Broadband Element Installation

The KS36000 posthole seismometer.
Paul Golden and Karl Thomason prepare the KS36000 posthole instrument for installation in a sand-packed borehole.

Originally designed to be installed in deep (100 meter) boreholes, the KS36000 and subsequent KS54000 are standard instruments used in sites across the world. By installing them in deep boreholes, the effect of wind noise is diminshed at the longer periods. The consturctuion of a deep borehole and subsequent instrument installation is a complex expensive operation. If a site is sufficiently quiet, or the longer periods are only of secondary interest, then a shallow posthole installation can provide substantial savings while still producing an instrument superior to most vault installations.

The posthole KS36000 ready to be lowered into the borehole.
Lowering was done by hand using the pulley and small A-frame.

The posthole version of the instrument requires none of the complex remote leveling mechanisms, does not require a hole lock or the equipment to install it. It also does not require a winch or leasing expensive orientation equipment. In the event there is a problem, pulling the instrument is a simple operation that does not usually result in instrument damage. In fact, this particular instrument was pulled for testing and reinstalled within a morning.

Examining the position and orientation of the instrument and cable prior to pouring the final sand pack. The bags in the foreground are full of sand-blasting sand, used in the sand pack.

Once the instrument is in place in the borehole (in this case a 9" diameter 20 foot deep cased hole), fine sand is poured around it to firmly couple it to the surrounding rock. The instrument is mechanically leveled from the surface (which sets a practical limit on the depth of the posthole) with long rods. Once leveled, as observed from the output, additional sand is added.

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