Regarding the magnitude of the Izmit event; since there is some
discussion as to what it really should be (aside from the various
ways of expressing it:Mb,Ms,Ml,Mm, etc), curiosity suggests that the
PSN see what its data provides. I don't know what WINQUAKE is giving
for those who have it; I don't have it here.

But everyone can use their own data and location to calculate Ms.
To use a particularly generic formula, Gutenbergs' old formula is: 

Ms = log(A/P) + 1.66*log(distance) - 0.18. , where A is the p-p ground
motion in nanometers (10^-9meter), P is the period in seconds, and the
distance is in degrees. The value of the corrector term (-0.18) is 
subject to much debate, and has large regional variations.

We can use the data from the STM-8B running here in the basement with the
B version of the multi-period feedback set for 40 seconds, and digitizing
with the RS multimeter set for 200mv full scale. The output of the VBB
seismometer is 5,293 Volts/meter/second after the line driver.

The signal actually clipped in the 12-bit digitizer during the surface 
waves at +,- 200 millivolts, or about 75 microns/second peak-peak. But 
graphic extrapolation of the plotted data gives a mean p-p amplitude of
about 150 microns/second at 24 seconds, which is a displacement (multiplying
150 by 24/2*pi) of 572 microns or 5.72*10^5 nanometers..

Using a globe to get the distance, I find that western Turkey is about 120
degrees from St. Louis.

So calculating the terms of the magnitude formula:

	log(A/P) = log[(5.72*10^5)/24] = 4.377

	1.66*log(distance) = 1.66*log(120) = 3.45

	So Ms = 4.377 + 3.45 - 0.18 = 7.65.

Considering the uncertainties, this is pretty close. Changing the numbers
by 10% changes the result by +,- 0.1 to 0.2 unit..

Regards,
Sean-Thomas

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