Guralp Systems CMG-3ESPCD - Manual (Page 11)

CMG-3ESPCD Digital Broadband Seismometer Installing the 3ESPCD
In seismic vaults, instruments are often installed on piers. It is important to
ensure that the interface between the pier and the floor does not introduce
noise, and that the pier itself does not have resonant frequencies within the
passband. Ideally, a seismic pier will be significantly wider than it is high (to
minimize flexing) and will form a single piece with the floor, e.g. by moulding
a poured concrete floor with a wooden frame.
Many situations do not allow for the construction of a seismic vault. For
example, you may need to deploy quickly to monitor the activity of a volcano
showing signs of rejuvenation, or to study the aftershocks of a major
earthquake; or the site itself may be too remote to ship in construction
equipment.
Temporary installations can be protected against spurious vibrations by
•
selecting a suitable site,
•
placing the instrument in a protective enclosure (an open-sided box of
5 cm expanded polystyrene slabs, placed over the instrument and taped
down to exclude draughts, makes an excellent thermal shield),
•
standing the sensor on bedrock where possible, or at least deep in
well-compacted subsoil;
•
clearing the floor of the hole of all loose material; and
•
using as little extra mass as possible in preparing the chamber.
After installation, the instrument case and mounting surface will slowly
return to the local temperature, and settle in their positions. This will take
around four hours from the time installation is completed. If you require
long-period recording, you should re-zero the instrument after this time.
3.3 Installing in vaults
You can install a 3ESPCD in an existing seismic vault with the following
procedure:
1. Unpack the sensor from its container, saving the shipping box for later
transportation.
2. Prepare the mounting surface, which should be smooth and free of
cracks. Remove any loose particles or dust, and any pieces of loose
surfacing. This ensures good contact between the instrument's feet and
the surface.
3. If it is not already present, inscribe an accurate North-South line on the
mounting surface.
4. Place the sensor over the scribed line, so that the brass and steel
pointers are aligned with the marked directions, with the brass pointer
MAN-C3E-0002 11 Issue B - November 2013