Word: crustal
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Dates: during 1970-1979
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...cause of the changes can be traced, at least in part, to plate tectonics, the movement of the great crustal plates that ride on the earth's semimolten mantle and provide its solid outer shell. Some 45 million to 50 million years ago, the plate that carries the Indian subcontinent was pushing up into the underbelly of Asia, slowly thrusting up the massive mountain range now called the Himalayas. This new barrier to global wind circulation helped change weather patterns, altering average temperatures around the world. By about 14 million years ago, climates that had been tropical had turned largely...
...meters (9,000 feet) below the waves, scientists aboard vessels from the Woods Hole Oceanographic Institution were looking for underwater geysers or "hot spots." They were conducting their search along the Galapagos Rift, where lava from the earth's molten interior rises toward the surface between two great crustal plates. Such depths are thought to be relatively barren of nutrients-and thus of life. But photographs from the deep revealed small areas, each around a warm spring, that were teeming with clams, mussels, tube worms and scavenger crabs. The probable explanation for the profusion of these organisms, announced last...
...been firmly locked for more than a century, while adjoining parts of the plate have slid as much as 30 ft. Some day, seismologists warn, the stalled sections are going to have to catch up with the main bodies of the plates. Strains are inexorably building up in the crustal rock. When-as it must -the rock finally fractures, the plates will jolt ahead, causing a major earthquake. In fact, the last significant plate movement in the Palmdale vicinity occurred in 1857, when a huge earthquake jolted the then sparsely populated area...
...interest in the subject. Geophysicist Christopher Scholz of Lamont-Doherty and Amos Nur at Stanford, both of whom had studied under Brace at M.I.T., independently published papers that used dilatancy to explain the Russian findings. Both reports pointed out an apparent paradox: when the cracks first open in the crustal rock, its strength increases. Temporarily, the rock resists fracturing and the quake is delayed. At the same time, seismic waves slow down because they do not travel as fast through the open spaces as they do through solid rock. Eventually ground water begins to seep into the new openings...
...exposed to water; the water thus comes in contact with more radioactive material and absorbs more radon-a radioactive gas that the Soviet scientists had noticed in increased quantities in Garm-area wells. In addition, because the cracking of the rock increases its volume, dilatancy can account for the crustal uplift and tilting that precedes some quakes. The Japanese, for instance, noticed a 2-in. rise in the ground as long as five years before the major quake that rocked Niigata in 1964. Scientists are less certain about how dilatancy accounts for variations in the local magnetic field but think...