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Re: Mistreatment of Seismology Issues

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At 11:57 AM 10/22/98 EDT, you wrote (among other things):

>For those who did not have a chance to read a summary of some of the
>government compiled statistics about (say) Northridge, here are some numbers:
>
>57 dead
>9300 injured
>$13 billion damage (the last number I saw was $22 billion)
>50,000 homeless
>13,000 buildings destroyed. 
>
>This was the toll of an earthquake of ONLY 6.7 magnitude !!!!!!!

Reply: Right. This tends to support the view expressed by many that Richter
magnitude does not have a direct or tidy relationship to structural damage
potential at a particular site. In other words, the Richter magnitude
describes the entire shaking event for the total geographical area affected.
A building, in contrast, is at risk due to the specific shaking it uniquely
experiences at its own location... the same way a severe electrical storm
still only zaps the spots the lightning hits, no matter how big a storm it
is. Northridge had a lot of hard zaps under a small, violent cloud, if you
will. 

You also asserted:
>Pasadena will find out that the quake the city was exposed to was about
8.1. This seems to be much larger than 6.8  It translates to about 50 times
more of total energy released by the San Andreas as opposed to "the local
fault" total
energy release - I did not use my calculator, but I think the ball park is in
>close neighborhood. 

Reply: OK, there are differences in energy release in the whole event, but
not in the same proportion at any building's site. Consider the total
acoustic energy release at an open-air Rock concert. Ruins the ears of
thousands, or maybe not quite. You can ruin your own ears even worse playing
the same music real loud at home, with far less total energy release. But
you can't take the neighborhood two blocks away along with you. 

Now, what point are we still trying to resolve? The Richter scale as the
defining parameter of structural damage probability, or perhaps something
beyond that? 

Charles O Greenlaw SE      Sacramento CA