Monday, October 26, 2009

October BSSA

After this year, I'm just getting my journals electronically, and I can probably read them on my book reader. This month's journal is over an inch thick, and quite heavy. It is all dedicated to ground motions, which are fun. This journal is behind the paywall, so you can't see it.

I liked the front review article entitled "Strong Ground Motions - Have we seen the worst?" It is a very interesting piece that explores how "records' are broken all the time, and what could be the maximum that we might see in the future. In this article, the concept of PGA being good for anything is shattered, and PGV has a better correlation with damage. Were I still in the old business, I would use this to get rid of PGA forever. PGA- peak ground acceleration, PGV - peak ground velocity.

If you use PGA and standard hazard probability, you have no limits as to the maximum magnitude. A Yucca analysis eventually got to 12 g for something like 10-8 chance per year. The article does not explore the physical limit to PGV on rock, which is linked to the maximum stress that wet, fractured rock can handle.

Finally, if we look at oceanic super-waves, there may be no known limit to seismic basin waves. If a bunch of these group waves all combined together for an instant, the PGV could hit several metres per second.

Most of the rest of the articles are on standard probablity seismic hazard, which I'm really starting to hate. I want more velocity time histories on solid rock.

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