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<DIV><FONT color=#0000ff> Klaus & Zhenming make a very important
point of care in using the single value of return period of one or more
events. Not only is this misleading to the public, the single value of
return period of one or more events is misleading to owners, public officials,
and those with casual use of statistics. </FONT></DIV>
<DIV><FONT color=#0000ff> It is much better in my opinion to use a
x% chance in 50 years of one or more events at a given magnitude. This is
a fully explained concept for multiyears without giving the misimpression that
there will NOT be another event over the single value of return period of one or
more events. </FONT></DIV>
<DIV><FONT color=#0000ff> While we may slip into more casual
use, it only needs to be misused and spread by a single newspaper or television
reporter to undo a great deal of effort. The public still misunderstands
that the odds of a tail in the next perfect coin toss after ten tosses of a head
remains 50%. </FONT></DIV>
<DIV><FONT color=#0000ff> With so much to learn about earthquakes,
we all should take care to be consistent and not overstate what is known.
A quoted seismologist in discussing the 18 APR 08 Mount Carmel, IL event said
"we don't to worry about a <STRONG><EM>MAJOR </EM></STRONG>[highlighted for
emphasis] New Madrid earthquake for another 300 years." It is my
understanding that we are overdue for a low M6 event (yet not 100% likelihood in
10 years) in the New Madrid region. A major event and a low M6 is too
casual of use and certainly feeds the misinformation to the public, because of a
slip of the tongue. </FONT></DIV>
<DIV><FONT color=#0000ff> It is not my intent to castigate
anyone. I just suggest that we state very carefully our comments
particularly for public consumption. </FONT></DIV>
<DIV><FONT color=#0000ff> Thanks, Zhenming and Klaus, for noting the
issue of recurrence. </FONT></DIV>
<DIV><FONT color=#0000ff></FONT> </DIV>
<DIV><FONT color=#0000ff>Regards,</FONT></DIV>
<DIV>Greg <BR>Greg Hempen, PhD, PE, RG<BR></DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=zmwang@email.uky.edu href="mailto:zmwang@email.uky.edu">Wang,
Zhenming</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=jacob@ldeo.columbia.edu
href="mailto:jacob@ldeo.columbia.edu">jacob@ldeo.columbia.edu</A> ; <A
title=ceus-earthquake-hazards@geohazards.usgs.gov
href="mailto:ceus-earthquake-hazards@geohazards.usgs.gov">Central and
EasternU.S. Earthquake Hazards Listserve</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Cc:</B> <A title="'olboyd@usgs.gov'"
href="mailto:olboyd@usgs.gov">olboyd@usgs.gov</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Sunday, May 18, 2008 6:39 AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: [CEUS-earthquake-hazards]
Comment on China quake and hazards map</DIV>
<DIV><BR></DIV>Klaus,<BR><BR>I agree with you that "Hence this earthquake is
VERY pertinent to the discussion of how to map seismic<BR>hazards in regions
with long recurrence periods for similar-sized earthquakes, New Madrid
included."<BR><BR>Attached is the Chinese national seismic design map (1956
intensity map). This historical intensity map could save some life if it was
used.<BR><BR>The problem may be the return period defined in PSHA. 500-year
return period derived from a PSHA study is just a numerical number and is not
equal to any recurrent interval of earthquake. Comparing return period of PSHA
with recurrent interval of earthquake is
misleading.<BR><BR>Thanks.<BR><BR>Zhenming<BR><BR><BR>________________________________________<BR>From:
<A href="mailto:jacob@ldeo.columbia.edu">jacob@ldeo.columbia.edu</A>
[jacob@ldeo.columbia.edu]<BR>Sent: Friday, May 16, 2008 10:43 PM<BR>To:
Central and Eastern U.S. Earthquake Hazards Listserve; Wang, Zhenming<BR>Cc:
<A
href="mailto:ceus-earthquake-hazards@geohazards.usgs.gov">ceus-earthquake-hazards@geohazards.usgs.gov</A>;
<A href="mailto:olboyd@usgs.gov">olboyd@usgs.gov</A><BR>Subject: Re:
[CEUS-earthquake-hazards] Comment on China quake and hazards
map<BR><BR>All:<BR><BR>Thanks Zhenming for the map.<BR><BR>>From what I can
decipher from the map, the region of the M7.9 earthquake is<BR>shown on the
10% in 50 years map as having PGAs between 10 and 20%g. Although I<BR>have not
heard any strong motion reports, I would guess that much of the<BR>region,
especially on the hanging wall side (the uplands, not in the basin)<BR>may
have seen PGA's of 0.5g and possibly larger.<BR><BR>The discrepancies between
map values and likely real PGAs are most likely due to<BR>the
following:<BR><BR>>From what little I know about the region's geology and
seismic history, there is<BR>no earthquakes as large as this one in the
historic record. Geological mapping<BR>of faults has (see cooperative work
between Burchfield's group at MIT<BR>and many Chinese geologists) seem to NOT
have found recently active SURFACE<BR>faulting in the area, and what they
found were seemingly older faults largely<BR>with strike slip components
(while this quake is largely a thrust with minor<BR>strike slip).<BR><BR>This
mapping may have missed that there could be a blind thrust with no
surface<BR>fault. But the topographic front looks formidable and needs
relatively recent<BR>thrusting/reverse faulting, blind or not
blind.<BR><BR>The point is: if there was no large historic quake in the
historic record, no<BR>recognized fault with measurable slip rate, and low
geodetic strain rates, then<BR>the topography should have been a warning,
albeit allowing for VERY LONG<BR>RECURRENCE PERIODS OF SEVERAL 1000 YEARS for
events on this fault or thrust<BR>belt. If the recurrence period is this long,
then it is hardly surprising that<BR>on the hazards map for 10% in 50 years
(average recurrence period 475 years)<BR>this does zone does not show up very
prominently.<BR><BR>This is exactly the reason why some time ago the US NEHRP
hazard maps (i.e.<BR>USGS maps) started to portray 2% in 50 years (2475 years
recurrence period), to<BR>catch regions like this with reasonably "safe" (
speak high) PGA values, or<BR>sufficiently high spectral acceleration values
for building code applications<BR>(like in the CEUS).<BR><BR>Hence this
earthquake is VERY pertinent to the discussion of how to map
seismic<BR>hazards in regions with long recurrence periods for similar-sized
earthquakes,<BR>New Madrid included.<BR><BR>Of course the tectonics is
entirely different, but there are lessons to be<BR>learned, and pertinent to
the issues we all discussed with such passion in this<BR>forum (but on
different sides of the fence) a few month ago.<BR><BR>Of course there is the
other issue about seismic building design and quality<BR>control) or lack of
both, but if there would have been full quality control,<BR>the 10% in 50 year
map PGA values don't provide sufficient protection.<BR><BR>And that is the
lesson of this Eq. for the CEUS, and perhaps China will change<BR>its code
after this quake to longer recurrence periods, closer to what we have<BR>for
the US right now (2% in 50 y, or at least 2/3 of these hazard levels
!!!!).<BR><BR>Best<BR>Klaus Jacob<BR></BLOCKQUOTE></BODY></HTML>