[time-nuts] Steve's new QTH...

Hal Murray hmurray at megapathdsl.net
Tue Sep 7 18:57:07 UTC 2010

> Many years ago I ran into a combined group on Mt. Wilson, our local
> broadcast farm in the mountains, from Cal Tech and MIT that was  measuring
> the movement between Southern California mountains using  lazers.  While
> this was scientifically fascinating, it gave me the willies. 

I'm in Silicon Valley.  There is a big USGS group here.

They used to have a laser setup between Black Mountain and Mt Diablo which 
are on opposite sides of the fault, roughly 50 miles apart.  They used to fly 
a helicopter along the beam, measuring the temperature so they could get a 
more accurate answer.

Fault motion is ballpark of 1 inch per year, the same as your fingernails 
grow.  So they would want to measure the distance to a (small) fraction of 

I did a quick search, but I didn't find the speed of light as a function of 
temperature.  50 miles is 3E6 inches so 1 PPM would be a big deal.

I think they do it with GPS now.

These are my opinions, not necessarily my employer's.  I hate spam.

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