EARTHQUAKES
Chapter 6 Honors earth science
http://earthquake.usgs.gov/
appsApps
• Quake Feed• Earthquake! Earthquake map and
alerts• Earthquake- Quake Tracker
LARGEST QUAKES SINCE 1900
• Chile 1960 9.5• Alaska 1964 9.2• Alaska 1957 9.1• Sumatra 2004 9.1• Japan 2011 9.0• Chile 2010 8.8
MAJOR RECENT QUAKES
• Sumatra 9.1 12/26/04 230,000• Haiti 7.0 1/12/10 316,000• Chile 8.8 2/27/10 810• Japan 9.0 3/11/11 28,000 +• Chile 8.2 2014 6• Nepal 7.8 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 faulttensional stressalong divergent boundaries
footwall
Hanging wall
Reverse (thrust) faultcompressional stressalong convergent boundaries
footwall
Hanging wall
Strike slipshearing stressalong 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– 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
• 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
• 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!