GTSM at Parkfield, California
Eades - EDT
1. 5.75 E of N
2. 125.75 E of N
3. 65.75 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 16 year record,(1986 - 2002).
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.
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. This station was taken off-line on April 24 2002, due to failure of the downhole electronics. This resulted from leakage, eventually after 16 years, from damage to the downhole cable during installation.
Data plots of interest:
Parkfield Regional Anomaly 1993-1997: multi- instrument event detail See papers.
September, 2000 Strain Creep event across the Parkfield array : tensor strain, dilatometer volumetric strain,creep detail
Selection of Characteristic Strain/Creep events at FLT: detail of several events over the years
Preliminary processing of San Simeon M6.5 as seen at our GTSM sites at DonnaLee, and Frohlich in Parkfield, and for San Juan Bautista.
Coseismic steps are approximately:-
DLT eadl 74ne, gam1dl 15.5ne, gam2dl 220ne
FLT eafl 700ne gam1fl -130ne gam2fl 890ne
SJT gam1sj -11ne gam2sj -26ne
These instruments provide strain data on
Medium term strain changes associated with earthquake activity and other fault processes.
Coseismic strain offsets useful for constraining earthquake source mechanisms,eg see San Simeon 2003, above.