![]() We know that earthquakes can originate at various depths within the Earth's solid core. A magnitude 7 earthquake ruptures a fault area of about 1000 km2 or about 50 km long and 20 km wide.Īlso depth is an important factor influencing earthquake severity. Hence the larger the rupture area, the larger is the earthquake. The size of an earthquake is not only a function of the amount of displacement but also the area of the fault plane that ruptures. Tectonic earthquakes can range in size from magnitudes less than zero, resulting from fault slippage of a few centimetres, to the largest events (magnitude greater than 9), where fault displacements are on the order of many metres. Video: How things work: How Does the Richter Scale Work? Highest magnitude ever recorded The amount of energy released increases 31.7 times between whole number values. ![]() That is, the wave amplitude in a level 6 earthquake is 10 times greater than in a level 5 earthquake, and the amplitude increases 100 times between a level 7 earthquake and a level 9 earthquake. In the case of the Richter scale, the increase is in wave amplitude. In other words, a two is 10 times more intense than a one and a three is 100 times greater. The Richter scale is a base-10 logarithmic scale, meaning that each order of magnitude is 10 times more intensive than the last one. Adjustments are included for the variation in the distance between the various seismographs and the epicentre of the earthquakes. The Richter magnitude involves measuring the amplitude (height) of the largest recorded wave at a specific distance from the seismic source. The magnitude of an earthquake is determined using information gathered by a seismograph. 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.Image: Richter Scale of Earthquake Energy 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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