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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>I want to thank Mark and Nico for their clarifications on the USGS
national hazard maps. “While USGS <i><span style='font-style:italic'>hazard
maps</span></i> are the basis for <i><span style='font-style:italic'>design
maps</span></i> in model building codes, hazard and design maps are not one in
the same (for example, due to the capping mentioned in note #3 above).
This was true of the 1996 and 2002 USGS hazard maps and the building code
design maps derived from them, and it continues to be true (more so, in part
due to notes #1-2 above) for the 2008 USGS hazard maps.” “As
far as I know, the USGS hazard maps have never been used directly in building
design.” These clarifications are important for healthy discussions on
seismic hazard assessment and engineering design. <o:p></o:p></span></font></p>
<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><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>I would like to point out that the hazard data will be the basis, “<u>the
new 2008 USGS <b><span style='font-weight:bold'>hazard data</span></b></u> will
be the basis for the seismic design maps in future editions of the NEHRP
Recommended Provisions,” not the hazard maps (the ground motions with
500, 1,000, 2,500 years return periods), “<b><u><span style='font-weight:
bold'>the 2008 USGS hazard maps</span></u> should not be substituted for the
model building code design maps nor should they be used with ASCE/SEI 41 or 31
for seismic rehabilitation or evaluation.”</b> <o:p></o:p></span></font></p>
<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><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Now let’s discuss how we can use “the new 2008 USGS hazard
data” for our discussions on the design ground motions. <o:p></o:p></span></font></p>
<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><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>In the central US, the large New Madrid earthquakes are the main
concern. So, we can follow the analyses (deterministic or scenario) by Art and
Mark. As shown by Art and Mark, the median PGA, 0.2s and 1.0s SAs are
about 0.30g, 0.60g and 0.16g in <st1:place w:st="on"><st1:City w:st="on">Memphis</st1:City></st1:place>,
respectively, if the large New Madrid earthquake (M7.7) occurs on the central
strand (Petersen, 2004, http://www.uky.edu/KGS/geologichazards/summary_usgskgsmeeting.pdf).
If we do not consider risk (probability of building damage in the next 50
years), these ground motion parameters (0.3g PGA, 0.6g 0.2s SA, and 0.16g 1.0s
SA) may be appropriate for seismic design in Memphis. <o:p></o:p></span></font></p>
<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><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Following the same analyses and assumptions by Art (see Art’s
email comments to Laurence last year), the risk is about 3.5-5% PE damage in 50
years for a building that is designed to the median ground motion in <st1:place
w:st="on"><st1:City w:st="on">Memphis</st1:City></st1:place>. From the
2008 USGS hazard database, the median PGA, 0.2s and 1.0s SAs are about 0.27, 0.59
and 0.21g in <st1:place w:st="on"><st1:City w:st="on">San Francisco</st1:City></st1:place>,
respectively (only the San Andreas earthquake, M7.9 with 350-y recurrence
interval, is considered). The risk is about 7% PE in 50 years for a building
that is designed to the median ground motion in <st1:place w:st="on"><st1:City
w:st="on">San Francisco</st1:City></st1:place>. To achieve the same risk level
(7% PE damage in 50 years) in Memphis, the design PGA, 0.2s and 1.0s SAs will
be about 0.17-0.21g, 0.35-0.42g, and 0.09-0.11g, respectively (a log standard
deviation of 0.7 is assumed).<o:p></o:p></span></font></p>
<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><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>These deterministic or scenario analyses demonstrate that the
recommended design ground motions for the NEHRP Provisions are too conservative
in <st1:place w:st="on"><st1:City w:st="on">Memphis</st1:City></st1:place>.</span></font><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Thanks,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Zhenming</span></font><o:p></o:p></p>
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