Guralp Systems CMG-40T - Manual (Page 22)

CMG-40T
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.
22 Issue A