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RE: Seismic Zones in Texas

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Byron,

Click on http://geohazards.cr.usgs.gov/eq/

Under SEISMIC HAZARD click on Hazard by Zip Code or Hazard by Lat/Lon; enter
your zip code or latitude and longitude, and it will kick out all of the
information you need.

Regards,
Harold Sprague
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,
> > Harold Sprague
> > The Neenan Company
> > harold.sprague(--nospam--at)neenan.com
> >
> >
> > -----Original Message-----
> > From: Powers, Tony [mailto:tpowers(--nospam--at)hdrinc.com]
> > Sent: Tuesday, January 05, 1999 10:18 AM
> > To: 'seaoc'
> > Subject: Seismic Zones in Texas
> >
> >
> > According to the Fig. 16-2 in the 1994 UBC (and I believe also the 1997
> > UBC), most of the state of Texas is in Seismic Zone 0.  I understand
> that
> > this is subject to change as the next code becomes more similar to ATC
> 32
> > (or we go to a national code), and that areas that are currently Zone 0
> may
> > no longer be so in the future.  Does anyone out there know if/where I
> can
> > find some information on these changes?  A revised seismic
> Zone/acceleration
> > coefficient map would be ideal.
> >
> > Thanks in advance.
> >
> > Tony Powers
> > HDR Engineering, Inc.
> > 916-351-3837
> > tpowers(--nospam--at)hdrinc.com
>
>
>