The ANSS event ID is ak013ctmxi36 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak013ctmxi36/executive.
2013/10/06 13:42:17 62.912 -150.573 104.7 4 Alaska
USGS/SLU Moment Tensor Solution
ENS 2013/10/06 13:42:17:0 62.91 -150.57 104.7 4.0 Alaska
Stations used:
AK.BPAW AK.BWN AK.CCB AK.DHY AK.KTH AK.MCK AK.MLY AK.PPLA
AK.RND AK.SKN AK.SSN AK.TRF AK.WAT1 AK.WAT2 AK.WAT3 AK.WAT4
AK.WAT5 AK.WAT6 AK.WAT7 AK.WRH IM.IL31 IU.COLA TA.HDA
TA.POKR TA.TCOL YE.PIC1 YE.PIC4
Filtering commands used:
cut a -30 a 120
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.60e+22 dyne-cm
Mw = 4.07
Z = 108 km
Plane Strike Dip Rake
NP1 295 60 65
NP2 158 38 126
Principal Axes:
Axis Value Plunge Azimuth
T 1.60e+22 65 159
N 0.00e+00 21 308
P -1.60e+22 12 43
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.84e+21
Mxy -8.59e+21
Mxz -8.02e+21
Myy -6.74e+21
Myz -2.39e+14
Mzz 1.26e+22
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##--------------------
###----------------------
###----------------------- P -
#####----------------------- ---
#########---------------------------
------#############-------------------
------##################----------------
------#####################-------------
-------########################-----------
--------#########################---------
--------###########################-------
--------#############################-----
--------############# #############---
---------############ T ##############--
---------########### ###############
---------###########################
----------########################
---------#####################
-----------#################
-----------###########
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Global CMT Convention Moment Tensor:
R T P
1.26e+22 -8.02e+21 2.39e+14
-8.02e+21 -5.84e+21 8.59e+21
2.39e+14 8.59e+21 -6.74e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131006134217/index.html
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STK = 295
DIP = 60
RAKE = 65
MW = 4.07
HS = 108.0
The NDK file is 20131006134217.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 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 340 45 -80 3.11 0.1944
WVFGRD96 2.0 330 45 -95 3.26 0.2539
WVFGRD96 3.0 345 40 -75 3.30 0.2036
WVFGRD96 4.0 210 65 30 3.29 0.1968
WVFGRD96 5.0 210 65 35 3.31 0.2177
WVFGRD96 6.0 205 70 35 3.32 0.2344
WVFGRD96 7.0 205 70 40 3.34 0.2518
WVFGRD96 8.0 210 65 45 3.41 0.2555
WVFGRD96 9.0 205 70 45 3.42 0.2677
WVFGRD96 10.0 210 65 50 3.44 0.2764
WVFGRD96 11.0 205 65 50 3.45 0.2823
WVFGRD96 12.0 205 65 50 3.47 0.2854
WVFGRD96 13.0 210 65 55 3.48 0.2864
WVFGRD96 14.0 210 65 55 3.50 0.2857
WVFGRD96 15.0 295 50 35 3.51 0.2857
WVFGRD96 16.0 295 50 35 3.52 0.2866
WVFGRD96 17.0 295 50 40 3.53 0.2871
WVFGRD96 18.0 295 50 40 3.54 0.2863
WVFGRD96 19.0 295 50 35 3.56 0.2845
WVFGRD96 20.0 295 50 40 3.56 0.2821
WVFGRD96 21.0 295 50 40 3.58 0.2785
WVFGRD96 22.0 295 50 35 3.59 0.2753
WVFGRD96 23.0 285 45 25 3.59 0.2717
WVFGRD96 24.0 295 60 35 3.62 0.2684
WVFGRD96 25.0 295 60 40 3.62 0.2661
WVFGRD96 26.0 295 60 40 3.62 0.2624
WVFGRD96 27.0 295 65 40 3.64 0.2608
WVFGRD96 28.0 295 65 40 3.64 0.2602
WVFGRD96 29.0 295 65 40 3.65 0.2594
WVFGRD96 30.0 295 65 40 3.66 0.2593
WVFGRD96 31.0 295 65 40 3.67 0.2586
WVFGRD96 32.0 295 55 30 3.68 0.2642
WVFGRD96 33.0 295 55 30 3.69 0.2706
WVFGRD96 34.0 295 60 30 3.70 0.2767
WVFGRD96 35.0 295 55 35 3.70 0.2819
WVFGRD96 36.0 295 55 35 3.71 0.2856
WVFGRD96 37.0 295 55 35 3.72 0.2880
WVFGRD96 38.0 55 50 -85 3.75 0.2891
WVFGRD96 39.0 55 50 -85 3.77 0.2925
WVFGRD96 40.0 60 50 -85 3.87 0.3008
WVFGRD96 41.0 60 50 -85 3.89 0.3024
WVFGRD96 42.0 60 50 -85 3.90 0.3022
WVFGRD96 43.0 305 45 60 3.86 0.3006
WVFGRD96 44.0 60 50 -85 3.92 0.2984
WVFGRD96 45.0 305 45 55 3.87 0.2976
WVFGRD96 46.0 305 45 55 3.88 0.2986
WVFGRD96 47.0 305 45 55 3.88 0.2979
WVFGRD96 48.0 95 55 -40 3.94 0.3027
WVFGRD96 49.0 95 55 -40 3.95 0.3068
WVFGRD96 50.0 95 55 -40 3.96 0.3108
WVFGRD96 51.0 110 85 -40 3.94 0.3163
WVFGRD96 52.0 110 85 -40 3.94 0.3235
WVFGRD96 53.0 110 85 -40 3.95 0.3310
WVFGRD96 54.0 110 85 -45 3.96 0.3375
WVFGRD96 55.0 305 60 65 3.92 0.3450
WVFGRD96 56.0 305 60 65 3.93 0.3561
WVFGRD96 57.0 305 60 65 3.94 0.3679
WVFGRD96 58.0 305 60 65 3.94 0.3785
WVFGRD96 59.0 305 60 65 3.95 0.3895
WVFGRD96 60.0 305 60 65 3.95 0.4010
WVFGRD96 61.0 305 60 65 3.96 0.4106
WVFGRD96 62.0 305 60 65 3.96 0.4222
WVFGRD96 63.0 305 60 65 3.97 0.4322
WVFGRD96 64.0 305 65 65 3.97 0.4426
WVFGRD96 65.0 305 65 65 3.98 0.4533
WVFGRD96 66.0 305 65 65 3.98 0.4636
WVFGRD96 67.0 300 65 65 3.99 0.4741
WVFGRD96 68.0 300 65 65 3.99 0.4838
WVFGRD96 69.0 300 65 65 4.00 0.4934
WVFGRD96 70.0 300 65 65 4.00 0.5031
WVFGRD96 71.0 300 65 65 4.00 0.5116
WVFGRD96 72.0 300 65 65 4.01 0.5210
WVFGRD96 73.0 300 65 65 4.01 0.5278
WVFGRD96 74.0 300 65 65 4.01 0.5368
WVFGRD96 75.0 300 65 65 4.02 0.5430
WVFGRD96 76.0 300 65 65 4.02 0.5510
WVFGRD96 77.0 300 65 65 4.02 0.5565
WVFGRD96 78.0 300 65 65 4.02 0.5628
WVFGRD96 79.0 300 65 65 4.03 0.5680
WVFGRD96 80.0 300 65 65 4.03 0.5733
WVFGRD96 81.0 300 65 65 4.03 0.5790
WVFGRD96 82.0 300 65 65 4.03 0.5817
WVFGRD96 83.0 300 65 65 4.03 0.5871
WVFGRD96 84.0 300 65 65 4.04 0.5897
WVFGRD96 85.0 300 65 65 4.04 0.5949
WVFGRD96 86.0 300 60 65 4.03 0.5972
WVFGRD96 87.0 300 60 65 4.04 0.6029
WVFGRD96 88.0 300 60 65 4.04 0.6061
WVFGRD96 89.0 300 60 65 4.04 0.6100
WVFGRD96 90.0 300 60 65 4.04 0.6142
WVFGRD96 91.0 300 60 65 4.04 0.6163
WVFGRD96 92.0 300 60 65 4.04 0.6206
WVFGRD96 93.0 300 60 65 4.05 0.6221
WVFGRD96 94.0 300 60 65 4.05 0.6252
WVFGRD96 95.0 300 60 65 4.05 0.6278
WVFGRD96 96.0 300 60 65 4.05 0.6294
WVFGRD96 97.0 300 60 65 4.05 0.6320
WVFGRD96 98.0 300 60 65 4.05 0.6337
WVFGRD96 99.0 300 60 65 4.05 0.6348
WVFGRD96 100.0 300 60 65 4.06 0.6369
WVFGRD96 101.0 300 60 65 4.06 0.6376
WVFGRD96 102.0 300 60 65 4.06 0.6379
WVFGRD96 103.0 300 60 65 4.06 0.6407
WVFGRD96 104.0 300 60 65 4.06 0.6391
WVFGRD96 105.0 300 60 65 4.06 0.6415
WVFGRD96 106.0 295 60 65 4.07 0.6422
WVFGRD96 107.0 295 60 65 4.07 0.6414
WVFGRD96 108.0 295 60 65 4.07 0.6433
WVFGRD96 109.0 295 60 65 4.07 0.6424
WVFGRD96 110.0 295 60 65 4.08 0.6428
WVFGRD96 111.0 295 60 65 4.08 0.6422
WVFGRD96 112.0 295 60 65 4.08 0.6428
WVFGRD96 113.0 295 60 65 4.08 0.6408
WVFGRD96 114.0 295 60 65 4.08 0.6419
WVFGRD96 115.0 295 60 65 4.08 0.6404
WVFGRD96 116.0 295 60 65 4.08 0.6388
WVFGRD96 117.0 295 60 65 4.08 0.6389
WVFGRD96 118.0 295 60 65 4.09 0.6374
WVFGRD96 119.0 295 60 65 4.09 0.6356
WVFGRD96 120.0 295 60 65 4.09 0.6347
WVFGRD96 121.0 295 60 65 4.09 0.6334
WVFGRD96 122.0 295 60 65 4.09 0.6313
WVFGRD96 123.0 295 60 65 4.09 0.6296
WVFGRD96 124.0 295 60 65 4.09 0.6282
WVFGRD96 125.0 295 60 65 4.09 0.6268
WVFGRD96 126.0 295 60 65 4.10 0.6229
WVFGRD96 127.0 295 60 65 4.10 0.6226
WVFGRD96 128.0 295 60 65 4.10 0.6208
WVFGRD96 129.0 295 60 65 4.10 0.6165
The best solution is
WVFGRD96 108.0 295 60 65 4.07 0.6433
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 0.10 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