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on Zoning !

 
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for_prof_arc at hotmai...
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PostPosted: Mon Jul 26, 2004 9:45 am    Post subject: on Zoning ! Reply with quote

1. My comments are based on participatory experience on evaluation of site
dependent earthquake parameters on nearly 100 sites and on the fact that
1970 revision was done in haste after the 1969 events. The IMD's initial
estimate of Mag 6.5 for Bhadrachalam event of 13 April 1969 was been
downgraded now to 5.5 by other agencies. The extension of zone III right
upto coast was not warrented even at that time.[subsequently this zone was
not downgraded, because of policy of no downgradation].

The 2002 version has gone overboard because Latur event could not be
predicted in all versions of the code from 1962 to 1984. Now, 2002 has gone
to other extreme. There is no justification to make Chennai, Nellore, etc as
in zone III.
Effectively, the forces in Chennai, Hyderabad & Bangalore have been
increased several fold but Mumbai & Kokata were untouched. Only marginal
increase in Delhi by 20%. [See my paper in 12SEE at IIT-R in Dec 2002].
I have revisited tectonics & seismicity of AP and I hold the view that 2002
has overestimated.

2. The map panel of IS:1893 consists of Geologists & Seismologists. Unless
there is an active interaction and debate with them by earthquake engineers
who also dabble in site dependent earthquake parameters, such incongruity
would continue.
We have to reflect on the fact that zone III of Bhadrachalam cannot  be as
severe as
zone III of Ahmedabad. [Chennai should not have been in zone III at all].

3. A lot of amount is being spent on Microzonation of some cities. It
appears to me that codal values will increase.
For example, the minimum in Delhi would be zone IV but in some regions it
will be higher. Ditto for Jabalpur.
Vigilance is called for before it is implemented in code.

4. It would be a good idea to spend research funds on Macrozonation -
evaluate site dependent parameters for a large number of sites. This will
lower earthquake forces.

5. We visited Bhadrachalam recently after a so called Mag 3.3 [hope the
initial estimate is reconfirmed and corrected soon]
on July 6th.  There is too much anxiety. Some Industrial Structures had been
designed for Zone IV even though it was zone III
to oversatisfy for Insurance. The bosses still got worried by this minor
event. In case of some other agency, they asked the designers to recheck for
this minor event even though the design was supposed to be for zone III.
That is probably because public feel that they have Ahmedabad like
situation. I feel it is very necessary to have a rethink and prove skeptics
like me as wrong or hopefully correct !!

ARC
----- Original Message -----
Message From  <cdeshpan@yahoo.com>
To: <for_prof_arc@hotmail.com>
Sent: Friday, July 23, 2004 12:36 AM
Subject: Daily Digest Thu Jul 22 23:00:03 2004


Quote:
Dear Sir,

I would appreciate if you can explain more regarding
your recent post :"I have serious reservations on
zoning in Peninsular India. During the past 40 years
upgradation has taken place only in Peninsular
India.Most of it is unjustified. "  Why do you
consider it unjustified?

Thanks in advance,

Chitra


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