The ANSS event ID is ak0118eu5xs2 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0118eu5xs2/executive.
2011/07/02 11:45:06 63.110 -150.843 122.9 4.3 Alaska
USGS/SLU Moment Tensor Solution
ENS 2011/07/02 11:45:06:0 63.11 -150.84 122.9 4.3 Alaska
Stations used:
AK.BPAW AK.BRLK AK.CAST AK.CCB AK.DHY AK.FIB AK.KLU AK.KTH
AK.MCK AK.MLY AK.PPLA AK.RC01 AK.SAW AK.SSN AK.SWD AK.TRF
AK.WRH AT.PMR IU.COLA
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 3.67e+22 dyne-cm
Mw = 4.31
Z = 132 km
Plane Strike Dip Rake
NP1 55 75 85
NP2 254 16 108
Principal Axes:
Axis Value Plunge Azimuth
T 3.67e+22 60 318
N 0.00e+00 5 56
P -3.67e+22 30 149
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.52e+22
Mxy 7.54e+21
Mxz 2.55e+22
Myy -3.11e+21
Myz -1.89e+22
Mzz 1.83e+22
--------------
---------#######------
------##################----
----########################--
---##############################-
---###############################-#
--########## ###################----
--########### T #################-------
-############ ###############---------
--#############################-----------
-###########################--------------
-#########################----------------
-#######################------------------
####################--------------------
#################-----------------------
#############-------------------------
#######----------------- ---------
----------------------- P --------
--------------------- ------
----------------------------
----------------------
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Global CMT Convention Moment Tensor:
R T P
1.83e+22 2.55e+22 1.89e+22
2.55e+22 -1.52e+22 -7.54e+21
1.89e+22 -7.54e+21 -3.11e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110702114506/index.html
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STK = 55
DIP = 75
RAKE = 85
MW = 4.31
HS = 132.0
The NDK file is 20110702114506.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 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 110 40 -70 3.38 0.2149
WVFGRD96 1.0 105 40 -80 3.42 0.2169
WVFGRD96 2.0 115 45 -65 3.52 0.2800
WVFGRD96 3.0 135 50 -40 3.56 0.2894
WVFGRD96 4.0 145 65 -15 3.54 0.2930
WVFGRD96 5.0 335 65 20 3.57 0.3044
WVFGRD96 6.0 335 65 20 3.60 0.3205
WVFGRD96 7.0 335 65 15 3.61 0.3315
WVFGRD96 8.0 340 60 20 3.66 0.3457
WVFGRD96 9.0 340 60 20 3.68 0.3557
WVFGRD96 10.0 340 60 20 3.69 0.3646
WVFGRD96 11.0 340 55 15 3.70 0.3676
WVFGRD96 12.0 340 55 15 3.71 0.3754
WVFGRD96 13.0 340 55 20 3.72 0.3788
WVFGRD96 14.0 340 55 20 3.73 0.3836
WVFGRD96 15.0 340 55 20 3.73 0.3884
WVFGRD96 16.0 340 60 20 3.74 0.3876
WVFGRD96 17.0 340 60 20 3.75 0.3896
WVFGRD96 18.0 340 60 20 3.75 0.3877
WVFGRD96 19.0 345 60 20 3.77 0.3865
WVFGRD96 20.0 345 60 20 3.78 0.3872
WVFGRD96 21.0 230 80 -35 3.76 0.3875
WVFGRD96 22.0 230 80 -35 3.77 0.3900
WVFGRD96 23.0 230 80 -35 3.78 0.3922
WVFGRD96 24.0 230 80 -35 3.78 0.3843
WVFGRD96 25.0 215 85 -35 3.79 0.3877
WVFGRD96 26.0 35 85 30 3.82 0.3912
WVFGRD96 27.0 35 85 30 3.83 0.3946
WVFGRD96 28.0 35 85 30 3.83 0.3881
WVFGRD96 29.0 35 85 30 3.84 0.3932
WVFGRD96 30.0 35 90 30 3.84 0.3970
WVFGRD96 31.0 35 90 30 3.85 0.4022
WVFGRD96 32.0 35 90 30 3.86 0.3957
WVFGRD96 33.0 40 85 30 3.87 0.4006
WVFGRD96 34.0 40 85 30 3.88 0.4053
WVFGRD96 35.0 40 85 30 3.89 0.3994
WVFGRD96 36.0 205 25 60 3.91 0.4070
WVFGRD96 37.0 205 25 60 3.92 0.4166
WVFGRD96 38.0 225 20 85 3.92 0.4162
WVFGRD96 39.0 50 70 90 3.93 0.4266
WVFGRD96 40.0 55 70 95 4.07 0.4413
WVFGRD96 41.0 230 20 90 4.08 0.4367
WVFGRD96 42.0 50 70 90 4.09 0.4389
WVFGRD96 43.0 55 70 95 4.09 0.4402
WVFGRD96 44.0 55 70 95 4.10 0.4399
WVFGRD96 45.0 225 20 85 4.11 0.4391
WVFGRD96 46.0 55 70 95 4.11 0.4350
WVFGRD96 47.0 220 20 80 4.12 0.4325
WVFGRD96 48.0 220 20 80 4.12 0.4296
WVFGRD96 49.0 195 70 -15 4.08 0.4358
WVFGRD96 50.0 195 70 -20 4.08 0.4353
WVFGRD96 51.0 195 70 -20 4.09 0.4408
WVFGRD96 52.0 195 70 -20 4.10 0.4454
WVFGRD96 53.0 195 70 -20 4.10 0.4492
WVFGRD96 54.0 195 70 -20 4.11 0.4523
WVFGRD96 55.0 195 70 -20 4.12 0.4560
WVFGRD96 56.0 195 70 -20 4.12 0.4593
WVFGRD96 57.0 195 70 -20 4.13 0.4628
WVFGRD96 58.0 195 70 -20 4.14 0.4665
WVFGRD96 59.0 195 70 -20 4.14 0.4687
WVFGRD96 60.0 195 70 -20 4.15 0.4721
WVFGRD96 61.0 195 70 -20 4.15 0.4737
WVFGRD96 62.0 55 65 80 4.18 0.4743
WVFGRD96 63.0 55 65 80 4.19 0.4852
WVFGRD96 64.0 55 65 80 4.19 0.4958
WVFGRD96 65.0 55 65 80 4.20 0.5067
WVFGRD96 66.0 60 65 85 4.20 0.5166
WVFGRD96 67.0 60 65 85 4.21 0.5263
WVFGRD96 68.0 60 65 85 4.21 0.5359
WVFGRD96 69.0 55 65 80 4.21 0.5443
WVFGRD96 70.0 55 70 80 4.21 0.5538
WVFGRD96 71.0 55 70 80 4.22 0.5641
WVFGRD96 72.0 55 70 80 4.22 0.5735
WVFGRD96 73.0 55 70 80 4.22 0.5842
WVFGRD96 74.0 55 70 80 4.22 0.5931
WVFGRD96 75.0 55 70 80 4.23 0.6013
WVFGRD96 76.0 55 70 80 4.23 0.6111
WVFGRD96 77.0 55 70 80 4.23 0.6197
WVFGRD96 78.0 55 70 80 4.23 0.6262
WVFGRD96 79.0 55 70 80 4.24 0.6347
WVFGRD96 80.0 55 70 80 4.24 0.6431
WVFGRD96 81.0 55 70 80 4.24 0.6498
WVFGRD96 82.0 55 70 80 4.24 0.6575
WVFGRD96 83.0 55 70 80 4.25 0.6651
WVFGRD96 84.0 55 70 80 4.25 0.6723
WVFGRD96 85.0 55 70 80 4.25 0.6782
WVFGRD96 86.0 55 70 80 4.25 0.6846
WVFGRD96 87.0 55 70 80 4.25 0.6915
WVFGRD96 88.0 55 70 80 4.25 0.6962
WVFGRD96 89.0 55 70 80 4.26 0.7024
WVFGRD96 90.0 55 70 80 4.26 0.7079
WVFGRD96 91.0 55 70 80 4.26 0.7126
WVFGRD96 92.0 55 70 80 4.26 0.7177
WVFGRD96 93.0 55 70 80 4.26 0.7223
WVFGRD96 94.0 55 70 80 4.26 0.7273
WVFGRD96 95.0 55 70 80 4.27 0.7313
WVFGRD96 96.0 55 70 80 4.27 0.7352
WVFGRD96 97.0 55 70 80 4.27 0.7397
WVFGRD96 98.0 55 70 80 4.27 0.7432
WVFGRD96 99.0 55 70 80 4.27 0.7462
WVFGRD96 100.0 55 70 80 4.27 0.7503
WVFGRD96 101.0 55 70 80 4.27 0.7531
WVFGRD96 102.0 55 70 80 4.27 0.7557
WVFGRD96 103.0 55 70 80 4.28 0.7588
WVFGRD96 104.0 55 70 80 4.28 0.7612
WVFGRD96 105.0 55 70 80 4.28 0.7638
WVFGRD96 106.0 55 70 80 4.28 0.7658
WVFGRD96 107.0 55 70 80 4.28 0.7680
WVFGRD96 108.0 55 70 80 4.28 0.7699
WVFGRD96 109.0 55 70 80 4.28 0.7722
WVFGRD96 110.0 55 70 80 4.28 0.7733
WVFGRD96 111.0 55 70 80 4.29 0.7750
WVFGRD96 112.0 55 70 80 4.29 0.7768
WVFGRD96 113.0 55 70 80 4.29 0.7779
WVFGRD96 114.0 55 70 80 4.29 0.7788
WVFGRD96 115.0 55 70 80 4.29 0.7803
WVFGRD96 116.0 55 70 80 4.29 0.7811
WVFGRD96 117.0 55 70 80 4.29 0.7819
WVFGRD96 118.0 55 70 80 4.29 0.7830
WVFGRD96 119.0 55 70 80 4.29 0.7835
WVFGRD96 120.0 55 70 80 4.30 0.7843
WVFGRD96 121.0 55 70 80 4.30 0.7849
WVFGRD96 122.0 55 70 80 4.30 0.7854
WVFGRD96 123.0 55 75 80 4.30 0.7860
WVFGRD96 124.0 55 75 80 4.30 0.7858
WVFGRD96 125.0 55 75 80 4.30 0.7867
WVFGRD96 126.0 55 75 80 4.30 0.7866
WVFGRD96 127.0 55 75 80 4.30 0.7874
WVFGRD96 128.0 55 75 80 4.30 0.7875
WVFGRD96 129.0 55 75 85 4.30 0.7880
WVFGRD96 130.0 55 75 85 4.31 0.7877
WVFGRD96 131.0 55 75 85 4.31 0.7874
WVFGRD96 132.0 55 75 85 4.31 0.7884
WVFGRD96 133.0 55 75 85 4.31 0.7883
WVFGRD96 134.0 260 20 110 4.31 0.7883
WVFGRD96 135.0 260 20 110 4.31 0.7876
WVFGRD96 136.0 55 75 85 4.31 0.7872
WVFGRD96 137.0 260 20 110 4.31 0.7877
WVFGRD96 138.0 55 75 85 4.31 0.7875
WVFGRD96 139.0 55 75 85 4.31 0.7864
The best solution is
WVFGRD96 132.0 55 75 85 4.31 0.7884
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
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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 WUS.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
Model after 8 iterations
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
1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00
6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00
13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00
19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00
0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 0.00 0.00 1.00 1.00