How sensitive are the gauges?
A single unit of measurement for our gauges represents 4pm of diameter change. This is 4 x 10 12 m, or 1/25 the radius of a hydrogen atom, or one ten millionth of the width of a human hair. This represents a strain of about 0.05 nano strain. The ground noise present in a borehole limits the useful sensitivity range, and depends on the time duration of the phenomena under study. Short term signals (such as seismic waves) are measured to about 0.1 nanostrain. Daily changes in earth strain are normal at about 1 nanostrain, and these normal changes further limit useful sensitivity measured to about 1 nanostrain (1 ne ).
