🚀 go-pugleaf

In article <11960@sun.uucp>, chuq%plaid@Sun.COM (Chuq Von Rospach) writes:

> ....I've always been fascinated by the geology of the area I live in
> (especially when it burps at 3 in the morning and tosses me out of bed) and
> I was thinking it would be neat to have a seismograph in my home.  Is this
> at all feasible?  Would it be out of financial reach or simply require stuff
> (like multi-hundred foot wells) that don't work for a hobbyist?
> 

Back in the mid-60's, Popular Science Magazine printed an article and plans
on how to build your own seismograph.  The most expensive part seemed to 
be the geared-down motor to turn the paper chart.  The other parts were
plywood, steel wire, and a big coffee can full of concrete.  Also a 
BIC pen.
	
It looked kind of like this:  (side view follows)

		|--|
		|  |\
		|  | \
		|  |  \
		|  |   \
		|  |    \
		|  |     \Steel wire
		|  |      \
		|  |       \
		|  |        \
		|  |         \
		|  |          \
		|  |           \
		|  |            \   
		|  | pivot       |"""|Coffee can full of concrete
		|  |<------------|   |
		|  |   rod       |---|-|Bic pen
		|  |                   |
		|  |                   O  slowly rotating drum
	
The whole thing is about four feet tall, and is sensitive to P-waves
running into/out of the page, and horizontal S-waves running left-right 
plane of the page.  So, they recommend you build two at right angles
to get everything except vertical S-waves (which are harder to detect).
	
The drum is usually on a threaded rod so that you get more than one 
rotation's worth of data on a sheet. Quiet traces will be written
as nice helicies and when the earth shakes, you'll be able to record
it.

Have an *accurate* clock nearby, so you can mark the start point of
any trace to within a second or two (by hand-swinging the pendulum
and writing the time).  There are amateur groups who share 
seismological information- with multiple stations and accurate timing,
you can get a good fix on the actual location of the fault.
A local universities' geology department can probably get you in 
touch with the proper group.

It works on the principle of inertia, so the post and drum *must* be 
solidly anchored to the earth.  Bolting it to the basement floor is good.
You vary the length of the steel wire with a turnbuckle to vary the 
stability of the coffee-can pendulum.  If the wire is too long, the pendulum
will droop too much at the center (straight-to-drum) position and it will
be insensitive (as well as having the pen lift from the paper on a real 
shock).  If the wire is too short, the pendulum will be unstable and 
will fall to one side or the other.  You have to hit it just right- and
it helps to have the BIC pen on some sort of hinged arm to let it track the 
drum surface rather than digging in/lifting free.
		
Dig up the article for all the gruesome (but very inexpensive) details.
	
	-Bill Yerazunis