On 2001-03-01 17:28 -0700, Dennis Brownridge wrote:
> Energy is surely one of the best arguments for adopting SI. Clearly, it
I definitely agree with that, especially when it comes to water heater
specs, food energy, and any other case where the energy is the base
quantity being measured.
However, the feeling I got from reading various web sites on the
definition of earthquake magnitudes is that the translatation from
magnitude to energy is not a precise science, and that the magnitude is
the more primary measurement. So rather than throw away the magnitudes
and report the energy of a quake with a large uncertainty, it's probably
better to report the magnitude first, then say something such as "this is
estimated to correspond to x joules, subject to further refinement." Of
course, there are different definitions for the magnitude, so there's
probably need for standardization there.
Additionally, there is not a direct correspondence between the energy
released in a quake and the intensity of shaking locally, which is
probably what most people care about more. In Japan, the media report not
the Richter-like magnitude, but a "shindo" ("degree of shaking") number in
the range of 0 to 7 (http://www.minc.ne.jp/kics/kbt/spring96/eqprep.html),
similar to the Modified Mercalli scale
(http://wwwneic.cr.usgs.gov/neis/general/handouts/mercalli.html) used in
the US.
(Re total energy vs intensity: I lose the same amount of gravitational
potential energy whether I hike down the mountain or fall off the cliffy
side. But there's a big difference in the effects on my body!)
Other parameters I've heard talked about in Japan are horizontal ground
accelerations and ground displacements, which are of course in SI units.
An article about the Kobe quake at
http://www.newscientist.com/nsplus/insight/quakes/kobe1.html quotes
some of these numbers.
I'll try to ask some experts about this in the near future.
> But all these sites seem to agree that the energy of a quake is
>
> E = (k) 10^(1.5 M)
>
> where E is the energy in joules, M is one of the innumerable magnitude
> scales, and k is a constant. The formulas only disagree on the value of the
> constant, which seems to range from 22 000 up to 63 000, depending on which
> "Richter scale" you use. For example, the big 1964 Alaska quake is rated
I saw a couple of web sites using an exponent of 1.44M rather than 1.5M
(e.g. http://lasker.princeton.edu/ScienceProjects/curr/eqmag/eqmag.htm).
Cheers,
Bruce
--
Bruce Raup
National Snow and Ice Data Center Phone: 303-492-8814
University of Colorado, 449 UCB Fax: 303-492-2468
Boulder, CO 80309-0449 [EMAIL PROTECTED]
