[CEUS-earthquake-hazards] alternative hazard maps

[Stephen C Harmsen]

While Buddy's response does point out many relevant issues, I contend that 
 Zhenming's question is not simple but is in fact baffling.
How often are ground motions observed depends on how many observers are 
present. The populations of these cities increase with time, at least that 
is the trend for a few centuries. Civil defense measures may evolve with 
time and we might hope that before the next NMSZ major event occurs some 
effort will be made to evacuate less seismically resistant buildings. 
People who live and work in these identified buildings may leave these 
cities for awhile, so simple population projections might not be valid. If 
we are talking about 200 years in the future, we should hope that 
continued science and technology improvements will lessen the number of 
observers at least the number of casualties. Those who want to ride the 
wave should be welcomed to do so after sober assessment of their odds. 
Then, there is the likelihood of several events in a short time span. Does 
an observation of each count as one or as several? What about observations 
of aftershocks? If the observer dies before he/she has a chance to report, 
does his/her observation count? Do pets' observations count?

In the NMSZ events of 1811-1812 most people lived and worked in 1-story 
buildings generally wood frame construction (how much sod?). Now, the 
built environment is much different and the number of hostages to vagaries 
of tall building response has increased. While there is considerable 
inertia to seismic resistant design in many counties it is difficult to 
predict how adequate the nation's and individual states' response to the 
seismic threat will be over the next few centuries. The difficulty lies in 
the many societal pressures that have been discussed in these various 
emails, what resources are dedicated to which threats, and whose voice is 
heard. These are indeed unpredictable factors. 

Stephen Harmsen
Research Physical Scientist
USGS 
(303) 273 8567
mailing address: USGS, Denver Federal Center, 
MS 966, Box 25046, Denver, CO 80225

USGS office (for overnight deliveries):
1711 Illinois Street, Golden, CO 80401




Eugene S Schweig <schweig at usgs.gov> 
Sent by: ceus-earthquake-hazards-bounces at geohazards.usgs.gov
02/07/2008 07:33 AM

To
"ceus-earthquake-hazards at geohazards.usgs.gov" 
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Subject
Re: [CEUS-earthquake-hazards] alternative hazard maps







Zhenming, 

While your question is simple, it is also misleading.  If we could count 
on M 7.7 earthquakes happenning every 500 years, and we could count on the 
ground motions always be the same at each of these locations for a New 
Madrid event, and if a repeat of 1811-1812 were the only thing that could 
cause that level of ground motions at each location, our leaders could go 
to bed happy that it would be at lest 200 hundred years before they had to 
start building safe buildings.  Sadly, none of this is true.  We have 
little information on the regularity of earthquake timing.  We know there 
can be significant variation in the ground motions generated by the same 
size earthquake from even to event because of a number of factors.  We 
also know that other earthquakes besides a repeat of the 1811-1812 
earthquakes may contribute to the possibility of large ground motions, 
particularly with increasing distance from New Madrid.  So while the 
question is simple, the answer is not, which I am sure you already know. 

Buddy 
Fading into the Central U.S.Seismic Sunset 
__________________________________________________________________
Eugene Schweig
Chief Scientist
Earth Surface Processes Team
U.S. Geological Survey

Denver Office:
MS980 Federal Center                                      (303) 236-5344
Denver, CO 80225-0046                         Fax: (303) 236-5690

Memphis office: 
3876 Central Ave., Ste. 2                                 (901) 678-4974
MEMPHIS, TN  38152-3050                     Fax: (901) 678-4897
___________________________________________________________________




"Wang, Zhenming" <zmwang at email.uky.edu> 
Sent by: ceus-earthquake-hazards-bounces at geohazards.usgs.gov 
02/07/08 07:24 AM 


To
Arthur D Frankel <afrankel at usgs.gov>, Seth Stein 
<seth at earth.northwestern.edu> 
cc
"ceus-earthquake-hazards at geohazards.usgs.gov" 
<ceus-earthquake-hazards at geohazards.usgs.gov> 
Subject
Re: [CEUS-earthquake-hazards] alternative hazard maps







  
Here is a simple question for every one: If an M7.7 earthquake occurs 
every 500 years in the New Madrid seismic zone, how often will the ground 
motion generated by that earthquake be observed in Memphis, St. Louis, or 
Paducah? 
  
Thanks. 
  
Zhenming 
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