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Re: Mistreatment of Seismology Issues

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Hello all, yes, you're right, as a seismologist student, I always have to
debate about the San Anderas and NYC earthquakes. Thanks, Michelle Trzecinski

Here's an attachments....

>I have listened to this thread with great interest.  The question has been
>discussed from the standpoint of what engineers need to do from a design
>standpoint.  Additionally, we have discussed what a design based
earthquake is.
>All answers have been well presented and raised some key issues--again
from the
>engineer's standpoint.
>
>>From my standpoint, I would like to hear now how this information is
given to
>the general public so they better understand what it means when they are told
>their building "is in conformance with the code" (whatever edition that may
>be).  Many of my projects relate directly to this concept.  When the firm
>evaluates a building and tells the owner they can expect a 25% to 30% loss
from
>a design based earthquake, they obviously get concerned.  Many will say, "but
>the building was built to code!"
>
>Any suggestions on how to present this issue to a building owner.  This
can also
>be the first step in addressing the overall question of the engineering
image to
>the public.  A wonderful task for a public relations committee (BTW--this
could
>easily be a virtual committee).  Any comments on this idea from the SEAOC
board
>or anybody else would be greatly appreciated.
>
>Rick Ranous
>(formerly OES) now EQE
>
>A.M.Zaki wrote:
>
>> I agree with Gillham.
>> To say that a specific structure can withstand an earthquake with a
>> specific Richter magnitude, the location (including soil characteristics),
>> and characterisitcs of both building and earthquake must be clearly
>> specified. Design earthquake should be simulated by an expert and used to
>> excite the building using time history analysis.
>>
>> A.M.Zaki
>> At 08:05 Õ 22/10/98 +1000, you wrote:
>> ><snip>
>> >
>> >Since general public knows very well what kind of damage can be expected
>> >when
>> >(say) 6.4 earthquake strikes but has absolutely no idea as to what kind of
>> >damage can result when "life-safety standard"-compliant structure is
hit by
>> >the same magnitude earthquake
>> >
>> ><snip>
>> >
>> >Beyond my geotech class, and associated material I learned or have read
>> >about relating to seismic design, I am not all that hip on the actual
>> >mechanics of earthquakes.  That being said, I would have to question (in a
>> >somewhat uninformed manner) the validity of the above statement.
>> >
>> >I would seem that there are at least 5 parameters that would help in
>> >determining the damage that can be expected from an earthquake:
>> >
>> >1) Richter magnitude
>> >
>> >2) Duration
>> >
>> >3) Frequency content
>> >
>> >4) The characteristics of the structures being excited.
>> >
>> >5) Accelerations
>> >
>> >To say that an area experienced a "6.4" earthquake does not, IMO, give a
>> >person enough information to even really guess the magnitude of damage
that
>> >should be expected.
>> >
>> >Case in point:
>> >
>> >Compare the Guam earthquake (Richter magnitude 8.2) to the Northridge
>> >(6.4?).
>> >
>> >Duration of strong motion on Guam - about 40 seconds
>> >
>> >Duration of strong motion for Northridge - about 15 seconds.
>> >
>> >VERY different frequency contents (Guam EQ caused by a subduction fault,
>> >located very deep, while Northridge I think was a strike slip fault EQ).
>> >Guam EQ was as I understand it a much longer period earthquake than NR.
>> >
>> >Very high accelerations for NR, estimated accelerations from Guam EQ are
>> >not nearly as high.
>> >
>> >
>> >Two major structural failures on Guam, a bunch more for NR (although you
>> >guys have a heck of a lot more buildings than we do!).
>> >
>> >No deaths on Guam.  More than that for NR.
>> >
>> >
>> >
>> >OK.  My point is that boiling down an earthquake to one single parameter
>> >can, IMO, be very misleading.  Using this method, the amount of damage,
>> >collapsed buildings, and deaths that resulted from the 8.2 on Guam should
>> >have far surpassed the results of the "smaller" NR earthquake.  But that
>> >did not happen.
>> >
>> >I don't wish to be just a naysayer, but at this time I don't feel that I
>> >have covered all the bases as far as relevant earthquake parameters are
>> >concerned.  Anyone care to add (or modify, or delete) from the above list?
>> >It might be informative (for me, at least!)
>> >
>> >
>> >
>> >Regards,
>> >
>> >T. Eric Gillham PE
>> >
>> >
>> >
>> >
>> >
>>
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