[CEUS-earthquake-hazards] Map of Chinese earthquakes

[Rogers, David]

Hi Everyone:

In regards to Klau's assumptions about the state of activity along the
fault I am providing some rudimentary comments about recurrence
frequency of the LongMenShan fault, which appears to have spawned the
May 12th M 7.9 Sichuan quake.  This same fault was responsible for six
major quakes over the past ~400 years; including M. 7.2 in 1976 and M.
7.5 events in 1933, just in the past 75 yrs.  

See Slides # 2 and #3 in the attachment, which shows portions of the
Chinese National Earthquake Map, which shows the recognized faults,
historic earthquake magnitudes, and dates of occurrence.  The black star
sows approximate location of the May 12th event.  These slides were
prepared by my colleague Prof. Steve Gow, who is a deep crustal
seismologist here at Missouri S&T and native of China.  

Best regards,

Dave  

J. David Rogers, Ph.D., P.E., R.G., C.E.G., C.H.G.
Karl F. Hasselmann Chair in Geological Engineering
Department of Geological Engineering
129 McNutt Hall, 1400 N. Bishop Avenue
Missouri University of Science & Technology
Rolla, MO 65409-0230
(573) 341-6198 voice
(573) 341-6935 fax
E-mail: rogersda at mst.edu
URL: www.mst.edu/~rogersda

Formerly the University of Missouri-Rolla

 

-----Original Message-----
From: ceus-earthquake-hazards-bounces at geohazards.usgs.gov
[mailto:ceus-earthquake-hazards-bounces at geohazards.usgs.gov] On Behalf
Of jacob at ldeo.columbia.edu
Sent: Friday, May 16, 2008 9:43 PM
To: Central and Eastern U.S. Earthquake Hazards Listserve; Wang,
Zhenming
Cc: olboyd at usgs.gov; ceus-earthquake-hazards at geohazards.usgs.gov
Subject: Re: [CEUS-earthquake-hazards] Comment on China quake and
hazards map

All:

Thanks Zhenming for the map.

>From what I can decipher from the map, the region of the M7.9
earthquake is
shown on the 10% in 50 years map as having PGAs between 10 and 20%g.
Although I
have not heard any strong motion reports, I would guess that much of the
region, especially on the hanging wall side (the uplands, not in the
basin)
may have seen PGA's of 0.5g and possibly larger.

The discrepancies between map values and likely real PGAs are most
likely due to
the following:

>From what little I know about the region's geology and seismic history,
there is
no earthquakes as large as this one in the historic record. Geological
mapping
of faults has (see cooperative work between Burchfield's group at MIT
and many Chinese geologists) seem to NOT have found recently active
SURFACE
faulting in the area, and what they found were seemingly older faults
largely
with strike slip components (while this quake is largely a thrust with
minor
strike slip).

This mapping may have missed that there could be a blind thrust with no
surface
fault. But the topographic front looks formidable and needs relatively
recent
thrusting/reverse faulting, blind or not blind.

The point is: if there was no large historic quake in the historic
record, no
recognized fault with measurable slip rate, and low geodetic strain
rates, then
the topography should have been a warning, albeit allowing for VERY LONG
RECURRENCE PERIODS OF SEVERAL 1000 YEARS for events on this fault or
thrust
belt. If the recurrence period is this long, then it is hardly
surprising that
on the hazards map for 10% in 50 years (average recurrence period 475
years)
this does zone does not show up very prominently.

This is exactly the reason why some time ago the US NEHRP hazard maps
(i.e.
USGS maps) started to portray 2% in 50 years (2475 years recurrence
period), to
catch regions like this with reasonably "safe" ( speak high) PGA values,
or
sufficiently high spectral acceleration values for building code
applications
(like in the CEUS).

Hence this earthquake is VERY pertinent to the discussion of how to map
seismic
hazards in regions with long recurrence periods for similar-sized
earthquakes,
New Madrid included.

Of course the tectonics is entirely different, but there are lessons to
be
learned, and pertinent to the issues we all discussed with such passion
in this
forum (but on different sides of the fence) a few month ago.

Of course there is the other issue about seismic building design and
quality
control) or lack of both, but if there would have been full quality
control,
the 10% in 50 year map PGA values don't provide sufficient protection.

And that is the lesson of this Eq. for the CEUS, and perhaps China will
change
its code after this quake to longer recurrence periods, closer to what
we have
for the US right now (2% in 50 y, or at least 2/3 of these hazard levels
!!!!).

Best
Klaus Jacob
==================


Quoting "Wang, Zhenming" <zmwang at email.uky.edu>:

> I would like to share with you all the Chinese National seismic design
map
> (PGA with 10% PE in 50 years). This may explain one of the reasons
that so
> many schools and hospitals collapsed in the Wenchuan earthquake.
>
> Thanks.
>
> ___________________________________
> Zhenming Wang, PhD, PE
> Head, Geologic Hazards Section
> Kentucky Geological Survey
> 228 Mining and Mineral Resources Building
> University of Kentucky
> Lexington, Kentucky 40506
> Phone:(859)257-5500x142
> Email: zmwang at uky.edu<mailto:zmwang at uky.edu>
> Website:
>
www.uky.edu/KGS/geologichazards<http://www.uky.edu/KGS/geologichazards>
> ____________________________________
>
>




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