Thanks, Dennis! I took this info into my first semester Introductory
Physics lab tonight and incorporated it into my lab briefing.
Jim
On Thu, 01 Mar 2001, Dennis Brownridge wrote:
> We can be happy the USGS gave distances in kilometers, and pronounced it
> correctly, but a much bigger problem is that they give the energy of quakes
> in those ridiculous "Richter scale" magnitudes, which few people--geologists
> included--seem to understand. I see on the USGS website that they use at
> least 6 different kinds of "magnitudes," tweaked from Richter's original
> arbitrary scale (1935). It appears that the energy of a quake (in joules) is
>
> E = (25 000) 10^(1.5 M)
>
> where M is the magnitude, although the constant ranges from about 22 000 to
> 26 000, depending on which "magnitude" they are using and which source you
> are reading. Of course, they don't explain this clearly anywhere. You have
> to convert from all sorts of non-SI garbage--"size," "tons of TNT" [really
> 10^9 thermochemical calories], "dyne-cm," and clumsy logarithms, although at
> one point they do mention "Newton-meters" [sic]. Considering that these guys
> are the experts, they do a really terrible job of explaining it, with lots
> of glaring mistakes and ambiguous terminology. Why can't we get scientists
> to read the Standards on measurement?
>
> Anyway, an increase of 1 magnitude represents an increase in quake energy of
> sqrt(1000), or 31.6 times (i.e., the energy released at the focus or
> hypocenter, the point of slippage deep underground). So, if we use 25 000
> for the constant,
>
> magnitude 2.0 = 25 MJ (the smallest quake you can feel)
> magnitude 3.0 = 800 MJ
> magnitude 4.0 = 25 GJ
> magnitude 5.0 = 800 GJ
> magnitude 6.0 = 25 TJ
> magnitude 7.0 = 800 TJ
> magnitude 8.0 = 25 PJ
> magnitude 9.0 = 800 PJ (about the biggest possible quake)
>
> Two significant digits is apparently the best they can get, given all the
> unknown variables such as the type of rock the quake waves are passing
> through.
>
> Think how quickly the public would come to understand and appreciate SI if
> the government just gave earthquake, food energy, and consumption statistics
> in joules, as they are supposed to! How interesting that the smallest quake
> you can feel has the same energy as the food you eat in a couple of days;
> that the Seattle quake released as much energy as the world's population
> uses in 1 minute; and that the largest quakes are bigger than the biggest
> H-bombs! But all that is lost on people because we use so damn many
> different units of energy.
>
> > -----Original Message-----
> > From: James R. Frysinger
> >
> > Our TV crew dodged it. They gave no numbers except for the magnitude,
> > "seven point oh".
--
James R. Frysinger University/College of Charleston
10 Captiva Row Dept. of Physics and Astronomy
Charleston, SC 29407 66 George Street
843.225.0805 Charleston, SC 29424
http://www.cofc.edu/~frysingj [EMAIL PROTECTED]
Cert. Adv. Metrication Specialist 843.953.7644
