Download 16 Earthquakes

Earthquakes
Selected learning objectives:
1. Define an earthquake, as well as its epicenter and focus.
2. Explain the relationship between earthquakes and faults.
3. Explain the occurrence of earthquakes according to elastic
rebound theory.
4. Describe where (in a Plate Tectonic sense) different types
of earthquakes are generated.
5. Describe the process of locating earthquake epicenters
using P and S waves.
6. Explain how earthquakes are used to reveal the deep
structure of the earth, particularly the liquid nature of the
outer core.
Where we are
• Today: Earthquakes & the deep earth
- Elastic Rebound Theory
- Types of seismic waves
- Measuring quake location & magnitude
• Next: Seismic Hazards
• Then: Climate
Current Quake Info
• Tons of info at:
- http://earthquake.usgs.gov
Tectonics in action
• When plates move, how do they move?
• [Show Pangaea animation]
How do quakes happen?
• Elastic Rebound Theory:
How do quakes happen?
• Elastic Rebound Theory:
- Stress builds up…
How do quakes happen?
• Elastic Rebound Theory:
- Stress builds up…
- until it exceeds the friction along a fault
surface
How do quakes happen?
• Elastic Rebound Theory:
- Stress builds up…
- until it exceeds the friction along a fault
surface
- (or breaks rock, forming a new fault surface)
Show elastic rebound
movie
Elastic Rebound
Theory
Winch and Brick Demonstration
(version 1.0)
Earthquake Waves
• Several different kinds generated by every
earthquake (e.g. P, S, surface)
• Differ in terms of particle motion
Show Seismic waves
movie
Do student waves
demo
Earthquake Waves
• Different wave motion allows us to determine
material properties (e.g. the outer core is liquid
(no S waves!))
Earthquake Waves
• Different wave motion allows us to determine
material properties (e.g. the outer core is liquid
(no S waves!))
Student wave demo
-
Earthquake Waves
• Different wave motion allows us to determine
•
material properties (e.g. the outer core is liquid
(no S waves!))
Student wave demo
What would we expect for the global
distribution of P & S waves?
-
Quick check
• In the brick and winch demo, the cranking
winch represents:
A. The movement of tectonic plates
B. The strain released during an earthquake
C. The steady build up of stress in the rocks
Quick check
• In the brick and winch demo, the stretching
bungee represents:
A. The movement of tectonic plates
B. The strain released during an earthquake
C. The steady build up of stress in the rocks
Measuring Quakes
• Different wave speeds allow location by
triangulation:
Measuring Quakes
• Different wave speeds allow location by
triangulation:
- Which is faster, P or S?
Measuring Quakes
• Different wave speeds allow location by
triangulation:
- Which is faster, P or S?
• Location
Measuring Quakes
• Different wave speeds allow location by
triangulation:
- Which is faster, P or S?
• Location
- Time lag between P & S wave
Measuring Quakes
• Different wave speeds allow location by
triangulation:
- Which is faster, P or S?
• Location
- Time lag between P & S wave
• Magnitude
Measuring Quakes
• Different wave speeds allow location by
triangulation:
- Which is faster, P or S?
• Location
- Time lag between P & S wave
• Magnitude
- Size of P wave at the given distance
CA Quake 4/08 M=5.3
Maple Falls
Helena, MT
Mammoth Lakes, CA
Show Seismograph
movie
Time since the earthquake
60
P
Mammoth, Mammoth
Lakes,SCA, USA BHZ
40
MLAC
Amplitude
microns/sec
Mammoth
CA
00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00
20
0
-20
-40
-60
P
S
Time since the earthquake
TA.A05A. .BHZ.2
P
S
4.00
A05A
Amplitude
microns/sec
Maple Falls
WA
00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00
2.00
0.00
-2.00
-4.00
-6.00
P
S
Time since the earthquake
8.00
East Helena, MT, USA BHZ P
S
6.00
E16A
Amplitude
microns/sec
Helena
MT
00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00
4.00
2.00
0.00
-2.00
-4.00
-6.00
-8.00
P
S
Time since the earthquake
60
lag
P
Mammoth, Mammoth
Lakes,SCA, USA BHZ
40
MLAC
Amplitude
microns/sec
Mammoth
CA
00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00
20
0
-20
-40
-60
P
S
Time since the earthquake
TA.A05A. .BHZ.2
lag
P
4.00
A05A
Amplitude
microns/sec
Maple Falls
WA
00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00
S
2.00
0.00
-2.00
-4.00
-6.00
P
S
Time since the earthquake
8.00
East Helena, MT, USA BHZ P
6.00
E16A
Amplitude
microns/sec
Helena
MT
00:00:00 00:01:00 00:02:00 00:03:00 00:04:00 00:05:00 00:06:00
lag
S
4.00
2.00
0.00
-2.00
-4.00
-6.00
-8.00
P
S
Maple Falls
Helena, MT
Mammoth Lakes, CA
Maple Falls
Helena, MT
Mammoth Lakes, CA
Maple Falls
Helena, MT
Mammoth Lakes, CA
Maple Falls
Helena, MT
Mammoth Lakes, CA
Maple Falls
Helena, MT
Mammoth Lakes, CA
Hawaii Seismograph (Idaho)
Hawaii Seismograph (Idaho)
Quake
occurs
(18:44
UTC)
Hawaii Seismograph (Idaho)
Quake
occurs
(18:44
UTC)
P-wave arrives
in Idaho
(18:57 UTC)
Hawaii Seismograph (Idaho)
S-wave
arrives
(19:08
UTC)
Quake
occurs
(18:44
UTC)
P-wave arrives
in Idaho
(18:57 UTC)
Hawaii Seismograph (Idaho)
S-wave
arrives
(19:08
UTC)
Quake
occurs
(18:44
UTC)
Surface wave
arrives (19:24
UTC)
P-wave arrives
in Idaho
(18:57 UTC)
N. CA (4/29/06) M5.3
N. CA (4/29/06) M5.3
Seismic Hazards
• How many have been in a decent-sized quake?
What kinds of seismic
hazards are there?
• Quakes (ground shaking)
• Liquefaction
• Tsunamis
• Landslides
• Volcanic eruptions?
Microsoft Office, Nisqually Quake, 2001
Microsoft Office, Nisqually Quake, 2001
Liquefaction: Kobe, Japan,
1995
Liquefaction: Kobe, Japan,
1995
Liquefaction: Niigata,
Japan, 1964
[show liquefaction
movie]
Shaking: Nimitz Freeway
(S.F., CA), 1957 & 1989
Shaking: Nimitz Freeway
(S.F., CA), 1957 & 1989
Alaska Way Viaduct,
Seattle
Possible risk of same thing?
Post-2001 Inspection
Seismic Hazards
• Where on earth are there lots of earthquakes?
Seismic Hazards
• Where on earth are there lots of earthquakes?
•
Seismic Risk
Where is there high
earthquake risk?
Risk = Probability x
Consequence
-
MMI VII = “...considerable
damage to ordinary buildings,
with partial collapse...”
Modified Mercalli Map for M6.5
•
Seismic Risk
Where is there high
earthquake risk?
Risk = Probability x
Consequence
New Madrid:
Probability > 90%
chance of >6.0 by 2040
Consequence:
• Building codes in area
are not as quakeconscious
•
-
MMI VII = “...considerable
damage to ordinary buildings,
with partial collapse...”
Modified Mercalli Map for M6.5
What controls death/damage?
• Nature of buildings
What controls death/damage?
• Nature of buildings
- “Quakes don’t kill people, buildings do!”
What controls death/damage?
• Nature of buildings
- “Quakes don’t kill people, buildings do!”
- Worst: brick
What controls death/damage?
• Nature of buildings
- “Quakes don’t kill people, buildings do!”
- Worst: brick
- Best: ? Tents ?
What controls death/damage?
• Nature of buildings
- “Quakes don’t kill people, buildings do!”
- Worst: brick
- Best: ? Tents ?
• Energy released by quake
What controls death/damage?
• Nature of buildings
- “Quakes don’t kill people, buildings do!”
- Worst: brick
- Best: ? Tents ?
• Energy released by quake
• Nature of geology:
What controls death/damage?
• Nature of buildings
- “Quakes don’t kill people, buildings do!”
- Worst: brick
- Best: ? Tents ?
• Energy released by quake
• Nature of geology:
- Best: Strong bedrock
What controls death/damage?
• Nature of buildings
- “Quakes don’t kill people, buildings do!”
- Worst: brick
- Best: ? Tents ?
• Energy released by quake
• Nature of geology:
- Best: Strong bedrock
- Worst: Fill / loose sediment
Variation in shaking / damage
Variation in shaking / damage
Bellingham Bay,
1998
Bellingham Bay,
1888
Bellingham Bay,
1888
Bellingham Bay,
1880’s