Notes concerning soil amplification:
1. Ground shaking is amplified in soft sediments and dampened in hard rock:
Flash animation:
"[URL amplification
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(Source: U.S. Geological Survey)
2. In the U.S. they have already made soil amplification maps for some areas in the U.S. to predict the level of shaking depending on soil quality. Here we have the map for LA area:
http://earthquake.usgs.gov/learn/glossary/images/amplification.jpg"
Flash animation and LA region amplification map can be found in this page:
http://earthquake.usgs.gov/learn/glossary/?term=amplification"
And here they have made a research concerning earthquake ground motions in the central U.S.:
http://gsa.confex.com/gsa/2002NC/finalprogram/abstract_31500.htm"
Do they have these kind of maps in Japan?
Surely they must have?
3. The differences between mudstone and bedrock:
The velocity of transmits shear waves (S-waves) is one contributor to the amplification rate. It's dependend on the area we are talking about. In the San Fransisco Bay area they have 5 level chart for soil types and shaking amplification. In that area mudstone and bedrock have different qualities:
http://earthquake.usgs.gov/regional/nca/soiltype/
Shaking is stronger where the shear wave velocity is lower. So it's stronger for mudstone than for bedrock.
4. Conclusion: To have nuclear plants built on bedrock and mudstone are two different things. Building on bedrock is safer.
If Fukushima plant's foundation is built on mudstone - not bedrock - and the local geological qualities for mudstone and bedrock differ in that area then it may have had some impact on the scale of the catastrophe.
But surely the Japanese must have made some calculations concerning the safety of building nuclear plants on mudstone if that happens to be the case?
)
