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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)
The moment of force, or torque, is a first moment: =, or, more generally, .; Similarly, angular momentum is the 1st moment of momentum: =.Momentum itself is not a moment.; The electric dipole moment is also a 1st moment: = for two opposite point charges or () for a distributed charge with charge density ().
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 scalar seismic moment is defined by the equation =, where μ {\displaystyle \mu } is the shear modulus of the rocks involved in the earthquake (in pascals (Pa), i.e. newtons per square meter) A {\displaystyle A} is the area of the rupture along the geologic fault where the earthquake occurred (in square meters), and
Kanamori and American seismologist Thomas C. Hanks developed the moment magnitude scale which replaced the Richter scale as a measurement of the relative strength of earthquakes. [1] [2] [3] Kanamori invented the method for calculating slip distribution on the fault plane by teleseismic waveform with Masayuki Kikuchi. In addition, they studied ...
Seismic magnitude scales, the energy in an earthquake, measures include: Moment magnitude scale, based on seismic moment, supersedes the Richter scale; Richter magnitude scale, the energy of an earthquake, superseded by Moment scale; Surface-wave magnitude, based on Rayleigh surface wave measurement through heat conduction
differential vector element of surface area A, with infinitesimally small magnitude and direction normal to surface S: square meter (m 2) differential element of volume V enclosed by surface S: cubic meter (m 3) electric field: newton per coulomb (N⋅C −1), or equivalently, volt per meter (V⋅m −1)
Magnetic moment (or magnetic dipole moment) m: The component of magnetic strength and orientation that can be represented by an equivalent magnetic dipole: N⋅m/T L 2 I: vector Magnetization: M: Amount of magnetic moment per unit volume A/m L −1 I: vector field Momentum: p →: Product of an object's mass and velocity kg⋅m/s L M T −1 ...