Earthquake dissipation rule of thumb?

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Old 02-07-08, 12:08 PM
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Earthquake dissipation rule of thumb?

Is there some rule of thumb for determining the dissipation of an earthquake's strength as it radiates from its epicenter? I'm sure this is a tough thing as it would, I imagine, depend on the geology of the area its forces radiate through.

We live in San Francisco. And I am trying to understand the difference in strength between 89's Loma Prieta quake (6.9, 60 miles away) and, say, movement on the San Andreas similar to 1906 (7.7 - 8.2, 10 miles away).

Thanks,

Gary
 
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Old 02-07-08, 03:04 PM
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Earthquake dissipation rule of thumb?

In addition the distance, the rock structure (solid or fractured), the soil type(clay, sand, etc.) and thickness over the rock are the major items.

In some situations, the magnitude can be lessened by conditions, but in others there is no cushion and there are great forces that can even be magnified by the soils.

There is no simple "rule of thumb".

Dick
 
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Old 02-07-08, 05:58 PM
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Gosh, Dick, your answer was so much better than the one I erased. I may have been castigated for it.
 
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Old 02-07-08, 06:38 PM
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Earthquake dissipation rule of thumb?

Earthquake danger and damage is very unpredictable.

I designed a couple of small buildings in CA and was there some minor quakes.

A few years later, I was in Northridge doing assesment of the main quake damage. I was standing in the middle of a high school tennis court when an aftershock hit and I thought was the end of the world because of the soils in the area. - You wanted to lay down and grab for something firm, but there was nothing.

There is no substitute for distance. - Hundreds of miles unless there is a tsunami, then you need altitude in addition to thousands of miles.
 
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Old 02-08-08, 03:37 AM
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I agree with distance being your best friend in that situation. That, in different words, was my original thoughts. I watch the news after the quakes, and ask, why did they spend so much money building a house in an area where quakes are prevalent. Houses getting swallowed up by the earth.
 
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Old 02-08-08, 05:51 AM
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Earthquake dissipation rule of thumb?

Distance always helps.

I lived in Virginia Beach and the was a coastal area in the south that frequently got pounded by storms.

There was a saying that sooner ot later, everyone wil have a oceanfront lot!

There are some exceptions if you build well. I saw some large waterfront (within 100 feet) homes in Mississippi that easily survived Katrina and the storm surge. They were the only structures left (including the municipal water tanks further inland). - Obviously, they were not wood construction.
 
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