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 Frequency BandCharacteristic Weeks -> yearsBorehole Compression Hours -> daysTidal Signal Step-free data sets Seconds -> HoursSeismic Shear

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

State of Compression Digital Counts B057, Lucas Valley, San Francisco Bay Area 4 gauges in compression Smooth, exponential trends Ideal Borehole Trends CH0 CH1 CH2 CH3 Extension +ve

B030, Patterson, Oregon Initial signal due to grout curing Signal turns to compression after 1-2 months Trends stabilize after ~10 months State of Compression Digital Counts Typical Borehole Trends CH0 CH1 CH2 CH3 Extension +ve

State of Compression Digital Counts 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! CH0 CH1 CH2 CH3 Extension +ve

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

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. Tidal Signal

Digital Counts CH0 CH1 CH2 CH3 Extension +ve B057, Lucas Valley, San Francisco B057, strong tidal signal Tidal signal visible in time series Dominant signal over days

Tidal Signal Digital Counts Extension +ve CH0 CH1 CH2 CH3 Extension +ve B057, Lucas Valley, San Francisco B057, strong tidal signal Tidal signal visible in time series Dominant signal over days

Tidal Signal Digital Counts B057, Lucas Valley, San Francisco CH0 CH1 CH2 CH3 Extension +ve 24 Hours of 1-sps Data

Signal To Noise Ratio Cycles per Day B087, Ford Ranch, Anza dB/cpd M2O to Expect to see peaks in the M2 and O1 tidal bands well above the background noise

Cycles per Day B017, Flink, Olympic Peninsula, dB/cpd No tidal signal to Signal To Noise Ratio Cycles per Day

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

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

B027 B028, Lester2, Central Oregon 10-minute interval gauge data Large step on only one gauge Is this tectonic? 0.9 ms Digital Counts CH0 CH1 CH2 CH3 Extension +ve

Steps in the Time Series B027 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? B028, Lester2, Central Oregon B m B027 Digital Counts 0.9 ms

Steps in the Time Series B072, Gold Hill2, Parkfield Digital Counts CH0 CH1 CH2 CH3 Extension +ve Too many steps Becomes a short period strainmeter

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

Seismic Shear M5.7 Southern California, , 04:26:58 UTC North South B006 records no shear

Comparison with Tidal Models =S. E ee +E nn E ee -E nn 2E en e0e1e2e3e0e1e2e3 M2 & O1 Tidal Prediction = S. Gauge Elongation No assumptions about: Orientation Shear and areal scale factors Relative gauge weightings

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

Self Consistency Two sets of equally spaced gauges allows examination of self consistency in the tidal band 120° CH0 CH2CH1 120° 90° CH3 CH1 3 gauge shear strain (4xCH1-2xCH2-2xCH0)/3 2 gauge shear strain CH1-CH3

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

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