Preliminary Results from a Shallow Borehole Tilt Array,

A shallow borehole tilt array has been installed within the boundaries of a deep borehole tilt array. Preliminary conclusions are: (1) Rainfall has obvious transient influences on the tilt signal, and may also be causing long term changes in drift rate and direction; (2) Diurnal tilts appear to be contaminated with thermal-elastic and direct temperature effects; (3) Barometric pressure fluctuations do not cause any noticeable variation in the tilt signal; and (4) A cursory attempt to pack the sand, by banging on the installation pipe, appears to have reduced the instrument drift. It is possible that some or all of the above effects can be removed by the appropriate data analysis techniques. (Author)