Richter+scale

=Richter Scale=

toc Read here about an exponential metric that varies across scales.

=Richter Scale= From Wikipedia:

The expression Richter magnitude scale refers to a number of ways to assign a single number to quantify the energy contained in an earthquake. In all cases, the magnitude is a base-10 logarithmic scale obtained by calculating the logarithm of the amplitude of waves measured by a seismograph. An earthquake that measures 5.0 on the Richter scale has a shaking amplitude 10 times larger than one that measures 4.0. There are several scales which have historically described as the "Richter scale," especially the local magnitude ML and the surface wave Ms scale. In addition, the body wave magnitude, mb, and the moment magnitude, Mw, have been widely used for decades, and a couple of new techniques to measure magnitude are in the development stage. All magnitude scales have been designed to be compatible. This goal has been achieved well for ML, Ms, and Mw. The mb scale gives somewhat different values than the other scales. The reason for so many different ways to measure the same thing is that at different distances, for different hypocentral depths, and for different earthquake sizes, the amplitudes of different types of elastic waves must be measured. ML is the scale used for the majority of earthquakes reported (tens of thousands) by local and regional seismological observatories. For large earthquakes worldwide, the moment magnitude scale is most common, although Ms is also reported frequently. The seismic moment, Mo, is proportional to the area of the rupture times the average slip that took place in the earthquake, thus it measures the physical size of the event. Mw is derived from it empirically as a quantity without units, just a number designed to conform to the Ms scale. A spectral analysis is required to obtain Mo, whereas the other magnitudes are derived from a simple measurement of the amplitude of a specifically defined wave. All scales, except Mw, saturate for large earthquakes, meaning they are based on the amplitudes of waves which have a wavelength shorter than the rupture length of the earthquakes. These short waves (high frequency waves are too short a yardstick to measure the extent of the event. The resulting effective upper limit of measurement for ML is about 6.5 and about 8 for Ms. New techniques to avoid the saturation problem and to measure magnitudes rapidly for very large earthquakes are being developed. One of these is based on the long period P-wave, the other is based on a recently discovered channel wave. The energy release of an earthquake, which closely correlates to its destructive power, scales with the 3⁄2 power of the shaking amplitude. Thus, a difference in magnitude of 1.0 is equivalent to a factor of 31.6 ( = (101.0)(3 / 2)) in the energy released; a difference in magnitude of 2.0 is equivalent to a factor of 1000 ( = (102.0)(3 / 2) ) in the energy released. The elastic energy radiated is best derived from an integration of the radiated spectrum, but one can base an estimate on mb because most energy is carried by the high frequency waves. The moment magnitude scale (abbreviated as MMS; denoted as MW) is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the seismic moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped. The scale was developed in the 1970s to succeed the 1930s-era Richter magnitude scale (ML). Even though the formulæ are different, the new scale retains the familiar continuum of magnitude values defined by the older one. The MMS is now the scale used to estimate magnitudes for all modern large earthquakes by the United States Geological Survey.