slide 1created by c. ippolito may 2009 updated 5/9/2009 earthquakes how and where do earthquakes...
TRANSCRIPT
Slide 1 Created by C. IppolitoMay 2009
Updated 5/9/2009
Earthquakes
How and where do earthquakes occur?How do scientists locate and measure
earthquakes?What types of damage do earthquakes
cause?
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 2
Causes of Earthquakes
• Earthquake– shaking of crust by release of energy– strain at faults/boundaries
• break in lithosphere with movement
• Elastic Rebound Theory– friction stop motion increases strain– strain deforms plate over comes friction– movement/snap back with different orientation
• Focus– point of initial movement
• Epicenter– point on surface directly above focus
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 3
Body Waves
• Waves– travel from focus through earth
• Primary (P) Waves– compressional waves – squeeze and stretch– solid rock, magma, ocean water, air
• Secondary (S) (Shear) Waves– perpendicular waves – move at right angle to
direction of movement– solid materials ONLY
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 4
Surface Waves
• Love Waves– particles move side to side perpendicular to
direction of travel
• Rayleigh Waves– particles move up and down in relation to
direction of travel
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 5
Locating and Measuring Earthquakes• Seismograph
– detect and record waves• Side to Side Motion• Up and Down Motion
– Seismograph Station• THREE machines
– Up and Down
– Side to Side (N-S)
– Side to Side (E-W)
• Seismogram– record sheet traces motions
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 6
Interpreting Seismogram
• P-waves move faster than S-waves– P-waves arrive before S-wave– greater the difference between P and S waves
farther away station is from epicenter
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 7
Measuring Earthquake Magnitude
• Magnitude– amount of energy released by earthquake
• Richter Scale– Charles Richter 1935
• based on amplitude of seismic wave • relatively easy to calculate quickly• each increase of number is 31x energy• measures intensity of ground movement• inaccurate with large quakes
– Moment Magnitude• measures the total amount of energy released• most accurate measure of size• good for very large earthquakes• requires detailed analysis of seismic waves
– Modified Mercali Index• based on survey of damage I-XII
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 9
Earthquake Hazards
• Damage– Ground Shaking and Foundation Failure
• Liquefaction – loose soil behaves like a liquid
– Aftershocks and Fire• aftershocks are smaller quakes• ruptured gas lines ignited fires
– Tsumanis• fast moving ocean wave from underwater quakes• 2004 Indonesia
Updated 5/3/2009 Created by C. IppolitoMay 2009
Slide 10
Earthquake Prediction
• Long Term– based on seismic gaps
• places where faults have not moved
• Short Term– relies on recognition of precursors
• land deformation• increased seismic activity• geomagnetic and geoelectric changes
(affects animal behavior?)• groundwater level changes