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  3. Using newly obtained petroleum industry data, scientists have identified a previously unknown earthquake fault that lies under t

Using newly obtained petroleum industry data, scientists have identified a previously unknown earthquake fault that lies under t

admin2010-03-25  81
问题    Using newly obtained petroleum industry data, scientists have identified a previously unknown earthquake fault that lies under the heart of densely populated Los Angeles, California. Details were published in the March 5, 1999, issue of the journal Science.
   Geologists John Shaw of Harvard University in Cambridge, Massachusetts, and Peter Shearer of the University of California at San Diego authored the report, which revealed the presence of the new fault (a crack in the earth’s crust along which rocks on either side of the crack have moved). Shaw and Shearer described it as a blind thrust fault, a type of fault that is characterized by the sudden upward movement of one side of rock over another. Thrust faults can push older rocks atop younger rocks, reversing the normal pattern in which young rocks lie atop older rocks. A blind fault is one that is not detectable on the surface, which makes it more difficult for geologists to discover. The fault was named after the nearby Puente Hills area.
   The Puente Hills fault, which actually has three different segments, runs from the centre of Los Angeles to the Coyote Hills in northern Orange County over an area of more than 800 sq km. Scientists now believe this fault system was responsible for the Whittier Narrows earthquake in the Los Angeles area on October 1, 1987. That quake measured 5.9 to 6.0 on the Richter scale, resulting in eight deaths and more than $ 350 million in damages.
   Seismologists had long suspected that more faults lay hidden beneath California’s largest city, but it had been very difficult to find them. The discovery came after oil companies shared subsurface data they had gathered while doing oil and gas exploration during the previous 50 years. The scientists used this information along with other aggregate data to pinpoint the existence and location of the fault.
   United States Geological Survey (USGS) officials said that the identification of a new fault was important but did not change the agency’s earthquake predictions for the area. They explained that this was because tectonic pressure, which causes serious earthquakes, is building up in the region at a constant rate. It is therefore just a matter of when and where the next major quake will occur.
   The geologists were unable to determine if any major quakes occurred on the Puente Hills fault in prehistoric times. But based on available data they project that each of the fault’s three segments could produce an earthquake of 6.5 magnitude every 250 to 1,000 years. If all three segments rupture together, the result could be a 7.0 earthquake, but this is only likely to happen about once every 2,000 years, the scientists said.
   The discovery highlights another potential location, and source, for a big Southern California earthquake. This knowledge could impact building codes and safety standards in the area. Some experts say that discoveries over the last few years of previously unknown seismic risks had called existing safety codes into question.
The newly discovered fault was extraordinary because
选项 A、it caused a severe local earthquake in the past.
B、it pushes older rocks on the top of younger rocks.
C、it has three segments and covers a relatively large area.
D、it was hidden beneath California’s largest city.
答案B
解析 新发现的断层之所以特殊，并不是因为A(在过去曾弓I起地震)、C(由三部分组成而且覆盖面甚广)、D(深藏在加州最大的城市下面)，这些都很平常，而是因为它的特殊结构与众不同，原文中的reversing the normal pattern很说明问题。
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