Wednesday, August 5, 2015

The Physics of Balancing Rocks

I've read these papers for years.  It's amazing how people can study these without a speck of physics.  They tried to estimate PGA for gawd sake!  These things are sensitive to PGV, as are all structures.  The PGV is related to induced shear strain, which is just the thing to knock these over.

Now what's the thing that reduces PGV to a very small value?  That's right, solid rock.  These rocks have been standing for thousands of years, and we know from the beach terraces that California gets one of those massive state-ripping M9'+'s every thousand years or so.  So, it doesn't really matter that the rupture 'jumps', these things shouldn't stand, following busgus philosphy.  They wouldn't know physics if it hit them on the head.

These things stand because they are on a piece of incredible rock.  This could be easily confirmed by a seismic survey.  You know that by the narrow foundations, you can easily estimate the strength, and the fact that it does not settle one micro-inch.  In Callie, there is no solid rock for the most part, but this rock is Yosemite-grade granite.  We can't have these in Canada because the frost would work to tip them.

Since Callie is a big mush bowl, you can have the biggest earthquakes, and the PGV on solid rock won't exceed a few cm/s.  That's not enough to even wake you up if you were sleeping right under one of these things.  :)

No comments: