[CEUS-earthquake-hazards] reply to Joe Tomasello; buildings codes and earthquake hazard

Fri Feb 15 16:36:22 MST 2008

I would like to offer a point of support to the discussion, while at the
same time a word of caution. 

The discussion surrounding the hazard is important and needs to be
addressed.  From my perspective these issues are fundamentally research
based and as such should be debated within the research community.  This
list serve, while sponsored by USGS and designed to allow such
discussion among professionals, it is not exclusive to the scientific
community, meaning any and everyone who wants to join can, i.e. elected
officials, media, emergency management, business owners, etc., most of
which have an interest in the hazard in the central US but no seismic
research/engineering background.  This mix can be unintentionally
problematic with discussions like these currently taking place, because
it breaks from what I would consider the proper forum to be in resolving
such an issue and adds to the overall confusion.  

There is a "time and place for everything" as the saying goes and I
don't feel this list serve is the place for this discussion.  The topic
is to technical and the end results of the debate, whichever way they
may go, need to be decided off line and within the scientific community.

Jim Wilkinson

Executive Director

Central United States Earthquake Consortium

________________________________

From: ceus-earthquake-hazards-bounces at geohazards.usgs.gov
[mailto:ceus-earthquake-hazards-bounces at geohazards.usgs.gov] On Behalf
Of Emitt C Witt
Sent: Friday, February 15, 2008 12:16 PM
To: Allen Jones
Cc: ceus-earthquake-hazards at geohazards.usgs.gov;
ceus-earthquake-hazards-bounces at geohazards.usgs.gov
Subject: Re: [CEUS-earthquake-hazards] reply to Joe Tomasello; buildings
codes and earthquake hazard

I concur with Allen. Unless the discussion gets personal, and it has
not, I'd like to see it stay open to everyone on this list serve. Not
being a seismologist or a practicing structural engineer, I have found
the discussion interesting and educational. 

Emitt 
________________________________________
Emitt C. Witt III, P.H.
Director, Mid-Continent Geographic Science Center
1400 Independence Road
Rolla, Missouri 65401
573-308-3679
573-308-3794 FAX
http://mcmcweb.er.usgs.gov/mcgsc

Allen Jones <jonesal at myuw.net> 
Sent by: ceus-earthquake-hazards-bounces at geohazards.usgs.gov 

02/15/2008 11:14 AM 

To

"ceus-earthquake-hazards at geohazards.usgs.gov"
<ceus-earthquake-hazards at geohazards.usgs.gov> 

cc

Subject

Re: [CEUS-earthquake-hazards] reply to Joe Tomasello; buildings codes
and earthquake hazard

Speaking for myself, I find these discussions very interesting and
informative.  I find think this sort of intellectual debate healthy and
provides a perspective missing from publications.  I encourage you to
keep the discussion public and appreciate everyone's efforts in taking
the time to respond.

Allen Jones
________________________
Allen Jones, PE, PhD
South Dakota State University
Department of Civil Engineering
CEH 148, Box 2219
Brookings, SD 57006

Direct: 605-688-6467
Fax: 605-688-6476

On Fri, 15 Feb 2008, Arthur D Frankel wrote:

> Zhenming,
>
>  I am sure many people on the bulletin board are getting tired of
these
> exchanges.
>
> I presented similar comparisons at the Applied Technology Council
> workshop in Memphis in March 2005.  As I recall, you and Joe Tomasello
> were in attendance.   So I think you have seen these comparisons.
>
> Of course, I don't see any contradiction in what I've said.   I think
it
> is reasonable to compare code values with the expected ground motions
from
> the next 1811-12 type earthquake and with ground motions estimated for
the
> 1811-12 earthquakes using intensity observations.
>
>  I think further discussion between us on these issues should be made
off
> of the bulletin board.
>
> -Art
>
>
> Art Frankel
> U.S. Geological Survey
> MS 966, Box 25046
> DFC
> Denver, CO 80225
> phone: 303-273-8556
> fax: 303-273-8600
> email: afrankel at usgs.gov
>
>
>
> "Wang, Zhenming" <zmwang at email.uky.edu>
> 02/15/2008 08:35 AM
>
> To
> Arthur D Frankel <afrankel at usgs.gov>
> cc
> James Cobb <cobb at uky.edu>, "Keifer, John D" <kiefer at email.uky.edu>,
> "ceus-earthquake-hazards at geohazards.usgs.gov"
> <ceus-earthquake-hazards at geohazards.usgs.gov>
> Subject
> RE: [CEUS-earthquake-hazards] reply to Joe Tomasello;   buildings
codes
> and earthquake hazard
>
>
>
>
>
>
> Art,
>
> This is the first time we see these comparisons:
>
> ?When I talk to code committees and other groups, I compare the
relative
> level of protection that designing to different probability levels of
> ground shaking will provide to buildings.  This can be assessed by
> comparing the ground-motion values for the probability levels in the
> building codes to the median ground motions expected when the next
1811-12
> type New Madrid earthquake occurs and by comparing code values to
> intensities observed in the Memphis area from the 1811-12
earthquakes.?
>
> The selected design ground motion should be consistent with the
scientific
> facts. However, these comparisons seem to be contradictory to your
early
> statements:
> 1.      ?In fact, we release seismic hazard curves (a range of ground
> motion, from 0.0 to 10g or larger) for a grid of sites across the
nation,
> so that users can calculate the ground motions at any probability
level
> they choose.? ?It should also be reiterated that the national seismic
> hazard maps are based on the average hazard curves from a variety of
input
> models and attenuation relations; they are not worst-case maps.?
> 2.      ?It is not correct to compare the intensity observations from
> 1811-1812 with the probabilistic hazard maps that also include the
hazard
> from earthquakes closer to St. Louis.?
>
> Thanks.
>
> Zhenming
>
> From: ceus-earthquake-hazards-bounces at geohazards.usgs.gov
> [mailto:ceus-earthquake-hazards-bounces at geohazards.usgs.gov] On Behalf
Of
> Arthur D Frankel
> Sent: Thursday, February 14, 2008 3:35 PM
> To: ceus-earthquake-hazards at geohazards.usgs.gov
> Subject: [CEUS-earthquake-hazards] reply to Joe Tomasello; buildings
codes
> and earthquake hazard
>
>
> Joe,
>
> The USGS policy is to support the process of the Building Seismic
Safety
> Council (BSSC) establishing probability levels and design procedures
for
> the national model building codes, such as the International Building
> Code.  The BSSC membership consists of a large group of engineers and
> stakeholders. The BSSC is a council of the National Institute of
Building
> Sciences. The code development process of the BSSC is funded by FEMA.
The
> design procedures are published in the NEHRP Recommended Provisions
for
> the Development of Seismic Regulations for New Buildings, which is
written
> by the BSSC/NIBS and published by FEMA.
>
> I think a key responsibility of the USGS is to provide the best
scientific
> information to decision makers.  Part of this scientific information
is
> assessment of the ground motions from the 1811-12 earthquakes and
> estimation of the ground motions for the next 1811-12 type earthquake.
>
> When I talk to code committees and other groups, I compare the
relative
> level of protection that designing to different probability levels of
> ground shaking will provide to buildings.  This can be assessed by
> comparing the ground-motion values for the probability levels in the
> building codes to the median ground motions expected when the next
1811-12
> type New Madrid earthquake occurs and by comparing code values to
> intensities observed in the Memphis area from the 1811-12 earthquakes.
>
> For example, the value of ground motions around 1 Hz with a 10%
> probability of exceedance in 50 years (10%/50) is substantially lower
than
> the median 1 Hz ground motion expected for the next 1811-12 type
> earthquake.   The new Memphis code adopted in 2006 uses the 10%/50
year
> ground motions from the 1996 vintage of the national maps (the 2002
maps
> are higher).  Here I am considering 1 Hz spectral accelerations
(S.A.),
> which are used for the design of buildings with about 10 stories.  For
a
> site in Memphis (35.15 N; 90.05 W), the 10%/50 value of  1 Hz spectral
> acceleration is 0.16g (from the 1996 maps and using an amplification
> factor of 2.4 for class D stiff-soil site relative to firm-rock site
from
> the NEHRP amplification factors).  This is much lower than the median
1 Hz
> S.A. of 0.36g expected in Memphis from a scenario earthquake with
moment
> magnitude 7.7 located on the portion of the current New Madrid
seismicity
> trend northwest of Memphis (using the stiff-soil amplification factor
from
> the NEHRP factors). This calculation of the expected spectral
acceleration
> is based on the average of the five attenuation relations used in the
2002
> national maps.  If the next large New Madrid earthquake was a moment
> magnitude 7.4, the calculated median 1 Hz S.A. at Memphis would be
0.29g
> for a stiff-soil site, still much higher than the 10%/50 value (0.16g)
> from the 1996 maps.
>
> The 10%/50 values for 1 Hz S.A. from the 2002 hazard maps would still
be
> significantly lower than the scenario ground motions. For 5 Hz S.A.,
the
> expected values of the median ground motions for a M7.7 earthquake are
> more sensitive to assumptions on the nonlinearity and attenuation of
> sediments in the Mississippi Embayment.
>
> The International Building Code (IBC) uses spectral accelerations that
are
> 2/3 times the values with a 2% probability of exceedance in 50 years
for
> most of the nation (there are some areas where IBC uses the median
> deterministic ground motions, depending on the level of the
probabilistic
> motions). For 1 Hz S.A., the 2006 IBC specifies a value of 0.42g for
> Memphis (stiff-soil site). This is similar to the median value of
0.36g
> expected for a M7.7 earthquake (see above).
>
> In my presentations, I also compare the code values to the ground
motions
> estimated from intensity reports in the Memphis area from past
> earthquakes.  Here I use peak ground accelerations (PGA) rather than
> spectral accelerations, because intensities are generally correlated
in
> the literature with PGA?s or peak ground velocities.
>
> Intensities in the Memphis area during the 1811-12 earthquakes have
been
> assigned as intensity VIII by Hough et al. (2000) and as intensity X
by
> Johnston (1996), depending on their interpretation of earthquake
effects.
> Intensity VIII corresponds to a peak ground acceleration between about
> 0.34 and 0.65g, based on the work David Wald did for Shakemap.  This
range
> is consistent with the calculated median PGA at Memphis of 0.39g for a
> M7.7 earthquake determined from the average of 5 attenuation relations
> used in the 2002 hazard maps (using the NEHRP amplification factors).
The
> calculated PGA for a M7.4 earthquake is 0.32g, close to the range of
the
> PGA?s estimated for intensity VIII.
>
> The new Memphis code procedure of using the 10%/50 values from the
1996
> maps results in a PGA of 0.23g (for a stiff soil site), which is
> substantially lower than the range of ground motions estimated from
the
> intensities reported in Memphis during the 1811-12 earthquake sequence
> (0.34-0.65g for intensity VIII).  A similar value of PGA (0.22g) is
found
> by taking the 5 Hz S.A. with 10%/50 and dividing by 2.0, which is the
> factor relating PGA to 5 Hz S.A. derived for M7.4-7.7 earthquakes from
the
> average of the five attenuation relations.
>
> Using a PGA that is 2/3 times the PGA with 2% probability of
exceedance
> in 50 years (2%/50), which corresponds to the procedure used for
spectral
> accelerations in the 2006 International Building Code for the Memphis
> area, gives a PGA value of 0.50g for Memphis (stiff soil site), which
is
> in the range of the values estimated from the 1811-12 intensities.
This
> is similar to the PGA value of 0.47g derived from the 5 Hz S.A.in the
IBC
> divided by a factor of  2.0 to convert to PGA. So, there is evidence
from
> intensity data that the ground motions specified in the IBC have been
> experienced in Memphis during the 1811-12 earthquakes
>
> In summary, the 1 Hz spectral accelerations with a 10% probability of
> exceedance in 50 years, as used in the current Memphis code, are
> substantially lower than the median 1 Hz spectral accelerations
expected
> for the next 1811-12 type earthquake. The 10%/50 value of PGA is
probably
> lower than the ground shaking experienced in Memphis during the
1811-12
> earthquakes, based on intensity data.
>
> The 1 Hz spectral accelerations specified in the International
Building
> Code (2/3 times the motions with a 2% probability of exceedance in 50
> years) are  similar to the  median  1 Hz spectral accelerations
expected
> for the next 1811-12 type earthquake. The PGA with 2/3 times the value
> with 2%/50 is probably comparable to the PGA experienced in Memphis
from
> the 1811-12 earthquakes, based on intensity data.
>
> -Art
>
>
>
> Art Frankel
> U.S. Geological Survey
> MS 966, Box 25046
> DFC
> Denver, CO 80225
> phone: 303-273-8556
> fax: 303-273-8600
> email: afrankel at usgs.gov
>

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