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Workshop Questions (Nov. 7, 2003)
• For the few near-fault records that include
fling response, should these effects be
explicitly removed before developing the
initial ground motion models?
YES
• How should fling effects be removed?
WORK IN PROGRESS
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TCU129, E-W
50
Velocity (cm/sec)
t2=50 sec
t1
File: C:\metu_03\rec_proc\129evfit_color.draw;Date: 2003-09-10;Time: 14:25:09
t2=30 sec
To model fling we need to
accurately recover the residual
displacement. Baseline
correction of recorded motion
is important step.
0
t2=70 sec
-50
20
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40
60
Time (sec)
NGA Workshop: Fling
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3
400
Although the results look
physically
TCU129, E-W can
plausible, the residual displacements
be sensitive to t1, t2
t2 = 70 sec
Quadratic fit to velocity gives best fit to GPS
residual displacement in this case
t2 = 50 sec
quadratic fit to velocity
GPS, station AF11
t2 = 30 sec
0
low-cut filter only, fc=0.02 Hz
remove mean only
-200
0
20
40
60
80
100
Time (sec)
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File: C:\metu_03\rec_proc\129ed4pp_color.draw;
Date: 2003-09-10;Time: 21:50:10
Displacement (cm)
200
TCU068 displacement
record baseline corrected
using Boore’s method
(modified Iwan) with three
choices of t2. For this
record there is not much
sensitivity to the choice of
t2 .
t1: acc > 50 cm/sec2
t2(1): Boore v0
t2(2): acc < 50 cm/sec2
t2(3): 2 x t2(2) – t1
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Sine-pulse fits to the three corrected
displacement records. The pulse
start times are all very close (33.24,
33.36, 33.42) as are the pulse periods
(4.39, 4.12, 3.83). The main difference
are the final displacements (617, 570,
528).
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Spectral acceleration for the
three tcu068 records with the
sine-pulse removed,
compared with SA for the
original (I.e., with fling) record
(magenta line).
1) There is some sensitivity to
t2 between 2 and 5 sec period
(difference btw red, green and
black lines). Max. difference is
about 60%.
2) There is a large difference
compared to original record,
with the fling-removed records
actually being much larger
than the original record up to
about 6-7 sec period.
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Similar analysis for tcu052 record.
The sensitivity of baseline correction
to t2 is greater than for tcu068.
However, the sensitivity in SA for the
fling-removed records is less.
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Conclusions
• Baseline correction of raw record must be done
with care.
• Sine-pulse model for fling is attractive because it
provides a time domain parameterization and
can be related to the underlying physical
process.
• Response spectra for sine-pulse corrected
records can show sensitivity to choice of
processing parametersIs this acceptable?
03/24/04
(9 m disp. at TCU068)
NGA Workshop: Fling
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