Kevin Mackey has pointed out an error I made in the distance for
the Izmit event. It appeared that I had not used the "Great Circle"
distance; I had, but I measured and scaled it wrong.

However, I was not pretending to do exact science at home; I have 
innumerable programs at the Univ for that. What I was trying to do 
was to show what a PSN member can do with home resources.  I used a 
ruler on a globe as an approximation to determine the epicentral 
distance from St. Louis. 

The upper limit is of course the longitudinal distance, with
St. Louis at 90W and the event at 29.8E. My antique globe has no
scale on it, so I "calibrated" the ruler with the distance between
St. Louis and San Francisco = 30 degrees, which led to over estimating
the distance to Izmit. The actual STL to SFO distance is about 21 degrees. 
This makes my "ruler" say 84 degrees to Izmit; Kevin says it is 81 
degrees. I should have suspected the error from the longitudinal information.

The point is that simple, not so accurate measurements, are useful.
At large distances, the effect of errors is not that significant.
The difference in the calculated magnitude between 120 degrees and 
81 degrees is 0.28. This reduces my magnitude estimate from 7.65 to
7.37, which is actually closer to todays' revised figure of 7.4.
(I get 7.41 if I use 84 degrees!).

I am more interested in how the amplitudes recorded by the PSN 
instruments worked out in determining the magnitude.

Unfortunately, even large variables in the magnitude estimate provide no
excuse for the hugh tragedy caused by shoddy building construction.
Of course cement is expensive in that part of the world, but if only
enough is used to keep the rain from washing out the mortar, it doesn't
take much to shake down an apartment building.


Regards,
Sean-Thomas


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