Nanometrics Trillium Compact, User Manual

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2. Lower the seismometer into the hole and stand it upright, not touching the sides of the
hole. The seismometer should stand approximately vertical, but it does not need to be
precisely leveled since it has an internal self-leveling mechanism. The top end of the
seismometer should be at least 90 cm (3 feet) below the ground surface so that it will
be well insulated once it is buried.
3. Rotate the seismometer to align its North line to geographic North (allowing for the
local declination with a magnetic compass). See "Aligning a Trillium Compact Posthole to
North" on page 27 .
1. The recommended practices for aligning a Trillium Compact Posthole vary based on
the depth of the hole where the unit is installed.
2. For recommendations on aligning a Trillium Compact Posthole in a shallow hole of
2 m or less, see "Aligning the Trillium Compact Posthole using a Surface Line" on
page 27 .
3. For recommendations on aligning a Trillium Compact Posthole in a deeper hole, see
"Aligning the Trillium Compact Posthole using a Surface seismometer" on page 28 .
4. Stabilize the instrument by compacting sand or other fill material to ensure that the
instrument is solidly coupled to the surrounding substrate and will not shift or move. It
is preferable to use clean dry sand since it will tend to flow easily. Leave the top of the
seismometer uncovered for the time being for easy removal in case of any problem.
5. Verify that the installation is level by checking that the mass positions are within an
acceptable range (at or very close to zero).
6. To provide strain relief to the cables, leave a coil of cable near the top of the
seismometer.
7. Fill the hole to the surface and mound additional material on the hole so that water will
run off and not collect in the hole.
8. Optionally, cover the installation with a plastic ground sheet to maintain a more
constant moisture level in the sediment around the seismometer.
9. Pile additional soil or rocks on top of the ground sheet to secure it.
10. Close the hole using the appropriate method for the type of hole ensuring that the
cable is not under any strain.
11. Check the seismic outputs to verify that the unit is undisturbed.
12. Place the digitizer in its final location.
13. Install any remaining station equipment such as additional batteries, and solar
equipment.
Chapter 2 - Installing a Trillium Compact Posthole Seismometer
16889R10 • 2020-11-12 Page 23