Guralp Systems CMG-6T - Manual (Page 18)

CMG-6T
2.9 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):
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.
18 Issue B