GTSM at Southern California
Pinon Flat Observatory (PFT)
PFT is situated at the Pinon Flat Observatory in the mountains southwest of Palm Desert
1. 65.5 E of N
2. 5.5 E of N
3. 125.5 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 +/- 0.6 microstrain per year for the period 1987 - 1998.
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 panel of 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.
The key outcome from this site has been the study of long term stability of the system, and the development of robust calibration procedures made possible by the intensive study of this area by many workers, in particular the UCSD group. Results of these studies are included papers referenced elsewhere on this site.