Signals and Trendsin Borehole Strainmeter Data

Signals and Trendsin Borehole Strainmeter Data

Strainmeter Short Course2009 Earthscope Meeting, Boise

May 12, 2009

Strainmeter Short Course2009 Earthscope Meeting, Boise

May 12, 2009

Signals and Trends

• State of borehole compression

• Earth tides

• Barometric pressure response

• Seismic signals

• Non-tectonic signals

• Strain transients

Trends: Borehole• Dominant signal over months is borehole relaxation.

• Long term trend should be areal compression.

3 gauge areal strain = (CH0+CH1+CH2)/3

120° 120°

90°

CH0

CH2 CH1

30°

Trends: Borehole

Extension +ve

areal strain=(CH0+CH2+CH3)/3

“Classic Trends”

Dig

ital C

ou

nts

(x1

03)

21

.3 M

icro

stra

in

Compression -ve

B087, Ford Ranch

Trends: Borehole

Extension +ve

Dig

ital C

ou

nts

(x1

03)

0.4

Mic

rost

rain

Compression -ve

B087, Ford Ranch

Network State of Compression

Extension +ve

Com

pre

ssio

n R

ate

(n

an

ost

rain

/day)

Compression -veDecember 15, 2008 - April 15, 2009

Extension +ve

Compression -ve

PBO BSM Network, Compression Rate74% in compression

Days since installation

Extension and steps

B040 , York, Northern California

GTSM21 designed to operate under compression

Dig

ital C

ounts

(x1

03)

14

7.3

M

icro

stra

in

16

.6 M

icro

stra

in

Extension and steps

B040 , York, Northern California

Dig

ital C

ounts

(x1

03)

More likely to see steps in non-compressional BSM

21% of BSMs record steps58% of non compressional BSMs record steps

Extension and steps

B040 , York, Northern California

Rate of steps decrease as BSM turns to compression

Dig

ital C

ou

nts

Dig

ital C

ounts

(x1

03)

2.7

Mic

rost

rain

Extension and steps

Source of step unknown:Nothing on other gaugesNothing on B009 or B011

16

.8

Mic

rost

rain

B010, PGC, Vancouver Island, Canada

Dig

ital C

ou

nts

(x1

03)

B009

B010

B011168m

250m

Trends: Seasonal

B009, PGC

B009, PGC, Vancouver Island, Canada

Dig

ital C

ounts

(x1

03)

Trends: Seasonal

B009, PGC

B009, PGC, Vancouver Island, Canada

mic

rost

rain

Herb Dragert reports farmer irrigating fields

Hydrostatic CouplingB006, Shores, Washington

Possibly hydrologically coupled• Little or no shear strain• Drifting phase in tidal signal• Little strain accumulated over 3.5 years

4.3

M

icro

stra

in

Dig

ital C

ou

nts

(x1

03)

Tidal signal

• Expect optimal performance in the tidal band

• M2 and O1 peaks should be visible in the spectrum

• Areal and shear consistency

Tidal signal

CH0

CH1

CH2

CH3

mic

rost

rain

B018, Delphi, Seattle, WA

Detrended gauge data

Tidal signal

M2O1

dB/c

pd

Band passed gauge data, 0.25 to 4 cpd (3 years)

B018 Delphi, Seattle, WA

Tidal Consistency

120° 120°

CH0

CH2 CH1

120°90°

CH3

CH1

3 gauge areal strain(CH0+CH1+CH2)/3

2 gauge areal strain(CH1+CH3)/2

Tidal Consistency

Areal ±10° 69% Shear ±10° 65%

Areal ±25 44% Shear ±25% 65%

Strainmeters

M2

Pha

se D

iffer

ence

M2

Am

plit

ude

Rat

io

B018, Delphi, Seattle, WA

Barometric Response

Barometric Pressure

mbar

Pressure increase = gauge compression

CH0

CH1

CH2

CH3

mic

rost

rain

Tides removed

Barometric Response

Barometric Pressure

mbar

CH0

CH1

CH2

CH3

mic

rost

rain

B018, Delphi, Seattle, WA

Pressure increase = gauge compression

Tides & barometric response removed

Barometric Response

Average barometric response coefficients

ParkfieldOlympic P.

Strainmeters

Anza MSH YSOR N.C Mojave

• Typical Range 2-10 nanostrain/millibar

9-12 second calibration signal, 30 minutes past the hourNull point before and after signal

9-12 second calibration signal, 30 minutes past the hourNull point before and after signal

High frequency signalsD

igit

al C

ou

nts

(x1

06)

B022 , May 31, 2008, 1-sps data

B022 , May 31, 2008, 1-sps data

High frequency signalsD

igit

al C

ou

nts

B022 Spectrogram, May 31, 2008

B006

M6.6 Mid Indian Ridge

Calibration spikes

MicroseismCH1

CH2

CH0

CH3

Seismic Shear: M5.4 LA, July 29, 2008

March 19, 2009

M7.6 Tonga, March 19, 2009

Olympic Peninsula: Seismic Shear

Non Tectonic Signals

Noise: Rainfall

• Several of the PBO BSMs show strain signals

correlated with rainfall

• When looking at transients check the rainfall

measurements, all PBO sites have rain gauges

Noise: B022 RainfallB022, Oregon CoastB022, Seaside, Oregon Coast

Site in river flood plain, prone to floodingD

igita

l Cou

nts

Rainfall (m

m/hr)

Noise: Pathfinder, Anza

Co-located, Pathfinder strainmeters

Mic

rost

rain

B082

B089

Mic

rost

rain

CH0 CH1 CH2 CH3

Noise: Pathfinder, Anza

Co-located, Pathfinder strainmeters

B082

B089

Mic

rost

rain

Mic

rost

rain

Noise: B001 PumpingB001, Golbeck, Washington

Dig

ital C

ou

nts

0.1

M

icro

stra

in

2 gauges compression2 gauge in extension

PNW: B001 B045 Anza: B082 B089 B088

Noise: StormsD

igit

al C

ou

nts

(x1

03)

B012, Ucluelet, Vancouver Island, Canada

February 4, 2006 February 4, 2006 February 5, 2006

Noise: Downhole TemperatureB022, Seaside, Portland

Cou

nts

Tem

perature °C

Downhole Temperature

Dig

ital C

ou

nts

(x1

03)

Increase in downhole temperature=> compression

Noise: Downhole TemperatureB012 restart, February 11, 2009

Tem

perature °CDownhole Temperature

Dig

ital C

ou

nts

(x1

03)

Instrument restart

Increase in downhole temperature=> compression

Solar Noise

• Noise is introduced when solar panels start to

charge up in early morning.

• Visible in the 1 and 20-sps data set.

• PBO engineers found that rerouting cables helped.

Solar Noise: 1 spsB916, Mojave, March 20, 2008B058 2009:083 1sps Spectrum

CH1

CH2

CH0

CH3

Solar Noise: 20 sps

CH1

CH2

CH0

CH3

B916, Mojave, March 25, 2008

Tectonic Signals

A Strain Transient: Cascadia ETS

B012 B009

B004

B003

B005-7 B001

Cascadia Episodic Tremor and Slip

A Strain Transient: Cascadia ETS

B012 B009

B004

B003

B005-7 B001

B018

Cascadia Episodic Tremor and Slip

B004, Hoko Falls, WA

2Ene Strain

Eee-Enn

Cascadia Episodic Tremor and Slip

2Ene Strain

2Ene Strain

Eee-Enn

2007 Tremor

2005 TremorB004

B004

mic

rost

rain

mic

rost

rain

Cascadia Episodic Tremor and Slip

2Ene Strain

2008 TremorB004

mic

rost

rain

Spring 2008 Cascadia ETS

B012 B009

B004

B003

B005-7 B001

B018

mic

rost

rain

Pacific Northwest BSMs: Shear strain

propagation of tremor (www.pnsn.org)

May 4

May 15

May 31

April 2008 May 2008

2009 Cascadia ETS ?

B012 B009

B004

B003

B005-7 B001

B018

Pacific Northwest BSMs: Shear strain

mic

rost

rain

April 2009 May 2009

ETS March 2009, B012, Vancouver Island

B012, Ucluelet, March 2009: Processed Gauge Data

mic

rost

rain

Detrended gauge dataTide removedTide and pressure removed

ETS March 2009, B012, Vancouver Islandm

icro

stra

in

Tensor Strain

Detrended gauge dataTide removedTide & pressure removed

Creep Events, ParkfieldMiddle Mountain Area, Parkfield

PBO-BSM

PBO-BSM

Creep Events, Parkfield

Middle Mountain Area, Parkfield

PBO-BSM

PBO-BSM

2Ene Strain

Eee-Enn

B073 Varian, Parkfield

mic

rost

rain

Right lateral creep events

Creep Events, ParkfieldB073 Varian, Parkfield

1-sps Gauge Data

Yellowstone Tremor

Yellowstone Tremorm

icro

stra

in

2Ene Strain Eee-Enn Eee+Enn

B208, Lake Junction, YellowstoneD

ec 2

7 M

3.5

Dec

29

M3.

9

Jan

2 M

3.5

Detrended areal and shear strain