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    Earthquakes Essay

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    Earthquakes have plagued our lives for as long as people have inhabitedthe earth. These dangerous acts of the earth have been the cause of many deathsin the past century. So what can be done about these violent eruptions that takeplace nearly with out warning? Predicting an earthquake until now has almostbeen technologically impossible.

    With improvements in technology, lives havebeen saved and many more will. All that remains is to research what takes placebefore, during, and after an earthquake. This has been done for years to thepoint now that a successful earthquake prediction was made and was accurate. This paper will discuss a little about earthquakes in general and then about howpredictions are made. Earthquake, “vibrations produced in the earth’s crust when rocks inwhich elastic strain has been building up suddenly rupture, and thenrebound.

    “(Associated Press 1993) The vibrations can range from barely noticeableto catastrophically destructive. Six kinds of shock waves are generated in theprocess. Two are classified as body wavesthat is, they travel through theearth’s interiorand the other four are surface waves. The waves are furtherdifferentiated by the kinds of motions they impart to rock particles.

    Primary orcompressional waves (P waves) send particles oscillating back and forth in thesame direction as the waves are traveling, whereas secondary or transverse shearwaves (S waves) impart vibrations perpendicular to their direction of travel. Pwaves always travel at higher velocities than S waves, so whenever an earthquakeoccurs, P waves are the first to arrive and to be recorded at geophysicalresearch stations worldwide. (Associated Press 1993)Earthquake waves were observed in this and other ways for centuries, butmore scientific theories as to the causes of quakes were not proposed untilmodern times. One such concept was advanced in 1859 by the Irish engineer RobertMallet. Perhaps drawing on his knowledge of the strength and behavior ofconstruction materials subjected to strain, Mallet proposed that earthquakesoccurred either by sudden flexure and constraint of the elastic materialsforming a portion of the earth’s crust or by their giving way and becomingfractured. (Butler 1995)Later, in the 1870s, the English geologist John Milne devised aforerunner of today’s earthquake-recording device, or seismograph.

    A simplependulum and needle suspended above a smoked-glass plate, it was the firstinstrument to allow discrimination of primary and secondary earthquake waves. The modern seismograph was invented in the early 20th century by the Russianseismologist Prince Boris Golitzyn. His device, using a magnetic pendulumsuspended between the poles of an electromagnet, “ushered in the modern era ofearthquake research. ” (Nagorka 1989)”The ultimate cause of tectonic quakes is stresses set up by movementsof the dozen or so major and minor plates that make up the earth’scrust. “(Monastersky Oct, 95) Most tectonic quakes occur at the boundaries ofthese plates, in zones where one plate slides past anotheras at the San AndreasFault in California, North America’s most quake-prone areaor is subducted(slides beneath the other plate). Subduction-zone quakes account for nearlyhalf of the world’s destructive seismic events and 75 percent of the earth’sseismic energy.

    They are concentrated along the so-called Ring of Fire, a narrowband about 38,600 km (about 24,000 mi) long, that coincides with the margins ofthe Pacific Ocean. The points at which crustal rupture occurs in such quakestend to be far below the earth’s surface, at depths of up to 645 km (400 mi). (Monastersky Dec, 95) Alaska’s disastrous Good Friday earthquake of 1964 is anexample of such an event. Seismologists have devised two scales of measurement to enable them todescribe earthquakes quantitatively. “One is the Richter scale named after theAmerican seismologist Charles Francis Richterwhich measures the energy releasedat the focus of a quake.

    It is a logarithmic scale that runs from 1 to 9; amagnitude 7 quake is 10 times more powerful than a magnitude 6 quake, 100 timesmore powerful than a magnitude 5 quake, 1000 times more powerful than amagnitude 4 quake, and so on. “(Associated Press 1992)The other scale, introduced at the turn of the 20th century by theItalian seismologist Giuseppe Mercalli, measures the intensity of shaking withgradations from I to XII. (Associated Press 1992) Because seismic surfaceeffects diminish with distance from the focus of the quake, the Mercalli ratingassigned to the quake depends on the site of the measurement. Intensity I onthis scale is defined as an event felt by very few people, whereas intensity XIIis assigned to a catastrophic event that causes total destruction. Events ofintensities II to III are roughly equivalent to quakes of magnitude 3 to 4 onthe Richter scale, and XI to XII on the Mercalli scale can be correlated withmagnitudes 8 to 9 on the Richter scale.

    ( Associated Press 1992)Attempts at predicting when and where earthquakes will occur have metwith some success in recent years. At present, China, Japan, Russia, and the U. S. are the countries most actively supporting such research. In 1975 the Chinesepredicted the magnitude 7.

    3 quake at Haicheng, evacuating 90,000 residents onlytwo days before the quake destroyed or damaged 90 percent of the city’sbuildings. One of the clues that led to this prediction was a chain of low-magnitude tremors, called foreshocks, that had begun about five years earlier inthe area. (Day 1988) Other potential clues being investigated are tilting orbulging of the land surface and changes in the earth’s magnetic field, in thewater levels of wells, and even in animal behavior. A new method under study inthe U. S.

    involves measuring the buildup of stress in the crust of the earth. Onthe basis of such measurements the U. S. Geological Survey, in April 1985,predicted that an earthquake of magnitude 5.

    5 to 6 would occur on the SanAndreas fault, near Parkfield, California, sometime before 1993. (Day 1988) Manyunofficial predictions of earthquakes have also been made. In 1990 a zoologist,Dr. Iben Browning, warned that a major quake would occur along the New Madridfault before the end of the year.

    Like most predictions of this type, it provedto be wrong. Groundwater has also played an important part in earthquakepredictions. A peak in radon in the groundwater at Kobe, Japan 9 days before the7. 2 earthquake cause quite a stir.

    Radon levels peaked 9 days before the quake,then fell below the normal levels 5 days before it hit. (Monastersky July, 95)In North America, the series of earthquakes that struck southeasternMissouri in 1811-12 were probably the most powerful experienced in the UnitedStates in historical time. The most famous U. S.

    earthquake, however, was the onethat shook the San Francisco area in 1906, causing extensive damage and takingabout 700 lives. (Nagorka 1989)The whole idea behind earthquake predicting is to save lives. With theimprovement in technology, lives have been saved. New ideas and equipment isstarting to prove to be very helpful in predicting were and when an earthquakewill strike. The time and research put into earthquake predicting has alreadystarted to pay off.

    It is only a matter of time before earthquakes will nolonger be a threat to us. BibliographyAssociated Press 1992, “The Big One: Recent Tremors May Be a `Final Warning'”;SIRS 1993 Earth Science, Article 12, Aug. 30, 1992, pg. J1+. Associated Press 1993, “Predicting the Effects of Large Earthquakes”; SIRS 1994Applied Science, Article 17, Sept.

    /Oct. 1993, pg. 7-17. Butler, Steven 1995, “Killer Quake”; SIRS 1995 Earth Science, Article 47, Jan.

    30, 1995, pg. 38-44. Day, Lucille, 1988, “Predicting The Big One”; SIRS 1989 Earth Science, Article 5,Summer 1988, pg. 34-41. Monastersky, R. 1995, “Electric Signals May Herald Earthquakes”; Science News, v.

    148, Oct. 21 ,1995, pg. 260-1. Monastersky, R.

    1995, “Quiet Hints Preceded Kobe Earthquake”; Science News, v. 148, July 15, 1995, pg. 37. Monastersky, R.

    1995, “Radio Hints Precede a Small U. S. Quake”; Science News, v. 148, Dec.

    23;30, 1995, pg. 431. Nagorka, Jennifer 1989, “Earthquakes: Predicting Where Is Easy–It’s WhenThat’s Tough”; SIRS 1990 Earth Science, Article 26, Oct. 29, 1989, pg. E1-2. Category: Science

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