Transcript Progress report on BSM data evaluation
Slide 1
Progress Report on Analysis of Existing Borehole
Strain Data
E. Roeloffs, K. Hodgkinson
October 17, 2003
Slide 2
Questions Posed by PBO Standing Committee
• How sensitive are the instruments to vertical strain?
• What are the error characteristics for a typical installation?
• Can we reconcile the tides recorded by the instruments with the
calculated tides?
• How do the instruments respond to pore pressure changes?
• Will we be able to use the pore pressure measurements planned for
PBO boreholes to define repeatable responses to pore pressure changes
that can be used to correct the data?
• Are some instruments decoupled from the regional strain field by local
fractures or other features, and if so, why?
• How do we assess the accuracy of step-like coseismic changes at
teleseismic distances where static strain should not be detectable?
• How does borehole strain data compare with data from other
instruments?
• Are there examples of events other than coseismic steps recorded using
borehole strainmeters?
Slide 3
Vertical Strain Sensitivity
Instrument
Site
RESPC(microstrain/mbar)
Dil atometer
Dil atometer
Dil atometer
Donna Lee ( Parkfield)
Frolich (Parkfield)
Vin eyard Cyn (Parkfield)
6.9e-3 ± 3e-5
3.5e-3 ± 3e-5
2.9e-2 ± 6e-5
Dil atometer
Dil atometer
Dil atometer
SES-3
Garin (SF Bay Area)
Sunol (SF Bay Area)
Coyote (SF Bay Area)
St. Vincent (SF Bay Area)
1.8e-2
3.4e-3
5.1e-3
1.0e-2
GTSM
Donna Lee ( Parkfield)
7.0e-5 ± 2e-5
±
±
±
±
6e-5
8e-5
2e-4
3e-4
• Atmospheric pressure response of GTSM’s is 2 to 3 orders of
magnitude lower than that of dilatometers or SES-3’s
• Implies dilatometers and SES-3’s have greater sensitivity to vertical
strain, which needs to be considered in the calibration process
Slide 4
Donna Lee
(Parkfield)
Dilatometer,
GTSM,
Atmospheric
Pressure
• Strain data have had
linear trends subtracted
• Calibrations are
approximate
Slide 5
Sizes and Frequencies/year of Steps in Dilatometer Data
Site
Big Springs
Chantry
Coyote Fla t
Garin
Motor Cross
Philips
Punch Bo wl
Sunol
Vin eyard Cyn
Frolich
Donna Lee
•
•
•
•
YEAR S
4
6
10
10
4
14
17.5
10
16.5
16.5
16.5
100-500
counts
2.3
34.7
7.9
1.9
16.3
9.4
1.1
3.2
11.0
3.2
2.2
500-4000
counts
0.25
6.8
1.5
0.8
10
4.3
7.2
1.3
9.7
2.1
1.3
>4000
counts
0.25
16.5
4.7
2.5
1.5
4.5
5.7
1
1.7
3.6
6.3
Dilatometers and SES-3’s contain valves that open to reset the instruments
when a certain strain value is exceeded
The valve-opening resets are large (typically > 4000 counts) and should be
easily identified and corrected for
However, data from some dilatometers contain additional step-like changes
2-3 smaller step-like changes per year is characteristic of well-performing
instruments (e.g., Frolich and Donna Lee)
Slide 6
Vineyard Cyn and Frohlich Step Sizes
•
•
Frolich steps are mostly valve-opening resets
Vineyard Cyn record contains smaller, unexplained steps (problem may have
been solved around 1996)
Slide 7
Solid Earth and Ocean Load Tides
Slide 8
Observed and Calculated Tides: Long Valley dilatometers
Site
Big Springs
Postpile
Motorcross
Phillips
M2 phase in data
341.14°±0.493
5.89°±0.65
5.48°±0.19
0.78°±1.57
M2 phase from SPOTL
4.64°
4.98°
4.83°
4.77°
• Ocean load corrections are small because site is 300 km from coast
• 3 of the 4 dilatometers have M2 phases within 5° of SPOTL-calculated
M2 phase
• Big Springs M2 phase differs by about 25° throughout life of
instrument - possibly a pore pressure drainage effect?
Slide 9
Observed and Calculated Tides: SF Bay Area Dilatometers
Site
Garin
Sunol
Coyote
Russell
Mill Cr
Phase Difference
5°
4°
-135°
2°
7°
• Phase differences are for M2 with respect to SPOTL-calculated tides
• Ocean loads are calculated to contribute about half the tidal strain
• Coyote Hills site is situated in poorly consolidated material near a
complex shoreline
Slide 10
Preliminary Summary: Comparison with Calculated Tides
• Ocean loading is unimportant at Long Valley (~300 km from coast),
measureable at Parkfield (~90 km from coast), and very significant in
San Francisco Bay area
• For most dilatometers, M2 phase is within about 5° of areal strain
phase calculated by SPOTL
• One dilatometer in Long Valley and one dilatometer in SF Bay area
have M2 phases significantly different from calculated values
• Tide phases for mini-PBO SES-3 instruments were previously found
by Duncan Agnew to differ significantly from SPOTL-calculated
phases.
Slide 11
Decoupling from Regional Strain Field?
• Some dilatometers record little net strain, and/or strain from grout
curing/hole relaxation is extensional (compare with Donna Lee
dilatometer, which behaves as expected)
• Local fractures, steep topography, high rates of extension, or
installation problems need to be investigated as possible causes
Slide 12
Brief List of Published Events Recorded by Borehole
Strainmeters
– Transient strain induced by the Landers earthquake at
Long Valley, as well as other earthquakes (Hill et al.,
JGR, 1995)
– Parkfield strain-rate change, 1993 (Gwyther et al.,
GRL, 1996; Langbein et al., GRL, 1999)
– Slow earthquakes at San Juan Bautista (Linde et al.,
Nature, 1996)
– Possible precursor to Kettleman Hills earthquake
(Roeloffs and Quilty, PAGEOPH, 1997)
– Strain-rate change prior to Loma Prieta earthquake
(Gladwin et al., GRL, 1991)
Slide 13
Dilatometer Data
Showing
Responses to
Summit Tilt
Event on Kilauea
Volcano
Slide 14
Preliminary Criteria for a Satisfactorily Functioning
Borehole Strainmeter
•
•
•
•
Instrument is stable to periods of 3 months.
No fluid pressure drainage effects at periods of 30 days
Barometric response is flat in the frequency domain.
Tides reconciled with calculated tides
• Repeatable pore pressure response
• Valves reset at appropriate times with no change in slope.
• Long-term strain is observed from grout curing and hole
relaxation
This list is intended for discussion and is expected to evolve.
Progress Report on Analysis of Existing Borehole
Strain Data
E. Roeloffs, K. Hodgkinson
October 17, 2003
Slide 2
Questions Posed by PBO Standing Committee
• How sensitive are the instruments to vertical strain?
• What are the error characteristics for a typical installation?
• Can we reconcile the tides recorded by the instruments with the
calculated tides?
• How do the instruments respond to pore pressure changes?
• Will we be able to use the pore pressure measurements planned for
PBO boreholes to define repeatable responses to pore pressure changes
that can be used to correct the data?
• Are some instruments decoupled from the regional strain field by local
fractures or other features, and if so, why?
• How do we assess the accuracy of step-like coseismic changes at
teleseismic distances where static strain should not be detectable?
• How does borehole strain data compare with data from other
instruments?
• Are there examples of events other than coseismic steps recorded using
borehole strainmeters?
Slide 3
Vertical Strain Sensitivity
Instrument
Site
RESPC(microstrain/mbar)
Dil atometer
Dil atometer
Dil atometer
Donna Lee ( Parkfield)
Frolich (Parkfield)
Vin eyard Cyn (Parkfield)
6.9e-3 ± 3e-5
3.5e-3 ± 3e-5
2.9e-2 ± 6e-5
Dil atometer
Dil atometer
Dil atometer
SES-3
Garin (SF Bay Area)
Sunol (SF Bay Area)
Coyote (SF Bay Area)
St. Vincent (SF Bay Area)
1.8e-2
3.4e-3
5.1e-3
1.0e-2
GTSM
Donna Lee ( Parkfield)
7.0e-5 ± 2e-5
±
±
±
±
6e-5
8e-5
2e-4
3e-4
• Atmospheric pressure response of GTSM’s is 2 to 3 orders of
magnitude lower than that of dilatometers or SES-3’s
• Implies dilatometers and SES-3’s have greater sensitivity to vertical
strain, which needs to be considered in the calibration process
Slide 4
Donna Lee
(Parkfield)
Dilatometer,
GTSM,
Atmospheric
Pressure
• Strain data have had
linear trends subtracted
• Calibrations are
approximate
Slide 5
Sizes and Frequencies/year of Steps in Dilatometer Data
Site
Big Springs
Chantry
Coyote Fla t
Garin
Motor Cross
Philips
Punch Bo wl
Sunol
Vin eyard Cyn
Frolich
Donna Lee
•
•
•
•
YEAR S
4
6
10
10
4
14
17.5
10
16.5
16.5
16.5
100-500
counts
2.3
34.7
7.9
1.9
16.3
9.4
1.1
3.2
11.0
3.2
2.2
500-4000
counts
0.25
6.8
1.5
0.8
10
4.3
7.2
1.3
9.7
2.1
1.3
>4000
counts
0.25
16.5
4.7
2.5
1.5
4.5
5.7
1
1.7
3.6
6.3
Dilatometers and SES-3’s contain valves that open to reset the instruments
when a certain strain value is exceeded
The valve-opening resets are large (typically > 4000 counts) and should be
easily identified and corrected for
However, data from some dilatometers contain additional step-like changes
2-3 smaller step-like changes per year is characteristic of well-performing
instruments (e.g., Frolich and Donna Lee)
Slide 6
Vineyard Cyn and Frohlich Step Sizes
•
•
Frolich steps are mostly valve-opening resets
Vineyard Cyn record contains smaller, unexplained steps (problem may have
been solved around 1996)
Slide 7
Solid Earth and Ocean Load Tides
Slide 8
Observed and Calculated Tides: Long Valley dilatometers
Site
Big Springs
Postpile
Motorcross
Phillips
M2 phase in data
341.14°±0.493
5.89°±0.65
5.48°±0.19
0.78°±1.57
M2 phase from SPOTL
4.64°
4.98°
4.83°
4.77°
• Ocean load corrections are small because site is 300 km from coast
• 3 of the 4 dilatometers have M2 phases within 5° of SPOTL-calculated
M2 phase
• Big Springs M2 phase differs by about 25° throughout life of
instrument - possibly a pore pressure drainage effect?
Slide 9
Observed and Calculated Tides: SF Bay Area Dilatometers
Site
Garin
Sunol
Coyote
Russell
Mill Cr
Phase Difference
5°
4°
-135°
2°
7°
• Phase differences are for M2 with respect to SPOTL-calculated tides
• Ocean loads are calculated to contribute about half the tidal strain
• Coyote Hills site is situated in poorly consolidated material near a
complex shoreline
Slide 10
Preliminary Summary: Comparison with Calculated Tides
• Ocean loading is unimportant at Long Valley (~300 km from coast),
measureable at Parkfield (~90 km from coast), and very significant in
San Francisco Bay area
• For most dilatometers, M2 phase is within about 5° of areal strain
phase calculated by SPOTL
• One dilatometer in Long Valley and one dilatometer in SF Bay area
have M2 phases significantly different from calculated values
• Tide phases for mini-PBO SES-3 instruments were previously found
by Duncan Agnew to differ significantly from SPOTL-calculated
phases.
Slide 11
Decoupling from Regional Strain Field?
• Some dilatometers record little net strain, and/or strain from grout
curing/hole relaxation is extensional (compare with Donna Lee
dilatometer, which behaves as expected)
• Local fractures, steep topography, high rates of extension, or
installation problems need to be investigated as possible causes
Slide 12
Brief List of Published Events Recorded by Borehole
Strainmeters
– Transient strain induced by the Landers earthquake at
Long Valley, as well as other earthquakes (Hill et al.,
JGR, 1995)
– Parkfield strain-rate change, 1993 (Gwyther et al.,
GRL, 1996; Langbein et al., GRL, 1999)
– Slow earthquakes at San Juan Bautista (Linde et al.,
Nature, 1996)
– Possible precursor to Kettleman Hills earthquake
(Roeloffs and Quilty, PAGEOPH, 1997)
– Strain-rate change prior to Loma Prieta earthquake
(Gladwin et al., GRL, 1991)
Slide 13
Dilatometer Data
Showing
Responses to
Summit Tilt
Event on Kilauea
Volcano
Slide 14
Preliminary Criteria for a Satisfactorily Functioning
Borehole Strainmeter
•
•
•
•
Instrument is stable to periods of 3 months.
No fluid pressure drainage effects at periods of 30 days
Barometric response is flat in the frequency domain.
Tides reconciled with calculated tides
• Repeatable pore pressure response
• Valves reset at appropriate times with no change in slope.
• Long-term strain is observed from grout curing and hole
relaxation
This list is intended for discussion and is expected to evolve.