The ANSS event ID is usp000jrdv and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000jrdv/executive.
2012/09/01 10:57:34 66.836 -135.612 20.0 4 Yukon, Canada
USGS/SLU Moment Tensor Solution
ENS 2012/09/01 10:57:34:0 66.84 -135.61 20.0 4.0 Yukon, Canada
Stations used:
AK.BPAW AK.CAST AK.CCB AK.COLD AK.DHY AK.DIV AK.DOT AK.FYU
AK.GHO AK.GLM AK.HDA CN.BVCY CN.CLVN CN.DAWY CN.INK IU.COLA
US.EGAK
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 8.32e+21 dyne-cm
Mw = 3.88
Z = 26 km
Plane Strike Dip Rake
NP1 359 82 145
NP2 95 55 10
Principal Axes:
Axis Value Plunge Azimuth
T 8.32e+21 30 311
N 0.00e+00 54 168
P -8.32e+21 18 52
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.82e+20
Mxy -6.73e+21
Mxz 9.02e+20
Myy -1.18e+21
Myz -4.64e+21
Mzz 1.36e+21
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##### ##########----------- --
###### T ###########---------- P ---
####### ###########---------- ----
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Global CMT Convention Moment Tensor:
R T P
1.36e+21 9.02e+20 4.64e+21
9.02e+20 -1.82e+20 6.73e+21
4.64e+21 6.73e+21 -1.18e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120901105734/index.html
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STK = 95
DIP = 55
RAKE = 10
MW = 3.88
HS = 26.0
The NDK file is 20120901105734.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 0.06 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 50 40 -90 3.71 0.3249
WVFGRD96 1.0 180 50 -80 3.53 0.3144
WVFGRD96 2.0 180 50 -85 3.60 0.3353
WVFGRD96 3.0 180 50 -80 3.66 0.3294
WVFGRD96 4.0 300 40 45 3.68 0.3125
WVFGRD96 5.0 290 40 35 3.72 0.3110
WVFGRD96 6.0 270 50 0 3.72 0.3137
WVFGRD96 7.0 265 45 -20 3.72 0.3192
WVFGRD96 8.0 260 40 -30 3.79 0.3262
WVFGRD96 9.0 260 40 -35 3.79 0.3358
WVFGRD96 10.0 260 40 -35 3.78 0.3441
WVFGRD96 11.0 260 45 -40 3.78 0.3525
WVFGRD96 12.0 260 40 -40 3.78 0.3596
WVFGRD96 13.0 265 45 -35 3.78 0.3658
WVFGRD96 14.0 265 45 -35 3.78 0.3714
WVFGRD96 15.0 90 50 -10 3.78 0.3757
WVFGRD96 16.0 100 45 20 3.78 0.3847
WVFGRD96 17.0 100 45 20 3.79 0.3951
WVFGRD96 18.0 100 45 20 3.79 0.4042
WVFGRD96 19.0 100 50 20 3.82 0.4121
WVFGRD96 20.0 100 50 20 3.82 0.4190
WVFGRD96 21.0 100 50 20 3.83 0.4240
WVFGRD96 22.0 100 50 15 3.84 0.4283
WVFGRD96 23.0 100 50 15 3.85 0.4319
WVFGRD96 24.0 95 55 10 3.87 0.4342
WVFGRD96 25.0 95 55 10 3.88 0.4357
WVFGRD96 26.0 95 55 10 3.88 0.4363
WVFGRD96 27.0 95 55 5 3.90 0.4362
WVFGRD96 28.0 95 55 5 3.90 0.4354
WVFGRD96 29.0 95 55 5 3.91 0.4339
WVFGRD96 30.0 95 55 5 3.92 0.4316
WVFGRD96 31.0 95 55 5 3.93 0.4287
WVFGRD96 32.0 95 55 5 3.93 0.4251
WVFGRD96 33.0 95 55 5 3.94 0.4210
WVFGRD96 34.0 95 60 5 3.97 0.4166
WVFGRD96 35.0 95 60 5 3.98 0.4117
WVFGRD96 36.0 310 60 30 3.96 0.4041
WVFGRD96 37.0 305 60 30 3.97 0.3988
WVFGRD96 38.0 305 60 30 3.99 0.3925
WVFGRD96 39.0 90 60 5 4.01 0.3855
WVFGRD96 40.0 95 45 10 4.07 0.3799
WVFGRD96 41.0 95 45 10 4.07 0.3733
WVFGRD96 42.0 100 45 15 4.08 0.3664
WVFGRD96 43.0 100 45 15 4.08 0.3594
WVFGRD96 44.0 95 50 10 4.10 0.3521
WVFGRD96 45.0 95 50 10 4.10 0.3444
WVFGRD96 46.0 95 50 10 4.11 0.3363
WVFGRD96 47.0 100 50 15 4.11 0.3283
WVFGRD96 48.0 100 50 15 4.12 0.3203
WVFGRD96 49.0 100 50 15 4.12 0.3119
The best solution is
WVFGRD96 26.0 95 55 10 3.88 0.4363
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 0.06 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