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<DIV>Zhenming,</DIV>
<DIV> </DIV>
<DIV>First, thank you very much for the maps. (Also thanks to Rogers for the
fault-quake maps).</DIV>
<DIV>I see the 1956 intensity map assigns a MMI ~ IX in the zone of 2008
earthquake.</DIV>
<DIV>Indeed, using this map (+ good structural designs) could save some
life.</DIV>
<DIV> </DIV>
<DIV>Regarding the PGA map, I think the problem is not the mean return
period for designing, </DIV>
<DIV>but the seismogenic source model used for developing the map.</DIV>
<DIV> </DIV>
<DIV>In the slides from Prof. Steve Gow one can see the 1713 earthquake on the
fault.</DIV>
<DIV>I attach a small map with this earthquake and others (1713, 1748, 1792 and
1793 earthquakes);</DIV>
<DIV>data taken from Ganse & Nelson's catalog (BSSA, vol. 72, pp. 873-877,
1992).</DIV>
<DIV>According this catalog, the 1713 earthquake reached MMI=VIII and the 1748
earthquake MMI=VII.</DIV>
<DIV>Now, according to Wald et al., (EQS, Vol. 15, pp. 537-555, 1999) for a VIII
earthq. one can </DIV>
<DIV>expect a PGA= 0.34 - 0.65 g, and for a VII earthquake PGA= 0.18 - 0.34
g. Both >> 0.1 g.</DIV>
<DIV> </DIV>
<DIV>The 1713 earthq. happened 295 years ago. Of course, a difficulty is
the unknown previous earthquake.</DIV>
<DIV>But, consideration of this earthquake must lead to expect a high PGA for a
475 years mean return period.</DIV>
<DIV>It is difficult to understand why a PSHA leads to ~0.1 g for this
period.</DIV>
<DIV>For a site practically on the fault, which seismogenic parameters are
supposed for obtaining a such PGA?</DIV>
<DIV>Because of these observations, I think the seismogenic source model used
was inexplicably wrong.</DIV>
<DIV> </DIV>
<DIV>Regards, </DIV>
<DIV>_______________________________________________________<BR>Julio J.
Hernández <BR>Consultant on Structural Engineering and Earthquake Engineering
<BR>Caracas, Venezuela <BR>e-mail: <A
href="mailto:julher@cantv.net">julher@cantv.net</A> <BR>cellphone:
+58-414-1293989</DIV>
<DIV> </DIV>
<DIV> </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 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 7:39 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>==================<BR><BR><BR>Quoting
"Wang, Zhenming" <<A
href="mailto:zmwang@email.uky.edu">zmwang@email.uky.edu</A>>:<BR><BR>> I
would like to share with you all the Chinese National seismic design
map<BR>> (PGA with 10% PE in 50 years). This may explain one of the reasons
that so<BR>> many schools and hospitals collapsed in the Wenchuan
earthquake.<BR>><BR>> Thanks.<BR>><BR>>
___________________________________<BR>> Zhenming Wang, PhD, PE<BR>>
Head, Geologic Hazards Section<BR>> Kentucky Geological Survey<BR>> 228
Mining and Mineral Resources Building<BR>> University of Kentucky<BR>>
Lexington, Kentucky 40506<BR>> Phone:(859)257-5500x142<BR>> Email: <A
href="mailto:zmwang@uky.edu<mailto:zmwang@uky.edu">zmwang@uky.edu<mailto:zmwang@uky.edu</A>><BR>>
Website:<BR>> <A
href="http://www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards">www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards</A>><BR>>
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