![]() ![]() Instruments are carefully calibrated with respect to each other. Records from instruments of identical manufacture. Earthquake-induced liquefaction of the earth-filled dam resulted in a landslide that caused partial collapseĪt first, the Richter Scale could be applied only to the Van Norman Dam, San Fernando, California, 1971. Than the amount associated with the preceding whole number Scale corresponds to the release of about 31 times more energy Magnitude represents a tenfold increase in measured amplitude asĪn estimate of energy, each whole number step in the magnitude The logarithmic basis of the scale, each whole number increase in Magnitude of 5.3 might be computed for a moderate earthquake, andĪ strong earthquake might be rated as magnitude 6.3. On the Richter Scale, magnitude isĮxpressed in whole numbers and decimal fractions. In the distance between the various seismographs and theĮpicenter of the earthquakes. Included in the magnitude formula to compensate for the variation The amplitude of waves recorded by seismographs. Magnitude of an earthquake is determined from the logarithm of Mathematical device to compare the size of earthquakes. ![]() Richter of the California Institute of Technology as a The Richter magnitude scale was developed in 1935 by Charlesį. The time, location, and magnitude of an earthquakeĬan be determined from the data recorded by seismograph Motions, can detect strong earthquakes from sources anywhere in Sensitive seismographs, which greatly magnify these ground Varying amplitude of ground oscillations beneath the instrument. Seismographs record a zig-zag trace that shows the Travel through the Earth they are recorded on instruments called Seismic waves are the vibrations from earthquakes that Highway interchange heavily damaged by the magnitude 6.5 earthquake The point on the Earth's surface directly above theįocus is called the epicenter of the earthquake. Rupture takes place is called the focus orĮarthquake. Shearing movements along faults in the crust of the Earth, anĮarthquake results. When this energy is released suddenly, for example by TheĮnergy from these forces is stored in a variety of ways within Interior that continuously affect the surface of the Earth. Thus represented by a single, instrumentally determined value.Įarthquakes are the result of forces deep within the Earth's It is based on theĪmplitude of the earthquake waves recorded on instruments which Released at the hypocenter of the earthquake. Magnitude is related to the amount of seismic energy The observer with respect to the earthquake epicenter. To place within the disturbed region depending on the location of On people, buildings, and natural features. Intensity is based on the observed effects of ground shaking ![]() The moment magnitude provides an estimate of earthquake size that is valid over the complete range of magnitudes, a characteristic that was lacking in other magnitude scales.The severity of an earthquake can be expressed in terms of both The result is called the moment magnitude. The moment is then converted into a number similar to other earthquake magnitudes by a standard formula. The moment can be estimated from seismogram s (and also from geodetic measurements). Moment is a physical quantity proportional to the slip on the fault multiplied by the area of the fault surface that slips it is related to the total energy released in the earthquake. In particular, for very large earthquakes, moment magnitude gives the most reliable estimate of earthquake size. In its range of validity, each is equivalent to the Richter magnitude.īecause of the limitations of all three magnitude scales (ML, Mb, and Ms), a new more uniformly applicable extension of the magnitude scale, known as moment magnitude, or Mw, was developed. Each is valid for a particular frequency range and type of seismic signal. These include body wave magnitude ( Mb) and surface wave magnitude ( Ms). In order to take advantage of the growing number of globally distributed seismograph stations, new magnitude scales that are an extension of Richter's original idea were developed. This is what was to eventually become known as the Richter magnitude.Īs more seismograph stations were installed around the world, it became apparent that the method developed by Richter was strictly valid only for certain frequency and distance ranges. This magnitude scale was referred to as ML, with the L standing for local. 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. Earthquake size, as measured by the Richter Scale is a well known, but not well understood, concept. ![]()
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