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Earthquakes Essay, Research Paper
An earthquake is a naturally induced shaking of the ground, caused by the fracture of rock within the Earth and the resulting sliding of rocks past one another along a geological fault The sudden movement of rocks along a fault causes vibrations that transmit energy through the earth in the form of waves. Waves that travel in the rocks below the surface of the earth are called body waves, and there are two types of body waves: primary, or P, waves, and secondary, or S, waves. The S waves, also known as shearing waves, cause the most damage during earthquake shaking, as they move the ground back and forth.
Body waves, or P and S waves, radiate out from the rupturing fault starting at the focus of the earthquake. P waves are compression waves because the rocky material in their path moves back and forth in the same direction as the wave travels alternately compressing and expanding the rock. P waves are the fastest seismic waves; they travel in strong rock at about 6 to 7 km (about 4 mi) per second. P waves are followed by S waves, which shear, or twist, rather than compress the rock they travel through. S waves travel at about 3.5 km (about 2 mi) per second. S waves cause rocky material to move either side to side or up and down perpendicular to the direction the waves are traveling, thus shearing the rocks. Both P and S waves help seismologists to locate the focus and epicenter of an earthquake. As P and S waves move through the interior of the earth, they are reflected and refracted, or bent, just as light waves are reflected and bent by glass. Seismologists examine this bending to determine where the earthquake originated.
Earthquakes also contain surface waves that travel out from the epicenter along the surface of the earth. one type of surface wave that occurs is the Love waves, named after British geophysicist A. E. H. Love. Surface waves also cause damage to structures, as they shake the ground underneath the foundations of buildings and other structures.
This type of surface wave, the Love wave, causes rock to move horizontally, or side to side at right angles to the direction of the traveling wave, with no vertical displacements. Love waves alway travel slower than P waves and usually travel slower than S waves.
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