[CEUS-earthquake-hazards] FW: alternative hazard maps

Fri Feb 8 08:12:44 MST 2008

We are discussing the basic understandings on earthquakes and some assumptions that have been used in the USGS national seismic hazard maps.

Are you saying that all these understandings and assumptions are wrong?

Are you saying that an observation can be counted as several events?

Thanks.

Zhenming

________________________________
From: ceus-earthquake-hazards-bounces at geohazards.usgs.gov [mailto:ceus-earthquake-hazards-bounces at geohazards.usgs.gov] On Behalf Of Stephen C Harmsen
Sent: Thursday, February 07, 2008 11:34 AM
To: Eugene S Schweig
Cc: ceus-earthquake-hazards at geohazards.usgs.gov; ceus-earthquake-hazards-bounces at geohazards.usgs.gov
Subject: Re: [CEUS-earthquake-hazards] alternative hazard maps

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" <ceus-earthquake-hazards at geohazards.usgs.gov>

cc

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:
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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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