The ANSS event ID is usp000gmv1 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000gmv1/executive.
2008/11/03 13:14:13 42.825 -105.182 5.0 3.5 Wyoming
USGS/SLU Moment Tensor Solution
ENS 2008/11/03 13:14:13:0 42.83 -105.18 5.0 3.5 Wyoming
Stations used:
IU.RSSD IW.LOHW IW.PHWY IW.SMCO TA.E20A TA.E21A TA.F21A
TA.G20A TA.G21A TA.H19A TA.H20A TA.H21A TA.H22A TA.H23A
TA.H24A TA.I19A TA.I20A TA.I21A TA.I22A TA.I23A TA.J17A
TA.J19A TA.J20A TA.J21A TA.J22A TA.J23A TA.K19A TA.K22A
TA.L20A TA.L21A TA.L22A TA.L23A TA.L24A TA.M21A TA.M22A
TA.M23A TA.M24A TA.N24A TA.N25A TA.O20A TA.O21A TA.O24A
TA.O25A TA.P22A TA.P25A TA.Q22A TA.Q25A US.ISCO US.LAO
US.RLMT
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.57e+21 dyne-cm
Mw = 3.54
Z = 18 km
Plane Strike Dip Rake
NP1 60 73 -121
NP2 305 35 -30
Principal Axes:
Axis Value Plunge Azimuth
T 2.57e+21 22 174
N 0.00e+00 30 70
P -2.57e+21 51 294
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.01e+21
Mxy 1.31e+20
Mxz -1.41e+21
Myy -8.02e+20
Myz 1.24e+21
Mzz -1.21e+21
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---------- --------------------##-----
---------- P --------------------#------
----------- ------------------####------
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############## T ###########
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Global CMT Convention Moment Tensor:
R T P
-1.21e+21 -1.41e+21 -1.24e+21
-1.41e+21 2.01e+21 -1.31e+20
-1.24e+21 -1.31e+20 -8.02e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081103131413/index.html
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STK = 305
DIP = 35
RAKE = -30
MW = 3.54
HS = 18.0
The NDK file is 20081103131413.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 0.10 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 0.5 225 45 90 3.35 0.3452
WVFGRD96 1.0 225 45 90 3.40 0.3571
WVFGRD96 2.0 250 45 90 3.45 0.3381
WVFGRD96 3.0 335 30 25 3.48 0.3091
WVFGRD96 4.0 335 30 25 3.48 0.3438
WVFGRD96 5.0 330 30 15 3.47 0.3708
WVFGRD96 6.0 330 30 15 3.46 0.3904
WVFGRD96 7.0 325 35 5 3.46 0.4047
WVFGRD96 8.0 315 35 -20 3.46 0.4177
WVFGRD96 9.0 315 35 -20 3.46 0.4292
WVFGRD96 10.0 315 35 -20 3.49 0.4372
WVFGRD96 11.0 310 35 -25 3.50 0.4459
WVFGRD96 12.0 310 35 -30 3.50 0.4522
WVFGRD96 13.0 310 35 -30 3.51 0.4577
WVFGRD96 14.0 310 35 -25 3.51 0.4619
WVFGRD96 15.0 310 35 -25 3.52 0.4650
WVFGRD96 16.0 305 35 -30 3.53 0.4673
WVFGRD96 17.0 310 35 -25 3.53 0.4688
WVFGRD96 18.0 305 35 -30 3.54 0.4693
WVFGRD96 19.0 305 35 -30 3.55 0.4690
WVFGRD96 20.0 305 35 -30 3.58 0.4677
WVFGRD96 21.0 310 35 -25 3.59 0.4656
WVFGRD96 22.0 310 35 -25 3.60 0.4626
WVFGRD96 23.0 310 35 -25 3.60 0.4583
WVFGRD96 24.0 310 35 -25 3.61 0.4533
WVFGRD96 25.0 310 35 -25 3.62 0.4479
WVFGRD96 26.0 310 30 -25 3.63 0.4418
WVFGRD96 27.0 310 30 -20 3.64 0.4350
WVFGRD96 28.0 310 30 -20 3.64 0.4273
WVFGRD96 29.0 310 30 -20 3.65 0.4186
WVFGRD96 30.0 310 30 -20 3.66 0.4092
WVFGRD96 31.0 310 30 -20 3.67 0.3996
WVFGRD96 32.0 310 30 -20 3.67 0.3891
WVFGRD96 33.0 310 35 -20 3.68 0.3785
WVFGRD96 34.0 310 35 -20 3.69 0.3675
WVFGRD96 35.0 310 35 -25 3.69 0.3564
WVFGRD96 36.0 310 35 -20 3.69 0.3452
WVFGRD96 37.0 310 35 -20 3.70 0.3346
WVFGRD96 38.0 340 30 25 3.70 0.3262
WVFGRD96 39.0 340 30 25 3.70 0.3199
WVFGRD96 40.0 340 20 20 3.82 0.3121
WVFGRD96 41.0 340 25 25 3.83 0.3016
WVFGRD96 42.0 250 75 65 3.80 0.2933
WVFGRD96 43.0 250 75 65 3.81 0.2866
WVFGRD96 44.0 250 75 60 3.81 0.2800
WVFGRD96 45.0 250 75 60 3.81 0.2734
WVFGRD96 46.0 215 65 -65 3.86 0.2689
WVFGRD96 47.0 215 65 -65 3.87 0.2669
WVFGRD96 48.0 215 65 -60 3.87 0.2647
WVFGRD96 49.0 215 65 -60 3.88 0.2631
WVFGRD96 50.0 215 65 -60 3.88 0.2612
The best solution is
WVFGRD96 18.0 305 35 -30 3.54 0.4693
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 0.10 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