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PBO BSMs : Tidal and Atmospheric Response Strainmeter Workshop Bozeman, MT, 24-26 Sept 2007

This workshop focused on comparing strainmeter measurements with known tidal signals and explaining the relationship between strain changes and atmospheric pressure variations. The participants calculated tidal corrections for specific tides and explored gauge weightings in various regions. The workshop concluded with insights on atmospheric pressure responses, gauge weightings, and the effectiveness of different methods in predicting tidal behaviors.

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PBO BSMs : Tidal and Atmospheric Response Strainmeter Workshop Bozeman, MT, 24-26 Sept 2007

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  1. PBO BSMs : Tidal and Atmospheric Response Strainmeter Workshop Bozeman, MT, 24-26 Sept 2007 Kathleen Hodgkinson

  2. Tidal Signal • Provide a known strain signal against which to compare the strainmeter measurements. • Provide a state-of-health check, amplitudes and phases should be constant with time.

  3. Tidal Correction • Calculate the phase and amplitude for the M2 and O1 tides for each gauge using BAYTAP-G. • The tidal correction can then be predicted using PIASD for any time window and sample interval . P403

  4. Atmospheric Pressure • Assume that the strain change is linearly related to atmospheric pressure change. • Calculate a coefficient that relates the change in atmospheric pressure to the change in strain using BAYTAP-G. • For PBO GTSM21s the coefficients are 2 to 10 nanostrain/millibar. P403

  5. Atmospheric Pressure Responses CH0 CH1CH2CH3 Pacific Northwest C&S Oregon ParkF Anza

  6. Barometric pressure CH0-trend CH0-trend-tide CH0-trend-pressure

  7. CH0 CH2 90° CH1 CH3 Tidal Self Consistency uo u2 u1 u3

  8. Relative Gauge Weightings CH1/CH0CH2/CH0CH3/CH0 Pacific Northwest C&S Oregon ParkF Anza

  9. PNW M2 Areal Strain PNW M2 Areal Strain B012 PGC TPXO6.2 Tide Model + Straits of Juan de Fuca B004 P403 Shores B001 Theory 20 nanostrain

  10. PNW M2 Areal Strain PNW M2 Areal Strain B012 PGC TPXO6.2 Tide Model + Straits of Juan de Fuca B004 P403 Shores B001 Hart et al., 1996 Theory Theory 20 nanostrain

  11. PNW M2 Areal Strain PNW M2 Areal Strain B012 PGC 120° 120° 30° 90° B004 P403 Shores B001 3 gauges Hart et al., 1996 Theory Theory 20 nanostrain

  12. 2 gauges 3 gauges Hart et al., 1996 Theory PNW M2 Areal Strain PNW M2 Areal Strain B012 PGC 120° 120° 30° 90° B004 P403 Shores B001 Theory 20 nanostrain

  13. 2 gauges 3 gauges Hart et al., 1996 Theory Seattle and Oregon M2 Areal

  14. 2 gauges 3 gauges Hart et al., 1996 Theory Lester, Central Oregon, B028 M2 Areal

  15. 2 gauges 3 gauges Hart et al., 1996 Theory Lester, Central Oregon, B028, B027 M2 Areal

  16. Central and Southern Oregon M2 Areal 2 gauges 3 gauges Hart et al., 1996 Theory

  17. 2 gauges 3 gauges Hart et al., 1996 Theory Grants Pass, Southern Oregon, B035 M2 Areal

  18. 2 gauges 3 gauges Hart et al., 1996 Theory Grants Pass, Southern Oregon, B035, B036 M2 Areal

  19. 2 gauges 3 gauges Hart et al., 1996 Theory Parkfield M2 Areal Strain

  20. 2 gauges 3 gauges Hart et al., 1996 Anza M2 Areal Strain

  21. 2 gauges 3 gauges Hart et al., 1996 Anza M2 Areal Strain

  22. Conclusions • Atmospheric pressure response 2-10 ns/millibars. • Relative gauge weightings generally in the 2-4 CH0 ratio range. • The Hart et al., 1996 method gives good results when comparing observed and predicted tides - disagreement suggest problems. • Better self-consistency, tidal agreement and lower response coefficients in Anza than the PMW - maybe a result of different rock type. • Expect a scatter of ~±5 degrees in M2 phase across the PBO BSM network.

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