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Assessing PBO Strainmeter Data Quality

Assessing PBO Strainmeter Data Quality. August 2010 UANVCO, Boulder, Colorado. Data Quality. How do you judge strainmeter quality? How to decide which strainmeters to include in your analysis?. Basic BSM Characteristics. State of Compression.

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Assessing PBO Strainmeter Data Quality

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  1. Assessing PBO Strainmeter Data Quality August 2010 UANVCO, Boulder, Colorado

  2. Data Quality • How do you judge strainmeter quality? • How to decide which strainmeters to include in your analysis?

  3. Basic BSM Characteristics

  4. State of Compression • Gladwin Tensor Strainmeters are designed to operate in a state of compression. • Dominant trend over weeks to years should be that of borehole compression

  5. CH0CH1 CH2CH3 Extension +ve State of Compression B057, Lucas Valley, San Francisco Bay Area Digital Counts Ideal Borehole Trends • 4 gauges in compression • Smooth, exponential trends

  6. CH0CH1 CH2CH3 Extension +ve State of Compression B030, Patterson, Oregon Typical Borehole Trends Digital Counts • Initial signal due to grout curing • Signal turns to compression after 1-2 months • Trends stabilize after ~10 months

  7. CH0CH1 CH2CH3 Extension +ve State of Compression B075 Flenge Flat , Parkfield Problem with Compression • No gauges in compression at this time • Not operating under the conditions for which it was designed • User beware! Digital Counts

  8. 1 April 2020 - 1 July 2010 Number of Gauges in Compression Strainmeters Summary: Compression • Ideally, you should have 3 gauges in compression • 72% of PBO BSMs are in compression State of Compression: PBO BSM Network

  9. Tidal Signal Strainmeters are optimized for the tidal band • Tides should be dominant signal over hours to days • Expect to see peaks in the M2 and O1 tidal bands well above the background noise.

  10. Tidal Signal B057, Lucas Valley, San Francisco Digital Counts • B057, strong tidal signal • Tidal signal visible in time series • Dominant signal over days CH0CH1CH2CH3 Extension +ve

  11. Tidal Signal B057, Lucas Valley, San Francisco Extension +ve Digital Counts • B057, strong tidal signal • Tidal signal visible in time series • Dominant signal over days CH0CH1CH2CH3 Extension +ve

  12. Tidal Signal B057, Lucas Valley, San Francisco 24 Hours of 1-sps Data Digital Counts CH0CH1CH2CH3 Extension +ve

  13. Signal To Noise Ratio Expect to see peaks in the M2 and O1 tidal bands well above the background noise B087, Ford Ranch, Anza 2007-01-01 to 2010-01-01 dB/cpd O1 M2 Cycles per Day

  14. Signal To Noise Ratio Expect to see peaks in the M2 and O1 tidal bands well above the background noise B017, Flink, Olympic Peninsula, 2007-10-18 to 2010-01-01 dB/cpd No tidal signal Cycles per Day Cycles per Day

  15. O1 M2 Signal To Noise Ratio Each strainmeter should have an SNR > 10 93% have M2 SNR > 10, 81% have O1 SNR > 10 Average Signal to Noise Ratio in the Tidal Band 1 March 2010 - 1 July 2010 SNR Strainmeters

  16. Steps in the Time Series • ALL strainmeter data will have some steps • It becomes a problem when it is difficult to isolate tectonic signals

  17. Steps in the Time Series B028, Lester2, Central Oregon • 10-minute interval gauge data • Large step on only one gauge • Is this tectonic? B027 Digital Counts 0.9 ms CH0CH1CH2CH3 Extension +ve

  18. B027 420 m B028 Steps in the Time Series B028, Lester2, Central Oregon B027 Digital Counts 0.9 ms • Is the step on all gauges ? • Is is recorded by any nearby instruments? • What is the size of the step? • Does the step interfere with interpretation?

  19. Steps in the Time Series B072, Gold Hill2, Parkfield • Too many steps • Becomes a short period strainmeter Digital Counts CH0CH1CH2CH3 Extension +ve

  20. Data Steps Across PBO Network • 80% of the strainmeters are relatively free of steps Number of Gauges Free of Data Steps 1 April 2010- 1 July 2010 Number of Gauges Strainmeters Assessed using CleanStrain+, Langbein, 2010

  21. Seismic Shear M5.7 Southern California, 2010-06-15, 04:26:58 UTC North B006 records no shear South

  22. Comparison with Tidal Models M2 & O1 Tidal Prediction = S . Gauge Elongation e0 e1 e2 e3 Eee+Enn Eee-Enn 2Een . = S • No assumptions about: • Orientation • Shear and areal scale factors • Relative gauge weightings

  23. Comparison with Tidal Models • 74% of strainmeters have an RMSE of < 2 • Vancouver Island sites have a poor fit, complicated regional tides Comparison of M2 and O1 Areal and Shear Strains To Models 1 April 2010- 1 July 2010 Vancouver Island RMSE Bay Area Strainmeters

  24. Self Consistency Two sets of equally spaced gauges allows examination of self consistency in the tidal band CH0 120° 120° 120° 90° CH2 CH1 CH1 CH3 3 gauge shear strain (4xCH1-2xCH2-2xCH0)/3 2 gauge shear strain CH1-CH3

  25. Self Consistency • Self consistency suggests gauge weighting is about equal • 40% differ < 5°, 68% differ < 15° Comparison of Shear Strain M2 Phase Difference between 2-gauge and 3-gauges phase +15° Difference in Phase -15° 1 April 2010- 1 July 2010 Strainmeters

  26. Is this information online? • Information is on processed data plots • Documentation Page

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