The Richter scale was designed for measuring earthquakes in Southern California the moment magnitude scale was developed to overcome the issue of magnitude saturation. An M6.0 is 1,000 times bigger than an M3.0, not twice its size, and at the top end of the scale, an M9.0 is a staggering 100,000,000 times bigger than an M1.0!Īn animation illustrating the exponential increase in amplitude size with each magnitude on the moment magnitude scale. The shaking from an M4.0 quake is 10 times bigger than that from an M3.0, 100 times bigger than an M2.0, and 1,000 times bigger than an M1.0. What this means in plain English is that each point on the scale marks shaking with an amplitude 10 times bigger than the point below it. To convey the huge range of earthquake ground motions and energy experienced, the Richter magnitude is defined as a base-10 logarithmic scale of the amplitude of the peak ground displacement recorded on a particular seismic recording instrument (the Wood Anderson seismogram) and scaled by an arbitrary reference displacement for magnitude zero earthquakes. The Richter and moment magnitude scales share one major feature in common-the scales do not linearly increase with their corresponding seismic parameters but follow logarithmic formulations. Since the 1970s the moment magnitude scale has been preferred in the United States. in the 1930s, and quantified the size of earthquakes by assigning them magnitude numbers. The more objective Richter scale was developed in the U.S. The first widely adopted intensity scale-the Italian Rossi–Forel scale-was used for about two decades until the 1902 introduction of the Mercalli intensity scale, which describes the intensity of earthquakes based on observed effects. Since the 1780s various scales have been devised in an effort to convey the power of earthquakes and several systems remain in use around the world today. Six tons is twice as heavy as three tons, and 60 mph is twice as fast as 30 mph-so why do M6.0 earthquakes release so much more than twice the destructive energy of M3.0 temblors? The answer lies in the way that earthquake magnitude is expressed.Įarthquakes range enormously in scale, from tiny temblors far too small to be felt to massive quakes that can actually move mountains.
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