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RE: Earth Quake in Pakistan: More than 30 die

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S. A.
I believe that the problem is associated with the lack of appropriate
historic records as is typical is almost all areas of the world. Our
recorded history of seismic events is only an instant of the age of the
earth. For each sizable earthquake that occurs, it becomes a learning
experience to the professional community and this leads to revisions in the
methodology that we use to design.
I would suspect that a conservative approach is best until which time that
there can be a general consensus among professionals from around the world
as to an appropriate solution for your area.
In other words, you might consider regions formerly designed to seismic zone
0 which experienced minimal damage in this earthquake to be updated to a
zone 2. Subsequently, those in zones 2 or 2a might be upgraded to a zone 3 -
simply as a measure of protection until such point as the professional
community is able to evaluate the seriousness of the event in all
surrounding regions.
I admit that this is beyond my capability as I have sufficient knowledge to
design after a quake to the provisions provided to me and to make judgment
calls as to the effectiveness of designs compared to the quality of
construction necessary to comply with the engineered design. However, in
issues of determining emergency provisions and in the determination for what
zone a region should be classified, I leave this to the seismologists and
geotechnical professionals.

You might draw on the emergency measures taken by the city of Los Angeles
California after the Whittier Narrows and Northridge Earthquakes to compare
against Unreinforced Masonry structures. You can also review the documents
of evaluation published by FEMA as well as the work done by many other
government organizations.

In my opinion, the performance of most buildings that have been engineered
are more a factor on how well they were constructed than on how well they
were designed. I know this is a broad statement that can get me a lot of
criticism, but my experience with damaged building has been more
consistently identified defects in construction and non-compliance to
structural drawings than from increasing the level of structural design.

Finally, you must consider some sort of "shock factor". In other words,
while damage may have occurred in a Zone Zero that was considered a low
risk, the question to be asked is if the damage could be mitigated in a cost
effective manner OR is the expectation of the public too high. In other
words, is an act of nature that causes minor damage to a structure an
acceptable level of performance?

I'm sure that there are many questions and debates to come from this that
may change the zone maps from this region. However, I suspect that this will
not be the last time that these learning experiences will occur throughout
the history of mankind.

Regards,
Dennis S. Wish, PE

-----Original Message-----
From: S. A. Masroor [mailto:smasroor(--nospam--at)gem.net.pk]
Sent: Saturday, January 27, 2001 3:36 AM
To: seaint(--nospam--at)seaint.org
Subject: Earth Quake in Pakistan: More than 30 die


This is frightening.
    My wife woke me up on the morning of 26th saying "You are snoring so
hard, the bed is shaking" I woke up and noticed the windows. Then I
grabbed her and went out.  She had never been in an earth quake before
and was quite shaken.
    Fortunately, all we felt in Karachi (zone 2) was window rattling and
ceiling fans vibrating.  Some panes broke and an odd wall cracked.
However, 34 people died in other parts of the country, due to structural
collapses.  Most of the damage occurred due to small masonry walls
collapsing across a large area designated mostly as zone zero or one.
(UBC 97 equivalent)
    I recently designed a hospital in MirPur Khas (Zone 0) and as per
local practice it had RCC roof over unreinforced brick masonry (luckily
it survived).  No tremors had been recorded in this general area in the
last 150 years. Historical records show a major earth quake c1815 which
changed the path of the mighty Indus and another big one in the 11th
century, which obliterated a major town.
    Observations from India and suggestions from all professionals on
how to approach structural design in this area will be very valuable to
us all.