disasters10.09notes

disasters10.09notes - 1 4.2 Ch 4 Earthquake Geology and...

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4.2: Ch. 4 – Earthquake Geology and Seismology Date: 10/9 Seismology : the study of Earthquakes . Each year, the Earth is shaken by millions of EQs , most of which are small. Seismometers detect Earth motions and records them on seismographs (in 3-D) as either north-south horizontal movements, east-west horizontal movements, or vertical movements. The official time is either tick-marked on the seismographic chart or imbedded within the digitized data. Waves Review: wavelength is the distance between successive waves, measured from either crest to crest (or trough to trough) amplitude is the displacement of the wave (equal to one-half the wave height , which is measured from trough up to crest) period is the time between waves (crests or troughs) frequency (measured in hertz , Hz ) is the number of waves passing a given point each second (where 1 Hz equals one cycle per second, or one full wave passage per second) period and frequency are inversely related: 1 period = ------------- frequency 1
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Seismic Waves : when an earthquake occurs, it releases energy in seismic wave that pass through the whole body of the planet ( body waves) and others that only move near the surface ( surface waves ). Body Waves: are fast moving and referred to as either primary or secondary waves are most abundant at high frequencies of 0.5 to 20 Hz (0.5 to 20 cycles per second) and are thus, called short-period waves. (These are the most energetic
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