The ANSS event ID is ak0139sm5zgh and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0139sm5zgh/executive.
2013/08/01 21:32:47 60.142 -152.916 127.6 4.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2013/08/01 21:32:47:0 60.14 -152.92 127.6 4.8 Alaska
Stations used:
AK.BPAW AK.BRLK AK.CAST AK.CNP AK.DHY AK.FID AK.GLI AK.HIN
AK.KNK AK.KTH AK.PPLA AK.RC01 AK.RND AK.SCM AK.SKN AK.SSN
AK.SWD AT.OHAK AT.PMR AT.SVW2 II.KDAK
Filtering commands used:
cut a -30 a 120
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 2.07e+23 dyne-cm
Mw = 4.81
Z = 130 km
Plane Strike Dip Rake
NP1 307 69 148
NP2 50 60 25
Principal Axes:
Axis Value Plunge Azimuth
T 2.07e+23 38 266
N 0.00e+00 52 97
P -2.07e+23 5 0
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.04e+23
Mxy 9.07e+21
Mxz -2.67e+22
Myy 1.28e+23
Myz -9.98e+22
Mzz 7.56e+22
------ P -----
---------- ---------
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#####----------------------------#
###########-----------------------##
################------------------####
####################--------------######
#######################----------#######
##########################-------#########
####### ##################----##########
####### T ####################-###########
####### ###################---##########
##########################-------#######
########################----------######
#####################-------------####
#################-----------------##
###########----------------------#
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Global CMT Convention Moment Tensor:
R T P
7.56e+22 -2.67e+22 9.98e+22
-2.67e+22 -2.04e+23 -9.07e+21
9.98e+22 -9.07e+21 1.28e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130801213247/index.html
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STK = 50
DIP = 60
RAKE = 25
MW = 4.81
HS = 130.0
The NDK file is 20130801213247.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:
cut a -30 a 120 rtr taper w 0.1 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 0.5 115 65 -35 3.86 0.2111
WVFGRD96 1.0 115 65 -35 3.89 0.2239
WVFGRD96 2.0 300 65 -25 3.97 0.2919
WVFGRD96 3.0 305 65 -15 4.00 0.3152
WVFGRD96 4.0 305 75 -5 4.01 0.3344
WVFGRD96 5.0 305 75 -5 4.04 0.3491
WVFGRD96 6.0 305 75 0 4.06 0.3603
WVFGRD96 7.0 305 80 15 4.09 0.3716
WVFGRD96 8.0 310 75 20 4.12 0.3810
WVFGRD96 9.0 310 75 20 4.14 0.3869
WVFGRD96 10.0 40 80 15 4.15 0.3923
WVFGRD96 11.0 40 75 15 4.17 0.4038
WVFGRD96 12.0 40 75 15 4.19 0.4141
WVFGRD96 13.0 40 75 15 4.20 0.4229
WVFGRD96 14.0 40 80 15 4.21 0.4304
WVFGRD96 15.0 40 80 15 4.23 0.4378
WVFGRD96 16.0 40 80 10 4.24 0.4453
WVFGRD96 17.0 40 80 10 4.25 0.4521
WVFGRD96 18.0 40 80 10 4.27 0.4584
WVFGRD96 19.0 40 80 10 4.28 0.4640
WVFGRD96 20.0 40 80 10 4.29 0.4702
WVFGRD96 21.0 40 80 10 4.30 0.4755
WVFGRD96 22.0 40 80 10 4.31 0.4802
WVFGRD96 23.0 40 80 10 4.32 0.4845
WVFGRD96 24.0 40 80 10 4.33 0.4886
WVFGRD96 25.0 40 80 10 4.34 0.4930
WVFGRD96 26.0 40 80 10 4.35 0.4967
WVFGRD96 27.0 40 80 10 4.36 0.4994
WVFGRD96 28.0 40 80 10 4.37 0.5020
WVFGRD96 29.0 40 80 10 4.38 0.5049
WVFGRD96 30.0 40 80 10 4.39 0.5072
WVFGRD96 31.0 40 80 10 4.40 0.5097
WVFGRD96 32.0 40 80 10 4.41 0.5112
WVFGRD96 33.0 40 80 10 4.42 0.5128
WVFGRD96 34.0 40 80 10 4.43 0.5142
WVFGRD96 35.0 40 80 10 4.45 0.5148
WVFGRD96 36.0 40 85 5 4.46 0.5168
WVFGRD96 37.0 40 85 5 4.48 0.5204
WVFGRD96 38.0 40 85 5 4.49 0.5259
WVFGRD96 39.0 40 85 5 4.51 0.5326
WVFGRD96 40.0 220 85 -10 4.54 0.5391
WVFGRD96 41.0 40 85 5 4.55 0.5415
WVFGRD96 42.0 40 90 5 4.56 0.5435
WVFGRD96 43.0 45 85 5 4.57 0.5453
WVFGRD96 44.0 220 90 -10 4.57 0.5469
WVFGRD96 45.0 45 85 5 4.59 0.5493
WVFGRD96 46.0 45 85 5 4.60 0.5512
WVFGRD96 47.0 220 90 -10 4.60 0.5523
WVFGRD96 48.0 40 85 10 4.60 0.5551
WVFGRD96 49.0 40 85 10 4.61 0.5572
WVFGRD96 50.0 40 85 10 4.61 0.5594
WVFGRD96 51.0 45 80 5 4.63 0.5616
WVFGRD96 52.0 45 80 5 4.63 0.5653
WVFGRD96 53.0 45 80 5 4.64 0.5695
WVFGRD96 54.0 45 80 5 4.65 0.5737
WVFGRD96 55.0 45 80 5 4.65 0.5777
WVFGRD96 56.0 45 75 5 4.65 0.5816
WVFGRD96 57.0 45 75 5 4.66 0.5862
WVFGRD96 58.0 45 75 5 4.66 0.5915
WVFGRD96 59.0 45 75 5 4.67 0.5967
WVFGRD96 60.0 45 75 5 4.67 0.6016
WVFGRD96 61.0 45 75 10 4.67 0.6060
WVFGRD96 62.0 45 75 10 4.68 0.6111
WVFGRD96 63.0 45 75 10 4.68 0.6162
WVFGRD96 64.0 45 75 10 4.69 0.6220
WVFGRD96 65.0 45 75 10 4.69 0.6277
WVFGRD96 66.0 45 75 10 4.69 0.6326
WVFGRD96 67.0 45 75 10 4.70 0.6367
WVFGRD96 68.0 45 75 10 4.70 0.6417
WVFGRD96 69.0 45 75 10 4.70 0.6468
WVFGRD96 70.0 45 75 10 4.71 0.6508
WVFGRD96 71.0 50 70 10 4.72 0.6547
WVFGRD96 72.0 50 70 10 4.72 0.6609
WVFGRD96 73.0 50 70 10 4.72 0.6658
WVFGRD96 74.0 50 70 10 4.73 0.6691
WVFGRD96 75.0 50 70 10 4.73 0.6743
WVFGRD96 76.0 50 70 10 4.73 0.6787
WVFGRD96 77.0 50 70 10 4.74 0.6813
WVFGRD96 78.0 50 70 10 4.74 0.6857
WVFGRD96 79.0 50 70 10 4.74 0.6892
WVFGRD96 80.0 50 70 15 4.74 0.6916
WVFGRD96 81.0 50 70 15 4.74 0.6965
WVFGRD96 82.0 50 70 15 4.75 0.6994
WVFGRD96 83.0 50 70 15 4.75 0.7021
WVFGRD96 84.0 50 65 15 4.75 0.7060
WVFGRD96 85.0 50 65 15 4.75 0.7077
WVFGRD96 86.0 50 65 15 4.75 0.7121
WVFGRD96 87.0 50 65 15 4.75 0.7146
WVFGRD96 88.0 50 65 15 4.75 0.7169
WVFGRD96 89.0 50 65 15 4.75 0.7199
WVFGRD96 90.0 50 65 15 4.76 0.7217
WVFGRD96 91.0 50 65 15 4.76 0.7250
WVFGRD96 92.0 50 65 20 4.76 0.7261
WVFGRD96 93.0 50 65 20 4.76 0.7294
WVFGRD96 94.0 50 65 20 4.76 0.7315
WVFGRD96 95.0 50 65 20 4.76 0.7344
WVFGRD96 96.0 50 65 20 4.77 0.7364
WVFGRD96 97.0 50 65 20 4.77 0.7385
WVFGRD96 98.0 50 65 20 4.77 0.7407
WVFGRD96 99.0 50 65 20 4.77 0.7429
WVFGRD96 100.0 50 65 20 4.77 0.7443
WVFGRD96 101.0 50 65 20 4.77 0.7464
WVFGRD96 102.0 50 65 20 4.77 0.7478
WVFGRD96 103.0 50 65 20 4.78 0.7495
WVFGRD96 104.0 50 65 20 4.78 0.7506
WVFGRD96 105.0 50 65 25 4.78 0.7528
WVFGRD96 106.0 50 65 25 4.78 0.7536
WVFGRD96 107.0 50 65 25 4.78 0.7558
WVFGRD96 108.0 50 65 25 4.78 0.7567
WVFGRD96 109.0 50 65 25 4.79 0.7586
WVFGRD96 110.0 50 65 25 4.79 0.7589
WVFGRD96 111.0 50 65 25 4.79 0.7614
WVFGRD96 112.0 50 60 25 4.78 0.7613
WVFGRD96 113.0 50 60 25 4.78 0.7634
WVFGRD96 114.0 50 60 25 4.79 0.7643
WVFGRD96 115.0 50 60 25 4.79 0.7650
WVFGRD96 116.0 50 60 25 4.79 0.7666
WVFGRD96 117.0 50 60 25 4.79 0.7666
WVFGRD96 118.0 50 60 25 4.79 0.7684
WVFGRD96 119.0 50 60 25 4.79 0.7677
WVFGRD96 120.0 50 60 25 4.79 0.7694
WVFGRD96 121.0 50 60 25 4.80 0.7697
WVFGRD96 122.0 50 60 25 4.80 0.7702
WVFGRD96 123.0 50 60 25 4.80 0.7711
WVFGRD96 124.0 50 60 25 4.80 0.7703
WVFGRD96 125.0 50 60 25 4.80 0.7718
WVFGRD96 126.0 50 60 25 4.80 0.7709
WVFGRD96 127.0 50 60 25 4.80 0.7716
WVFGRD96 128.0 50 60 25 4.80 0.7720
WVFGRD96 129.0 50 60 25 4.81 0.7713
WVFGRD96 130.0 50 60 25 4.81 0.7721
WVFGRD96 131.0 50 60 25 4.81 0.7709
WVFGRD96 132.0 50 60 25 4.81 0.7713
WVFGRD96 133.0 50 60 30 4.81 0.7716
WVFGRD96 134.0 50 60 30 4.81 0.7702
WVFGRD96 135.0 50 60 30 4.81 0.7716
WVFGRD96 136.0 50 60 30 4.81 0.7702
WVFGRD96 137.0 50 60 30 4.82 0.7706
WVFGRD96 138.0 50 60 30 4.82 0.7707
WVFGRD96 139.0 50 60 30 4.82 0.7688
The best solution is
WVFGRD96 130.0 50 60 25 4.81 0.7721
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
cut a -30 a 120 rtr taper w 0.1 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