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Long-term trends in PBO BSMs

Long-term trends in PBO BSMs. Bozeman, September 23-26, 2007 Kathleen Hodgkinson - UNAVCO. Why model the trends?. Over periods of weeks to years borehole trends dominate borehole strainmeter data.

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Long-term trends in PBO BSMs

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  1. Long-term trends in PBO BSMs Bozeman, September 23-26, 2007 Kathleen Hodgkinson - UNAVCO

  2. Why model the trends? • Over periods of weeks to years borehole trends dominate borehole strainmeter data. • The trend generated by borehole deformation must be removed to identify transients of that period.

  3. Current modeled borehole trends • PBO provides a very simple model of the borehole trend as a Level 2 products. • Currently the trend is modeled by fitting a linear term plus one to two exponentials to the data.

  4. Why ? • Used in the past. • Reduces likelihood of removing the transient with the trend. • Transparency: users can regenerate trend Really just an average trend over the instrument lifetime, secondary detrending usually needed.

  5. Why ? • Used in the past. • Reduces likelihood of removing the transient with the trend. • Transparency: users can regenerate trend • Shortcomings: Really just an average trend over the instrument lifetime, secondary detrending usually needed.

  6. B004, Hoko Falls, PNW

  7. Why is it important?

  8. Current Method • Forward modeling, then an inversion to get the best fitting set of parameters. • Model updated every 3 to 4 months. • Parameters determined 3 months ago are used as the starting point.

  9. B087, Ford Ranch, Anza Installed June 2006

  10. B087, Ford Ranch, Anza Data up to April 4, 2007 microstrain CH2 Days since install

  11. B087, Ford Ranch, Anza ch2=10.758+30.294*exp(-0.00925*t)-0.043*t Data up to April 4, 2007 microstrain CH2 Model Days since install

  12. B087, Ford Ranch, Anza ch2=10.758+30.294*exp(-0.00925*t)-0.043*t Data up to July 13, 2007 microstrain CH2 Model Days since install

  13. B087, Ford Ranch, Anza ch2=10.758+30.294*exp(-0.00925*t)-0.043*t ch2=12.519+36.327*exp(-0.00681*t)-0.025*t Data up to July 13, 2007 microstrain CH2 Model Updated Model Days since install

  14. B087, Ford Ranch, Anza ch2=10.758+30.294*exp(-0.00925*t)-0.043*t ch2=12.519+36.327*exp(-0.00681*t)-0.025*t microstrain Days since install

  15. Areal and shear trends • Once the trend is estimated for each gauge they are combined into trend for the areal and shear trends.

  16. Do PBO BSMs exhibit classic trends? • BSMs exhibiting classic trends • Transients superimposed • BSMS exhibiting non-classic trends • Data good quality • BSMs non-classic trends • Steps, unexplained transients

  17. B004 Hoko Falls microstrain

  18. B004 Hoko Falls Heavy rainfall 3-6 Nov 2006 microstrain

  19. B011 PGC-3 Trend

  20. BSM Trends

  21. BSMs with classic trends C&S OR B028 B035 B036 ParkF B073 Anza B081 B082 (p) B084 B086 B087 B089 (p) MSH B202 B203 B204 SJB PNW B001 (p) P403 (r) B004 B012 B017 B018 B022 (r)

  22. Non-classic trends, but good data PNW B005 B006 B009 B011 Oregon B027 ParkF Anza B088? MSH SJB

  23. Non-classic trends, poor data PNW B007 B010 B013 Oregon B026 ParkF B072 B075 B076 B078 B079 B900 Anza MSH SJB B058 B065 B067

  24. Conclusion • Currently only providing trends for a subset of BSMs • Probably could improve on what we are doing • Even BSMs with classical trends show residual trends • Spline fits or lowpass filtering may give a better result BUT they have to be produced consistently for all BSMs • No reason to describe non-classic trends as suspect • Amy’s poroeslastic work suggests otherwise • Set of BSMs that have poor quality data • Detrending may be valid over short time periods

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