Intro to geology

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• Intro to geology
• Plate tectonics
• Minerals
• Rocks
• Igneous rocks
• Volcanism
• Weathering erosion
• Sediments and Sedimentary rocks
• Metamorphic rocks
• Rock record and Geologic time
• Rock deformation
• 19. Earthquakes
• 20. Evolution of continents
• 21. Exploring Earths Interior
• 17. Earth beneath the ocean, shorelines
• 12. Mass wasting
• 13. Hydrologic cycle and Groundwater
• 14. Streams
• 15. Deserts winds

Where are we?
Dynamic motions
External factors
Resources
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CHAPTER 19 Earthquakes

1. Some recent Earthquakes
2. What is an Earthquake
3. Seismology
4. Locating an Earthquake
5. Earthquake intensity and magnitude
6. Earthquake and plate tectonics
7. Earthquake destruction

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Earthquakes Study questions

• Know the definition of an earthquake and how it
  is related to fault movement
• Foreshocks, aftershocks, elastic rebound
• What is the difference between earthquake focus
  and epicenter?
• Know the three different kinds of seismic waves,
  and their characteristic motion, and properties
  of propagation.
• How is an earthquake epicenter located?
• Earthquake depth and how they are related to
  different kinds of plate boundaries and
  increasing distance from a subduction zone.
• Know the Richter magnitude scale and what each
  unit means with respect to increase in wave
  amplitude and energy.
• Which factors contribute to the destruction
  caused by earthquakes?

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2) What is an earthquake?
Fault - crack in Earth where slip occurs
Earthquake vibration of earth, often caused by
slippage along a fault
Earthquake focus - fault slip location
Epicenter point on earths surface directly
above focus
From Tarbuck/Lutgens Earth
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Remember from Ch. 11 Rock deformation
Fault definition a fracture where displacement
has occurred rocks on either side of fault have
moved relative to each other.
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2) What is an earthquake?

• elastic rebound
• - plates are continually moving fault is stuck
• - crust starts deforming (stores elastic energy)
• fault breaks, releases elastic energy, rock
  snaps back

Fig. 19.12
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2) What is an earthquake?
aftershocks small earthquakes
that follow an initial earthquake in same
vicinity
foreshocks small earthquakes
that sometimes precede a large one
by few days
See Fig. 19.3
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3) Seismology
seismology - the study of earthquake waves,
earthquakes, Earth
seismogram - recording of ground shaking from
seismographs
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3) Seismology Types of seismic waves
body waves P-waves (P for primary) S-wave
s (S for secondary)
travel in Earths interior
surface waves
travel on Earths surface
Figure Story 19.5
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3) Seismology Types of seismic waves
Motion produced by the different wave types
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4) Locating an earthquake
P-waves S-wave travel at different speeds
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4) Locating an earthquake
See Fig. 9.16
1. Measure time between P and S wave on
seismogram 2. Use travel-time graph to get
distance to epicenter 3. Draw circle on a map
with radius of that distance 4. Three or more
circles should intersect at EQ!
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5) Earthquake Intensity and magnitude

• Richter Magnitude
• Moment Magnitude

• Richter magnitude - concept introduced by Charles
  Richter in 1935
• Amplitude of the largest seismic wave recorded
  (P, S, or surface) and distance
• Note Logarithmic scale

Fig. 19.7

• Related to physical properties of faulting
• Proportional to seismic energy released
• Proportional to area of fault break

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5) Earthquake Intensity and magnitude

• Large Earthquakes occur less frequently than
  smaller ones!

Fig. 19.8
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5) Earthquake Intensity and magnitude
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6) Earthquake and plate tectonics

• recall fault types (from Ch. 11)

See Fig. 19.10
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6) Earthquake and plate tectonics
Shallow Normal faulting, transform faulting,
thrust (reverse) fault
Intermediate Deep subduction zones
See Fig. 19.13 and 19.12
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7) Earthquake destruction

• important factors

Intensity duration of shaking Soil type (soft?
hard rock?) Building design

• other effects

Liquifaction Tsunamis
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7) Earthquake destruction

• important factors

Intensity duration of shaking Soil type (soft?
hard rock?) Building design

• other effects

Liquifaction Tsunamis
Seismic hazard map (see Fig. 19.21)
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7) Earthquake destruction

• important factors

Intensity duration of shaking Soil type (soft?
hard rock?) Building design

• other effects

Liquifaction Tsunamis
Fig. 19.18
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Earthquakes A few sample MC
  What does the elastic rebound theory
describe? A. the build-up and release of stress
during an earthquake B. the fluctuations in
groundwater prior to an earthquake C. the
formation of mountain ranges by successive
earthquakes D. the uplift of the crust in
response to erosion
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Earthquakes A few sample MC
  What causes the up-and-down wiggles on the
seismogram? A. electromagnetic pulses B.
ground vibrations C. tsunami waves D.
variations in air pressure
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Earthquakes A few sample MC
  Which of the following correctly lists the
order in which seismic waves arrive at a
seismograph station? A. P waves ? surface waves
? S waves B. P waves ? S waves ? surface
waves C. S waves ? P waves ? surface waves D.
surface waves ? P waves ? S waves
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Earthquakes A few sample MC
  An earthquakes Richter magnitude is based on
______. A. the amount of energy released during
an earthquake B. the amount of ground movement
caused by seismic waves C. the distance between
the earthquake and the seismograph station D.
the observed effects on people and structures
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Earthquakes A few sample MC
  The ground motion during a Richter magnitude 8
earthquake is ______ times greater than the
ground motion during a Richter magnitude 6
earthquake. A. 2 B. 10 C. 100 D. 1000
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Earthquakes A few sample MC
  How many seismograph stations are needed to
locate the epicenter of an earthquake? A. 1 B.
2 C. 3 D. 4
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Earthquakes A few sample MC
Shallow earthquakes, less than 20 km deep, are
associated with ___________. A. convergent
plate boundaries B. divergent plate
boundaries C. transform plate boundaries D. all
of the above