[CEUS-earthquake-hazards] alternative hazard maps

[Wang, Zhenming]

Buddy,

You are mixing the temporal measurement (occurrence of earthquake or its consequence (ground motion) at a site in time) with the spatial measurement (occurrence of earthquake or its consequence (ground motion) at a site in space).

In time, one earthquake generates one ground motion at a site. No earthquake, no ground motion. Poisson and non-Poisson models that have been discussed are being used to predict earthquake behavior, including uncertainty, in time.

In space, "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."  The factors may include different locations and source parameters that vary in space.

The temporal and spatial measurements are two fundamental and critical elements for quantifying earthquake and seismic hazard. The temporal and spatial measurements are also two basic elements of our society. Mixing these two measurements one way or the other will cause problem.

Thanks.

Zhenming

________________________________
From: ceus-earthquake-hazards-bounces at geohazards.usgs.gov [mailto:ceus-earthquake-hazards-bounces at geohazards.usgs.gov] On Behalf Of Eugene S Schweig
Sent: Thursday, February 07, 2008 9:34 AM
To: ceus-earthquake-hazards at geohazards.usgs.gov
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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