The U.S. Geological Survey (USGS) has announced the release of new public web pages that show the probability of earthquake shaking in the next 24 hours in California. These maps graphically illustrate the change in earthquake probability during aftershock and possible foreshock sequences.
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The study of earthquakes and their causes has been an active area of research since the late nineteenth century. John Milne's development of the seismograph in the 1890s and subsequent establishment of a network of seismographs enabled seismologists to detect and locate earthquakes. It also allowed scientists to use seismic waves to probe the interior of the planet and infer the planetary structure (see From Earthquakes to Continental Drift). Against this backdrop of knowledge, Alfred Wegener suggested in 1915 that the seven continents were once one large land mass that broke apart creating the continents, which then drifted to their current locations. Strong support of this idea did not come until the mid 1950's, when paleomagnetic data supported Wegener's claim (see Magnetic Clues). Scientists used sonar measurements to map the ocean floor leading to the discovery of a large undersea mountain ranges with midocean ridges. To explain the ridges, Henry Hess theorized that the seafloor was slowly spreading away from the ridges, driven by convection currents in the mantle (see Insights from the Ocean). Confirmation of Hess's theory of seafloor spreading came from a magnetic survey of the material on either side of a midocean ridge (see Of Magnetism and Time). Examining the ridges and faults radiating from the ridges helped show that the earth's crust is made up of several plates (see Plates in Motion).
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Scientists studied the winds and rains in the eastern Indian Ocean for hints at developing El Ninos. They used that information to create an "Index" or gauge that accurately predicted the El Nino of 2002-2003.
El Nino is signaled by a warming of the ocean surface off the western coast of South America that occurs every 4 to 12 years when cold, nutrient-rich water does not come up from the ocean bottom. It causes die-offs of plankton and fish and affects Pacific jet stream winds, altering storm tracks and creating unusual weather patterns in various parts of the world.
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