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RE: Seismic Zones in Texas

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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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