2011 Tōhoku earthquake and tsunami for the event was based on a calculation that requires only about 3 minutes. This calculation is, in turn, based on the maximum amplitude of the seismic wave. The amplitude of the seismic wave is measured using the , which is similar to Richter magnitude scale. However, these scales "saturate" for earthquakes that are above a certain magnitude (magnitude 8 on the JMA scale); that is, in the case of very large earthquakes, the scales' values change little despite large differences in the earthquakes' energy. This resulted in an underestimation of the tsunami's height in initial reports. Problems in issuing
Richter magnitude scale isolated area. Several scales have historically been described as the "Richter scale", especially the "local magnitude" formula_2 and the surface wave formula_3 scale. In addition, the "body wave magnitude", formula_4, and the "moment magnitude", formula_5, abbreviated MMS, have been widely used for decades. A couple of new techniques to measure magnitude are in the development stage by seismologists. All magnitude scales have been designed to give numerically similar results. This goal has been achieved well for formula_2, formula_3, and formula_5. The formula_4 scale gives somewhat different values than the other scales. The reason for so many different ways to measure