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earthquk

# earthquk - Earthquakes What is an earthquake Causes of...

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Earthquakes What is an earthquake? Causes of earthquakes (Fig. 1) Stress buildup causes a new fault Stress buildup causes movement on an existing fault plane. Definitions: Seismic wave Seismology Earthquake focus (Fig. 1) Earthquake epicenter (Figs. 1, 2) Recording earthquakes Seismographs: (Fig. 3) Seismograms (Fig. 4) Seismometers Types of seismic waves Body waves (i) Primary waves: 6 - 7 km/sec; compression and dilation (Fig. 5) (ii) Secondary (shear waves): 3.5 km/sec, particles move perpendicular to the direction of wave motion (Fig. 6) Longitudinal (surface waves): up and down + side to side movement; drag + shear!, slowest. Intensity of earthquakes Mercalli intensity scale Magnitude of earthquakes Richter's scale: For a Wood - Anderson type seismograph located ~ 100 km from epicenter in California (or where the rocksaffected are similar to those in California), the magnitude of an earthquake "M" according to this scale, is given by a formula similar to: M = log (A . 10 4 ) where A is the amplitude (in mm) of the largest wave on a seismogram. However, the

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earthquk - Earthquakes What is an earthquake Causes of...

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