<br><font size=2 face="sans-serif">Ellis,</font>
<br>
<br><font size=2 face="sans-serif"> I don't think the example
you cite is applicable to the case of the logic tree we use for New Madrid
magnitudes. In our logic tree we are trying to account for the uncertainty
in the magnitude of characteristic (1811-12 type) earthquakes in the New
Madrid source zone. </font>
<br>
<br><font size=2 face="sans-serif"> In your example with two faults,
a probabilistic hazard assessment would use the range of magnitudes specific
for each fault. It does not average the magnitude between the two faults.
</font>
<br>
<br><font size=2 face="sans-serif"> In your earlier email, you expressed
doubt about determining the rates of large earthquakes by extrapolating
the rates of smaller earthquakes using a "b-line." </font>
<br><font size=2 face="sans-serif">This is not what is done for the New
Madrid characteristic earthquakes (1811-12 type earthquakes). The
average recurrence rate for the 1811-12 type earthquakes is determined
from the dating of sand blows (see Tuttle et al., 2002 BSSA), which shows
that previous such events occurred around 1450 and 900 A.D. </font>
<br>
<br><font size=2 face="sans-serif">-Art</font>
<br>
<br>
<br>
<br><font size=2 face="sans-serif">Art Frankel<br>
U.S. Geological Survey<br>
MS 966, Box 25046<br>
DFC<br>
Denver, CO 80225<br>
phone: 303-273-8556<br>
fax: 303-273-8600<br>
email: afrankel@usgs.gov</font>
<br>
<br>
<br>
<table width=100%>
<tr valign=top>
<td width=40%><font size=1 face="sans-serif"><b>"Krinitzsky, Ellis
L ERDC-GSL-MS Emeritus" <Ellis.L.Krinitzsky@usace.army.mil></b>
</font>
<p><font size=1 face="sans-serif">02/22/2008 08:40 AM</font>
<td width=59%>
<table width=100%>
<tr valign=top>
<td>
<div align=right><font size=1 face="sans-serif">To</font></div>
<td><font size=1 face="sans-serif">"Arthur D Frankel" <afrankel@usgs.gov>,
"Wang, Zhenming" <zmwang@email.uky.edu></font>
<tr valign=top>
<td>
<div align=right><font size=1 face="sans-serif">cc</font></div>
<td><font size=1 face="sans-serif"><ceus-earthquake-hazards@geohazards.usgs.gov></font>
<tr valign=top>
<td>
<div align=right><font size=1 face="sans-serif">Subject</font></div>
<td><font size=1 face="sans-serif">RE: [CEUS-earthquake-hazards] FW: reply
to Joe Tomasello; buildings codes and earthquake hazard</font></table>
<br>
<table>
<tr valign=top>
<td>
<td></table>
<br></table>
<br>
<br>
<br><font size=2><tt>Art,<br>
<br>
I saw elsewhere you came to your values using a logic tree.<br>
<br>
Suppose you had two faults, one with a potential for M6, another for M8.
If<br>
you average them you have an M7. If you designed for that M7 and you had
an<br>
M8, you would be under designed. Yet the logic tree makes you do exactly<br>
that. Plus other illogical moves.<br>
<br>
You need to solve those problems first.<br>
<br>
Ellis <br>
<br>
-----Original Message-----<br>
From: ceus-earthquake-hazards-bounces@geohazards.usgs.gov<br>
[mailto:ceus-earthquake-hazards-bounces@geohazards.usgs.gov] On Behalf
Of<br>
Arthur D Frankel<br>
Sent: Tuesday, February 19, 2008 10:01 PM<br>
To: Wang, Zhenming<br>
Cc: ceus-earthquake-hazards@geohazards.usgs.gov<br>
Subject: Re: [CEUS-earthquake-hazards] FW: reply to Joe Tomasello; buildings<br>
codes and earthquake hazard<br>
<br>
Zhenming,<br>
<br>
These two statements are not contradictory, when taken in the context
that<br>
I wrote them.<br>
<br>
In the quote from my response to my comment, I was referring to
the ground<br>
motions observed at any given location over time. At any particular site
the<br>
ground motions with a 2% chance of being exceeded in 50 years, will occur,
on<br>
average, once in 2500 years. As I said before, another way to express this
is<br>
that these ground motions have a 1/2500 chance of being exceed each year.<br>
<br>
The point of my recent email is that each time an 1811-12 type
earthquake<br>
occurs, there will be some locations that will experience the 2%/50 ground<br>
motions or larger, because of the spatial variability of ground motions.
The<br>
set of sites that experience these higher ground motions will likely be<br>
different for each occurrence of this type of earthquake, because of the<br>
variability of ground motions from earthquake to earthquake. This apparent<br>
temporal variability of ground motions will occur even for successive<br>
earthquakes on the same fault, because of differences in rupture propagation<br>
and slip on the fault from earthquake to earthquake. <br>
<br>
As you design buildings to ground motions with lower probability levels,
you<br>
are protecting a larger fraction of buildings from the range of ground<br>
motions expected during the next 1811-12 type earthquake.<br>
<br>
Art Frankel<br>
U.S. Geological Survey<br>
MS 966, Box 25046<br>
DFC<br>
Denver, CO 80225<br>
phone: 303-273-8556<br>
fax: 303-273-8600<br>
email: afrankel@usgs.gov<br>
<br>
<br>
-----ceus-earthquake-hazards-bounces@geohazards.usgs.gov wrote: -----<br>
<br>
<br>
<br>
To: "ceus-earthquake-hazards@geohazards.usgs.gov"<br>
<ceus-earthquake-hazards@geohazards.usgs.gov><br>
From: "Wang, Zhenming" <zmwang@email.uky.edu><br>
Sent by: ceus-earthquake-hazards-bounces@geohazards.usgs.gov<br>
Date: 02/19/2008 07:34AM<br>
Subject: [CEUS-earthquake-hazards] FW: reply to Joe Tomasello;<br>
buildings codes and earthquake hazard<br>
<br>
<br>
<br>
Here is another inconsistent statement on the national seismic hazard<br>
maps.<br>
<br>
<br>
<br>
" You have the mistaken notion that 2%/50 values are only observed<br>
once in 2500 years. This is flat out wrong. " <br>
<br>
<br>
<br>
In a response to our comment (Wang and others, 2005) that was<br>
published on Seismological Research Letter (Frankel, 2005), the<br>
interpretation was "the ground motion with 2% PE in 50 years is exceeded<br>
once, on average over 2,500 years, so that it has a 1/2500 annual probability<br>
of being exceeded." <br>
<br>
<br>
<br>
<br>
<br>
<br>
<br>
As demonstrated earlier, for a single M7.7 earthquake with 500 year<br>
recurrence interval in the New Madrid seismic zone, ground motion with<br>
2,500-year return period (2% PE in 50 years) means there is about 20 percent<br>
probability that ground motion will be exceeded if the M7.7 earthquake<br>
occurs. In other words, if the ground motion with 2,500-year return period
is<br>
selected for engineering design, we has a confidence level of 80% (not
being<br>
exceeded) if the M7.7 earthquake occurs. <br>
<br>
<br>
<br>
Thanks. <br>
<br>
<br>
<br>
Zhenming <br>
<br>
<br>
<br>
<br>
________________________________<br>
<br>
<br>
From: ceus-earthquake-hazards-bounces@geohazards.usgs.gov<br>
[mailto:ceus-earthquake-hazards-bounces@geohazards.usgs.gov] On Behalf
Of<br>
Arthur D Frankel <br>
Sent: Friday, February 15, 2008 1:50 PM <br>
To: Joe Tomasello <br>
Cc: ceus-earthquake-hazards@geohazards.usgs.gov; mpetersen@usgs.gov <br>
Subject: Re: [CEUS-earthquake-hazards] reply to Joe Tomasello;<br>
buildings codes and earthquake hazard <br>
<br>
<br>
<br>
<br>
Joe, <br>
<br>
I feel I need to reply to you on the bulletin board, since you seem<br>
to want to keep this discussion going and you directly ask me questions.
My<br>
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<br>
said that the IBC values (2/3 times the ground motions with 2% probability
of<br>
exceedance in 50 years [2%/50]) were probably experienced inMemphis during<br>
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<br>
motions) are only observed once in a millenium. You have the
mistaken<br>
notion that 2%/50 values are only observed once in 2500 years. This is
flat<br>
out wrong. Some locations will experience 2/3 times the 2%/50
ground<br>
motions during the next 1811-12 type earthquake. Some locations
will<br>
experience the 2%/50 ground motions during the next 1811-12 type earthquake.<br>
This is a simple consequence of the observed variability of earthquake
ground<br>
motions. <br>
<br>
As far as the magnitude issue you bring up, the USGS uses
the<br>
range of magnitudes that various seismologists have determined for
the<br>
1811-12 earthquakes from the intensity data. The central values of
these<br>
moment magnitude determinations range from 7.4-7.5 (Hough et al.,
2000 in<br>
JGR) to 7.8 (Bakun and Hopper, 2004 in BSSA) to 8.0-8.1 (Johnston,
1996 in<br>
Geophysical Journal). In the national maps we use a logic tree to
express<br>
this range, with a value of 7.7 given the highest weight. I used
M7.7 in<br>
the scenario in my previous email, because it is in the center of the range<br>
of magnitudes determined for the 1811-12 earthquakes. I also gave
results<br>
for a M7.4 earthquake. <br>
<br>
In the example in my previous email, I placed the scenario<br>
earthquake where the current seismicity trend for the New Madrid seismic
zone<br>
is located. The closest distance to downtown Memphis is about 60 km. <br>
<br>
-Art <br>
<br>
<br>
<br>
<br>
Art Frankel <br>
U.S. Geological Survey <br>
MS 966, Box 25046 <br>
DFC <br>
Denver , CO 80225 <br>
phone: 303-273-8556 <br>
fax: 303-273-8600 <br>
email: afrankel@usgs.gov <br>
<br>
<br>
<br>
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