Slide 1Created by C. Ippolito May 2009 Updated 5/9/2009 Earthquakes How and where do earthquakes occur? How do scientists locate and measure earthquakes?

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 8

Richter Measurement

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