Guralp Systems CMG-6T - Manual (Page 12)

CMG-6T
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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;
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installations may be required in remote locations, or otherwise
in circumstances where it is infeasible 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
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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.
In temporary installations, environmental factors are also important.
The sensor needs to be well protected against
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fluctuations in temperature,
•
turbulent air flow around walls or trees, or around sharp
corners or edges in the immediate vicinity of the sensor;
•
vibration caused by heavy machinery (even at a distance), or by
overhead power lines.
This can be done by selecting a suitable site, and 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.
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.
2.7 Installing in vaults
You can install a CMG-6T in an existing seismic vault with the
following procedure:
12 Issue B