[time-nuts] Re: in-ground clock room - geophones

[John Moran, Scawby Design]

Poul-Henning Kamp writes:

"There are a number of footnotes about geophones, the primary one being
that they have a resonance frequency in the 4-7 Hz range and therefore
provide no usable information below that.

The second is that it is anyones guess what their sensitivity is,
in particular if you buy it on eBay from somebody who found it
lying in a field after percussive oil-exploration, so buy more
than one."

For something a little more reliable and trustworthy than an eBay gamble,
albeit probably more expensive, there is an organisation that caters for people 
nuts about vibrations -

https://raspberryshake.org/

They offer some very nice products and would allow correlation of time glitches
from pendulums (an interest of mine), and other clocks, with earthquakes and other such disturbances.

John