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Topic: Moment magnitude scale


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In the News (Wed 21 Aug 19)

  
  Richter magnitude scale - Free net encyclopedia   (Site not responding. Last check: 2007-10-21)
It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude of the largest displacement from zero on a seismometer output.
The diminution of amplitude due to distance between the earthquake epicenter and the seismometer is corrected for by subtracting the common logarithm of the expected amplitude of a magnitude 0 event at that distance.
By the beginning of the 21st century, most seismologists considered the traditional magnitude scales to be largely obsolete, being replaced by a more physically meaningful measurement called the seismic moment which is more directly relatable to the physical parameters, such as the dimension of the earthquake rupture, and the energy released from the earthquake.
www.netipedia.com /index.php/Richter_scale   (829 words)

  
 Page 19 -- Measuring Earthquakes
Seismic Moment: Not actually a magnitude scale, seismic moment is an estimate of the energy of an earthquake, and as such, is typically given in units of Newton-meters (Nm).
Moment Magnitude: The moment magnitude scale is a way of rating the seismic moment of an earthquake with a simple, logarithmic numerical scale similar to the original Richter magnitude scale.
Surface-wave Magnitude: Surface-wave magnitude is calculated using the amplitude, on a long-period vertical seismometer, of surface waves with a 20-second period.
www.data.scec.org /Module/sec3pg19.html   (545 words)

  
 Wallace Creek Trail Guide | Glossary
All magnitude scales are calibrated to yield approximately the same value for any given earthquake; however, since the moment magnitude scale is not based on the same measurements as Richter (local or surface-wave) magnitudes, the different magnitudes do not always agree, particularly for very large quakes.
Surface-wave magnitude is calculated using the amplitude, on a long-period vertical seismometer, of surface waves with a 20-second period.
The moment magnitude scale is a way of rating the seismic moment of an earthquake with a simple, logarithmic numerical scale similar to the original Richter magnitude scale.
www.scec.org /wallacecreek/misc/defs.html   (2649 words)

  
 UALR Arkansas Earthquake Center - The Moment Magnitude Scale - Modified Mercalli Scale, MM scale, measuring earthquake ...
Moment magnitude is the measurement and term generally prefered by scientists and seismologists to the Richter scale because moment magnitude is more precise.
Moment Magnitude is not based on instrumental recordings of a quake, but on the area of the fault that ruptured in the quake.
Moment Magnitude is calculated in part by multiplying the area of the fault's rupture surface by the distance the earth moves along the fault
quake.ualr.edu /public/moment.htm   (140 words)

  
 Moment magnitude scale - Wikipedia, the free encyclopedia
The moment magnitude scale was introduced in 1979 by Tom Hanks and Hiroo Kanamori as a successor to the Richter scale and is used by seismologists to compare the energy released by earthquakes.
The constants in the equation are chosen so that estimates of moment magnitude roughly agree with estimates using other scales such as the Richter magnitude scale.
One advantage of the moment magnitude scale is that, unlike other magnitude scales, it does not saturate at the upper end.
en.wikipedia.org /wiki/Moment_magnitude_scale   (428 words)

  
 Earthquake - MSN Encarta
The Richter scale measures the amplitude, or height, of seismic surface waves.
Seismologists calculate moment magnitude by measuring the seismic moment of an earthquake, or the earthquake’s strength based on a calculation of the area and the amount of displacement in the slip.
The moment magnitude of the 1906 San Francisco earthquake was 7.6; the Alaskan earthquake of 1964, about 9.0; and the 1995 Kōbe, Japan, earthquake was a 7.0 moment magnitude; in comparison, the Richter magnitudes were 8.3, 9.2, and 6.8, respectively for these tremors.
encarta.msn.com /encyclopedia_761571674_5/Earthquake.html   (2048 words)

  
 Richter magnitude scale   (Site not responding. Last check: 2007-10-21)
Richter's local magnitude scale was originally to be used only in a particular area in California and on seismograms recorded a particular instrument the Wood-Anderson torsion seismometer.
Richter magnitude is a logarithmic scale obtained by calculating the logarithm of combined horizontal amplitude of the largest displacement from zero a seismogram.
The diminution of amplitude due to between the earthquake epicenter and the seismometer is corrected for subtracting the logarithm of the expected amplitude a magnitude 0 event at that distance.
www.freeglossary.com /Richter_scale   (673 words)

  
 The San Andreas Fault - VIII. "Magnitude" and "Intensity"   (Site not responding. Last check: 2007-10-21)
Magnitude is a measure of the size of an earthquake.
As the Richter scale does not adequately differentiate between the largest earthquakes, a new "moment magnitude" scale is being used by seismologists to provide a better measure.
On the moment magnitude scale, the San Francisco earthquake is estimated at magnitude 7.7 compared to an estimated Richter magnitude of 8.3.
pubs.usgs.gov /gip/earthq3/magnitude.html   (332 words)

  
 UALR Arkansas Earthquake Center - Richter Scale, Modified Mercalli Intensity Scale, Moment Magnitude Scale,
The Richter magnitude scale was developed in 1935 by Charles F. Richter of the California Institute of Technology as a mathematical device to compare the size of earthquakes.
The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs.
Because of the logarithmic basis of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.
quake.ualr.edu /public/richter.htm   (487 words)

  
 Earthquakes - Discover Our Earth
Modern seismologists prefer a magnitude scale that reflects the actual area of rupture along a fault caused by an earthquake, this is the moment magnitude.
This moment magnitude scale is also logarithmic, and has been adjusted to look similar to the familiar Richter Scale.
Earthquakes of magnitude 5 and above are those that cause damage to structures and loss of human life, and these are the quakes reported in the news.
atlas.geo.cornell.edu /education/student/earthquakes/magnitude_i.html   (185 words)

  
 Richter Magnitude
He calibrated his scale of magnitudes using measured maximum amplitudes of shear waves on seismometers particularly sensitive to shear waves with periods of about one second.
Both the magnitude and the seismic moment are related to the amount of energy that is radiated by an earthquake.
For this moment is in units of dyne-cm, and energy is in units of ergs.
www.seismo.unr.edu /ftp/pub/louie/class/100/magnitude.html   (1477 words)

  
 The Big One: Curriculum
This scale, commonly known as the Richter scale, measures the energy released by an earthquake.
An increase of one unit of magnitude (for example, from 4.5 to 5.5) represents a 10-fold increase in wave amplitude on a seismogram or approximately a 30-fold increase in the energy released.
The moment magnitude scale measures more of the ground movements produced by an earthquake and is especially useful for large scale earthquakes.
www.washington.edu /burkemuseum/earthquakes/cur-magnitude.html   (816 words)

  
 PDC HAZUS Glossary   (Site not responding. Last check: 2007-10-21)
The idea of a logarithmic earthquake magnitude scale was first developed by Charles Richter in the 1930's for measuring the size of earthquakes occurring in southern California using relatively high-frequency data from nearby seismograph stations.
The moment magnitude scale was developed to yield much the same results as the earlier magnitude scales such as ML (local magnitude), MS (surface-wave magnitude), and Mb (body-wave magnitude).
The two main features of the moment magnitude scale that make it superior to the earlier ones are: (1) moment magnitude measures a physical property of the earthquake source, and (2) moment magnitude accurately measures the size of large earthquakes relative to small earthquakes.
www.pdc.org /hha/html/hzsglossary.jsp   (1971 words)

  
 Measurement
Magnitude does not depend on population and effects to ground structures, but rather on wave amplitude and distance.
This magnitude scale is logarithmic, meaning each step in magnitude is exponentially greater than the last.
These magnitude scales differ by the type of wave amplitude that is measured from the seismogram and the mathematical formula used to determine the magnitude.
scign.jpl.nasa.gov /learn/eq8.htm   (492 words)

  
 Richter Scale, etc.   (Site not responding. Last check: 2007-10-21)
He decided on a scale that would emulate the stellar magnitude scale used by astronomers to measure the strength of stars.
That's why a new magnitude scale was developed in the 1980's; the moment-magnitude scale relies on the lowest seismic frequencies, which are most sensitive to the scale of the earthquake-producing fault.
The different magnitude scales used by seismologists are why we often hear different values reported about the same earthquake.
amos.indiana.edu /library/scripts/richter.html   (251 words)

  
 Thanks 4 Supporting. Us :: 2004 Indian Ocean Earthquake   (Site not responding. Last check: 2007-10-21)
The moment magnitude scale (a successor to the Richter Scale), was introduced by Hiroo Kanamori and is used by seismologists to compare the energy released by earthquakes.
On the moment magnitude scale, which is more accurate for quakes of this size, the earthquake's magnitude was first reported as 8.1 by the United States Geological Survey, but after further analysis they increased this first to 8.5 and 8.9 and finally 9.0.
The moment of inertia of Earth is believed to have decreased a bit due to the earthquake, and because angular momentum is conserved, this would result in an increase of the angular velocity of Earth's rotation.
www.thanks4supporting.us /2004-indian-ocean-earthquake.html   (1691 words)

  
 Earthquake - Free net encyclopedia   (Site not responding. Last check: 2007-10-21)
The scale currently used in the United States is the Modified Mercalli Intensity Scale, while a number of other scales used in different parts of the world: the Shindo scale in Japan, the European Macroseismic Scale in the European Union, the Rossi-Forel scale in Latin America, the MSK-64 in Russia and the CIS.
It is obtained by measuring the maximum amplitude of a recording on a Wood-Anderson torsion seismometer (or one calibrated to it) at a distance of 600 km from the earthquake.
This is because seismic moment is derived from the concept of moment in physics and therefore provides clues to the physical size of an earthquake—the size of fault rupture and accompanying displacement and length of slippage—as of as well as the amount of energy released.
www.netipedia.com /index.php/Earthquake   (2359 words)

  
 Richter Magnitude Scale for Measuring the Size of an Earthquakes
However, the energy of an earthquake is proportional to the square root of the cube of the amplitude.
stellar magnitude scale used in astronomy to describe the brightness of stars and other celestial objects.
Japanese seismic intensity scale, are used to describe relative earthquake effects.
www.edinformatics.com /inventions_inventors/richter_scale.htm   (752 words)

  
 Plate Tectonics
The Richter magnitude is based on the size of the largest waves arriving at a particular type of instrument, the Wood Anderson seismograph.
Until January, the USGS used the surface wave magnitude scale to determine the official magnitudes of earthquakes.
Its official surface-wave magnitude is 7.1, but on the moment scale it's only a 6.9.
www.platetectonics.com /article.asp?a=74&c=1   (1347 words)

  
 Untitled Document
Since instruments such the seismograph and accelerometer have made it possible to accurately measure ground motions, a quantitative measure of the size of an earthquake is possible.
There are several magnitude scales in use, which often leads to confusion in the reporting of magnitudes.
The best scale for scientific and engineering purposes is the moment magnitude (Mw) scale since it is related to the rupture parameters.
peer.berkeley.edu /course_modules/eqrd/EQDef/eqdef5.htm   (424 words)

  
 Moment Magnitude   (Site not responding. Last check: 2007-10-21)
I don't believe that it is correct to describe the moment magnitude as a new scale.
Now, getting back to earthquakes, the moment magnitude has been "defined" to agree as well as possible with all of the other magnitude measurements techniques that refer back to the original Richter magnitude scale.
The original Richter magnitude determination technique was limited to moderate-sized, shallow earthquakes located in California and recorded within 600 km on a Wood-Anderson horizontal instrument.
www.jclahr.com /science/earth_science/mag_dist/moment_magnitude.html   (278 words)

  
 How is the strength of earthquakes measured? - Answerbag.com
Magnitude does not depend on population and effects to ground structures, but rather on wave amplitude and distance from the epicenter.
The scale used to measure magnitude is the Richter scale.
The moment magnitude scale is calibrated so that at the lower magnitudes is corresponds to the richter magnitudes.
www.answerbag.com /q_view.php/2390   (501 words)

  
 Florida Oceanographic Online-Earthquake Magnitude & Intensity Scale
Although numerous intensity scales have been developed over the last several hundred years to evaluate the effects of earthquakes, the one currently used in the United States is the Modified Mercalli (MM) Intensity Scale.
The lower numbers of the intensity scale generally deal with the manner in which the earthquake is felt by people.
In general, the Ms magnitude is more reliable than the MB magnitude as a means of yielding the relative "size" of a shallow-focus earthquake.
www.floridaoceanographic.org /reference/earthquake.htm   (1263 words)

  
 Exploratorium: Faultline
.Magnitude is a measure of the energy released during an earthquake, and it's related to the size of its waves on a seismogram.
Seismologists use several different magnitude scales to desribe the size of a quake.
In both scales, a jump of one number is equal to a 10-fold increase in the size of the waves in a seismogram and a 30-fold increase in energy released.
www.exploratorium.edu /faultline/basics/measure.html   (870 words)

  
 Oregon earthquake epicenter map
This energy release, or magnitude, is measured on the familiar Richter scale, invented by Charles F. Richter in 1934.
Magnitude 3 and 4 earthquakes are commonly felt, but rarely cause damage.
Moment magnitude is generally used now to describe earthquakes, but the categories are about the same.
www.oregongeology.com /sub/earthquakes/EqEpicentermap.htm   (1030 words)

  
 Moment Magnitude - Boston College   (Site not responding. Last check: 2007-10-21)
Seismic moments from old events will be gathered as known or computed as needed for those earthquakes for which instrumental data or details of the felt areas exist.
They calibrated their coda amplitude moment meas urements using the coda amplitudes of two events for which seismic moments had been determined.
For each system, the constant C is determined in the same way; the seismic moment for a set of events is found from some independent method and then the con stant C in the moment formula given above is calibrated to give the correct seismic moment for that system.
www.bc.edu /research/westonobservatory/researchlist/momentmag   (902 words)

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