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NASA astronauts are going back to the moon and when they get there they may need quake-proof housing Thats the surprising conclusion of Clive R Neal associate professor of civil engineering and geological sciences at the University of Notre Dame after he and a team of 15 other planetary scientists reexamined Apollo data from the 1970s The moon is seismically active he told a gathering of scientists at NASAs Lunar Exploration Analysis Group LEAG meeting in League City Texas last October Between 1969 and 1972 Apollo astronauts placed seismometers at their landing sites around the moon The Apollo 12 14 15 and 16 instruments faithfully radioed data back to Earth until they were switched off in 1977 And what did they reveal There are at least four different kinds of moonquakes 1 deep moonquakes about 700 km below the surface probably caused by tides 2 vibrations from the impact of meteorites 3 thermal quakes caused by the expansion of the frigid crust when first illuminated by the morning sun after two weeks of deep-freeze lunar night and 4 shallow moonquakes only 20 or 30 kilometers below the surface The first three were generally mild and harmless Shallow moonquakes on the other hand were doozies Between 1972 and 1977 the Apollo seismic network saw twenty-eight of them a few registered up to 55 on the Richter scale says Neal A magnitude 5 quake on Earth is energetic enough to move heavy furniture and crack plaster Furthermore shallow moonquakes lasted a remarkably long time Once they got going all continued more than 10 minutes The moon was ringing like a bell Neal says On Earth vibrations from quakes usually die away in only half a minute The reason has to do with chemical weathering Neal explains Water weakens stone expanding the structure of different minerals When energy propagates across such a compressible structure it acts like a foam sponge-it deadens
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