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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

Assessing PBO Strainmeter Data Quality

August 2010

UANVCO, Boulder, Colorado


Data quality
Data Quality

  • How do you judge strainmeter quality?

  • How to decide which strainmeters to include in your analysis?



State of compression
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 compression1

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


State of compression2

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


State of compression3

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


Summary compression

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


Tidal signal
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.


Tidal signal1
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


Tidal signal2
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


Tidal signal3
Tidal Signal

B057, Lucas Valley, San Francisco

24 Hours of 1-sps Data

Digital Counts

CH0CH1CH2CH3

Extension +ve


Signal to noise ratio
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


Signal to noise ratio1
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


Signal to noise ratio2

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


Steps in the time series
Steps in the Time Series

  • ALL strainmeter data will have some steps

  • It becomes a problem when it is difficult to isolate tectonic signals


Steps in the time series1
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


Steps in the time series2

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?


Steps in the time series3
Steps in the Time Series

B072, Gold Hill2, Parkfield

  • Too many steps

  • Becomes a short period strainmeter

Digital Counts

CH0CH1CH2CH3

Extension +ve


Data steps across pbo network
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


Seismic shear
Seismic Shear

M5.7 Southern California, 2010-06-15, 04:26:58 UTC

North

B006 records no shear

South


Comparison with tidal models
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


Comparison with tidal models1
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


Self consistency
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


Self consistency1
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


Is this information online
Is this information online?

  • Information is on processed data plots

  • Documentation Page


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