[CEUS-earthquake-hazards] alternative hazard maps

[jacob at ldeo.columbia.edu]

Zhenming:

What tell us about recurrence periods etc. is quite familiar to most folks
working in this field; if I recall correctly we had conversations with Jeff
Kimbell and others about related issues way back in the 90's during the
NRC/LLNL TIP study for the East Tennessy seismic zone (I participated in TIP).
Yet the NRC, nor even the nuclear industry, EPRI etc., has a problem with
"YOUR" issue, although NPP must consider even lower proability hazards in the
order of 10^-4/year.

The reason why you pay higher insurance rates, I believe, is largely because you
haven't had adequate building codes, while SF has had codes for a long time; so
the RISK per insured asset units is higher in KY than SF, while the hazard for
most reasonable probability levels is higher in SF than KY. Only for the
lowest probabilities it may become higher (slope of hazards curve is flatter, or
because you have these low annual probabilities for your largest earthquakes,
which are of course much shorter in SF). Therefore I believe your argument is
circular: You don't like the high insurance, but don't want to build safer. But
you don't blame your high RISK, you blame the high HAZRARD, and in consequence
USGS as the messenger.

Can you imagine what opposition we had to overcome in NYC, with 100s of billions
in built assets !!!!!
But what the scientific and engineering community did jointly here in NYC
was the following: We invited the Real Estate Board of NY, one of the most
powerful interest groups and lobbies in the City to SIT AT THE NEGOTIATING TABLE
AND LEARN ABOUT THE RISKS of NOT (!!) PROTECTING THE ASSETS, AND PAY INSTEAD A
LOT TO INSURERES. They were sma rt enough to get it. There were other reasons
why they and the Mayor/Building Commissioner became convinced to adopt the
code. If you want to read more about it as analyzed by sociologists, not by
scientists, go to:
http://www.urban.uiuc.edu/faculty/olshansky/papers/PSS%20Background%20Papers.pdf
( see pp. 4-9 of this FEMA report)

Best
Klaus Jacob

=======================



Quoting "Wang, Zhenming" <zmwang at email.uky.edu>:

> Klaus,
>
> It is good to know that you had served on NEHRP code committees for 8 years.
> Fortunately, that became the history, and you don't need to answer the
> questions: "why does Paducah has a higher design ground motion or has to pay
> higher insurance premium than San Francisco?" or "why 2,500-year event is
> better than 500-year event?"
>
> Unfortunately, I do not come to the same conclusion as you do. As discussed
> in the past several days, the recurrence interval of earthquake is different
> from the return period defined in PSHA. It took all most 8 years for the USGS
> (hazard mapping group) to acknowledge this difference. Jeff Kimball also
> pointed out this difference at the ATC-USGS workshop on December 7-8, 2006 in
> San Mateo, CA. Therefore, the comparison between the recurrence interval for
> maximum magnitude earthquake (100-200 years) and the return period (500
> years) is not appropriate. In other words, the comparing the slope of hazard
> curves is not appropriate and is misleading.
>
> Thanks.
>
> Zhenming
>
> -----Original Message-----
> From: jacob at ldeo.columbia.edu [mailto:jacob at ldeo.columbia.edu]
> Sent: Wednesday, February 13, 2008 5:06 PM
> To: Wang, Zhenming
> Cc: jacob at ldeo.columbia.edu
> Subject: RE: [CEUS-earthquake-hazards] alternative hazard maps
>
> Zhenming:
>
> Your last quote is nothing else but repeating in different words what I
> referred
> to as the slope of hazard curves argument. Thanks for coming to the same
> conclusion.
>
> And as far as history goes: If you want to bring coals to Newcastle, go
> ahead. I
> was part of this history, the ATC workshop, NEHRP code committees for 8 years
> and all. But may be some outsiders know better than life witnesses.
>
> Best
>
> Klaus
> ==============Quoting "Wang, Zhenming" <zmwang at email.uky.edu>:
>
> >
> > The history is much more complicated and the true reasons may not be found
> > anywhere in the documents.
> >
> > However, the fact is that the recommended design ground motion in coastal
> > California (where the experience learned) is the median ground motion from
> > the maximum considered earthquake (deterministic), not the ground motion
> with
> > 500-year return period (probabilistic). There is a scientific reason for
> > this: "This review identified a unique issue for coastal California in that
> > the recurrence interval of the estimated maximum magnitude earthquake is
> less
> > than the recurrence interval represented on the probabilistic map, in this
> > case the 10 percent probability of exceedance in 50 years (500-year return
> > period) maps (i.e., recurrence interval for maximum magnitude earthquake is
> > 100 to 200 years versus 500 years)" (page 291 in 1997 NEHRP Provision -
> > Commentary).
> >
> > Zhenming
> >
> >
> > -----Original Message-----
> > From: ceus-earthquake-hazards-bounces at geohazards.usgs.gov
> > [mailto:ceus-earthquake-hazards-bounces at geohazards.usgs.gov] On Behalf Of
> > jacob at ldeo.columbia.edu
> > Sent: Wednesday, February 13, 2008 12:33 PM
> > To: Joe Tomasello
> > Cc: ceus-earthquake-hazards at geohazards.usgs.gov
> > Subject: Re: [CEUS-earthquake-hazards] alternative hazard maps
> >
> > A bit of history:
> >
> > USGS produces computations and maps for several probabilities.
> > NIBS/SSC under FEMA funding developed the NEHRP guidelines, and its NEHRP
> > code
> > committee, and ground motion/geotechnical subcommittee voted to use the 2%
> in
> > 50 years as base for the nation-wide recommended NEHRP model code with the
> > very
> > important provisio that only 2/3 of the mapped values would go into the
> > design
> > basis.
> >
> > This idea emerged at a national ground motion workshop organized by ATC in
> > California (I forgot when and where it was, probably in the early 90s). It
> > was
> > attended by more than 300 stakeholders/experts and it was essentialy the
> > battle
> > about a resolution whether probabilistic or deterministic hazards
> assessment
> > would be used for the basis of the the NEHRP model code.
> >
> > The reasoning was: using 2/3 (based on some conservatism inherent in
> > buildings)
> > is allowed and would get the design values back to the ground motion values
> > in
> > high-hazards regions represented by the 10% in 50 years values. And the
> > Californians insisted on that. But they would also provide sufficient
> safety
> > for buildings  and structures in the low seismicity regions, where the 10%
> in
> > 50 years don't buy you much safety when the really damamging earthquekes
> come
> > along that have recuurence periods often way beyond 475 years. And the low
> > seismicity folks insisted on that safety.
> >
> > It was a smart compromise. If you really want to understand the physics and
> > details behind this argument, read the ground motion commentary chapters in
> > the
> > NEHRP documents; and familiarize yourselve with the steep slopes of hazards
> > curve for CA vs flat slopes of hazards curves in much of the CEUS.
> >
> > Klaus Jacob
> > ====================== Quoting Joe Tomasello <JT at reavesfirm.com>:
> >
> > > Art, et al:
> > >
> > >
> > >
> > > Regarding item 1 below: The statement indicates that USGS has been
> > > contracted only to make maps, not policy.  Why then does it appear before
> > > state commissions advocating only using 2%PE in 50 years? Isn't the 10%
> PE
> > > just as valid? You, yourself, have appeared before at least one
> commission
> > > in Tennessee, not to mention CERI. At that time, representing USGS, you
> > > advocated the use of the 2% PE map over any other.  This is why most of
> us
> > > in the private sector understand USGS's policy to be one for strong
> > mandated
> > > seismic mitigation. That is USGS policy, isn't it?
> > >
> > >
> > >
> > >
> > >
> > > Joseph Tomasello, PE
> > >
> > > 5880 Ridge Bend Rd.
> > >
> > > Memphis, TN 38120
> > >
> > >
> > >
> > > Phone:
> > >
> > > (901) 761-2016 office
> > >
> > > (901) 821-4968 direct
> > >
> > > (901) 412-8217 mobile
> > >
> > > 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: Wednesday, February 06, 2008 12:55 PM
> > > To: ceus-earthquake-hazards at geohazards.usgs.gov
> > > Subject: Re: [CEUS-earthquake-hazards] alternative hazard maps
> > >
> > >
> > >
> > >
> > > Seth,
> > >
> > >   I have some quick comments on your paper with James Hebden that I think
> > > would also be of interest to members of the CEUS hazards bulletin board.
> > >
> > > 1) On page 3 of your paper,  you mistakenly claim that the national
> seismic
> > > hazard maps (i.e., Frankel et al. 1996, 2002) define "the hazard" at 2%
> > > probability of exceedance in 50 years.  You state "Frankel et al. (1996;
> > > 2002) define the hazard as the maximum shaking predicted at a geographic
> > > point with 2% probability of exceedance in 50 years, or about once in
> 2,500
> > > years."   Actually, the USGS makes national seismic hazard maps at a
> > variety
> > > of probability levels, based on scientific information such as earthquake
> > > recurrence rates and ground-motion attenuation relations. In fact, we
> > > release seismic hazard curves for a grid of sites across the nation, so
> > that
> > > users can calculate the ground motions at any probability level they
> > choose.
> > > I assume you are referring to the 2/3 times the  2% probability of
> > > exceedance in 50 year level that is used in seismic DESIGN maps in the
> > NEHRP
> > > Recommended Provisions written by the Building Seismic Safety Council,
> > > published by FEMA, and adopted in the International Building Code (IBC)
> and
> > > the ASCE standards.   This probability level for design was not decided
> by
> > > the U.S. Geological Survey.     This probability level and design
> procedure
> > > were decided by a group of engineers under the Building Seismic Safety
> > > Council (funded by FEMA) and voted on and approved by a wide set of
> > > engineers and engineering groups.   It is based on their engineering
> > > judgement of acceptable risk.   It's also important to note that in some
> > > areas of the country the design maps are based on a deterministic
> > > calculation of the median ground motions for a characteristic earthquake
> on
> > > a specific fault.  In the 2006 IBC, for example, the design values around
> > > the New Madrid area are based on the median ground motions calculated for
> a
> > > M7.7 earthquake, averaging five different attenuation relations.
> > >
> > > 2) In the same sentence of your paper you say "the maximum shaking...
> with
> > > 2% probability of exceedance in 50 years..."   This is not correct.  It
> is
> > > not the maximum shaking.  Probabilistic ground motions are the ground
> > > motions with a specified probability of being exceeded.   They are not
> the
> > > maximum shaking.   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.
> > >
> > > 3) There seems to be something wrong with some of your calculations. In
> > your
> > > Figure 7, you show significant changes to the seismic hazard in the
> > > northeast U.S. and southeast Canada, compared to the USGS map, when you
> > > change the magnitude and add time dependence for the New Madrid and
> > > Charleston sources.   The changes in your hazard maps extend past 1000 km
> > > from these sources. It is very unlikely that the changes you made in New
> > > Madrid and Charleston would significantly affect the hazard at these
> > > distances.   As you probably know, we use a 1000 km maximum distance when
> > > calculating the hazard in the CEUS for the national maps, so there is no
> > way
> > > changes in New Madrid and Charleston would affect the hazard calculated
> for
> > > the northeast U.S.
> > >
> > > 4) You use a Gaussian distribution of recurrence times, rather than the
> > > log-normal distribution or Brownian Passage Time model that are typically
> > > used in modern earthquake probability studies, such as the Working Group
> on
> > > California Earthquake Probabilities (WGCEP, 1995 and 2002). The
> coefficient
> > > of variation (COV; standard deviation divided by the mean recurrence
> time)
> > > is very important in calculating time-dependent probabilities and is a
> > > source of uncertainty. Values centered at 0.5 are often assigned the
> > highest
> > > weight in California probability studies (e.g., WGCEP, 1995. 2002),
> > > reflecting the substantial variation in recurrence times that are
> observed
> > > in many areas that have long enough paleo-event chronologies.
> > >
> > > 5) Using a time-dependent model with a log-normal distribution of
> > recurrence
> > > times with a COV of 0.5, the USGS calculated a 7% probability of a
> 1811-12
> > > type New Madrid earthquake in the next 50 years, as opposed to the 10%
> > > probability found from the time-independent model.  This probability
> range
> > > (7-10%) was stated in the USGS fact sheet on New Madrid (FS-131-02).
> > >
> > > 6) Of course, key questions are whether a time-dependent model is
> > > appropriate for an intraplate area and what distribution of recurrence
> > times
> > > and COV to use in a probability calculation for these areas.  As many
> > > studies have shown, when a large earthquake occurs on one fault it can
> > > increase the stress on nearby faults and increase the probability of
> having
> > > an earthquake on these faults.  So a time dependent model where the
> hazard
> > > in a region is zero right after a large earthquake is very naive (it also
> > > ignores aftershocks). We know the New Madrid source zone is actually a
> > fault
> > > system rather than a single fault and we might expect a complicated
> pattern
> > > of loading and unloading not described by the simple time dependent model
> > > used in your paper.  In addition, intraplate fault systems are not loaded
> > in
> > > the same way as faults along plate boundaries, which are being
> continually
> > > loaded by the displacements of tectonic plates.
> > >
> > >
> > > 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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> >
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>
>
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