Guralp Systems CMG-40T - Manual (Page 19)

Operator's guide
3.2 Installing in pits
For outdoor installations, high-quality results can be obtained by constructing a
seismic pit.
Depending on the time and resources available, this type of installation can suit
all kinds of deployment, from rapid temporary installations to medium-term
telemetered stations.
Ideally, the sensor should rest directly on the bedrock for maximum coupling to
surface movements. However, if bedrock cannot be reached, good results can be
obtained by placing the sensor on a granite pier on a bed of dry sand.
1. Prepare a hole of 60 – 90 cm depth to compacted subsoil, or down to the
bedrock if possible.
2. On granite or other hard bedrock, use an angle grinder to plane off the
bedrock at the pit bottom so that it is flat and level. Stand the instrument
directly on the bedrock, and go to step 7.
3. On soft bedrock or subsoil, you should install a pier as depicted below.
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