GTSM at Parkfield, California
Frohlich - FLT
1. 39.75 E of N
2. 159.75 E of N
3. 99.75 E of N
Note that the gauge residuals have a Y axis scale range of +/- 4 microstrain for each component, and show that excluding known tectonic events, all variation in gauge strain rates have been less than +/- 0.1 microstrain per year for the whole of the 17 year record,(1986 - ).
The residual linear borehole recovery strain rate over the total record is shown in microstrain/year as the "slope" on each plot.
Residual data are recovered from the raw data by extracting least squares fitted exponential(s) and a linear function which describe the processes of curing of the grout and recovery of the borehole, after drilling and installation disturbance of the virgin stress field.
Regions used in the least squares fitting are marked in red on the X axis, and the fit parameters are printed in the upper panelof the figure and are also tabulated elsewhere.
In August 2003, the borehole recovery exponentials were updated from values determined in the early 1990's to incorporate the additional 10 years of data length now available. Changes of strain rates calculated from these residuals are unaffected by the exponential removal procedure and allow the very long term stability(see gauge 1 , gauge 2, and gauge 3) of the instruments to be quantified.
Raw gauge data for this site shows uphole electronics affected by diurnal temperature variations. Temperature correction is applied to linearised gauge data before producing strain data for the final archive.
Since May 2003, a non-tectonic temperature related artifact is being produced in the data stream from Channel 2, necessitating sporadic deletion of data initially, up to daily deletions in 2004. Attempts to rectify this were made on 2004 field trip without success.