Geostuff offers a selection of wall-lock borehole geophones. Model BHG-2 contains a 3-component geophone in an X-Y-Z orientation. The outside diameter is 1.85 inches (47 mm), small enough to fit inside a schedule-40, 2-inch plastic pipe. The clamping mechanism is a robust, steel spring compressed by a DC electric motor.There are no rubber bladders to break or tubes to leak, and operation is relatively independent of depth. BHG-2 models have been used to depths of 500 meters. Geophone elements are available with 10, 14, 28 or 40 Hz natural frequencies.
This unit is also available as the BHG-2C with a flux-gate compass which will indicate the orientation of the geophone in the hole (except for steel-cased holes). Interest is growing in horizontal anisotropy as awareness of the problem increases.