Guralp Systems CMG-6TD User Manual
Page 26
Installing the 6TD
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.
26
Issue F - February 2014