The ANSS event ID is usp000gpuv and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000gpuv/executive.
2008/12/03 02:47:30 60.829 -138.019 1.0 4.2 Yukon, Canada
USGS/SLU Moment Tensor Solution
ENS 2008/12/03 02:47:30:0 60.83 -138.02 1.0 4.2 Yukon, Canada
Stations used:
AT.SKAG CN.DAWY CN.PLBC CN.WHY
Filtering commands used:
hp c 0.02 n 3
lp c 0.08 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.11e+22 dyne-cm
Mw = 4.15
Z = 6 km
Plane Strike Dip Rake
NP1 125 60 109
NP2 270 35 60
Principal Axes:
Axis Value Plunge Azimuth
T 2.11e+22 69 75
N 0.00e+00 17 295
P -2.11e+22 13 201
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.72e+22
Mxy -6.06e+21
Mxz 6.26e+21
Myy -1.45e+14
Myz 8.66e+21
Mzz 1.72e+22
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#-----########################------
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###--################################---
##----################################--
#-------################# #############-
#--------################ T #############-
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--- P ----------------
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Global CMT Convention Moment Tensor:
R T P
1.72e+22 6.26e+21 -8.66e+21
6.26e+21 -1.72e+22 6.06e+21
-8.66e+21 6.06e+21 -1.45e+14
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081203024730/index.html
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STK = 270
DIP = 35
RAKE = 60
MW = 4.15
HS = 6.0
The NDK file is 20081203024730.ndk The waveform inversion is preferred.
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) the waveform inversion are shown in the next figure.
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The program wvfgrd96 was used with good traces observed at short distance to determine the focal mechanism, depth and seismic moment. This technique requires a high quality signal and well determined velocity model for the Green's functions. To the extent that these are the quality data, this type of mechanism should be preferred over the radiation pattern technique which requires the separate step of defining the pressure and tension quadrants and the correct strike.
The observed and predicted traces are filtered using the following gsac commands:
hp c 0.02 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 250 65 30 3.99 0.5117
WVFGRD96 1.0 245 70 30 3.98 0.5143
WVFGRD96 2.0 260 35 30 4.12 0.5355
WVFGRD96 3.0 260 45 35 4.08 0.5534
WVFGRD96 4.0 265 40 45 4.11 0.5663
WVFGRD96 5.0 270 35 55 4.15 0.5854
WVFGRD96 6.0 270 35 60 4.15 0.5960
WVFGRD96 7.0 260 40 50 4.11 0.5957
WVFGRD96 8.0 255 40 45 4.10 0.5914
WVFGRD96 9.0 245 45 35 4.08 0.5840
WVFGRD96 10.0 245 45 35 4.10 0.5844
WVFGRD96 11.0 245 45 30 4.09 0.5776
WVFGRD96 12.0 240 50 25 4.09 0.5708
WVFGRD96 13.0 240 50 20 4.09 0.5640
WVFGRD96 14.0 240 50 20 4.10 0.5586
WVFGRD96 15.0 240 50 20 4.10 0.5517
WVFGRD96 16.0 240 50 20 4.11 0.5434
WVFGRD96 17.0 235 55 15 4.12 0.5358
WVFGRD96 18.0 235 55 15 4.12 0.5266
WVFGRD96 19.0 235 55 15 4.13 0.5178
WVFGRD96 20.0 240 50 15 4.15 0.5081
WVFGRD96 21.0 240 50 15 4.16 0.4966
WVFGRD96 22.0 240 50 15 4.17 0.4855
WVFGRD96 23.0 240 50 15 4.18 0.4733
WVFGRD96 24.0 240 45 15 4.19 0.4607
WVFGRD96 25.0 240 45 15 4.20 0.4476
WVFGRD96 26.0 240 40 10 4.21 0.4355
WVFGRD96 27.0 240 35 10 4.22 0.4234
WVFGRD96 28.0 240 35 10 4.22 0.4122
WVFGRD96 29.0 240 30 10 4.23 0.4008
WVFGRD96 30.0 235 30 5 4.24 0.3898
WVFGRD96 31.0 235 30 5 4.25 0.3785
WVFGRD96 32.0 235 30 5 4.25 0.3670
WVFGRD96 33.0 235 30 5 4.26 0.3552
WVFGRD96 34.0 235 30 5 4.26 0.3440
WVFGRD96 35.0 235 30 5 4.27 0.3324
WVFGRD96 36.0 245 40 0 4.25 0.3220
WVFGRD96 37.0 245 40 0 4.25 0.3131
WVFGRD96 38.0 245 40 0 4.26 0.3057
WVFGRD96 39.0 245 45 -5 4.27 0.3000
The best solution is
WVFGRD96 6.0 270 35 60 4.15 0.5960
The mechanism corresponding to the best fit is
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The best fit as a function of depth is given in the following figure:
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The comparison of the observed and predicted waveforms is given in the next figure. The red traces are the observed and the blue are the predicted. Each observed-predicted component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number it the time shift required for maximum correlation between the observed and predicted traces. This time shift is required because the synthetics are not computed at exactly the same distance as the observed, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. A positive time shift indicates that the prediction is too fast and should be delayed to match the observed trace (shift to the right in this figure). A negative value indicates that the prediction is too slow. The lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
hp c 0.02 n 3 lp c 0.08 n 3 br c 0.12 0.25 n 4 p 2
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| Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. Each solution is plotted as a vector at a given value of strike and dip with the angle of the vector representing the rake angle, measured, with respect to the upward vertical (N) in the figure. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
The CUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
MODEL.01 CUS Model with Q from simple gamma values ISOTROPIC KGS FLAT EARTH 1-D CONSTANT VELOCITY LINE08 LINE09 LINE10 LINE11 H(KM) VP(KM/S) VS(KM/S) RHO(GM/CC) QP QS ETAP ETAS FREFP FREFS 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00