EarthQuakes Essay example -- essays research papers fc

seisms      Earthquakes, one of the well-nigh destructive natural phenomena, consist of rapid vibrations of rock near the earths surface. Because of their aleatory occurrence and enormous capacity of destruction, they have brought fear to mankind since antique times. A single shock usually pull rounds no more than a few seconds, but a series of low-pitcheder quakes may last for as long as five minutes. The quake felt on the surface is always the result, not the cause of some under found geological process, and in many cases the damage done is immense. The Greek word for shaking, and (when apply to the earth) earthquake, is seismos. Therefore, the science of earthquakes is called seismology (World Book Dictionary 1985).           Earthquakes have been recorded as early on as 526 A.C., but seismology is comparatively new. Until the 18th century, few accurate descriptions of earthquakes were recorded, and footling was known more or less what caused them. When seismology was introduced it was learned that many earthquakes be the result of sea floor spreading, but most are caused by volcanic eruptions and cuticle tectonics. The plate tectonic theory explains that the earth is made up of 20 different plates that are always moving slowly past individually other. This action pulls and compacts the plates, creating intense forces that cause the plates to break. This, in turn, causes earthquakes. The energy released then travels along fault lines in seismic waves (World Book Encyclopedia).      Seismic waves are each P-waves (primary), or S-waves (secondary). P-waves create a relatively low wave pick out and arrive at the surface first. On the surface they create a push-pull effect, thus moving the surface up and down. Their low amplitude and upright piano movement create an effect much like a suspension system slinky. S-waves arrive second and are much more damaging. The high amplitude of S-waves, combined with their horizontal movement cause crippling effects on the earths surface and man made structures (Watkins, Bottino, and Morisawa 30-32).           Earthquakes occur rough us all the time. Most are too small to bank note and cause little to no damage. However, every so often thumping earthquakes do occur. Large earthquakes leave catastrophic damage a... ...On shifting ground p.17-19) Earthquakes that occur in the area surrounding the peaceful Ocean, at the edges of the Pacific plate, are responsible for an average of 80 percent of the energy released in earthquakes worldwide. Japan is shaken by more than 1000 tremors greater than 3.5 in magnitude each year. The western coasts of North and South America are very also active earthquake zones, with several thousand small to moderate earthquakes each year. (U.S.G.S.) Intraplate earthquakes are less frequent than plate enclosure earthquakes, but they are still caused by the internal fracturing of rock masses. The peeled Madrid, Missouri, earthquakes of 1811 and 1812 were extreme examples of intraplate seismic events. Scientists estimate that the three main earthquakes of this series were about magnitude 8.0 and that there were at least 1500 aftershocks. (The ocean of truth p.67-69) Bibliography "Earthquake World Book Encyclopedia. Vol. 6. 1987. "Seismos." World Book Dictionary. Vol. L-Z. Ed. Barnhart, Clarence L., and Robert K. Barnhart. 1987 Watkins, Joel s., Michael L. Bottino, and Marie Morisawa. Our Geological Environment. Philadelphia W.B. Saunders Company, 1975.