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Re: Mistreatment of Seismology Issues

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At 09:56 PM 10/25/98 EST, Yank 2002 wrote several more points variously
interrelating the concept of "acceptable level of risk", one or more
interpretations of the Jennings "Fault Activity Map of California", Richter
Magnitude -or its facelifted Moment Magnitude successor, and observed
structural damage at Northridge. 

Some of these points appear plausible but others still seem to scramble
unrelated concepts. It is not clear how many conclusions were drawn, other
than that "acceptable level of risk" has been dismissed as faulty.

A few comments of mine in reply follow:

First, that fault map surely has its uses, but it is only the map of what's
known up to when it was released. Lots remains unknown. The map is not the
territory, it is a human-contrived abstraction. The territory will not obey
the map, and it will not keep the promises humans thought they discerned.

No problem with me about conceptualizing California into three seismic
parts. As Julius Caesar would have said, Omnes California divisa in partes
tres --just like Gaul was. But still, what does a map really control?

As for "'western' California as an irregularly formed spider web consisting
of hundreds of seismic faults stretching from the Mexican border to
Mendocino and beyond", well sure it is a mess of faults, but not all are
necessarily seismic. An enlightening book on this is "Assembling
California", by John McPhee, and prominently featuring renowned plate
tectonicist Eldridge Moores of U.C. Davis. The dustjacket aptly illustrates
California being assembled from pieces of a jigsaw puzzle. Recently I
explained to a friend that I had learned from this book that geologically,
California is like a giant train wreck where the jumble of smashed rolling
stock is still settling and smoking and groaning. (I met Dr Moores before I
knew what he was a professor of. He retained me to evaluate his century-old
farmhouse outside Davis for seismic fitness. It had been moved onto new
foundations already. I explained "all about" earthquake risk in his area,
and gave my conclusion that the house was in good shape for the seismicity
at the site. He listened without correcting me or revealing his expertise. I
guess he found me either a fool or acceptably credible.) I would regard all
of California as a fault spider web, not just the western part, but not
everywhere of identical risk of frequency or intensity of seismic lurch.

Scaling down the M magnitude according to a site's distance from the
causative fault is a point that appears to mix metaphors and scramble
concepts. Magnitude does not apply to a site, it applies to the whole damned
event. And accordingly there is no such thing as a "design magnitude" on the
M scale for building design. Just because newspapers have salted the Richter
scale into public awareness is no reason to confuse ourselves with this
non-sequitur.

Now for another doubtful conclusion drawn from reasonable evidence. You said,

>What is interesting about the myth of "acceptable level of risk" concept is
>that after you took a walk, after the Northridge disaster, along Ventura Blvd
>in Sherman Oaks or Encino which are located about 10 miles south from
>Northridge (all three communities lie within the San Fernando Valley, near Los
>Angeles), and observed hundreds of badly damaged or partially collapsed
>commercial structures, then walked along the side streets where many single
>story wood construction residences and almost EVERY 2, 3 or 4 story apartment
>structure (and there were hundreds of them) were red-tagged and every tenant
>was forced to leave the area, you knew that something very basic is wrong with
>the concept of "acceptable level of risk".

It does not follow from the observed damage that the CONCEPT of "acceptable
level of risk" is wrong in any way whatever. Visit a junk yard of wrecked
cars. The newer ones all had bumbers intended to prevent any damage in
collisions up to 5 miles per hour. But these cars are total losses. Were the
bumpers basically wrong in concept? No, they were not intended to help in
high speed collisions.

What IS clear from the observed Northridge damage is that the collapsed or
otherwise ruined buildings were not, in their as-built condition, strong
enough to withstand what they were subjected to. Fingers of blame may be
pointed in every direction as to why, but the concept of acceptable level of
risk would not be among the targets. Not unless you are willing to assert
that the service-level speed limit for cars should be 5mph divided by 1.4,
or about 3mph, so as to eliminate all risk. Or that car bumpers should be
designed for 1.4 times the maximum speed of the car.

You already offered subsurface conditions as one of the surprise factors in
excessive damage at Northridge. Yes. Also, how about underestimation of
severity of shaking, and overestimation of structural resistance? How about
overreliance on construction being perfectly executed? How about code-source
SEAOC Seismology not being interested enough in low-rise mundane
construction to consider and articulate how to cope with its peculiarities?
(Been there, seen it, done it myself.) These are human nature phenomena:
people desiring to do the right things but making imperfect and ill-starred
choices. So I will accept that in a broad sense, as you say, "the codes
under which all these structures were designed were wrong, and in many
cases, they were deadly wrong."

I submit however that remedying the "wrongness" of code is necessarily a
people interaction issue very much like creating political legislation and
making sausage: a messy and uncertain mixing process. 

In my opinion, far too many rash and overreactive code detail remedies have
been promulgated, almost in kneejerk fashion, in the Los Angeles area on the
heels of the emotional shock Northridge caused. But it's hardly
unprecedented. Consider the 1941 attack on Pearl Harbor. Despite sound
evidence, nobody was willing to risk ridicule by admitting such an attack
was possible or preparing to resist it. Big embarassing shock when it
happened. Then began the overreactions instigated by the shocked parties:
Shoot down our own planes arriving. Deny all blame. Round up and jail all
Japanese Americans on the West Coast. (An excellent discussion on the
reasoning incapacitation of military leaders who have suffered unexpected
defeats or disasters is in "Military Misfortunes" by Cohen and Gooch.) 

Unlike in the military, where defeated commanders are replaced with
unimpaired ones, after Northridge the same officials who allowed the failed
buildings to be built oversaw a great patchwork of remedial code changes. No
reflection on the integrity of those officials, but I think all those code
changes should be regarded as temporary, and replaced by simpler and more
coherent ones formulated from a distance and free from control by those
having personal responsibility at the time of the disaster. Code needs a
fresh, dispassionate remake, hopefully not (as before) understating the
earthquake shaking or overstating material performance in the as-built
realities. And it needs to be brought back within an ordinary engineer's
ability to grasp and correctly follow. 

Charles O. Greenlaw,  SE     Sacramento  CA