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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'>Hi,<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'>I guess people may argue one way or the
other. But I do see some indication from the following paragraph of the open
file of 2008 hazard map. I am happy to see these changes although I expect
more. So I am fine with that these changes are called “improvement”
instead of “back off”.<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'>Best,<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'>Qingsong Li<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'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2
face=Univers-Condensed><span style='font-size:11.0pt;font-family:Univers-Condensed'>Earthquake
Recurrence<o:p></o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face=Times-Roman><span
style='font-size:10.0pt;font-family:Times-Roman'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='text-autospace:none'><font size=2 face=Times-Roman><span
style='font-size:10.0pt;font-family:Times-Roman'>Estimated recurrence intervals
of large New Madrid earthquakes have been refined with additional paleoseismic data.
In 1996, sparse data loosely constrained recurrence intervals; Frankel and
others (1996) estimated an average value of 1,000 years. By 2002,
paleoliquefaction and historical-earthquake data provided evidence for a 500-year
recurrence (Cramer, 2001; Frankel and others, 2002; Tuttle and others, 2002). At
least one large earthquake at about A.D. 300 and three sequences of large
earthquakes at about A.D. 900, A.D. 1450, and A.D. 1811–1812 were
recognized from crosscutting relationships and radiometric dating of
liquefaction features (Tuttle and others, 2002; Tuttle and others, 2005). The
occurrence of three sequences between A.D. 300 and A.D. 1811–1812 (about
1,500 years) implies an average recurrence of about 500 years. However, it is
unclear whether or not the northern arm ruptured in the A.D. 1450 sequence. If
it did not, then this arm has experienced only two events in the past 1,500
years, suggesting an average recurrence of about 750 years. We have weighted
the 500-year and 750-year earthquake recurrence alternatives for the northern
arm equally (fig. 6). In addition to these alternative recurrence models, some recent
research suggests that the New Madrid seismic zone may rupture on average every
1,000 years as suggested by abrupt changes in meander patterns of the
Mississippi River that were used to estimate earthquake activity on the
Reelfoot fault (Holbrook and others, 2006). They infer that large, reverse-faulting
ruptures are episodic. Within relatively active periods, average recurrence
intervals are several centuries long, but during the less common quiescent
periods, average recurrence intervals are interpreted to be about 1,000 years. Accordingly,
we added a 1,000-year branch to the recurrence model. At present the
meander-pattern methodology cannot detect small reverse-slip ruptures of the
Reelfoot fault or large strike-slip ruptures of other faults in the seismic
zone, so we assigned the 1,000-year branch a weight of 0.1.</span></font><o:p></o:p></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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