Classroom presentations to accompany Understanding Earth, 3rd edition

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Classroom presentations to accompany
Understanding Earth, 3rd edition

• prepared by
• Peter Copeland and William Dupré
• University of Houston

Chapter 18 Earthquakes
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Part III Internal Processes, External Effects
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Earthquakes
Eric Marti/AP Photo
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Earthquakes

• earthquake movement of rock bodies past other
• fault locus of the earthquake movement
• faults come at all scales, mm to separation of
  lithospheric plates (e.g., San Andreas).

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Earthquake terms

• focus site of initial rupture
• epicenter point on surface above the focus

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Elastic Rebound Theory
Fig. 18.1a
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Elastic Rebound Theory
Fig. 18.1b
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Elastic Rebound Theory
Fig. 18.1c
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Elastic Rebound Theory
Fig. 18.1d
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1906 San Francisco Earthquake
Fig. 18.2
G.K. Gilbert
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1906 San Francisco Earthquake
Fault Offset (2.5m)
Fault Trace
Fig. 18.2
G.K. Gilbert
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Seismic Waves Radiate from the Focus of an
Earthquake
Fig. 18.3
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Seismology

• Study of the propagation of mechanical energy
  released by earthquakes and explosions through
  the Earth.
• When energy is released in this fashion, waves of
  motion (like the effect of a pebble tossed into a
  pond) are set up in the rocks surrounding the
  source of the energy (the focus).

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Seismic waves

• Waves are started because of initial tension or
  compression in the rock.
• Instruments used to measure these waves are
  called seismographs.

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Global Positioning System (GPS) to Monitor Ground
Motion
Fig. 18.4
Jet Propulsion Lab/NASA
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Seismographs Record Vertical or Horizontal Ground
Motion
Vertical
Horizontal
Fig. 18.5a,b
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Modern Seismograph
Fig. 18.5c
Kinematics
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Seismograph Record and Pathway of Three Types of
Seismic Waves
Fig. 18.6
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Two kinds of waves from earthquakes

• P waves (compressional) 68 km/s. Parallel to
  direction of movement (slinky), also called
  primary waves. Similar to sound waves.
• S waves (shear) 45 km/s. Perpen- dicular to
  direction of movement (rope) also called
  secondary waves. Result from the shear strength
  of materials. Do not pass through liquids.

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Comparison of P-wave and S-wave Motion
Fig. 18.7
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Two Types of Surface Waves
Fig. 18.8
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Time Lag Between S and P waves as with Distance
from Epicenter
Fig. 18.9a
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Seismic Travel-time Curve
Fig. 18.9b
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Locating the Epicenter
Fig. 18.9c
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Locating an epicenter

• The difference between the arrival times of the P
  and S waves at a recording station is a function
  of the distance from the epicenter.
• Therefore, you need three stations to determine
  the location of an epicenter.

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Measuring the force of earthquakes

• 1. Surface displacement
• 1964 Alaska earthquake displaced some parts of
  the seafloor by 50 ft.
• 1906 San Francisco earthquake moved the ground
  8.5 ft.
• 2. Size of area displaced
• Alaska 70,000 sq. miles

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Measuring the force of earthquakes

• 3. Duration of shaking
• Up to tens of seconds
• 4. Intensity scales
• Based on damage and human perception
• 5. Magnitude scales
• Based on amount of energy released

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Modified Mercalli Intensity Scale

• I Not felt
• II Felt only by persons at rest
• IIIIV Felt by persons indoors only
• VVI Felt by all some damage to plaster,
  chimneys
• VII People run outdoors, damage to poorly built
  structures
• VIII Well-built structures slightly damaged
  poorly built structures suffer major damage
• IX Buildings shifted off foundations
• X Some well-built structures destroyed
• XI Few masonry structures remain standing
  bridges destroyed
• XII Damage total waves seen on ground objects
  thrown into air

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Measuring the force of earthquakes

• 5. Magnitude scales, based on amount of energy
  released
• Richter scale amount of energy received 100 km
  from epicenter
• largest quake ever recorded 8.9 (rocks not
  strong enough for more). Earthquakes less than
  M2 are not felt by people

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Richter scale

• Richter scale amount of energy received 100 km
  from epicenter
• Largest quake ever recorded 8.9 (rocks not
  strong enough for more).
• Earthquakes less than M 2 are not felt by
  people.
• Scale is logarithmic
• Increase 1 unit 10 times greater shaking
• Increase 1 unit 30 times greater energy

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Maximum Amplitude of Ground Shaking Determines
Richter Magnitude
Fig. 18.10
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Richter Magnitude Versus Energy
Fig. 18.11
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Before Fault Movement
Fig. 18.12a
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Normal Fault
Fig. 18.12b
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Thrust (reverse) Fault
Fig. 18.12c
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Strike-slip Fault
Fig. 18.12d
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First Motion of P wave Arrivals
Fig. 18.13
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Distribution of earthquakes

• Not random
• Focused around plate margins (but also seen in
  plate interiors)

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World Seismicity, 19632000
Fig. 18.14
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Earthquakes Associated with Divergent and
Transform Margins
Fig. 18.15
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Earthquakes Associated with Convergent Plate
Margins
Fig. 18.16
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Damage due to earthquakes

• 1. Ground movement
• Earthquakes dont kill people,
• buildings kill people.
• 2. Fire
• 3. Tidal waves (tsunami)
• generate speeds up to 500800 km/hr
• in open ocean only 1m high but get
• larger when water gets shallow.

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Damage due to earthquakes

• 4. Landslides
• All kinds of mass wasting
• Liquifaction sudden loss of strength of
  water-saturated sediment
• Buildings fall down intact
• 5. Flood
• Dam break courses of rivers change

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Effects of the 1994 Northridge, CA, Earthquake
Fig. 18.17
1994 Chronmo Sohn/Sohn/Photo Resewarchers, Inc
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Effects of the 1995 Kobe, Japan, Earthquake
Fig. 18.18
Reuters/Corbis-Bettmann
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Generation of a Tsunami
Fig. 18.19
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Destruction Caused by 1998 Tsunami, Papua New
Guinea
Fig. 18.20
Brian Cassey/AP Photo
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Tsunami Barrier in Taro, Japan
Courtesy of Taro, Japan
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Earthquake prediction

• Long termimprecise (can be done)
• Short termprecise (very difficult)
• We can't stop earthquakes, so we have to be
  prepared for them.

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Seismic Hazard Map
Fig. 18.21
Courtesy of Kaye M. Shedlock, USGS
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New Housing Built Along the 1906 Trace of the San
Andreas Fault
Fig. 18.22
R.E. Wallace, USGS
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Demonstrating Earthquake Safety in Japan
Yves Gelie/Matriz
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Recent Earthquakes of Special Interest
Izmit
Loma Prieta
Kobe
Northridge
Papua
Table 18.1
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Stress Changes Caused by Regional Earthquakes in
Southern California (1979-1992)
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Table 18.1
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Table 18.1