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Re: California Earthquake Problems

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To Kenneth Tarlow:

You have said:

> Dear Yank

> I want you to know my house was originally constructed in the 1950's
> and thus has survived many vey high richter scale magnitude
> earthquakes.  It survived the Alaska earthquake which I think was
> magnitude 9.2.  It survived the whittier Narrows,Northridge, Sylmar
> and Loma Prieta earthquakes.

> Of course my house is in the South bay area of Southern California.

> Maybe richter scale magnitude isn't very relavent.

My response to the above is: 

I have experienced a similar situation. My house in Valencia (near Los
Angeles) survived all earthquakes you mentioned (Alaska, Whittier Narrows,
Northridge, Sylmar and Loma Prieta). It is interesting that after the
Northridge earthquake I noticed that all houses along the street where I lived
(basically flat area) were partially damaged (requiring substancial financial
commitment) except for my house. For all practical purposes my house was
untouched exept for one broken window. To the best of my knowledge, all
different model houses on the street were built by the same contractor and
designed by the same architect (and probably designed by the same structural
engineer). The house of the model identical to mine, on the same street, was
pretty badly damaged. 

The question is (using your phraseology): "Why Richter scale magnitude (or any
other meaningful scale system) was not relevant for my house but was relevant
to all other houses on the street?."  The only reasonable answer I can think
of is that God liked me more than he liked my neighbors. I, for sure, did not
reinforce my house with W14X370 steel members neither horizontally, vertically
nor diagonally. For that matter, I did not touch the house neither
architectually nor structurally from the day I've purchased it. 

Also, please note that my EMail message in two or three places mentions
"Richter scale or any other generally recognized  meaningful scale system for
comparison purposes only". I believe that "pounds or kilograms of exploded
TNT" would be just as good as long as structural engineers and the general
public know what damage can be expected by "a unit of TNT exploded". The
military uses this kind of notation. Maybe we should join them in our
nomenclature of destruction description so we all know what we are talking
about. Old Nevada nuclear explosion tests used double description system: (1)
the equivalent of exploded TNT and (2) equivalent of Richter scale earthquake
magnitude. In the meantime we are playing with  structural earthquake detail
definitions that even structural engineers do not understand. Here is such an
example, posted on this list-server yesterday:

"The peak ground accelerations corresponding to these two periods can be used
to construct a site-specific response spectrum similar to the generalized one
at the end of Chapter 16 in UBC.  The flat part of the spectrum is defined by
Sa = 2.5*PGA@0.2sec <mailto:2.5*PGA@0.2sec> , and the curved part by Sa =
PGA@1.0sec/T."  

I wonder what is the percentage of structural engineers who understand the
above procedure without spending a considerable amount of time studying and
trying to figure out what it all means and attempting to fit it to another
similarly simple equation from the people who have created it, and attempting
to fit it to another ... etc. 

One or two more steps in this direction and we will win an award for the most
complicated manual in modern Americal business environment. The IRS Tax Code
Manual will be number two. 

Your comments would be appreciated. 

P.S. If you live in your house long enough and are lucky enough to experience
the release of seismic energy by neighboring Inglewood-Newport fault (capable
of magnitude MM7.0 - MM7.3 as established by seismologists), you will able to
test and subsequently determine whether Richter magnitude of (say) 7.1 or
thereabouts will be "relevant" with respect to your house. In the meantime, as
you said before, you should not worry about a big earthquake in the San
Francisco Bay or in the Los Angeles area and their influence on your house.
Besides, earthquakes happen to other people; they never happen to us. The
trick is to belong to the "us" group rather than to "the other people" group.
And since you have done it so many times, I am sure you know how to stay with
the right group.