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".
