Chapter 8
Earthquake - the vibration of the earthproduced by a rapid release of energy.
•Focus is the point inside earth that starts theearthquake.
•The epicenter is located on the surface of theearth above the focus
•Fault is a fracture where movement has occurred
the rocks first bend then break, releasingthe potential energy as kinetic energy.
Intense shaking lasts for seconds tominutes; however, additional movementscan last many days
Aftershocks are smaller shakes that occurafter the main shake (can still causedamage)
Forshocks can happen days or yearsbefore a major earthquake
Depends on:
•intensity and duration of vibrations
•material structure is built on
•structure design – steel frame can withstandvibrations better than unreinforced brick orstone buildings
1.Liquefaction – loosely consolidatedsediments are saturated with water, thenthe soil becomes liquid
•soil can’t support buildings bridges, etc.
•underground storage and sewer lines may floatupward
2.Tsunami – NOT the same as Tidal Wave
•triggered by underwater landslide caused by vibrationsor earthquake vertical displacement of ocean floor alongfault, or detonation of nuclear device in ocean
•can travel 500-900km/hr
•not noticeable in open ocean because wave is less than 1m
•in shallow coastal waters, waves are slowed and pile up toheights of 30m
•Tsunami Warning System located in Hawaii – when largeearthquake reported, a warning is put out
•only 1-2 a year and 1 in 10 years that cause damage andloss of life
3.Landslides – soiland rock slopes failbecause of thevibrations
4.Ground subsidence –large sections of theground collapse,liquefy, or subside
5.fire – gas andelectric linesbreak/cut
•water linesbreak duringearthquake, butcan’t put out thefires
SHORT RANGE PREDICTION
LONG RANGE PREDICTION
provides early warning andmagnitude of largeearthquake
-measures uplift, strain, andsubsidence of rocks nearactive faults, water levelsand pressure, radon gasemissions, andelectromagnetic changes inrocks
-no success so far
based on the idea of repetitiveor earthquake cycles
-study the history of earthquakes, patterns ofreoccurrence, and seismicgaps (area along a fault whereno activity has occurred in awhile)
-scientists don’t reallyunderstand enough to predictlong term earthquake
SEISMOGRAM
SEISMOGRAPH
Record from seismograph
Machine itself
1.Body waves – interior of Earth, do notcause surface damage
•P-wave: ‘compression’ like a slinky
same kind of wave as sound wave
moves in straight line, hits first
•S-wave: move at right angles to p-wave
cause the Earth to move up and down
2.Surface wave: travel along the groundand cause ground and anything on it tomove in all directions
•travels the slowest
The differencebetween p wavesand s waves helps usto locate theepicenter
The greater thedistance between pand s the deeper thesource
Use intensity (amount of shaking atlocation) and magnitude (measure of sizeof seismic waves / amount of energyreleased) to measure
1.Richter Scale: measures magnitude
•Uses logarithmic scale
•Only useful for small, shallow earthquakes within500 km of epicenter
•Scientists don’t use anymore
2.Moment Magnitude:
•Measures average amount of movement alongfault, area of surface break, and strength ofbroken rock
•Together these measure how much energy rockcan store before release/break
Circum-pacific belt – “ring of fire”
Mediterranean-Asian belt
Worlds ocean system – oceanic ridges
