MOMENT MAGNITUDE SCALE FORMULA HOW TO

MOMENT MAGNITUDE SCALE FORMULA HOW TO

Richter then worked out how to adjust for epicentral distance (and some other factors) so that the logarithm of the amplitude of the seismograph trace could be used as a measure of 'magnitude' that was internally consistent and corresponded roughly with estimates of an earthquake's energy. The initial step in determining earthquake magnitudes empirically came in 1931 when the Japanese seismologist Kiyoo Wadati showed that the maximum amplitude of an earthquake's seismic waves diminished with distance at a certain rate. Large and destructive earthquake that can destroy large cities.Īt the beginning of the twentieth century, very little was known about how earthquakes happen, how seismic waves are generated and propagate through the earth's crust, and what information they carry about the earthquake rupture process the first magnitude scales were therefore empirical. Will not cause damage to well-designed buildings, but can cause damage or destroy small or poorly-designed ones.Ĭan be destructive in areas up to about 100 kilometers across where people live.Ĭonsidered a 'major earthquake' that causes a lot of damage. Generally felt by people, but it rarely causes damage. People would not feel it, but it would be recorded by Geologists Subtypes of the moment magnitude scale (M ww, etc.) reflect different ways of estimating the seismic moment. Geological Survey for reporting large earthquakes (typically M > 4), replacing the local magnitude (M L) and surface wave magnitude (M s) scales. It has become the standard scale used by seismological authorities like the U.S. It is more directly related to the energy of an earthquake than other scales, and does not saturate-that is, it does not underestimate magnitudes as other scales do in certain conditions. Moment magnitude (M w) is considered the authoritative magnitude scale for ranking earthquakes by size. Like the similar and older Richter scale, it is logarithmic, with a base of ten. It is the energy of the earthquake at the moment it happens. The higher the number, the bigger the earthquake. The moment magnitude scale ( MMS denoted explicitly with M w or Mw, and generally implied with use of a single M for magnitude), is a way to measure the power of earthquakes.

Moment magnitude scale formula