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RE: Seismic Zones in Texas

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James,

The 0.2 and 1.0 second are the defined short period events and long period
events.  In the IBC and 1997 NEHRP both events must be evaluated.  Some
structures will be more susceptible to short period events and some will be
more susceptible to long period events.

And you are correct in your inference that earthquakes will not necessarily
have these frequencies.  The intent is the 0.2 and the 1.0 second are the
representative design events.

Regards,
Harold Sprague
The Neenan Company
harold.sprague(--nospam--at)neenan.com


-----Original Message-----
From: james korff [mailto:jgkorff(--nospam--at)yahoo.com]
Sent: Saturday, January 09, 1999 3:23 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Seismic Zones in Texas



Clarification requested:

0.2 and 1.0 periods in the maps.
What do they refer to?
What about periods in between?

jgk



---Harold Sprague <harold.sprague(--nospam--at)neenan.com> wrote:
>
> Byron,
> 
> I was kind of interested.  This is what the 63701 zip code looks
like from
> the USGS inquiry.  There are some serious ground motions there, and
this is
> a big change from previous codes.
> 
> 
> The input zip-code is 63701.   ZIP CODE                        63701
>    LOCATION                        37.3168 Lat.  -89.5427 Long.
>    DISTANCE TO NEAREST GRID POINT  4.2226 kms
>    NEAREST GRID POINT              37.3 Lat.  -89.5 Long.
>    Probabilistic ground motion values, in %g, at this point are:
>                10%PE in 50 yr   5%PE in 50 yr   2%PE in 50 yr
>       PGA       18.213730        38.806042       98.324257
>    0.2 sec SA   35.674648        77.149208      190.823502
>    0.3 sec SA   26.288179        56.461510      153.224792
>    1.0 sec SA    8.352530        19.436411       59.417992
> 
> Regards,
> Harold Sprague, P.E.
> The Neenan Company
> harold.sprague(--nospam--at)neenan.com
> 
> 
> -----Original Message-----
> From: BYRON DIETRICH [mailto:byrond(--nospam--at)tetercon.com]
> Sent: Thursday, January 07, 1999 4:31 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Seismic Zones in Texas
> 
> 
> I read your reply with interest.  Do you by any chance have the
seismic zone
> (similar information as below) for a site in Cape Girardeau, Missouri?
> 
> Byron
> 
> -----Original Message-----
> From: Deneff, Chris [mailto:deneff(--nospam--at)allendale.com]
> Sent: Thursday, January 07, 1999 2:15 PM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: RE: Seismic Zones in Texas
> 
> 
> > I have just started looking at the IBC 2000 draft and FEMA 273 and
302, so
> > what follows is based on only a cursory review.
> > I believe the IBC 2000 maps are the same as the maps for "Maximum
> > Considered Earthquake" that come with FEMA 273 and 302 (NEHRP
guidelines
> > for seismic design of existing and new buildings).  The maps in
the draft
> > of the IBC are very hard to read (the United States fits on two
8.5" x11"
> > pages in the IBC - the FEMA map for the US is 36"x48").
> > I went to the USGS web site and the values for 0.2 sec. and 1.0 sec.
> > spectral accelerations for a 2% probability of exceedance (PE) in
50 years
> > matched fairly closely with the FEMA maps (as long as you remember
to put
> > in longitudes as negative numbers at the USGS site).  As far as I
can
> > tell, the "Maximum Considered Earthquake" has a 2% PE in 50 years
(2475
> > year return period if I did the calculation correctly) as opposed
to the
> > current 475 year design earthquake (10% PE in 50 years).  It looks
like
> > the higher 2475-year accelerations are compensated for (at least
in part)
> > because they are factored by 2/3 to come up with the design spectral
> > response accelerations.  It is not clear to me whether this will
result in
> > accelerations that are close to the current 475-year
accelerations.  The
> > 2475-year accelerations were about 2.1 to 2.4 times the 475-year
> > accelerations for the points I picked on the USGS site.
> > Since the spectral accelerations from the USGS site and the FEMA
maps are
> > based on site class B, there is a factor applied to the
accelerations for
> > other soil types.  For site class A (hard rock), the accelerations
are
> > multiplied by a factor of 0.8.  For site class D (stiff soil), the
mapped
> > accelerations are multiplied by factors ranging from 1.0 to 2.5
depending
> > on the value of the mapped accelerations.
> > It also looks like values of "R" have been modified in some cases
and "I"
> > can be up to 1.5 for essential buildings. After all the factors are
> > accounted for, I'm not sure if the final design force will be more
or less
> > than currently required, however, I suspect it will be more.
> > I generated the following tables for the NEHRP maps from FEMA. 
Maps 1-24
> > are for the Maximum Considered Earthquake. Maps 25-32 are
apparently used
> > in some manner in FEMA 273 and 302 (and maybe by the IBC?).  I
haven't
> > gotten deep enough into the criteria to figure out when these maps
are
> > used.
> > Regards.
> > Chris Deneff
> > deneff(--nospam--at)allendale.com
> > Listing of NEHRP Maps
> > Prepared for USGS/BSSC Project 97
> > Listing of maps for:
> > Maximum Considered Earthquake Ground Motion
> > 0.2 second or 1.0 second Spectral Response Acceleration (as
specified in
> > table)
> > 5% of critical damping
> > Site Class B
> > Map No.	Location	Period (Seconds)
> > 1	United States	0.2
> > 2	United States	1.0
> > 3	California/Nevada	0.2
> > 4	California/Nevada	1.0
> > 5	Southern California	0.2
> > 6	Southern California	1.0
> > 7	San Francisco	0.2
> > 8	San Francisco	1.0
> > 9	Pacific Northwest	0.2
> > 10	Pacific Northwest	1.0
> > 11	Salt Lake City and Intermountain	0.2
> > 12	Salt Lake City and Intermountain	1.0
> > 13	New Madrid	0.2
> > 14	New Madrid	1.0
> > 15	Charleston, South Carolina	0.2
> > 16	Charleston, South Carolina	1.0
> > 17	Alaska	0.2
> > 18	Alaska	1.0
> > 19	Hawaii	0.2
> > 20	Hawaii	1.0
> > 21	Puerto Rico, Culebra, Vieques, St. Thomas, St. John, St.
Croix	0.2
> > 22	Puerto Rico, Culebra, Vieques, St. Thomas, St. John, St.
Croix	1.0
> > 23	Guam and Tutuila	0.2
> > 24	Guam and Tutuila	1.0
> >
> > Listing of maps for:
> > Probabilistic Earthquake Ground Motion
> > 0.2 second or 1.0 second Spectral Response Acceleration (as
specified in
> > table)
> > 10% or 2% Probability of Exceedance in 50 years (as specified in
table)
> > 5% of critical damping
> > Site Class B
> > Map No.	Location	Period (Seconds)	Probability of
> > Exceedance (%)
> > 25	United States	0.2	10
> > 26	United States	1.0	10
> > 27	United States	0.2	2
> > 28	United States	1.0	2
> > 29	California/Nevada	0.2	10
> > 30	California/Nevada	1.0	10
> > 31	California/Nevada	0.2	2
> > 32	California/Nevada	1.0	2
> >
> >
> > >From: Harold Sprague <harold.sprague(--nospam--at)neenan.com>
> > >To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
> > >Subject: RE: Seismic Zones in Texas
> >
> > >Ken,
> >
> > >The seismic accelerations obtained from the USGS web site are the
same
> > values that will be in the IBC 2000 maps. (USGS >created the maps
also.)
> > There might be some refinement, but generally the values are the
starting
> > point.
> >
> > >It is kind of true that the values are based on bedrock.  (How's
that for
> > ambiguity?)  The values must be modified for the actual soil >at the
> > building site, proximity to a fault, etc.; those modifications are
> > contained in the 1997 NEHRP Provisions.  All this will still >boil
down to
> > a base shear.
> >
> > >I would strongly urge you to look at the Provisions and the Draft
2000
> > IBC. I would like to receive your comments.
> >
> > >Regards,
> > >Harold Sprague
> > >The Neenan Company
> > >harold.sprague(--nospam--at)neenan.com
> >
> >
> > >-----Original Message-----
> > >From: Kenneth Tarlow [mailto:ktarlow(--nospam--at)yahoo.com]
> > >Sent: Tuesday, January 05, 1999 3:51 PM
> > >To: seaint(--nospam--at)seaint.org
> > >Subject: RE: Seismic Zones in Texas
> >
> >
> > >Dear Harold,
> >
> > >The USGS maps are not very accurate.  Even in there website they
indicate
> > that the acceleration values are based on bedrock.  >The actual
ground
> > accelerations can be much higher.
> >
> > >Will there be any other kind of refinement short of structural
Engineers
> > dealing with attenuation equations?
> >
> > >Thanx
> > >Ken Tarlow
> >
> >
> >
> > >---Harold Sprague <harold.sprague(--nospam--at)neenan.com> wrote:
> > >
> > > The IBC 2000 (which will soon be the only national building code
in the
> > > US)will be using the 1997 NEHRP as its basis.  There will be no
more
> > > "seismic zones".  The seismicity will be determined using seismic
> > spectral
> > > ordinates.  Check out the USGS site at
> > http://geohazards.cr.usgs.gov/eq/.
> > >
> > > You will note in the left hand column under "Seismic Hazard" a
listing
> > for
> > > Hazard by Zip Code and another listing for Hazard by Lat/Lon. 
Use these
> > to
> > > determine the seismicity of the site and question.  Then follow
along in
> > the
> > > 1997 NEHRP to see what provisions apply.
> > >
> > > Regards,
> 
=== message truncated ===

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