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  3. The devastating effects of earthquakes on human lives and property have encouraged the search for earthquake prediction. This ch

The devastating effects of earthquakes on human lives and property have encouraged the search for earthquake prediction. This ch

admin2011-04-26  35
问题     The devastating effects of earthquakes on human lives and property have encouraged the search for earthquake prediction. This challenge remains and contemporary seismologists continue to seek reliable methods for pinpointing the time, place and magnitude of individual quakes.
    One prediction technique involves an analysis of the recurrence rates of earthquakes as indicators of future seismic activity. Earthquakes are concentrated in certain areas of the world where tectonic plates such as the Pacific Plate, the Eurasian Plate and the African Plate meet and create fault zones and it is in these areas that seismologists focus their investigations.
    The tectonic plate model provides another tool for earthquake prediction by calculating the accumulated strain at plate boundaries. When the strain reaches a certain magnitude the pressure must be released and it is therefore hypothesized that in such eases an earthquake is imminent.
    The search for premonitory phenomena has received particular attention. In contrast to the ancient Greeks and Romans, who relied on the howling of dogs as a warning sign, modern seismologists have focused on physical evidence for an impending earthquake. Evidence of plate strain can be found by measuring relative movements in geodetic stations, while chemical changes also offer signals for seismologists. Using chemical-detection techniques, scientists established a link between the rise in the concentration of radon gas in mineral water and the subsequent earthquake.
    Analysis of the changes in magnetic properties and conductivity of rocks provides further data for prediction. The electrical and magnetic properties of crustal rocks particularly sensitive to strain and studies measuring changes which occur in these properties have provided promising results. The conductivity of crustal rock is determined by the degree to which the rock is saturated with fluid and the electrolytic properties of those fluids. Before large earthquakes, small fractures develop in rocks, which change the quantity of fluid present. These changes can be measured and provide useful predictive data. However, similar changes in the fluid-bearing capacity of rock can occur as a result of other factors such as changes in the water table, and therefore this technique is not entirely reliable.
    The belief that the behavior of birds, eats and dogs provides evidence of imminent earthquakes has recently gained credence. It is hypothesized that the animals are sensitive to the seismic waves which precede major quakes.
    In zones where earthquakes are known to occur,  improved construction techniques can significantly reduce the effects of seismic waves. If more accurate information regarding the time and magnitude were available, governments could take even more effective measures to reduce the impact on human life. If an entirely accurate prediction technique became available, there would be significant social and political implications. An earthquake prediction in a major urban area would require  governments to provide  an effective  evacuation strategy,  necessitating massive resource and political will.
According to Paragraph 5, measuring the conductivity of fluid in rock may not be a reliable earthquake predictor, because ______.
选项 A、other factors may account for changes in conductivity
B、rock may be saturated with fluid
C、these changes can be measured
D、the conductivity of crustal rock is inherently variable
答案A
解析
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