Earthquakes

After hearing of the devastation in Haiti, I was surprised to learn (a consequence of old age, I reckon) that they don't use the Richter scale any more. I had written a tutorial describing good ol' Richter and now I have to understand the sexy new scale. They no longer say: "7.0 on the Richter scale". They say: "A magnitude 7.0 earthquake". On the Richter scale (measured by the amplitude of oscillation on a seismograph), going from 6.0 to 7.0 means a tenfold increase in the amplitude of ground motion. That factor-of-ten thing is because the Richter number is based upon a logarithm to base 10. Since 1 + log10[A]) = log10[10A], adding "1" to the Richter number means that A, the amplitude of oscillation, is 10 times larger. These days, seismologists are more interested in the energy released by an earthquake, not the amplitude of ground motion. It's been found that Energy varies as the 2/3 power of the amplitude of oscillation. If A is the amplitude, that suggests using A2/3 to measure the energy released. That suggests the "new" measure of the energy should be: log10[A2/3]. This is now called the Moment Magnitude Scale: MW. If MW increases by 1, then: 1 + log10[A2/3] = log10[10A2/3] = log10[ (103/2A)2/3]. That is, the amplitude increases by 103/2 ... about 31. Mamma mia!------------------------------------------------I figure I should write about this stuff here ... jest in case people still read gummy-stuff.org ------------------------------------------------ P.S. Michaelle Jean: The Canadian Governor General Born in Haiti