The moment magnitude scale takes a much long time period to determine the size of the earthquake.Ĭomparing magnitudes of the two scales After the 1960 Chile earthquake the Richter scale registered the earthquake size at magnitude 8.5. Seismographs near the epicenter were used to determine the largest seismic wave and the news was quickly reported to radio and television stations within hours of the earthquake. Richter scale The reason the Richter scale was so popular with news agencies is the speed the news could be spread to people on radio and television broadcasts. The majority of earthquakes felt worldwide are less than 3.5 magnitude. Other scales including the Richter scale are used for earthquakes less than 3.5 magnitude. Measuring moderate to large earthquakes Today the moment magnitude scale supersedes other scales and is used to estimate the magnitudes for all moderate to large earthquakes. when do scientists use the different scales ![]() Formerly the United States Geological Survey used the Richter Scale when describing an earthquake's magnitude. It also includes the size of the seismic waves recorded on seismograms by seismographs. Measuring fault rupture and slippage The moment magnitude includes the area of the fault rupture and slippage along the fault. Map of the 1964 Great Alaska Earthquake USGS What the moment magnitude measures The moment of an earthquake is a physical quantity related to the total energy released during the earthquake. Total energy released by an earthquake The moment magnitude scale avoids many of the problems of these earlier scales. ![]() The Richter scale is an open-ended scale that becomes saturated when earthquakes near 9.0. The Richter scale The Richter scale did not adequately show the magnitude and size of what happened during these two great earthquakes because it only measures the height of largest wave recorded on a seismogram to determine the magnitude of the earthquake. ![]() Measuring the entire earthquake The moment magnitude scale in determining an earthquake's magnitude takes in "the entire moment" of the earthquake. The moment magnitude scale developed in recent years avoids the problem of gathering information from only one type of ground motion and not looking at all aspects of an earthquake. These great subduction zone earthquakes broke along fault lines that were hundred of kilometers long. Moment magnitude scale The moment magnitude scale (MMS) was devised by scientists after the 1960 Chilean earthquake and the 1964 Alaskan earthquake. Moment magnitude scale Measuring Great earthquakes
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