Installing the 40T
Some installations introduce a layer of ceramic tiles between a rock or concrete
plinth and the seismometer (left):
However, noise tests show that this method of installation is significantly inferior to
the same concrete plinth with the tiles removed (right). Horizontal sensors show
shifting due to moisture trapped between the concrete and tiling, whilst the vertical
sensors show pings as the tile settles.
Other installations have been attempted with the instrument encased in plaster of
Paris, or some other hard-setting compound (left):
Again, this method produces inferior bonding to the instrument, and moisture
becomes trapped between the hard surfaces. We recommend the use of fine dry sand
(right) contained in a box if necessary, which can also insulate the instrument
against convection currents and temperature changes. Sand has the further
advantage of being very easy to install, requiring no preparation.
Finally, many pit installations have a large space around the seismometer, covered
with a wooden roof. Large air-filled cavities are susceptible to currents which
produce lower-frequency vibrations, and sharp edges and corners can give rise to
turbulence. We recommend that a wooden box is placed around the sensor to protect
it from these currents. Once in the box, the emplacement may be backfilled with
fresh turf to insulate it from vibrations at the surface, or simply roofed as before.
By following these guidelines, you will ensure that your seismic installation is ready
to produce the highest quality data.
23
Issue F - June 2019
