![]() The Richter scale has two shortcomings, however. “The fundamental thing is that you relate what you measure for a particular seismic arrival in the seismogram directly to the magnitude of the earthquake,” van der Hilst says. The larger the recorded waves, the bigger the earthquake - a 7.0 earthquake is 10 times as large as a 6.0 - and the more energy it releases. Richter and Gutenberg measured these waves by using seismographs, delicate instruments featuring a balance and a scroll of paper when the Earth moves, a seismograph records the amplitude, or height, of a wave. By contrast, surface waves move across the surface of the Earth with lower frequency but more destructive force. Some types of seismic waves, called body waves, travel through the interior of the Earth with relatively high frequency but less force. To be sure, the Richter scale, introduced by Charles Richter and Beno Gutenberg, employs a clear logic. “It is a very good measure of the total energy that is being radiated.” ![]() “The moment magnitude is a measure that relates more to what is going on at the fault itself,” says Robert van der Hilst, the Cecil and Ida Green Professor of Geophysics at MIT. It is thus better able to estimate the total energy of earthquakes, and can also relate these observations to the physical features of a fault. Compared to the Richter scale, the moment magnitude scale can account for more types of these waves, and at more frequencies. An earthquake produces many types of waves, which radiate from its epicenter and move with a wide variety of frequencies. Instead, scientists use the moment magnitude scale, developed in the 1970s. Seismologists today do not use the Richter scale as a universal tool for measuring earthquakes, because it does not accurately measure the energy emitted in jolts as big as the one that hit Japan. But this was not, as some people may assume, as registered on the Richter scale, the famed measuring system dating to the 1930s. The powerful earthquake that struck Japan in March was a 9.0-magnitude event.
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