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<DIV><SPAN class=056585614-13022008><FONT face=Arial color=#0000ff
size=2>Seth</FONT></SPAN></DIV>
<DIV><SPAN class=056585614-13022008><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=056585614-13022008><FONT face=Arial color=#0000ff size=2>As an
academic exercise it might be acceptable to fall back on, "<FONT
face="Times New Roman" color=#000000>We have lots of models that give different
numbers and there's little reason to believe that any of them are particularly
good or better than the others."</FONT></FONT></SPAN></DIV><SPAN
class=056585614-13022008><FONT face=Arial color=#0000ff><FONT
face="Times New Roman" color=#000000></FONT><FONT face="Times New Roman"
color=#000000></FONT>
<DIV><FONT size=2></FONT><BR><FONT size=2>Of course no one can predict
earthquakes, there are too many variables and too little data. However,
please remember that real dollars must be spent complying with building codes
and real lives can be put at risk if the building codes are inadequate for
the task of limiting earthquake damage. </FONT></DIV>
<DIV><FONT size=2></FONT> </DIV>
<DIV><FONT size=2>There is real value <SPAN
class=056585614-13022008>in</SPAN> trying to find the "best
available" method to estimate the potential for earthquakes and the levels
of the shaking that may be incurred.</FONT></FONT></SPAN></DIV>
<DIV><SPAN class=056585614-13022008><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=056585614-13022008><FONT face=Arial color=#0000ff size=2>Chris
Fostel</FONT></SPAN></DIV>
<DIV><SPAN class=056585614-13022008><FONT face=Arial color=#0000ff
size=2>Seismic Safety Worker bee</FONT></SPAN></DIV>
<DIV><SPAN class=056585614-13022008><FONT face=Arial color=#0000ff
size=2>.</FONT></SPAN></DIV>
<DIV></DIV>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B>
ceus-earthquake-hazards-bounces@geohazards.usgs.gov
[mailto:ceus-earthquake-hazards-bounces@geohazards.usgs.gov] <B>On Behalf Of
</B>Seth Stein<BR><B>Sent:</B> Tuesday, February 12, 2008 5:37 PM<BR><B>To:</B>
Chris Harold Cramer (ccramer)<BR><B>Cc:</B>
ceus-earthquake-hazards@geohazards.usgs.gov<BR><B>Subject:</B>
[CEUS-earthquake-hazards] no "right" answer<BR><BR></FONT></DIV><!-- Converted from text/plain format -->
<P><FONT size=2>Chris,<BR><BR>I doubt that there's much to be gained by debating
the "right" way to<BR>estimate earthquake probabilities. We have lots of models
that<BR>give different numbers and there's little reason to believe that
any<BR>of them are particularly good or better than the others.<BR><BR>We
haven't yet resolved the simplest question: whether<BR>the probability of
earthquakes is better modeled<BR>as constant with time or changing.<BR>Different
researchers assume one or the other, and<BR>your group - USGS for New Madrid -
use both.<BR><BR>Since we're not even sure how useful time dependent models
are,<BR>we certainly can't say convincingly which of the time<BR>dependent
models is better.<BR><BR>As such, I see little case to say that any way of
estimating the<BR>parameters of any particular time dependent model from the
limited<BR>earthquake data is "right" or "wrong".<BR><BR>I think this will be
the case until we can show that a particular<BR>approach best predicts the
recurrence of future earthquakes. There may<BR>be no one best approach, and
different approaches may turn out better in<BR>different places.<BR><BR>This
seems unlikely to be resolved soon. Recall that Kagan and Jackson<BR>(1991)
estimated that in California, where earthquakes are 30-100 times<BR>more common
that in New Madrid, it would take 3000 years of data to<BR>distinguish whether
time dependent or time independent models did better.<BR><BR>Hence I think it's
interesting to compare the probabilities predicted by<BR>different models with
different parameters, but wouldn't place great<BR>significance on any of the
specific values. For New Madrid, they range<BR>about 0-10%, but beyond that I
doubt one could convincingly say more.<BR><BR>I think the best overall
assessment is from<BR>Savage's (1991) criticism of earthquake probability
estimates<BR>for California, where the data are much better than for<BR>New
Madrid and the slip process resulting from steady plate motion<BR>seems to be
much less variable with time:<BR><BR>"The range of possible 30-year conditional
probabilities for many<BR>of the fault segments is so great due to the
uncertainty in the average<BR>recurrence time for that segment that the assigned
probability is<BR>virtually meaningless."<BR><BR>"This suggests that the
conditional probability is not resolved beyond<BR>broad categories like low
(0-10%), intermediate (10-90%), and high<BR>(90% or more) risk. A more
quantitative assessment is not justified."<BR><BR>This strikes me as wise
humility in the face of<BR>the poorly understood complexity of
nature.<BR><BR>Cheers,<BR><BR>Seth<BR><BR>Kagan, Y. Y., and D. D. Jackson,
Seismic gap hypothesis: ten years<BR>after, J. Geophys. Res., 96, 21,419-21,431,
1991.<BR><BR>Savage, J. C., Criticism of some forecasts of the national
earthquake<BR>prediction council, Bull. Seismol. Soc. Am., 81, 862-881,
1991.<BR><BR>--<BR>Seth Stein<BR>William Deering Professor<BR>Department of
Earth and Planetary Sciences<BR>1850 Campus Drive<BR>Northwestern University,
Evanston, IL 60208<BR>(847) 491-5265 FAX: (847) 491-8060 E-MAIL:
seth@earth.northwestern.edu<BR><A
href="http://www.earth.northwestern.edu/people/seth">http://www.earth.northwestern.edu/people/seth</A><BR>_______________________________________________<BR>CEUS-Earthquake-Hazards
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