Re: not the "Richter" scale anymore

could be wrong, but I suspect that Hiroo was motivated primarily
by the troubling observation that the size of the very largest
earthquakes was being systematically underestimated by standard
magnitude scales. My guess is that whether Mw was intended as
a measure of strain energy or radiated energy was a secondary,
though still quite interesting, concern.

I'm not sure I see the two as separable. I.e., I think you're right
that the original motivation was to more faithfully capture the size of
the largest earthquakes, but from the earliest days of magnitude scale
development, seismologists were talking about the desirability of using
strain energy to measure earthquake size.

Mw, or the seismic moment Mo, is often fairly well constrained,
but seismic energy is often uncertain by a factor of 5 for a single
earthquake, so I don't think there is a consensus yet on seismic
moment vs. seismic energy - even for big earthquakes.

Another colleague of mine, initials AM, once showed a plot of static
stress drop to his father and commented that the quanity is
scale-invariant, of course with the usual scatter of <1 to >500 bars.
I forget the father's exact words in reply, but it was something to the
effect that it was an interesting field of science, if parameters were
only constrained to within 3 orders of magnitude. (Of course it isn't
quite that bad: some of that variation is clearly real.)

Since a real earthquake - one of any
size at least - is no doubt quite complicated,

Little earthquakes seem to be complicated as well.

, because I think that in a
real earthquake the stress drop can be partial over parts of the
fault, complete over other parts of the fault, and there is even
evidence of overshoot in some earthquakes. Since the average
stress drop, radiated energy, and seismic moment are the sum
total of a combination of such behaviors, I'm not sure what we
learn by studying that sum

And yet, when one manages to resolve them with high-res methods,
radiated spectra are awfully well-behaved. It's always impressed me,
how well spectra seem to conform to first-order principals: corner
frequency inversely correlated to rupture size, apparently consistent
omega-square decay at high frequencies. If rupture processes aren't
well-behaved, they seem to be complicated in ways that conspire to give
well-behaved results on average. Either way, presumably there is
something to be learned. (If not, geez, maybe we should all hang up
our hats and go write biographies or something.)

Susan

.

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