Guralp Systems CMG-3ESPCD - Manual (Page 16)

CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
seismometer on top of this stone. This method emulates that in step 3,
but can be performed on-site with no additional equipment.
7. Set up the instrument as described in Section 3.3 on page 11.
8. The instrument must now be shielded from air currents and
temperature fluctuations. This is best done by covering it with a
thermal shield.
An open-sided box of 5 cm expanded polystyrene slabs is
recommended. If using a seismic plinth on sand (from steps 3–4 or 5),
ensure that the box is firmly placed in the sand, without touching the
plinth at any point. 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.
3.5 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, as shown in the left-hand picture below:
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.
MAN-C3E-0002 16 Issue B - November 2013