Chapter 8

 Earthquake - the vibration of the earth produced by a rapid release of energy. Focus is the point inside earth that starts the earthquake. The epicenter is located on the surface of the earth above the focus Fault is a fracture where movement has occurred

 the rocks first bend then break, releasing the potential energy as kinetic energy.

 Intense shaking lasts for seconds to minutes; however, additional movements can last many days  Aftershocks are smaller shakes that occur after the main shake (can still cause damage)  Forshocks can happen days or years before a major earthquake

 Depends on: intensity and duration of vibrations material structure is built on structure design – steel frame can withstand vibrations better than unreinforced brick or stone buildings

1. Liquefaction – loosely consolidated sediments are saturated with water, then the soil becomes liquid soil can’t support buildings bridges, etc. underground storage and sewer lines may float upward

2. Tsunami – NOT the same as Tidal Wave triggered by underwater landslide caused by vibrations or earthquake vertical displacement of ocean floor along fault, or detonation of nuclear device in ocean can travel km/hr not noticeable in open ocean because wave is less than 1 m in shallow coastal waters, waves are slowed and pile up to heights of 30m Tsunami Warning System located in Hawaii – when large earthquake reported, a warning is put out only 1-2 a year and 1 in 10 years that cause damage and loss of life

3. Landslides – soil and rock slopes fail because of the vibrations

4. Ground subsidence – large sections of the ground collapse, liquefy, or subside

5. fire – gas and electric lines break/cut water lines break during earthquake, but can’t put out the fires

SHORT RANGE PREDICTIONLONG RANGE PREDICTION  provides early warning and magnitude of large earthquake  -measures uplift, strain, and subsidence of rocks near active faults, water levels and pressure, radon gas emissions, and electromagnetic changes in rocks  -no success so far  based on the idea of repetitive or earthquake cycles  -study the history of earth quakes, patterns of reoccurrence, and seismic gaps (area along a fault where no activity has occurred in a while)  -scientists don’t really understand enough to predict long term earthquake

SEISMOGRAMSEISMOGRAPH  Record from seismograph  Machine itself

1. Body waves – interior of Earth, do not cause 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 ground and cause ground and anything on it to move in all directions travels the slowest

 The difference between p waves and s waves helps us to locate the epicenter  The greater the distance between p and s the deeper the source

 Use intensity (amount of shaking at location) and magnitude (measure of size of seismic waves / amount of energy released) to measure

1. Richter Scale: measures magnitude Uses logarithmic scale Only useful for small, shallow earthquakes within 500 km of epicenter Scientists don’t use anymore

2. Moment Magnitude: Measures average amount of movement along fault, area of surface break, and strength of broken rock Together these measure how much energy rock can store before release/break

 Circum-pacific belt – “ring of fire”  Mediterranean-Asian belt  Worlds ocean system – oceanic ridges