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**moment magnitude scale**( MMS; denoted explicitly with Mw or Mw, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. It was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori.

Moment

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**magnitude**scale –**Mw**or**M w**– developed by Kanamori (1977) and Hanks & Kanamori (1979), is based on an earthquake's seismic moment, M 0, a measure of how much work an earthquake does in sliding one patch of rock past another patch of rock.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 measure of an earthquake's**magnitude**("size" or strength) based on its seismic moment. It was defined in a 1979 paper by Thomas C. Hanks and Hiroo Kanamori.Dec 08, 2020 · The moment

**magnitude**scale –**Mw**or**M w**– developed by Kanamori (1977) and Hanks & Kanamori (1979), is based on an earthquake's seismic moment, M 0, a measure of how much work an earthquake does in sliding one patch of rock past another patch of rock.Seismic

**magnitude****scales**is part of WikiProject Geology, an attempt at creating a standardized, informative, comprehensive and easy-to-use geology resource. If you would like to participate, you can choose to edit this article, or visit the project page for more information.- History
- Current Use
- Definition
- Relations Between Seismic Moment, Potential Energy Released and Radiated Energy
- Comparative Energy Released by Two Earthquakes
- Subtypes of MW
- See Also
- External Links

Richter scale: the original measure of earthquake

**magnitude**At 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. 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...

Single couple or double couple

The study of earthquakes is challenging as the source events cannot be observed directly, and it took many years to develop the mathematics for understanding what the

**seismic**waves from an earthquake can tell us about the source event. An early step was to determine how different systems of forces might generate**seismic**waves equivalent to those observed from earthquakes. The simplest force system is a single force acting on an object. If it has sufficient strength to overcome any resistance...Dislocation theory

A double couple model suffices to explain an earthquake's far-field pattern of

**seismic**radiation, but tells us very little about the nature of an earthquake's source mechanism or its physical features. While slippage along a fault was theorized as the cause of earthquakes (other theories included movement of magma, or sudden changes of volume due to phase changes), observing this at depth was not possible, and understanding what could be learned about the source mechanism from the**seismic**wav...Moment magnitude is now the most common measure of earthquake size for medium to large earthquake magnitudes,[scientific citation needed] but in practice, seismic moment (M0 ), the seismological parameter it is based on, is not measured routinely for smaller quakes. For example, the United States Geological Survey does not use this scale for earthquakes with a magnitude of less than 3.5,[citation needed]which includes the great majority of quakes. Popular press reports most often deal with significant earthquakes larger than M~ 4. For these events, the preferred[who?] magnitude is the moment magnitude Mw , not Richter's local magnitude ML.

The symbol for the moment magnitude scale is Mw , with the subscript "w" meaning mechanical work accomplished. The moment magnitude Mw is a dimensionless value defined by Hiroo Kanamorias 1. Mw=23log10(M0)−10.7,{\\displaystyle M_{\\mathrm {w} }={\\frac {2}{3}}\\log _{10}(M_{0})-10.7,} where M0 is the

**seismic**moment in dyne⋅cm (10−7 N⋅m). The constant values in the equation are chosen to achieve consistency with the magnitude values produced by earlier scales, such as the local magnitude and the surface wave magnitude. Thus, a magnitude zero microearthquake has a seismic moment of approximately 1.2×109 N⋅m, while the Great Chilean earthquake of 1960, with an estimated moment magnitude of 9.4–9.6, had a seismic moment between 1.4×1023 N⋅m and 2.8×1023 N⋅m.Seismic moment is not a direct measure of energy changes during an earthquake. The relations between seismic moment and the energies involved in an earthquake depend on parameters that have large uncertainties and that may vary between earthquakes. Potential energy is stored in the crust in the form of elastic energy due to built-up stress and gravitational energy. During an earthquake, a portion ΔW{\\displaystyle \\Delta W}of this stored energy is transformed into 1. energy dissipated Ef{\\displaystyle E_{f}}in frictional weakening and inelastic deformation in rocks by processes such as the creation of cracks 2. heat Eh{\\displaystyle E_{h}} 3. radiated seismic energy Es{\\displaystyle E_{s}} The potential energy drop caused by an earthquake is related approximately to its seismic moment by 1. ΔW≈σ¯μM0{\\displaystyle \\Delta W\\approx {\\frac {\\overline {\\sigma }}{\\mu }}M_{0}} where σ¯{\\displaystyle {\\overline {\\sigma }}} is the average of the absolute shear stresses on the fault before and...

Assuming the values of σ̄/μ are the same for all earthquakes, one can consider Mw as a measure of the potential energy change ΔW caused by earthquakes. Similarly, if one assumes ηRΔσs/2μ{\\displaystyle \\eta _{R}\\Delta \\sigma _{s}/2\\mu } is the same for all earthquakes, one can consider Mw as a measure of the energy Esradiated by earthquakes. Under these assumptions, the following formula, obtained by solving for M0 the equation defining Mw , allows one to assess the ratio E1/E2{\\displaystyle E_{1}/E_{2}} of energy release (potential or radiated) between two earthquakes of different moment magnitudes, m1{\\displaystyle m_{1}} and m2{\\displaystyle m_{2}}: 1. E1/E2≈1032(m1−m2).{\\displaystyle E_{1}/E_{2}\\approx 10^{{\\frac {3}{2}}(m_{1}-m_{2})}.} As with the Richter scale, an increase of one step on the logarithmic scale of moment magnitude corresponds to a 101.5 ≈ 32 times increase in the amount of energy released, and an increase of two steps corresponds to a 103 = 1000 times increase in...

Various ways of determining moment magnitude have been developed, and several subtypes of the Mwscale can be used to indicate the basis used. 1. Mwb – Based on moment tensor inversionof long-period (~10 – 100 s) body-waves. 2. Mwr – From a moment tensor inversionof complete waveforms at regional distances (~ 1,000 miles). Sometimes called RMT. 3. Mwc – Derived from a centroid moment tensor inversionof intermediate- and long-period body- and surface-waves. 4. Mww – Derived from a centroid moment tensor inversionof the W-phase. 5. Mwp (Mi) – Developed by Seiji Tsuboifor quick estimation of the tsunami potential of large near-coastal earthquakes from measurements of the P-waves, and later extended to teleseismic earthquakes in general. 6. Mwpd – A duration-amplitude procedure which takes into account the duration of the rupture, providing a fuller picture of the energy released by longer lasting ("slow") ruptures than seen with Mw.

Perspective: a graphical comparison of earthquake energy release – Pacific Tsunami Warning Center- Overview
- History
- Comparison with other seismic scales

The Japan Meteorological Agency Seismic Intensity Scale is a

**seismic intensity scale**used in Japan to**categorize**the intensity of local**ground shaking caused**by earthquakes. Map of Japan showing the distribution of maximum JMA Seismic Intensities by prefecture for the 2011 Tōhoku Earthquake The JMA intensity scale should not be confused or conflated with magnitude measurements like the moment magnitude and the earlier Richter scales, which represent how much energy an earthquake releases...The JMA first defined a four-increment intensity scale in 1884 with the levels bi, jaku, kyo, and retsu. In 1898 the scale was changed to a numerical scheme, assigning earthquakes levels 0–7. In 1908, descriptive parameters were defined for each level on the scale, and the intensities accompanying an earthquake were assigned a level according to perceived effect on people at each observation site. This was widely used during the Meiji period and revised during the Shōwa period with the ...

A 1971 study that collected and compared intensities according to the JMA and the Medvedev–Sponheuer–Karnik scales showed that the JMA scale was more suited to smaller earthquakes whereas the MSK scale was more suited to larger earthquakes. The research also suggested that for small earthquakes up to JMA intensity 3, a correlation between the MSK and JMA values could be calculated with the formula MSK = JMA1.5 + 1.5, whereas for larger earthquakes the correlation was MSK = JMA1.5 + 0.75.

Seismology (/ s aɪ z ˈ m ɒ l ə dʒ i /; from Ancient Greek σεισμός (seismós) meaning "earthquake" and -λογία (-logía) meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies.

Seismic

**magnitude****scales**are used to describe the overall strength or size of an earthquake. These are distinguished from seismic intensity**scales**that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at a given location.