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Re: PGA fema maps (NEHRP Design Maps)

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The maps used in the 1997 NEHRP Provisions and proposed for the 2000 IBC
are maps of response spectral ordinates for 0.2 sec and 1.0 sec.  These
maps are based on USGS probabilistic maps with important modifications by a
BSSC committee to obtain what are referred to as the Maximum Considered
Earthquake Ground Motion maps for use with the NEHRP Provisions.  Both the
probabilistic and MCE Ground Motion maps are on the USGS web site at  The NEHRP maps are somewhat hard to find
at this address since they have only recently been posted and the NEHRP map
area is still under construction.  However the address will take the user
directly to the NEHRP maps.  I had not intended easy access until some
additional narrative about the maps was included with the maps since there
are important differences between the two types of maps, particularly near
faults in California and along the Washington/Oregon coastline.  However, I
wanted to respond to Mr. Tarlow's email with as much information as is
available at this time.  Access will improve next week when our webmaster
returns from vacation.  Some of the differences between the maps are
described in my posting of 1/12/99 under the subject "Seismic Zones in
Texas - Some USGS Comments".  The subject title might seem a little unusual
but it was in keeping with the thread that had already been started.

Although the maps (in pdf format) can be viewed with various versions of
Acrobat Reader, I recommend Acrobat 4.0.  This version eliminates some
nasty problems, such as elimination of county boundaries, encountered with
Acrobat 3 when printing to some inkjet printers.  It also gives greater
flexibility in zooming and printing the zoomed areas.  If you are thinking
about downloading the files, remember the printed map is the same size as
the original, about 30" x 42" for the US map.  It more convenient to use
Acrobat to zoom in to an area of interest and print that area out.
Postscript files are also available.  GIS contour files will also be added
in the future to accomodate those with GIS capability.

As for the CD.  There are two.  One for the USGS probabilistic maps and one
for the NEHRP design maps.  Both prepared use on a PC using Windows 95 or
98.  The approach is menu driven with point and click access. The design CD
is being prepared by USGS in cooperation with BSSC and FEMA.  Both CDs go
out for final review this week.  They will not be available for
distribution until review is completed.  This should not be too long since
they have already undergone several rounds of review.  The design CD being
sent out this week differs from earlier versions, including a demonstration
I gave at the Costa Mesa IBC code hearing in March, in several respects.
In addition to design values for the 1997 NEHRP Provisions/2000 IBC, I have
added capability to obtain design values for the 2000 IRC and the Rehab
Guidelines.  Along with the map values, the user can also view a design
spectrum for a site specified by lat-long or zip code.  Soil factors, other
than the default value, may be included in the calculations using NEHRP
site coefficients or as specified by the designer.  All data can be viewed,
printed, and/or saved to a file.  Additionally all 32 maps of the NEHRP map
package, the IBC maps, and the IRC map are included on the CD along with
Acrobat Reader 4.0.  In short, the CD can be used in lieu of the rather
formidable map package.  It will be far easier to obtain site values using
the CD rather than by interpolating from a paper map.

I will post the information on how to obtain the CDs (both of them) as soon
as the information is available.  If there are any changes in the USGS web
address after construction of the design map area is completed, I will also
post that information.

E. V. Leyendecker
USGS National Seismic Hazard Mapping Project

At 11:00 AM 7/6/1999 -0700, you wrote:
>I am looking for the USGS maps that go along with the new FEMA code.  I
>understand that they are on now on CD Rom that can be accesed by LONg
>and LAT as well as Zip code.  If anyone knows where I can a copy of the
>CD rom please le me know.
>Ken Tarlow
>Do You Yahoo!?
>Get your free address at