Word: seismicity
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...most important signal, they said, was a change in the velocity of vibrations that pass through the earth's crust as a result of such disturbances as quakes, mining blasts or underground nuclear tests. Earth scientists have long known that tremors spread outward in two different types of seismic waves. P waves cause any rock in their path to compress and then expand in the same direction as the waves are traveling. S waves move the rock in a direction that is perpendicular to their path. Because P waves travel faster than S waves, they reach seismographs first...
...1960s, while studying the reaction of materials to great mechanical strains, a team of researchers under M.I.T. Geologist William Brace had discovered that as rock approaches its breaking point, there are unexpected changes in its properties. For one thing, its resistance to electricity increases; for another, the seismic waves passing through it slow down...
...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 in the dilated rock. Then the seismic-wave velocity quickly returns to normal. The water also has another effect...
...M.I.T. Geologist Frank Press toured Chinese earthquake-research centers in October 1974, they were astonished to learn that the country had some 10,000 trained earthquake specialists (more than ten times the American total). They were operating 17 major observation centers, which in turn receive data from 250 seismic stations and 5,000 observation points (some of which are simply wells where the radon content of water is measured). In addition, thousands of dedicated amateurs, mainly high school students, regularly collect earthquake data...
...seismic collapse of Europe in 1914 brought on the modern age of political assassinations. Russia's Prime Minister Pyotr Stolypin had already been killed in 1911 by Dimitri Bogrov, who may have been acting as a revolutionary or a police agent. Then Serbian nationalists assassinated Austrian Archduke Franz Ferdinand-a dissident act that brought on the first World...