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Title: Introduction to Seismology:


1
Introduction to Seismology
  • Jesse F. Lawrence

2
Earthquakes
  • Earthquakes have long excited the minds of man.

3
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4
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5
Fundamental Idea of Seismology
  • The Earth ruptures, releasing vibrational energy.
  • Vibrational energy travels through the Earth.
  • A seismometer records the vibrations some
    distance away.

6
Ray Theory
  • Seismic waves can be idealized as rays.
  • They fan out in all directions from an earthquake.

7
Ray Theory Examples
  • Seismic waves can be idealized as rays.
  • The rays fan out in all directions from an
    earthquake.
  • The rays can bounce off of objects in the Earth.
  • The surface
  • The core

8
Ray Theory Examples
  • Sometimes the waves make multiple bounces up and
    down through the Earth.

9
Ray Theory Examples
  • Energy can also bounce off of smaller interfaces
  • Like interfaces between sediment layers
  • The crust-mantle boundary

10
Seismic Reflection Survey
  • Man made sources and receivers can be placed at
    regular distances.
  • Energy bounces off of interfaces at shallow
    depths.

11
First Motion Fault Orientation
  • Energy leaving an Earthquake can have positive or
    negative amplitude
  • Motion toward (positive) or away (negative) from
    the receiver.
  • We can back out the direction of motion of the
    fault.

12
Inversion
  • Based on the data, we develop a model of the
    Earth.
  • Calculate synthetic data based on the input
    model
  • Reduce misfit with the real data.

13
Data v. Uncertainty
  • As the amount of data goes up, the uncertainty
    goes down

14
Fault Planes Plate Boundaries
15
Fault Planes Plate Boundaries
16
Fault Planes Plate Boundaries
17
Earthquake Frequency v. Magnitude
18
Earthquake Frequency v. Magnitude
  • There are fewer large Earthquakes than small, but
    the large earthquakes release more energy than
    the small earthquakes.

19
Notable Earthquakes
20
Earthquakes Need not be Disastrous
  • In 1996 it was determined that on average in the
    US more people died of skateboarding than
    Earthquakes
  • Building codes
  • Earthquake preparedness
  • Search rescue

21
Likelihood of Building Collapse EQ Intensity
22
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23
Most Active Region in the US
24
San Andreas Fault
25
Seismic Hazard
  • Seismic hazard is effected by
  • Closeness to Earthquake
  • Likelihood of Flood
  • Likelihood of Landslide
  • Likelihood of Tsunami
  • Ground Stability

26
Seismic Energy and Distance
27
Seismic Hazard
28
Seismic Hazard
29
Seismic Gaps
30
Vibrational Energy Attenuates
31
Damage in Valdez after 1964 Alaska EQ
32
Displacement after 1906 San Andreas
33
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34
Loma Prieta, 1989 Liquefaction Effects
35
Bay Bridge after Loma Prieta, 1989
36
Van Norman Dam after 1971 San Fernando EQ
  • Liquefaction made the dam sink

37
Bridge After Northridge
38
Bridge After Northridge
39
Liquefaction During Northridge
40
Tsunami, 1964, Alaska
41
Landslide From Loma Prieta, 1989
42
Animals Earthquakes?
  • Elephants communicate over kilometers at
    frequencies similar to earthquakes.
  • Some animals may sense the first-arriving P-wave
    and act up.
  • Humans only notice the later arriving surface
    waves that knock over buildings.

43
Nuclear Sources
Lots of Energy coupled to the ground!!!!
44
Nuclear Sources
45
Sizes of Nuclear Tests
46
Earthquakes v. Nuclear Sources
  • Nuclear sources tend to have only higher
    frequencies

47
Earthquakes v. Nuclear Sources
  • Nuclear explosions have less long-period energy,
    so estimations of source size based on surface
    waves is much lower.
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