Gladwin Borehole Tensor Strain Measurements
at Tsengwen Reservoir, Taiwan.
High precision and high stability measurements
of the horizontal strain field in a region are to be made in Taiwan
using a Gladwin Tensor Strain Measurement instrument (GTSM). These instruments
are installed at a depth of 100-200 metres at 7 sites in California,
and at approximately 160 meters in Taiwan. The sites are shown in red in the accompanying
map for sites at Reservoir South and
Reservoir North and in the map for Reservoir
South and Eighteen Curves .
-
RST is
close to
Chi Chien at the southern end of Tsengwen Reservoir, to the
east of
Chia-i, and to the south of
Taipei, as the
first GTSM installed in a prospective array in Taiwan by the Central
Geological Survey of Taiwan.
Gauge angles
-
#0. 218 E of N
-
#1. 158 E of N
-
#2. 98 E of N
-
#3. 68 E of N
These instruments provide 3 component strain
data on
- Long term raw data accumulation. Long
term data records at this site (RST)since installation in
late October 2003 are available.
- Coseismic strain offsets useful for constraining earthquake
source mechanisms.
Raw, exponential models, and residual plots
for each measured channel are shown for
gauge 1, gauge 2, for
gauge 3, and for gauge 4.
Note that the gauge residuals have a Y axis scale
range of +/- 5 microstrain for each component, and show that excluding
known tectonic events, all variation in gauge strain rates have
been less than +/- 0.5 microstrain per year for the whole of
the current record..
The residual linear borehole recovery strain rate
over the total record is shown in microstrain/year as the "slope"
on each plot.
Residual data are recovered from the raw data by extracting
least squares fitted exponential(s) and a linear function which
describe the processes of curing of the grout and recovery of the
borehole, after drilling and installation disturbance of the virgin
stress field.
Regions used in the least squares fitting are marked
in red on the X axis, and the fit parameters are printed in the
upper panel of the figure .
Changes of strain rates calculated from these residuals
are unaffected by the exponential removal procedure and allow the
very long term stability of the instruments (see
gauge 1 , gauge 2,
and gauge 3 exemplified
at the Californian site of San Juan Bautista) to be quantified.
Zoomed plot of detrended component data from this
site is shown for RST.
Nominally calibrated component data to July 17, 2005 is shown.
Nominally calibrated STRAIN data to July 17, 2005 is shown.
-
RNTis
close to
Chi Chien at the northern end of Tsengwen Reservoir, to the
east of
Chia-i, and to the south of
Taipei, as the
second GTSM installed in a prospective array in Taiwan by the Central
Geological Survey of Taiwan.
Gauge angles
-
#0. 289 E of N
-
#1. 229 E of N
-
#2. 169 E of N
-
#3.139 E of N
- Long term raw data accumulation. Long
term data records at this site (RNT) are available.
- Coseismic strain offsets useful for constraining earthquake
source mechanisms.
Raw, exponential models, and residual plots
for each measured channel are shown for
gauge 1, gauge 2, for
gauge 3, and for gauge 4.
Note that the gauge residuals have a Y axis scale
range of +/- 5 microstrain for each component, and show that excluding
known tectonic events, all variation in gauge strain rates have
been less than +/- 0.5 microstrain per year for the whole of
the current record..
The residual linear borehole recovery strain rate
over the total record is shown in microstrain/year as the "slope"
on each plot.
Residual data are recovered from the raw data by extracting
least squares fitted exponential(s) and a linear function which
describe the processes of curing of the grout and recovery of the
borehole, after drilling and installation disturbance of the virgin
stress field.
Regions used in the least squares fitting are marked
in red on the X axis, and the fit parameters are printed in the
upper panel of the figure .
Changes of strain rates calculated from these residuals
are unaffected by the exponential removal procedure and allow the
very long term stability of the instruments (see
gauge 1 , gauge 2,
and gauge 3 exemplified
at the Californian site of San Juan Bautista) to be quantified.
Zoomed plot of detrended component data from this
site is shown for RNT.
- ECT is close to Chi Chien
and to the south of Taipei, as the third GTSM installed in
a prospective array in Taiwan by the Central Geological Survey of
Taiwan.
-
#0. 229 E of N
-
#1. 169 E of N
-
#2. 109 E of N
-
#3. 79 E of N
- Long term raw data accumulation. Long
term data records at this site (ECT) are available.
- Coseismic strain offsets useful for constraining earthquake
source mechanisms.
Raw, exponential models, and residual plots
for each measured channel are shown for
gauge 1, gauge 2, and for gauge 4.
Note that the gauge residuals have a Y axis scale
range of +/- 5 microstrain for each component, and show that excluding
known tectonic events, all variation in gauge strain rates have
been less than +/- 0.5 microstrain per year for the whole of
the current record..
The residual linear borehole recovery strain rate
over the total record is shown in microstrain/year as the "slope"
on each plot.
Residual data are recovered from the raw data by extracting
least squares fitted exponential(s) and a linear function which
describe the processes of curing of the grout and recovery of the
borehole, after drilling and installation disturbance of the virgin
stress field.
Regions used in the least squares fitting are marked
in red on the X axis, and the fit parameters are printed in the
upper panel of the figure .
Changes of strain rates calculated from these residuals
are unaffected by the exponential removal procedure and allow the
very long term stability of the instruments (see
gauge 1 , gauge 2,
and gauge 3 exemplified
at the Californian site of San Juan Bautista) to be quantified.
Zoomed plot of detrended component data from this
site is shown for ECT.
Data plots of interest:
- May 19, 2004, at RST Mag 6.5 Taitung : event
detail plot. This event was captured on the 1 second recording
rate, before enabling of higher resolution collection.
- May 19, 2004, at RNT Mag 6.5 Taitung : event
detail plot. This event was captured on the 100Hz recording
rate, after enabling of higher resolution collection in
early May 2004.
- May 19, 2004, at ECT Mag 6.5 Taitung : event
detail plot. This event was captured on the 100Hz
recording rate, after enabling of higher resolution
collection in early May 2004.
A map showing location of GTSMs
along with this
earthquake may be found
The initial report on this work has been published
elsewhere.
Some other related sites :
