Chapter 5: EARTHQUAKES &EARTH’S INTERIOR
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Transcript of Chapter 5: EARTHQUAKES &EARTH’S INTERIOR
Chapter 5: EARTHQUAKES &EARTH’S INTERIOR
Earthquakes & earthquake hazards• Earthquake
– Sudden release of energy • Seismology
– Scientific study of earthquakes & seismic waves
• Seismic waves– Shock waves traveling out
in all directions from earthquake’s source
Earthquake Hazards & Predictions• Primary hazard –
ground motion– Collapsing buildings,
bridges & other structures
– Aftershocks
Earthquake Hazards &Predictions• Secondary hazards
– Landslides– Fires– Ground liquefaction– Tsunamis
Earthquake Hazards &Predictions
Earthquake Hazards &Predictions• Recent Tsunami
– 2004 Sumatra– Magnitude 9.1– ~ 30 ft– 225,000
casualties
– 2011 Japan– Magnitude 9.0– ~25 ft.– 15,000
casualties
Earthquake prediction• Short-term
prediction & early warning– Precursor
phenomena– Foreshocks
• Long-term forecasting
• Paleoseismology– Study of prehistoric
earthquakes
Earthquake Readiness• Mercalli Intensity Scale
– Based on observations & damage to structures
– Subjective
The Science of Seismology• Seismograph
– Instrument to detect & measure vibrations of Earth’s surface
• Seismogram– Record made by a seismograph
Seismic waves• Body wave
– Travels through Earth’s interior• Surface wave
– Travels along Earth’s surface• Focus
– Where rupture occurs & earthquake’s energy is first released
• Epicenter– Point on Earth’s surface
directly above earthquake’s focus
Locating earthquakes• P (Primary) or Compressional waves:
– Alternating pulses of compression & expansion– Pass through all states of
matter• S (Secondary) or Shear
waves:– Side to side or up &down
movement– Pass only through solids– Travel slower than P waves
Locating earthquakes• Surface or L (Love)
wave:– Pass around Earth, not
through it– Cause most ground
shaking & damage– Slower than P & S
waves
Locating earthquakes• Finding the epicenter
– S – P lag time– Triangulation (3 points needed)
Measuring Earthquakes• Richter Magnitude
Scale– Magnitude vs. Intensity– Based on amplitudes of
seismic waves shown on seismograph
– Logarithmic scale• 10 fold increase in
amplitude = 1 unit increase
• 32-fold increase in energy = 1 unit increase
Measuring Earthquakes• Moment Magnitude Scale
– Based on rupture size, rock properties, & amount of displacement along fault surface
– Used for large earthquakes
Studying Earth’s Interior• Seismic
discontinuity– Boundary inside
Earth where seismic wave velocities change abruptly
Studying Earth’s Interior• 3 things can happen to seismic waves if they meet
a boundary:– Refraction: waves bend as they pass from one material to
another– Reflection: some or all of wave energy bounces back – Absorption: some or all of wave energy is blocked
How geologists look into Earth’s interior• Direct observation
– Drilling– Xenoliths
How geologists look into Earth’s interior• Indirect observation
– Magnetism– Astronomical observations
• Density– Meteorites
A Multilayered Planet• Crust
– Outermost compositional layer of solid Earth, part of lithosphere• Lithosphere = brittle
& solid– Thickness varies
• 8 km (oceanic) • 45 km (continental)
– Moho boundary
A Multilayered Planet• Mantle
– Middle compositional layer of Earth, between core & crust
– Asthenosphere: mantle where rock is near melting • Plastic & weak
– Mesosphere– Mantle-core
boundary
• Core– Innermost layer
• Where magnetic field is generated & most geothermal energy resides
– Outer core (liquid) – Inner core
(solid)
A Multilayered Planet