)
• define Benioff zones
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