Transcript Earth`s Seismicity

EARTHQUAKES
Chapter 6
Honors earth science
http://earthquake.usgs.gov/
Apps
apps
• Quake Feed
• Earthquake! Earthquake map and alerts
• Earthquake- Quake Tracker
LARGEST QUAKES SINCE 1900
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Chile
Alaska
Alaska
Sumatra
Japan
Chile
1960
1964
1957
2004
2011
2010
9.5
9.2
9.1
9.1
9.0
8.8
MAJOR RECENT QUAKES
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Sumatra
Haiti
Chile
Japan
Chile
Nepal
9.1
7.0
8.8
9.0
8.2
7.8
12/26/04 230,000
1/12/10
316,000
2/27/10
810
3/11/11
28,000 +
2014
6
4/25/2015 8,000+
What is an Earthquake?
• Vibration of earth
from rapid release of
energy (from plate
boundaries)
• Focus-
• Epicenter-
After shocks
• Smaller quakes following “main shock”
• Plate readjusting to new location
faults
Normal fault
tensional stress
along divergent boundaries
footwall
Hanging wall
Reverse (thrust) fault
compressional stress
along convergent boundaries
footwall
Hanging wall
Strike slip
shearing stress
along transform boundaries
San Andreas Fault
EARTHQUAKE WAVES
A seismogram records wave
amplitude vs. time
GPS seismometer
Seismograph
P waves
• Primary
• travel fastest
• travels through solids
AND liquids
• compressional wave
– push/pull
Primary (P) waves
S waves
• Secondary
• travels only through
solids (NOT liquids)
• Up and down motion
Secondary (S) waves
Surface waves
• Travel on surface
• slow
• Movement is similar
to water waves
Michigan quake 5/2/15
Mantle info:
core info: outer=
inner=
A time-travel graph is used to
find the distance to the
epicenter
The epicenter is located using
three or more seismograph
INTENSITY OF QUAKE
• Depends on
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energy released (magnitude)
distance from epicenter
rock type (soft=worse)
Depth (shallow=worse)
SCALES
• Richter (1935)
• 1 to ?
– each step 10x more
energy than previous
step
• Moment Magnitude
– Mw
– Good for large quakes
– Most accurate
• Mercalli (1902)
– measures damage
– I- XII
Who wants to move to CA?
Intra plate earthquakes
• Occasionally a quake will occur in the
middle of a plate- INTRAPLATE
– stress fractures? Ancient faults
– Volcanic?
Michigan earthquakes
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Year Date
Lat. Long. Mag. City
1877 Aug 17 42.40 83.25 3.2 Greenfield
1938 Mar 13 42.08 83.17 3.8 Gibralter
1938 Mar 14 42.08 83.17 ? Gibralter
1947 Aug 10 41.928 85.004 4.7 Coldwater
1977 Oct 26 47.1 87.1 2.7 L Superior
1980 Apr 29 47.2 87.8 0.5 L Superior
1982 Nov 26 42.17 85.48 2.5 Scotts
1994 Sep 02 42.57 84.64 3.4 Central Lansing
2001 Oct 23 42.34 84.76 2.9 Prairie L
NEW MADRID EARTHQUAKES
•• Magnitude 8.1
(approx)
• Dec. 1811-1812
• 5th worst earthquake
in US history
• Rang church bells in
Detroit
• Made Mississippi
River flow backwards
Earthquake hazards
• Structural damage
– Most common
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Tsunamis
Fires (electrical lines + gas lines)
Landslides
liquifaction
Liquifaction
Formation of a tsunami
Japan tsunami 2011 video
tsumami
Bay Bridge 1989
Kobe, Japan
Alaskan school, Good Friday 1964
Olympia Washington, 1949
Bird’s eye view of tents among
rubble in Tangshan
Pakistan 2005
What to do in a earthquake?
• Protect yourself from
falling debris
– Under tables
– Duck and cover
• DO NOT
– Light fire (gas leaks?)
– Go to basement!