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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Here is another inconsistent statement on
the national seismic hazard maps.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'>“</span></font>You have the mistaken
notion that 2%/50 values are only observed once in 2500 years. This is flat out
wrong.<font color=navy><span style='color:navy'>”<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'>In a response to our comment (Wang and
others, 2005) that was published on Seismological Research Letter (Frankel, 2005),
the interpretation was “the ground motion with 2% PE in 50 years is
exceeded once, on average over 2,500 years, so that it has a 1/2500 annual
probability of being exceeded.” <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 color=navy face="Times New Roman"><span
style='font-size:12.0pt;color:navy'> <img width=619 height=464
id="_x0000_i1026" src="cid:image002.gif@01C872DC.7612BC10"></span></font><font
color=navy><span style='color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>As demonstrated earlier, for a single M7.7
earthquake with 500 year recurrence interval in the New Madrid seismic zone,
ground motion with 2,500-year return period (2% PE in 50 years) means there is
about 20 percent probability that ground motion will be exceeded if the M7.7
earthquake occurs. In other words, if the ground motion with 2,500-year return
period is selected for engineering design, we has a confidence level of 80%
(not being exceeded) if the M7.7 earthquake occurs. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Thanks.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Zhenming<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
ceus-earthquake-hazards-bounces@geohazards.usgs.gov [mailto:ceus-earthquake-hazards-bounces@geohazards.usgs.gov]
<b><span style='font-weight:bold'>On Behalf Of </span></b>Arthur D Frankel<br>
<b><span style='font-weight:bold'>Sent:</span></b> Friday, February 15, 2008
1:50 PM<br>
<b><span style='font-weight:bold'>To:</span></b> Joe Tomasello<br>
<b><span style='font-weight:bold'>Cc:</span></b>
ceus-earthquake-hazards@geohazards.usgs.gov; mpetersen@usgs.gov<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re:
[CEUS-earthquake-hazards] reply to Joe Tomasello; buildings codes and
earthquake hazard</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'><br>
Joe, <br>
<br>
I feel I need to reply to you on the bulletin board, since you seem to
want to keep this discussion going and you directly ask me questions. My
apologies to Paul Segal and others who are fed up with this. <br>
<br>
I guess you missed one of the key points of my previous email. I
said that the IBC values (2/3 times the ground motions with 2% probability of
exceedance in 50 years [2%/50]) were probably experienced in <st1:City w:st="on"><st1:place
w:st="on">Memphis</st1:place></st1:City> during the 1811-12 earthquakes, based
on intensity data from those earthquakes. <br>
<br>
You have this mistaken notion that IBC values (2/3 times the 2%/50
motions) are only observed once in a millenium. You have the
mistaken notion that 2%/50 values are only observed once in 2500 years. This is
flat out wrong. Some locations will experience 2/3 times the 2%/50
ground motions during the next 1811-12 type earthquake. Some locations
will experience the 2%/50 ground motions during the next 1811-12 type
earthquake. This is a simple consequence of the observed
variability of earthquake ground motions. <br>
<br>
As far as the magnitude issue you bring up, the USGS uses the
range of magnitudes that various seismologists have determined for the
1811-12 earthquakes from the intensity data. The central values of these
moment magnitude determinations range from 7.4-7.5 (Hough et al., 2000 in
JGR) to 7.8 (Bakun and Hopper, 2004 in BSSA) to 8.0-8.1 (Johnston, 1996
in Geophysical Journal). In the national maps we use a logic tree to
express this range, with a value of 7.7 given the highest weight. I used
M7.7 in the scenario in my previous email, because it is in the center of the
range of magnitudes determined for the 1811-12 earthquakes. I also gave
results for a M7.4 earthquake. <br>
<br>
In the example in my previous email, I placed the scenario
earthquake where the current seismicity trend for the New Madrid seismic zone
is located. The closest distance to downtown <st1:place w:st="on"><st1:City
w:st="on">Memphis</st1:City></st1:place> is about 60 km. <br>
<br>
-Art <br>
<br>
<br>
<br>
<br>
Art Frankel<br>
<st1:country-region w:st="on"><st1:place w:st="on">U.S.</st1:place></st1:country-region>
Geological Survey<br>
MS 966, Box 25046<br>
DFC<br>
<st1:place w:st="on"><st1:City w:st="on">Denver</st1:City>, <st1:State w:st="on">CO</st1:State>
<st1:PostalCode w:st="on">80225</st1:PostalCode></st1:place><br>
phone: 303-273-8556<br>
fax: 303-273-8600<br>
email: afrankel@usgs.gov <br>
<br>
<o:p></o:p></span></font></p>
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