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<DIV>Dear Zhenming,</DIV>
<DIV> </DIV>
<DIV>What I mean is that, for example, in an accepted variant of PSHA (Cornell,
1968), one assigns to each source (faults, ....) seismogenic parameters
representative of its activity (b-value of Gutenberg-Richter's law,
rate of activity for a minimum magnitude M0, maximum magnitude Mu,
etc.). Given a fault that can lead to MMI = VIII in some
site, those assigned parameters should not lead to PGA = 0.1 g
in the same site for MRP = 475 years, unless that event is
very rare for sure.</DIV>
<DIV> </DIV>
<DIV>Due to uncertainties, it is not "correct" to assign to this
fault so low parameters as if its long term activity were very low
with certainty. In my opinion a good seismogenic model should not drive to
that PGA in this case. Such a model must take into account geological data,
seismological data and macroseismic data. </DIV>
<DIV>In several cases using only a kind of data leads to biased models. It is
important to place emphasis in multidisciplinary studies.</DIV>
<DIV>Usually, when strange results are found the wrong thing is not the PSHA
methodology but the input data.</DIV>
<DIV> </DIV>
<DIV>On the other hand, the mean return period (MRP) for a value
of PGA does not only depend on the MRP of the possible earthquakes. It
also depends on the variability of the attenuation of ground motion. Even in an
extremely deterministic scenario, with only a possible magnitude with a known
return period in one fault, the PGA has many different possible values, with
an expected value and a standard deviation. Obviously, it is possible to
get a PGA for a given MRP while none earthquake has the same MRP. And if we
have some earthquake with MRP < 475 years, we get a value of PGA
with MRP ~ 475 years. </DIV>
<DIV>For example, regarding the strange PGA of the Chinese map, even with a low
hazard given for a sole M6.5 earthquake (near the site) with MRP ~ 300
years, using the Abrahamson & Silva (1997) attenuation law, in rock at
10 km from rupture, we get PGA ~ 0.36 g for MRP ~ 475 years.</DIV>
<DIV> </DIV>
<DIV>Best regards, Julio J.</DIV>
<DIV> </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=julher@cantv.net
href="mailto:julher@cantv.net">Julio J. Hernández</A> ; <A
title=ceus-earthquake-hazards@geohazards.usgs.gov
href="mailto:ceus-earthquake-hazards@geohazards.usgs.gov">Central and Eastern
U.S. Earthquake Hazards Listserve</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Monday, May 19, 2008 5:02 PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: [CEUS-earthquake-hazards]
Comment on China quake and hazards map</DIV>
<DIV><BR></DIV>Dear Julio,<BR><BR>There are enough studies and historical
records in the area. The problem is not the seismogenic source model used, but
PSHA. As you shown, recurrence interval of the large earthquake (like the May
12, 2008, event) is about 350-400 years. 500-year return period derived from
PSHA do not really account for the ground motion from the large
earthauke.<BR><BR>Thanks.<BR><BR><BR>Zhenming<BR><BR><BR>________________________________<BR>From:
Julio J. Hernández [julher@cantv.net]<BR>Sent: Monday, May 19, 2008 2:23
PM<BR>To: Central and Eastern U.S. Earthquake Hazards Listserve<BR>Cc: Wang,
Zhenming<BR>Subject: Re: [CEUS-earthquake-hazards] Comment on China quake and
hazards map<BR><BR>Zhenming,<BR><BR>First, thank you very much for the maps.
(Also thanks to Rogers for the fault-quake maps).<BR>I see the 1956 intensity
map assigns a MMI ~ IX in the zone of 2008 earthquake.<BR>Indeed, using this
map (+ good structural designs) could save some life.<BR><BR>Regarding
the PGA map, I think the problem is not the mean return period for
designing,<BR>but the seismogenic source model used for developing the
map.<BR><BR>In the slides from Prof. Steve Gow one can see the 1713 earthquake
on the fault.<BR>I attach a small map with this earthquake and others (1713,
1748, 1792 and 1793 earthquakes);<BR>data taken from Ganse & Nelson's
catalog (BSSA, vol. 72, pp. 873-877, 1992).<BR>According this catalog, the
1713 earthquake reached MMI=VIII and the 1748 earthquake MMI=VII.<BR>Now,
according to Wald et al., (EQS, Vol. 15, pp. 537-555, 1999) for a VIII earthq.
one can<BR>expect a PGA= 0.34 - 0.65 g, and for a VII earthquake PGA= 0.18 -
0.34 g. Both >> 0.1 g.<BR><BR>The 1713 earthq. happened 295 years
ago. Of course, a difficulty is the unknown previous earthquake.<BR>But,
consideration of this earthquake must lead to expect a high PGA for a 475
years mean return period.<BR>It is difficult to understand why a PSHA leads to
~0.1 g for this period.<BR>For a site practically on the fault, which
seismogenic parameters are supposed for obtaining a such PGA?<BR>Because of
these observations, I think the seismogenic source model used was inexplicably
wrong.<BR><BR>Regards,<BR>_______________________________________________________<BR>Julio
J. Hernández<BR>Consultant on Structural Engineering and Earthquake
Engineering<BR>Caracas, Venezuela<BR>e-mail: <A
href="mailto:julher@cantv.net<mailto:julher@cantv.net">julher@cantv.net<mailto:julher@cantv.net</A>><BR>cellphone:
+58-414-1293989<BR><BR><BR>----- Original Message -----<BR>From: Wang,
Zhenming<<A
href="mailto:zmwang@email.uky.edu">mailto:zmwang@email.uky.edu</A>><BR>To:
<A
href="mailto:jacob@ldeo.columbia.edu<mailto:jacob@ldeo.columbia.edu">jacob@ldeo.columbia.edu<mailto:jacob@ldeo.columbia.edu</A>>
; Central and EasternU.S. Earthquake Hazards Listserve<<A
href="mailto:ceus-earthquake-hazards@geohazards.usgs.gov">mailto:ceus-earthquake-hazards@geohazards.usgs.gov</A>><BR>Cc:
<A
href="mailto:olboyd@usgs.gov<mailto:olboyd@usgs.gov">olboyd@usgs.gov<mailto:olboyd@usgs.gov</A>><BR>Sent:
Sunday, May 18, 2008 7:39 AM<BR>Subject: Re: [CEUS-earthquake-hazards] Comment
on China quake and hazards map<BR><BR>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<mailto:jacob@ldeo.columbia.edu">jacob@ldeo.columbia.edu<mailto: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<mailto:ceus-earthquake-hazards@geohazards.usgs.gov">ceus-earthquake-hazards@geohazards.usgs.gov<mailto:ceus-earthquake-hazards@geohazards.usgs.gov</A>>;
<A
href="mailto:olboyd@usgs.gov<mailto:olboyd@usgs.gov">olboyd@usgs.gov<mailto: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<mailto:zmwang@email.uky.edu">zmwang@email.uky.edu<mailto: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<mailto:zmwang@uky.edu<mailto:zmwang@uky.edu">zmwang@uky.edu<mailto:zmwang@uky.edu<mailto: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<http://www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards">www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards</A>>><BR>>
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