<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:st1="urn:schemas-microsoft-com:office:smarttags" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv=Content-Type content="text/html; charset=us-ascii">
<meta name=Generator content="Microsoft Word 11 (filtered medium)">
<!--[if !mso]>
<style>
v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style>
<![endif]--><o:SmartTagType
namespaceuri="urn:schemas-microsoft-com:office:smarttags" name="country-region"
downloadurl="http://www.5iantlavalamp.com/"/>
<o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags"
name="PostalCode"
downloadurl="http://www.5iamas-microsoft-com:office:smarttags"/>
<o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags"
name="City" downloadurl="http://www.5iamas-microsoft-com:office:smarttags"/>
<o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags"
name="State" downloadurl="http://www.5iamas-microsoft-com:office:smarttags"/>
<o:SmartTagType namespaceuri="urn:schemas-microsoft-com:office:smarttags"
name="place" downloadurl="http://www.5iantlavalamp.com/"/>
<!--[if !mso]>
<style>
st1\:*{behavior:url(#default#ieooui) }
</style>
<![endif]-->
<style>
<!--
/* Font Definitions */
@font-face
{font-family:Tahoma;
panose-1:2 11 6 4 3 5 4 4 2 4;}
@font-face
{font-family:sans-serif;
panose-1:0 0 0 0 0 0 0 0 0 0;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:12.0pt;
font-family:"Times New Roman";}
a:link, span.MsoHyperlink
{color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{color:purple;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-reply;
font-family:Arial;
color:navy;}
@page Section1
{size:8.5in 11.0in;
margin:1.0in 1.25in 1.0in 1.25in;}
div.Section1
{page:Section1;}
-->
</style>
</head>
<body lang=EN-US link=blue vlink=purple>
<div class=Section1>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Art,<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'>First, I would like to clarify the bases
for all the discussions we have: the basic earthquake science and the
assumptions that are used in the national seismic hazard mapping. <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'>Second, as you describe bellow, there are
temporal measurements (including uncertainty) (</span></font><font size=2
face=Arial><span style='font-size:10.0pt;font-family:Arial'>such as the timing
of earthquakes)<font color=navy><span style='color:navy'>, some are spatial
measurements (</span></font>such as the severity of ground motions produced by
rupture on a fault)<font color=navy><span style='color:navy'>, and others are
instrumental measurements (such as carbon dating). All my comments and
discussions are on temporal and spatial measurements of earthquakes. <o:p></o:p></span></font></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'>The main point is that “The temporal
and spatial measurements are two fundamental and critical elements for
quantifying earthquake and seismic hazard. The temporal and spatial
measurements are also two basic elements of our society. Mixing these two
measurements one way or the other will cause problem.”<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'>Your probability estimates for </span></font><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>a 1811-12
type New Madrid earthquake and the ground motions at a site from this 1811-12
type New Madrid earthquake demonstrates the problem. Under the assumption that
earthquake occurrence follow Poisson distribution, y<font color=navy><span
style='color:navy'>ou have calculated </span></font>10% probability of having a
1811-12 type New Madrid earthquake in the next 50 years, derived from
considering a 500 year AVERAGE recurrence time. As demonstrated in your
paper (Frankel, 2004), you can provided a range of probability, 10, 5, 2, 1,
…, percents, of having the ground motions for this 1811-12 type New
Madrid earthquake in the next 50 years (hazard curve), by mixing temporal measurement
(500-year recurrence interval) and spatial measurement (ground motion
uncertainty). These probability estimates are contradictory.
<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 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>“the </span></font><font size=2
face=Arial><span style='font-size:10.0pt;font-family:Arial'>seismic hazard maps
also include the possibility of magnitude 6 earthquakes, which will be more
frequent than the 1811-12 events.” This hazard calculation could
only be done by mixing the temporal and spatial measurements.<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 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>
<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>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<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> Thursday, February 07, 2008
2:56 PM<br>
<b><span style='font-weight:bold'>To:</span></b>
ceus-earthquake-hazards@geohazards.usgs.gov;
ceus-earthquake-hazards-bounces@geohazards.usgs.gov<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re:
[CEUS-earthquake-hazards] alternative hazard maps</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><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><br>
</span></font><font size=2 face=sans-serif><span style='font-size:10.0pt;
font-family:sans-serif'>Zhenming,</span></font> <br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>
I would like to amplify some of the points that Buddy Schweig made in his
excellent response to you.</span></font> <br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>
When deciding on measures for public safety, such as building codes, it is
critical to consider the random variability that occurs in natural processes,
such as the timing of earthquakes and the severity of ground motions produced
by rupture on a fault.</span></font> <br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>
The 7-10% probability of having a 1811-12 type New Madrid earthquake in the
next 50 years is derived from considering a 500 year AVERAGE recurrence
time, along with an assumption on the probability distribution around that
average recurrence time. Unfortunately, there is randomness to earthquake
occurrence and there is a significant probability that we will have an 1811-12
type earthquake in the next 50 years, well before the 500 year average interval
has elapsed. </span></font><br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>Take
the example of great earthquakes on the Cascadia subduction zone (CSZ) of the <st1:place
w:st="on">Pacific Northwest</st1:place>. There is good paleoseismic
evidence stretching back at least 5000 years that great earthquakes occur along
the entire CSZ with an average recurrence time of about 500 years (see <st1:City
w:st="on"><st1:place w:st="on">Atwater</st1:place></st1:City> and
Hemphill-Haley, 1997, USGS Professional Paper 1576; Nelson et al., 2006 in
Quaternary Research). Of course, there is uncertainty in our dating of
these past earthquakes. Furthermore, there is natural variability in the
occurrence of these earthquakes. For example, two great earthquakes (the U and
W events described in <st1:City w:st="on"><st1:place w:st="on">Atwater</st1:place></st1:City>
and Hemphill-Haley) may have occurred as little as 100 years apart, given
the closeness in time of the central estimates of their dates and the
uncertainites in the dating. </span></font><br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>The
variability in earthquake recurrence times is understandable: we know that slip
on a fault during an earthquake is usually very heterogeneous, with some
patches on a fault slipping a great deal and other areas of the fault hardly
slipping at all. Slip on these other areas is sometimes observed to be
taken up by the next earthquake (see the 1940 and 1979 <st1:place w:st="on">Imperial
Valley</st1:place> earthquakes for example). It is also likely
that the rate of loading of faults is not constant in time or space. As I
said in my previous email, the occurrence of a large earthquake can increase
stress in some areas and affect the timing of other earthquakes in a region,
adding to the randomness of earthquake occurrence.</span></font> <br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>
Buddy is also correct in noting that the seismic hazard maps also include
the possibility of magnitude 6 earthquakes, which will be more frequent than
the 1811-12 events.</span></font> <br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>
When an 1811-12 type New Madrid earthquake occurs again, it will produce
a range of ground motions, even for locations at similar distances from the
earthquake fault. Of course, there are differences in soil conditions
that will affect the ground shaking and we can predict that areas of soft soils
will have stronger shaking on average. Even considering sites with
similar soils at similar distances from the earthquake, there will be
substantial variation of ground shaking. For example, if a large
earthquake on the Reelfoot fault ruptures from northwest to southeast, it will
produce higher ground motions than average for some locations in northwest <st1:State
w:st="on"><st1:place w:st="on">Tennessee</st1:place></st1:State> because of the
strong pulse of velocity produced by rupture directivity. Areas of the
fault where there is larger slip during the earthquake will likely produce
larger ground velocities at nearby sites. These areas of larger slip
will vary from earthquake to earthquake, as could the direction of rupture. Thus,
we can't predict in advance (at least at our present stage of knowledge) where
the areas of higher (and lower) than average ground motions will occur. But
we can account for this variability in our seismic hazard calculations and in
our building codes. That is the essence of probabilistic seismic hazard
assessment.</span></font> <br>
<br>
<br>
<font size=2 face=sans-serif><span style='font-size:10.0pt;font-family:sans-serif'>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</span></font><o:p></o:p></p>
</div>
</body>
</html>