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The formula above made it much easier to estimate the energy-based magnitude M w , but it changed the fundamental nature of the scale into a moment magnitude scale. USGS seismologist Thomas C. Hanks noted that Kanamori's M w scale was very similar to a relationship between M L and M 0 that was reported by Thatcher & Hanks (1973)
An earthquake's seismic moment can be estimated in various ways, which are the bases of the M wb, M wr, M wc, M ww, M wp, M i, and M wpd scales, all subtypes of the generic M w scale. See Moment magnitude scale § Subtypes for details. Seismic moment is considered the most objective measure of an earthquake's "size" in regard of total energy. [50]
The formula to calculate surface wave magnitude is: [3] = + (), where A is the maximum particle displacement in surface waves (vector sum of the two horizontal displacements) in μm, T is the corresponding period in s (usually 20 ± 2 seconds), Δ is the epicentral distance in °, and
Officially it's called the moment magnitude scale. It's a logarithmic scale , meaning each number is 10 times as strong as the one before it. So a 5.0 earthquake is ten times stronger than a 4.0.
While the "Richter" and moment magnitude scales are similar, they do differ, particularly for earthquakes stronger than about M 6.5, or deeper than about 50 km. In general: where any source specifies magnitude on a scale other than "Richter", or uses "M" (or "m") with one or more other letters (such as ML, Mw, Ms, or mb), that can be relied on ...
The concept of Earthquake Duration Magnitude – originally proposed by E. Bisztricsany [1] in 1958 using surface waves only – is based on the realization that on a recorded earthquake seismogram, the total length of the seismic wavetrain – sometimes referred to as the CODA – reflects its size. Thus larger earthquakes give longer ...
The connection between seismic moment and a torque is natural in the body-force equivalent representation of seismic sources as a double-couple (a pair of force couples with opposite torques): the seismic moment is the torque of each of the two couples. Despite having the same dimensions as energy, seismic moment is not a measure of energy.
The original "body-wave magnitude" – mB or m B (uppercase "B") – was developed by Gutenberg (1945b, 1945c) and Gutenberg & Richter (1956) [2] to overcome the distance and magnitude limitations of the M L scale inherent in the use of surface waves. mB is based on the P- and S-waves, measured over a longer period, and does not saturate until ...