Surface deployed Distributed Acoustic Sensing (DAS) for seismic monitoring: An example of the Stanford Array Data

Gang Fang*, Yunyue Elita Li, Yue Du, Joseph Ho Yin Ma, Eileen Martin and Diming Yu

2018-5-18

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Near-surface geohazards in urban environments

➢ Urban sinkhole

A sinkhole appeared in the centre lane of Clementi Road of Singapore on 06 Mar 2013

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➢ Urban sinkhole

A sinkhole appeared in the centre lane of Clementi Road of Singapore on 06 Mar 2013

Near-surface geohazards in urban environments

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A giant sinkhole caused by the rains

of tropical storm Agatha in Guatemala

City, June 2010. At least 175 people

are killed in this disaster.

➢ Urban sinkhole

Near-surface geohazards in urban environments

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Landslide in eastern China on Nov 16, 2015 that has killed at least 25 people. Shenzhen landslide on 20 December 2015, 73 people was dead and 4 people

reported missing.

➢ Landslide

Near-surface geohazards in urban environments

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• Distributed Acoustic Sensing (DAS)

• Near-surface monitoring with Stanford DAS data

Outlines

6

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Distributed Acoustic Sensing (DAS)

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Distributed Acoustic Sensing

It is a laser-based sensor system measuring vibration along the

length of a fiber optic sensing cable.

DAS Advantages:

✓Non-intrusive

✓Permanent

✓Low-cost

✓High spatial resolution

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➢ DAS VSP

• Hydraulic fracturing characterization

• Time-lapse monitoring of the reservoirs fluids

• CO2 injection monitoring

➢ Surface DAS

• Earthquakes analysis

• Near surface geophysical detection

(From OptaSense)

(Lindsey et al. 2017)

Distributed Acoustic Sensing

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Near-surface monitoring with Stanford DAS data

10

⚫ Stanford DAS Array

⚫ Quarry blasts data

⚫ Seismic interferometry

⚫ Construction monitoring

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Stanford DAS Array

Layout of Stanford DAS Array （Biondi et al., 2017）

Construction sites138

156

241

48

5277

108

184 Fiber line

184 Channel number

Front array

Back array

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138

156

241

48

5277

108

184

Stanford DAS Array

Layout of Stanford DAS Array （Biondi et al., 2017）

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138

156

241

48

5277

108

184

Stanford DAS Array

Layout of Stanford DAS Array （Biondi et al., 2017）

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138

156

241

48

5277

108

184

DAS Array parameters

- 2 x 2.45 km fiber-optic cable

- 2 x 305 channels

- ~8 m sensor spacing

- 7 m gauge length

- Continuous recording

- 0-25 Hz digital recording

- OptaSense DAS (ODH 3.1)

- Single-mode fibre

Stanford DAS Array

Layout of Stanford DAS Array （Biondi et al., 2017）

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Near-surface monitoring with Stanford DAS data

15

⚫ Stanford DAS Array

⚫ Quarry blasts data

⚫ Seismic interferometry

⚫ Construction monitoring

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Quarry blasts data

138

156

241

48

5277

108

184

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Construction A is begin at

2016/11/7.Compare blast

data before and after the

construction.

Challenges:

• High frequency noise

Quarry blasts data — raw data

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Quarry blasts data — BP filtering(0.25~2.5HZ)

Construction A is begin at

2016/11/7.Compare blast

data before and after the

construction.

Challenges:

• High frequency noise

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Quarry blasts data — Surface wave

Construction A is begin at

2016/11/7.Compare blast

data before and after the

construction.

Challenges:

• High frequency noise

Surface waves from a blast

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Traffic noise

Quarry blasts data — Traffic noise

Construction A is begin at

2016/11/7.Compare blast

data before and after the

construction.

Challenges:

• High frequency noise

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Traffic noise

Quarry blasts data — Traffic noise

Construction A is begin at

2016/11/7.Compare blast

data before and after the

construction.

Challenges:

• High frequency noise

• Traffic noise

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2016/10/12 2016/11/15

Challenges:

• High frequency noise

• Traffic noise

• Inconsistent source wavelets

Quarry blasts data — Denoise

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2016/10/12 2016/11/15

Solution:

• Seismic interferometry

Challenges:

• High frequency noise

• Traffic noise

• Inconsistent source wavelets

Quarry blasts data — Denoise

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Near-surface monitoring with Stanford DAS data

24

⚫ Stanford DAS Array

⚫ Quarry blasts data

⚫ Seismic interferometry

⚫ Construction monitoring

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Seismic interferometry

RS

RA

RB

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Seismic interferometry

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Wavefield at RA :

Wavefield at RB :

Seismic interferometry

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Source wavelet

Wavefield at RA :

Wavefield at RB :

Seismic interferometry

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Source wavelet

Green function

Seismic interferometry

Wavefield at RA :

Wavefield at RB :

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Cross-correlation :

Source wavelet

Green function

Seismic interferometry

Wavefield at RA :

Wavefield at RB :

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Cross-correlation :

Source wavelet

Green function

Seismic interferometry

Wavefield at RA :

Wavefield at RB :

Redatum the source position from RS to RA.

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Cross-correlation :

Source wavelet

Green function

Seismic interferometry

Wavefield at RA :

Wavefield at RB :

Redatum the source position from RS to RA.

Normalized Cross-correlation :

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Cross-correlation :

Source wavelet

Green function

Seismic interferometry

Wavefield at RA :

Wavefield at RB :

Redatum the source position from RS to RA.

Normalized Cross-correlation :

Remove the influences from amplitudes.

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Near-surface monitoring with Stanford DAS data

34

⚫ Stanford DAS Array

⚫ Quarry blasts data

⚫ Seismic interferometry

⚫ Construction monitoring

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Applied normalized cross-correlation

Wavelets of virtual source

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Normalized Cross-correlation :

Applied normalized cross-correlation

Wavelets of virtual source

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Normalized Cross-correlation :

Applied normalized cross-correlation

Wavelets of virtual source

Spectra of the normalized cross-correlation

2016/10/12

2016/11/15

0

0.6

1.2

0 1 2 3 4 5

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Velocity changes

Normalized cross-correlation

Calculated time-delays according to the reference velocity, 816m/s

Picked time-delays of the normalized cross-correlation

Front Back

2016/10/12Front Back

2016/11/15

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• Surface DAS

An efficient geophysical tool to monitor near-surface changes;

• Normalized cross-correlation interferometry method

Detect subsurface velocity changes caused by the basement construction;

• Passive seismic monitoring

Uneven coupling, strong traffic noise …

Kinematic information is more reliable than amplitude information.

Conclusions

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◆ Thanks Biondo Biondi for providing the data.

◆ Thanks Siyuan Yuan for discussion.

◆ Thanks all developers of Madagascar.

Acknowledgements

40

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Continuous seismic data acquisition system➢ Geophone seismic array ➢ Surface DAS seismic array

• long-term costs: expansive

• spatially sparse dataset

• long-term costs: low

• spatially dense dataset

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Repeatability of the blasts data

43

2016/11/4 2016/9/14

JRSC seismometer

Lindsey et al. 2017, Fiber-Optic Network Observations of Earthquake Wavefields, Geophysical Research Letters, 44, 11,792–11,799

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Earthquakes analysis

Lindsey et al. 2017, Fiber-Optic Network Observations of Earthquake Wavefields, Geophysical Research Letters, 44, 11,792–11,799

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Distributed Acoustic Sensing

The strain rate is proportional to extension (compression) of fiber

between two points a gauge length apart.