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• Introduction • Seismic Waves – Locating Earthquakes – Probing Earth’s interior • Effects of Earthquakes • Earthquake Risks and Predictions • Waiting for the BIG ONE 1 San Francisco CA - San Andreas Strike Slip Fault M=7.0 Loma Prieta EQ, 1989 Bay Bridge collapse 2 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 3 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 4 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. 5 • 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 6 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 7 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 8 • 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 9 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 10 M = 7.0 M = 8.3 First P wave First S wave Richter magnitude / EQ frequency / Energy released 11 • 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 – P-wave Shadow Zones S-wave Shadow Zone 12 • 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 • • • • • • Ground motion Landslides Ground displacement Liquefaction Tsunamis Aftershocks 13 Effects of Earthquakes • Ground motion • Landslides • Permanent ground displacement Effects of Earthquakes • • • • Ground motion Landslides Ground displacement Liquefaction 14 Effects of Earthquakes • • • • Ground motion Landslides Ground displacement Liquefaction • Tsunamis - seismic sea waves Effects of Earthquakes • • • • • • Ground motion Landslides Ground displacement Liquefaction Tsunamis Aftershocks 15 • 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 • • • • • 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 16 Earthquake Prediction and Risk • Microseisms, small strains near fault • Example: Parkfield, California 17 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 18 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 19 Earthquake Prediction • Animal behavior • Foreshocks • Patterns of earthquakes in time and space – Seismic Gaps Seismic Risk Map 20 Waiting for the BIG ONE The San Andreas fault • • • • 1906 San Francisco M 8.3 1857 Fort Tejon M=7.6 1994 Northridge M=6.4 1989 Loma Prieta M=7.0 • With respect to great EQs, EQs, southern section has been inactive longer— longer— – Is this region due for a great earthquake? • M 8 quake releases 32 times the energy of M 7 quake ! Earthquake distribution • narrow belts reflect plate boundary behavior 21 Earthquakes at Plate Boundaries • Divergent – depth: shallow • Transform • depth: shallow-intermediate < 20 km • Convergent • depth: shallow - intermediate - very deep (< 670 km) • define Benioff zones 22 23