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A Discussion On Earthquakes

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    Perhaps Mother Nature offers no greater force than that of the earthquake.

    Across the span of time, earthquakes have been recorded for their incredibledestructive forces, and their abilities to awe mankind with their unparalleledforce. Earthquakes can often strike without any notice, leveling large citiesand killing scores of innocent people. Not only can earthquakes bring harm tosociety through these methods of destruction, but they can also cause millionsof dollars worth of damage to the areas they destroy, causing economic chaos.

    An earthquake is a natural phenomenon, occurring throughout the history of theworld. Descriptions as old as recorded history show the significant effectsearthquakes have had on people’s lives. Long before there were scientifictheories for the cause of earthquakes, people around the world created folkloreto explain them. Until recent times, science has not had a completeunderstanding of how earthquakes are caused, and what can be done to predictwhen they will strike. This essay will discuss how earthquakes are formed andoccur, how scientists can more accurately predict the arrival of earthquakes.

    Before contemplating how earthquakes might possibly be prevented, it isessential that the process and formation of and earthquake be understood.

    Earthquakes are caused when the earth’s crustal plates move, rub, or pushagainst each other. The earth’s crust (the outer layer of the earth) is made upof seven major plates and approximately thirteen smaller ones. The name plateis used to describe these portions of the earth’s crust because they areliterally plates or sections, composed of dirt and rock. These plates floaton molten lava, called magma. Since the plates are floating on magma, they canslowly move. The place where friction occurs between plates is called a fault.

    A fault is a crack in a plate or a place where two or more plates meet. Anexample of a fault where two plates meet is the San Andrea’s fault in California,where the Pacific and North American plates meet. The plates are about 30miles thick under land and can be one to five miles thick beneath the ocean.

    The plates move because of convection currents. Magma has currents like theocean does, that move in a circular motion beneath the plates. When two platesare pushing against each other, they are constantly building up tension on thefault. When two plates finally slip, they release a great amount of energy inthe form of shock waves. These shock waves cause vibrations, which in turncause the ground around the fault line to move and shake. This phenomenon isknow as an earthquake.

    Because of the incredible destructive capabilities of earthquakes,scientists are constantly trying to devise ways to ensure their early detection.

    Earth scientists have begun to forecast damaging earthquakes in California.

    Although quake forecasting is still maturing, it is now reliable enough to makeofficial earthquake warnings possible. These warnings help government, industry,and private citizens prepare for large earthquakes and conduct rescue andrecovery efforts in the aftermath of destructive shocks. In recent years,earthquake forecasting has advanced from a research frontier to an emergingscience. This science is now being applied in quake-plagued California, whereshocks are closely monitored and have been studied for many years. Earthquakeforecasts declare that a temblor has a certain probability of occurring within agiven time, not that one will definitely strike. In this way they are similarto weather forecasts. Scientists are able to make earthquake forecasts becausequakes tend to occur in clusters that strike the same area within a limited timeperiod. The largest quake in a cluster is called the mainshock, those before itare called foreshocks, and those after it are called aftershocks.

    In any cluster, most quakes are aftershocks. Most aftershocks are toosmall to cause damage, but following a large mainshock one or more may bepowerful. Such strong aftershocks can cause additional damage and casualties inareas already devastated by a mainshock, and also threaten the lives of rescuerssearching for the injured. In the first few weeks after the 1994 magnitude 6.7Northridge, California, earthquake, more than 3,000 aftershocks occurred. Onemagnitude 5.2 aftershock caused $7 million in damage just in electric utilityequipment in the Los Angeles area alone. The U. S. Geological Survey (USGS)first began forecasting aftershocks following the 1989 magnitude 7.1 Loma Prieta,California, earthquake. By studying previous earthquakes, scientists haddetected patterns in the way aftershocks decrease in number and magnitude withtime. With such knowledge, scientists can estimate the daily odds for theoccurrence of damaging aftershocks following large California temblors. Theseforecasts are relayed directly to the California Office of Emergency Services(OES) as well as to the public.

    Some of the more larger earthquakes are preceded by foreshocks.

    Knowledge of past earthquake patterns allows scientists to estimate the oddsthat an earthquake striking today is a foreshock and will soon be followed by alarger mainshock in the same area. These odds depend on the earthquake’smagnitude and the same seismic history of the fault on which it occurred. Whena moderate earthquake hits California, scientists immediately estimate theprobability that a damaging mainshcck will follow. If the threat is significant,a warning is issued. This warning process was put into action in June, 1988when a magnitude 5.1 shock–one of the largest in the San Francisco Bay regionsince the great 1906 earthquake–struck 60 miles south of San Francisco.

    Alerted by the USGS that there was a 1 in 20 chance of a larger earthquake inthe next five days, the California OES issued an advisory to warn the public.

    (The usual daily odds of a large earthquake in the Bay region are 1 in 15,000.)The warning period passed without further activity. In August, 1989, anotherearthquake hit the same area and a similar advisory was issued. Again nothinghappened in the specified warning period. However, 69 days later, the area wasrocked by the magnitude 7.1 Loma Prieta earthquake, which killed 63 people andcaused $6 billion of damage in the San Francisco Bay region.

    The lessons learned from these observations have already enabled earthscientists and emergency response officials to build a framework within whichthey communicate rapidly and effectively. Based on this experience, similaralert plans have been devised for geologic hazards in other areas of the UnitedStates. The development of modern seismic monitoring networks and the knowledgegained from past shocks, earthquake forecasts and warnings are now a reality.

    Continued effective communication of these forecasts to the public will helpreduce the loss of life and property in future earthquakes.

    In conclusion, earthquakes are a powerful force of nature. Althoughthese destructive giants are indeed deadly, scientists are continually utilizingresearch data collected from previous earthquakes and observations, so that amore effective and efficient warning system may be put in place. Because ofthese scientist’s work, society benefits from this advanced knowledge of when anearthquake will most probably strike. With the continued study of collecteddata, perhaps one day their will be a warning system that will be able to giveenough advanced notice, so that casualties might be minimized even further.

    Category: Social Issues

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