Guralp Systems CMG-40T - Manual (Page 14)

CMG-40T
Systems; otherwise, you can use the casing of the sensor itself as a
support.
The steel sensor housing can be removed with an Allen key.
3. Whilst monitoring the mass position outputs (channels M8, M9 and MA),
adjust the potentiometers as above.
2.4 Installation notes
For the best possible results, a seismometer should be installed on a seismic pier
in a specially-built vault, where conditions are near perfect. Here, wave-trains
arriving at the instrument reflect very well the internal motion of subsurface
rock formations. However, this is not always feasible. For example,
• instruments may need to be deployed rapidly, perhaps to monitor the
activity of a volcano showing signs of rejuvenation, or to study the
aftershocks of a major earthquake;
• installations may be required in remote locations, or otherwise in
circumstances where it is unfeasible to build a vault.
In these situations, the seismometer and its emplacement need to be considered
as a mechanical system, which will have its own vibrational modes and
resonances. These frequencies should be raised as high as possible so that they
do not interfere with true ground motion: ideally, beyond the range of the
instrument. This is done by
• 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.
14 Issue A