Download Chapter 19 Notes

Chapter 19 Notes
Earthquakes
Stress and Strain
• Earthquakes occur when stress builds up and
causes movement in the Earth’s crust
• Compression: squeezing forces
• Tension: pulling forces
• Shear: opposing parallel forces/twisting
• Elastic deformation: initial response to stress
• plastic deformation occurs under high stress
just before breaking
Faults
• Normal fault:
produced by
tension forces
• Reverse fault:
produced by
compression forces
• Strike-slip fault:
produced by shear
forces
Earthquake Waves
• Body Waves
– Primary (P-waves): compression waves; move
parallel to the direction of wave motion
– Secondary (S-waves): transverse waves; move at
right angles to the direction of wave motion
• Surface waves: move sideways and up and
down
Earthquake Waves
• P-waves move
fastest
• Surface waves are
slowest, last the
longest, and are the
most destructive
Earthquake location
• Focus: the origin of
the EQ waves
• Epicenter: “above”
the center
Earthquake Measurement
• Seismometer: an instrument that records EQ
waves
• Seismogram: the record of EQ waves
Time travel curves
• The difference in arrival time of the P-waves
and S-waves can show how far the waves have
travelled.
Clues to Earth’s Interior
• EQ waves are
reflected and
refracted in
different ways
by the different
materials inside
the Earth
Measuring Earthquakes
• Richter Scale:
– measures magnitude
– energy released
– numeric scale (no true upper limit)
• Modified Mercalli Scale:
– measures intensity
– based on the amount of damage
– Roman numerals I to XII
Richter Scale
Mercalli Isoseismic Map
Locating an Earthquake
• The P-wave and Swave arrival times
determine the
distance a station is
to an EQ
• Three stations are
required to locate
the epicenter of an
EQ
Seismic Belts
• Circum-Pacific and Mediterranean-Asian belts
Earthquake Hazards
• “Earthquakes don’t kill people, buildings do.”
• Structural failures
– Brittle building materials cause more damage
– Building height oscillations
• Land and soil failure
– Soil liquefaction
• Tsunami
– Ocean wave generated by sea floor movement
U.S. Earthquake Risk