EARTHQUAKES

1
EARTHQUAKES
2
What are Earthquakes?

• The shaking or trembling caused by the sudden
  release of energy
• Usually associated with faulting or breaking of
  rocks
• Continuing adjustment of position results in
  aftershocks
• Usually occur at plate boundaries

3
Elastic rebound theory - explains how energy is
released during an earthquake
Elastic Rebound Theory

• Rocks deform or bend
• Rocks rupture when pressure accumulates in rocks
  on either side of a fault and build to a level
  which exceeds the rocks' strength.
• Finally, rocks rebound and return to their
  original shape when the accumulated pressure is
  released.

4
(No Transcript)
5

• Earthquake Vocabulary

• The point within Earth where faulting begins is
  the focus. This is where energy is released.
• The point directly above the focus on the surface
  is the epicenter.

6
Vocabulary Continued

• Seismology study of earthquakes
• Seismogram the record of an earthquake
• Seismograph instrument used to record
  earthquakes (creates seismograms)

7

• Seismogram

8
Seismic Waves

• Most of the damage and the shaking people feel
  during an earthquake is from the seismic waves.
• Earthquake vibrations or seismic waves are of two
  kinds body waves and surface waves.
• Body waves travel through Earth
• Surface waves travel along or just below the
  surface

9
Body Waves

• P or primary waves
• fastest waves
• travel through solids, liquids, or gases
• compressional wave, material movement is in the
  same direction as wave movement
• S or secondary waves
• slower than P waves
• travel through solids only
• shear waves - move material perpendicular to wave
  movement

10
(No Transcript)
11
Surface Waves R and L waves

• Surface Waves
• Travel just below or along the grounds surface
• Slower than body waves
• Rayleigh rolling motion
• Love side-to-side motion
• Especially damaging to buildings

12
(No Transcript)
13
How is an Earthquakes Epicenter Located?

• P waves arrive first, then S waves, then L and R
• Average speeds for all these waves is known
• After an earthquake, the difference in arrival
  times at a seismograph station can be used to
  calculate the distance from the seismograph to
  the epicenter

14
How is an Earthquakes Epicenter Located?

• Time-distance graph showing the average travel
  times for P- and S-waves.
• The farther away a seismograph is from the focus
  of an earthquake, the longer the interval between
  the arrivals of the P- and S- waves

15
(No Transcript)
16
How is an Earthquakes Epicenter Located?

• 3 seismograph stations are needed to locate the
  epicenter
• A circle where the radius equals the distance to
  the epicenter is drawn
• The intersection of the circles locates the
  epicenter

17
(No Transcript)
18
(No Transcript)
19
Measuring the Size Strength of an Earthquake

• Intensity is a qualitative measurement
• Mercalli Scale
• Scale of I XII
• Measures damage/sensations

20
Mercalli Scale - Intensity

• Modified Mercalli Intensity Map
• 1994 Northridge, CA earthquake, magnitude 6.7

21
(No Transcript)
22
Measuring the Size Strength of an Earthquake

• Magnitude is a quantitative measurement
• Richter Scale
• Measures total energy released
• Amplitude of largest wave
• Exponential scale (30-fold energy increase for
  each unit)
• 6.5 releases 30x more energy than 5.5
• 6.5 releases 900x more energy than 4.5 (30 x 30)
• Strongest recorded 8.6 (S.Chile)

23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
The Destructive Effects of Earthquakes

• Ground Shaking
• The most destructive of all earthquake hazards is
  ground shaking.
• An area's geology, earthquake magnitude, the type
  of building construction, and duration of shaking
  determine the amount of damage caused.

Fig. 8.13, p. 202, Fig. 8.15, p. 203
27
The Destructive Effects of Earthquakes

• Liquefaction occurs when clay loses its cohesive
  strength during ground shaking

Fig. 8.14, p. 203
28
The Destructive Effects of Earthquakes

• Fire occurs when gas and water lines break

Geo-inSight 4. and 7. , p. 205
29
The Destructive Effects of Earthquakes

• Tsunami Killer Waves in 2004, a magnitude 9.0
  earthquake offshore from Sumatra generated the
  deadliest tsunami in history.

Fig. 8.16, p. 207
30
Stepped Art
Fig. 8-16b, p. 207
31
The Destructive Effects of Earthquakes

• Ground Failure landslides and rock slides are
  responsible for huge amounts of damage and many
  deaths.

Fig. 8.17, p. 208
32
San Andreas Fault

• Ground failure can result in building / road
  collapse

Geo-inSight 5. and 6. p. 205
33
San Andreas Fault
Geo-inSight 1-3., p. 204