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- To: seaint(--nospam--at)seaint.org
- Subject: Re: California Earthquake Problems
- From: Yank2002(--nospam--at)aol.com
- Date: Wed, 13 Jan 1999 07:37:33 EST
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.
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- From: Sleiman Serhal
- Re: California Earthquake Problems
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