Guralp Systems CMG-40T - Manual (Page 21)

Operator's guide
In other installations, tape the box down to the surface to exclude
draughts.
9. Alternatively, if a box is not available, cover the instrument with fine
sand up to the top.
The sand insulates the instrument and protects it from thermal
fluctuations, as well as minimizing unwanted vibration.
10.Ensure that the sensor cable is loose and that it exits the seismometer
enclosure at the base of the instrument. This will prevent vibrations from
being inadvertently transmitted along the cable.
11.Cover the pit with a wooden lid, and back-fill with fresh turf.
Other installation methods
The recommended installation methods have been extensively tested in a wide
range of situations. However, past practice in seismometer installation has
varied widely.
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):
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