Installing the 3ESP
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.
3.5
Installing in post-holes
The 3ESP is suitable for installation in post-holes. In soft subsoil, a hole 2 – 4 m
deep and 20 cm wide can be conveniently excavated using a tractor-mounted or
17
Issue G - February 2016
