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

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

27. 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.