2053-37 Advanced Workshop on Evaluating, Monitoring and...

2053-37

Advanced Workshop on Evaluating, Monitoring and CommunicatingVolcanic and Seismic Hazards in East Africa

David Mencin

17 - 28 August 2009

UNAVCO, BoulderUSA

Borehole Strainmeters

The EarthScope Plate Boundary Observatory

Borehole Strainmeters

David MencinSenior Engineer

BSM/Seismic Operations Manager

2009 ICTP East Africa Volcanic and Seismic Hazards August 26th, 2009

Wednesday, August 26, 2009

What is a strainmeter?

• A strainmeter measures the relative displacement of points within a body.

• A borehole strainmeter is cemented into the bottom of a hole and measures the change in the shape of the hole over time.


What is a strainmeter?

Gladwin Strainmeters

•8 feet long , 110 lbs.

•4 strain gauges

• Sensitivity: 4 pmeters ~ one ten millionth the width of a human hair

•Range: 0.05 ns to 100’s ms


Strain Gauge Cross-section

Three steel plates act as capacitors

free plate

fixed gap

4’’

Free plate moves as hole is squeezed, causes change in capacitance

Two fixed plates

Ratio of the gap between each set of plates is converted to change in strain.


Tensor Strainmeters

•Three gauges oriented at 120°

•Fourth gauge gives redundancy

CH0

CH2 CH1

CH3

120° 120°

90°30°


Period (s)

Strain Rate Sensitivity

Period (s)

Strain Rate Sensitivity

Strainmeters in PBO

GPSSAR

Plate Boundary Strain Rates


0

20

40

60

80

100

120

1980 1985 1990 1995 2000 2005 2010

Pre-PBO Installations

Year

US Borehole Strainmeter Installations

miniPBO

HI

Bay AreaParkfield

Experiment

S.Cal

SJB

LA

Nu

mb

er

of

str

ain

me

ters

PBO

2 bsm/yr

21 bsm/yr


BSM & Seismic Stations

Region BSM Installations

Vancouver Island, BC 7

Olympic Peninsula, WA 14

Oregon & N. California 14

Mt. St. Helens, WA 4

Yellowstone, WY 5

Mendocino, CA 4

San Francisco, CA 2

San Juan Bautista, CA 4

Parkfield, CA 8

Mojave, CA 4

Anza, CA 8

TOTAL 74


InstallationAcoustic Televiewer

Image


Installation


Strainmeter Site

• Strainmeter

• Seismometer

• Barometer

• Rainfall Gauge

• Temperature sensor

• Pore Pressure Sensor

• Tiltmeter

• Accelerometer

• GPS


Processed Strainmeter Data

Product Method

Borehole Trends Modeled using linear & exponential terms

Tidal Model BAYTAP-G, PIASD

Barometric Response BAYTAP-G, PIASD

Offset Estimation TSVIEW, PIASD

Areal and shear strain Generated with nominal scale factors


Performance Metrics

•� State of borehole compression

•� Presence of steps in data

•� Barometric response

•� Instrument self consistency

•� Comparison with tidal models

•� Seismic shear signals

LO

W F

RE

QU

EN

CY

TID

AL B

AN

D

SE

ISM

IC


-60

-40

-20

0

20

40

0 100 200 300 400 500

CH0

CH1

CH2

CH3

Borehole Compression

B028 Lester , Central OregonM

icro

str

ain

Days since installation

March 2007 September 2008

Extension +ve

Areal Strain

CH0

CH2 CH1


BSM Performance

74% of PBO BSMs in compression

PBO Borehole Compression Rates

•� Dominant trend should be borehole compression

•� Lack of compression may indicate poor coupling

December 15, 2008 - April 15, 2009

Compression -ve

Extension +ve


-0.4

-0.2

0

0.2

0.4

10-May-2008 14-May-2008 18-May-2008-0.4

-0.2

0

0.2

0.4

10-May-2008 14-May-2008 18-May-2008

Strain Tides

Barometric pressure increase = gauge compression

CH0

CH1

CH2

CH3

mic

rostr

ain

Barometric Pressure

100

102

KP

a

CH0

CH1

CH2

CH3

Barometric Pressure

B018, Delphi, Seattle


Strain Tides

B087: Ford Ranch, Anza

O1 M2

Power Spectral Density: Strain Data

Power Spectral Density: Barometric Data

Pow

er/

Fre

quency (

dB

/cpd)

Pow

er/

Fre

quency (

dB

/cpd)


BSM Performance

•� 99% of the BSMs record seismic shear N

an

ostr

ain

B011

B010

B009

B007

B006

B005

B001

B003

B004

PG

C, B

.C.

Sh

ore

s, W

A

Magnitude 7.6 - Tonga 2009 March 19 18:17:40 UTC

Three gauge shear strain


BSM Performance

Metric Performance

State of borehole compression 74% in compression

Presence of steps in the data 79% have minimal steps

Self consistency in M2 tidal band

Amplitude 44-65 % self consistent

Phase 65-69% self consistent

Comparison to tidal models 73% RMSE < 1.5

Barometric Response 76% range < 50% of CH0

Seismic shear 99% record seismic shear

LO

W F

RE

QU

EN

CY

TID

AL B

AN

D

SE

ISM

IC


Cascadia ETS Time Series

Cascadia Episodic Tremor and Slip

2007 Tremor

B012 B009

B004

B003

B005-7 B001

B018

propagation of tremor (www.pnsn.org)

May 4

May 15

May 31

B018

gggaaaaaaaaaaaaaaatttttttttttttttttttttttttiiiiiion of treeeeeeeeeeemmmmoooooooooooooooorrrppppppppppnnnnnnnnnnnnnnnnnnnssssssssssssssssssnn.oorrrrggg))))))

M


But what else?

Tremor & Slip Data for Southern Vancouver Island

1. Blue Dots: Changes in daily east-west position wrt Penticton

1.

2.

2. Green Line: Long-term (interseismic) linear motion

3.

3. Red Lines: Short-term (inter-slip) linear motion followed by reversals

4.

4. Blue graph: Tremor activity on southern Vancouver Is.

Question: What about the tremor activity between resolved slip events?

Dragert, 2007Wednesday, August 26, 2009

Nov 2006Tremor Region

Jan/Feb 2007Tremor Region

Need higher resolution

24

16

8

Tremorhrs/day

24

16

8

Tremorhrs/day

Dragert, 2007


Higher Resolution

Gamma1

Gamma2

Areal

TofinoDaily

Rainfall

B012 Smoothed Residual Strain Components

Period ofPronounced tremor

activity

}Hrs of TremorPer Day

0

12

24

10

0 n

str

ain

12

0 m

m

Dragert, 2007

Small, more randomly occurring tremor episodes are accompanied by crustal strain changes that are not well resolved by GPS but are clearly observable by PBO BSM’s.

Strain patterns can be replicated by elastic slip dislocation on simple asperities, suggesting that shorter and prolonged ETS events are identical in nature, differing mainly in the size of the slip asperity.


Creep Events

Parkfield , Central California

Varian Donna Lee

San A

ndreas Fault

Frolich

2Ene Strain

Eee-Enn

B073 Varian, Parkfield

mic

rostr

ain

Right lateral creep events

Middle Mountain

Borehole trends removed

John Langbein, 2008


Yellowstone

Taka’aki Taira and Bob Smith, 2008

6 cm dike over .35 km^2


Yellowstone Seiche

10 11 12 13 14 15 16 17 18 19

July 2009, UTC

0.08

0.10

0.12

0.14

0.16

0.18

10 11 12 13 14 15 16 17 18 19

10 11 12 13 14 15 16 17 18 19

July 2009, UTC

5000

5400

5800

6200

6600

10 11 12 13 14 15 16 17 18 19

Shear Strain, Eee-Enn, Yellowstone 10-20 July 2009

B206, Canyon

B205, Norris

B944, Grant

Detrended dataTide removed

Mic

rost

rain

Dis

char

ge,

Cu

bic

Fee

t Pe

r Sec

on

d USGS 06186500 Yellowstone River at Yellowstone Lk Outlet YNP

(http://waterdata.usgs.gov/wy/nwis)

Discharge

• Preliminary interpretation, small possibility it could be pumping - but no question it’s real

• No signal on GPS

• No signal on Seismic

• Visible 30 km away


Typhoon triggered slow earthquakes

Liu ChiChing, Alan Linde, Aelwyn Sacks, 2009Wednesday, August 26, 2009

The future questions...


BSM - E&O Show


2053-37 Advanced Workshop on Evaluating, Monitoring and...

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