Download Earthquakes

Earthquakes
What is an Earthquake?
• Earthquake—the vibration of Earth produced
by the rapid release of energy
– Most often caused by slippage along a fault in
Earth’s crust
• Focus—the zone within Earth where rock
displacement produces an earthquake
• Produces waves that carry the energy
throughout the Earth
What is an Earthquake?
• Earthquakes and Faults
– A fault is a large fracture in Earth’s crust
– Most earthquakes occur along plate boundaries
What is an Earthquake?
• Elastic Rebound
– 1906 San Francisco Earthquake
• San Andreas fault—780 miles
• Boundary between the North American plate and the
Pacific plate
• Pacific plate moved as much as 15 feet northward past
the North American plate
– Sudden release of stored up energy in rocks that
results in movement along a fault—acts like a
stretched rubber band
What is an Earthquake?
– Fault creep—slow, gradual displacement which
occurs relatively smoothly
– Some segments regularly slip, producing small
earthquakes
– Stick-slip—remain locked and store elastic energy
for a long time before releasing energy in a great
earthquake
– Fault scarp—cliff resulting from vertical
displacement in which one side is lifted higher in
relation to the other
What is an Earthquake?
• Foreshocks
– Small earthquakes that precede a major
earthquake by days or by several years
• Aftershocks
– Small earthquakes that are the result of
adjustment of faults after a major earthquake
Earthquake Waves
• Seismology—study of earthquake waves
• Seismographs—instruments that record
earthquake waves
• Seismograms—records from the seismographs
Earthquake Waves
• Body waves
– P waves (primary waves)
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Push/pull
Particles move in the same direction as the waves
Longitudinal
Change volume of intervening material
– S waves (secondary waves)
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Shake
Particles move at right angles to the waves
Transverse
Change shape of the material that transmits them
Earthquake Waves
• Surface waves
– Travel along the ground
– Moves ground like the ocean tosses a ship
– Up and down motion and side to side motion
Finding Earthquake Epicenters
• Epicenter—location on the surface of the
Earth directly above the focus
• Scientists use triangulation to determine the
epicenter
– Distance of the wave from three different seismic
stations
Earthquake Intensity and Magnitude
• Mercalli intensity scale
– Assesses damage
– Strength, distance from the epicenter, nature of
surface materials, and building design
• Richter scale
– Measures magnitude
– Amplitude of the largest wave recorded on the
seismogram
– Logarithmic scale—tenfold increase for every
number—30 fold increase in magnitude