|
The Richter magnitude scale (also Richter scale) assigns a magnitude number to quantify the energy released by an earthquake. The Richter scale, developed in the 1930s, is a base-10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude. As measured with a seismometer, an earthquake that registers 5.0 on the Richter scale has a shaking amplitude 10 times that of an earthquake that registered 4.0, and thus corresponds to a release of energy 31.6 times that released by the lesser earthquake.〔(The Richter Magnitude Scale )〕 The Richter scale was succeeded in the 1970s by the Moment Magnitude Scale (MMS). This is now the scale used by the United States Geological Survey to estimate magnitudes for all modern large earthquakes. But, earthquake magnitudes are still sometimes incorrectly reported by the press as "an earthquake of XX on the Richter scale", when the correct terminology using the MMS is "a magnitude XX earthquake".〔(【引用サイトリンク】title=USGS Earthquake Magnitude Policy (implemented on January 18, 2002) )〕 == Development == In 1935, the seismologists Charles Francis Richter and Beno Gutenberg, of the California Institute of Technology, developed the (future) Richter magnitude scale, specifically for measuring earthquakes in a given area of study in California, as recorded and measured with the Wood-Anderson torsion seismograph. Originally, Richter reported mathematical values to the nearest quarter of a unit, but the values later were reported with one decimal place; the local magnitude scale compared the magnitudes of different earthquakes.〔 Richter derived his earthquake-magnitude scale from the apparent magnitude scale used to measure the brightness of stars.〔 〕 Richter established a magnitude 0 event to be an earthquake that would show a maximum, combined horizontal displacement of 1.0 µm (0.00004 in.) on a seismogram recorded with a Wood-Anderson torsion seismograph 100 km (62 mi.) from the earthquake epicenter. That fixed measure was chosen to avoid negative values for magnitude, given that the slightest earthquakes that could be recorded and located at the time were around magnitude 3.0. The Richter magnitude scale itself has no lower limit, and contemporary seismometers can register, record, and measure earthquakes with negative magnitudes. (local magnitude) was not designed to be applied to data with distances to the hypocenter of the earthquake that were greater than 600 km (373 mi.).〔 For national and local seismological observatories, the standard magnitude scale in the 21st century is still . This scale saturates at around = 7, because the high frequency waves recorded locally have wavelengths shorter than the rupture lengths of large earthquakes. Later, to express the size of earthquakes around the planet, Gutenberg and Richter developed a surface wave magnitude scale () and a body wave magnitude scale ().〔 〕 These are types of waves that are recorded at teleseismic distances. The two scales were adjusted such that they were consistent with the scale. That adjustment succeeded better with the scale than with the scale. Each scale saturates when the earthquake is greater than magnitude 8.0. Because of this, researchers in the 1970s developed the moment magnitude scale (). The older magnitude-scales were superseded by methods for calculating the seismic moment, from which was derived the moment magnitude scale. About the origins of the Richter magnitude scale, C.F. Richter said: 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「richter magnitude scale」の詳細全文を読む スポンサード リンク
|