Richter Scale

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Equation / Last modified by Administrator on 2015/06/09 07:14
vCalc.Richter Scale

This equation computes the magnitude of a seismic event such as an earthquake using the Richter Scale method, which expresses magnitude relative to a standard amplitude (S).

The input is the intensity of the earthquake typically measured 100 kilometers from the epicenter of the event.  The standard amplitude (S) is defined to be 1 micron (0.001mm)


How do we measure an earthquake's intensity?  And how do we compare the magnitudes of earthquakes.  This formula defines a scale devised in 1935 by Charles Richter and commonly used today, which derives a comparative magnitude for a seismic event.

The intensity of an earthquake, I, is typically measured as the seismic amplitude recorded approximately 100 km from the epicenter of the event.  The Richter Scale then defines the relative magnitude to be:

`"Magnitude"_"Eathquake"` = log `(I/S)`, where the standard earthquake's intensity, S, has an amplitude of 1 micron.  One micron amplitude is then zero on the Richter Scale.

The difference in intensities of earthquakes can be enormous, so the scale provides a more manageable way to compare earthquake magnitudes.  Because it is a logarithmic scale, each integer increase on  the Richter scale (from 1.0 to 2.0 to 3.0 to 4.0 etc) represents an intensity increase by a factor of ten.

Early in the century the earthquake in San Francisco registered 8.3 on the Richter scale. In the same year, another earthquake was recorded in South America that was four time stronger. What was the magnitude of the earthquake in South American?