[Geysers] FW: Earthquake swarm - Question

[Craig Messerman]

I don't know about 18-wheeler-impact-equivalents, but the Mercalli  
Intensity scale give a good indication of what you would experience.  
It's not tied directly to magnitude, however, because it involves  
mostly the effects on human's and their structures. If an earthquake  
occurs in a forest...

 From http://earthquake.usgs.gov/learning/topics/mercalli.php

The following is an abbreviated description of the 12 levels of  
Modified Mercalli intensity.

     I. Not felt except by a very few under especially favorable  
conditions.

     II. Felt only by a few persons at rest, especially on upper  
floors of buildings.

     III. Felt quite noticeably by persons indoors, especially on  
upper floors of buildings. Many people do not recognize it as an  
earthquake. Standing motor cars may rock slightly. Vibrations similar  
to the passing of a truck. Duration estimated.

     IV. Felt indoors by many, outdoors by few during the day. At  
night, some awakened. Dishes, windows, doors disturbed; walls make  
cracking sound. Sensation like heavy truck striking building.  
Standing motor cars rocked noticeably.

     V. Felt by nearly everyone; many awakened. Some dishes, windows  
broken. Unstable objects overturned. Pendulum clocks may stop.

     VI. Felt by all, many frightened. Some heavy furniture moved; a  
few instances of fallen plaster. Damage slight.

     VII. Damage negligible in buildings of good design and  
construction; slight to moderate in well-built ordinary structures;  
considerable damage in poorly built or badly designed structures;  
some chimneys broken.

     VIII. Damage slight in specially designed structures;  
considerable damage in ordinary substantial buildings with partial  
collapse. Damage great in poorly built structures. Fall of chimneys,  
factory stacks, columns, monuments, walls. Heavy furniture overturned.

     IX. Damage considerable in specially designed structures; well- 
designed frame structures thrown out of plumb. Damage great in  
substantial buildings, with partial collapse. Buildings shifted off  
foundations.

     X. Some well-built wooden structures destroyed; most masonry and  
frame structures destroyed with foundations. Rails bent.

     XI. Few, if any (masonry) structures remain standing. Bridges  
destroyed. Rails bent greatly.

     XII. Damage total. Lines of sight and level are distorted.  
Objects thrown into the air.

Craig Messerman
Sentinel High School, Missoula, MT
IRIS Seismographs in Schools Station SHMT
406-728-2400, ext. 7067
cmesserman at mcps.k12.mt.us
cmflyer at bresnan.net



On Jan 20, 2009, at 7:14 PM, Carlton Cross wrote:

>
>
>
>
> From: Goh83642 at wmconnect.com [mailto:Goh83642 at wmconnect.com]
> Sent: Monday, January 19, 2009 11:00 PM
> To: geysers-bounces at lists.wallawalla.edu
> Subject: Earthquake swarm - Question
>
>
>
> Gazers,
>
>   I have a question about the recent earthquake swarm in the north  
> end of Yellowstone lake.  My question isn't so much about the swarm  
> as it is about a relative analogy of how much an earthquake  
> intensity is.  In other words, if an earthquake has a magitude of  
> 1.0, how can I compare that to something I can see on a real time  
> example: such as: dropping an 18 wheeler tractor from 100 feet will  
> cause an equivalent of a 1.0 magitude earthquake.
>   Since there were hundreds of earthquakes in magitudes of 1.0 -  
> 3.9 in the swarm, it would sure help to visualize how much shaking  
> it really did to the surface of the earth.
>   If there are any specialists on earthquakes out there, please  
> give this request some thought and let us all know the answer.
>
>   Regards,  Gary Henderson
>                  Meridian, Idaho
>
> _______________________________________________
> Geysers mailing list
> Geysers at lists.wallawalla.edu
> 

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