The ANSS event ID is ak0128tllrpw and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0128tllrpw/executive.
2012/07/10 04:06:54 63.439 -149.394 104.0 4.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2012/07/10 04:06:54:0 63.44 -149.39 104.0 4.2 Alaska
Stations used:
AK.BPAW AK.BWN AK.CCB AK.GHO AK.GLM AK.KNK AK.KTH AK.MDM
AK.MLY AK.NEA AK.PAX AK.PPLA AK.SAW AK.SCM AK.TRF AK.WRH
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 3.31e+22 dyne-cm
Mw = 4.28
Z = 122 km
Plane Strike Dip Rake
NP1 324 58 138
NP2 80 55 40
Principal Axes:
Axis Value Plunge Azimuth
T 3.31e+22 51 290
N 0.00e+00 39 114
P -3.31e+22 2 23
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.65e+22
Mxy -1.61e+22
Mxz 4.64e+21
Myy 6.50e+21
Myz -1.56e+22
Mzz 2.00e+22
------------ P
---------------- ---
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############------------------
#################-----------------
####################----------------
#######################---------------
#########################---------------
######### ###############-------------
########## T ################------------#
########## #################----------##
###############################-------####
################################----######
-##############################--#######
----#########################---########
-------###############---------#######
-------------------------------#####
------------------------------####
----------------------------##
--------------------------##
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Global CMT Convention Moment Tensor:
R T P
2.00e+22 4.64e+21 1.56e+22
4.64e+21 -2.65e+22 1.61e+22
1.56e+22 1.61e+22 6.50e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120710040654/index.html
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STK = 80
DIP = 55
RAKE = 40
MW = 4.28
HS = 122.0
The NDK file is 20120710040654.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 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 110 50 -90 3.15 0.2028
WVFGRD96 1.0 310 45 -55 3.17 0.1923
WVFGRD96 2.0 295 40 -80 3.35 0.2756
WVFGRD96 3.0 295 40 -75 3.41 0.2676
WVFGRD96 4.0 335 60 -20 3.37 0.2360
WVFGRD96 5.0 170 50 10 3.41 0.2509
WVFGRD96 6.0 170 55 10 3.44 0.2703
WVFGRD96 7.0 165 50 5 3.44 0.2881
WVFGRD96 8.0 165 45 10 3.50 0.3005
WVFGRD96 9.0 165 50 10 3.53 0.3100
WVFGRD96 10.0 180 60 20 3.59 0.3185
WVFGRD96 11.0 180 65 20 3.63 0.3261
WVFGRD96 12.0 180 65 20 3.65 0.3329
WVFGRD96 13.0 180 65 20 3.66 0.3338
WVFGRD96 14.0 180 65 20 3.68 0.3361
WVFGRD96 15.0 180 65 20 3.69 0.3362
WVFGRD96 16.0 180 65 20 3.71 0.3315
WVFGRD96 17.0 185 65 20 3.73 0.3303
WVFGRD96 18.0 185 65 20 3.74 0.3259
WVFGRD96 19.0 185 65 20 3.76 0.3241
WVFGRD96 20.0 185 65 20 3.77 0.3211
WVFGRD96 21.0 190 65 15 3.79 0.3083
WVFGRD96 22.0 190 65 15 3.81 0.3042
WVFGRD96 23.0 190 65 15 3.81 0.2951
WVFGRD96 24.0 190 70 15 3.83 0.2748
WVFGRD96 25.0 190 70 15 3.84 0.2659
WVFGRD96 26.0 240 45 30 3.70 0.2595
WVFGRD96 27.0 240 50 25 3.71 0.2610
WVFGRD96 28.0 240 50 25 3.72 0.2627
WVFGRD96 29.0 240 50 25 3.73 0.2601
WVFGRD96 30.0 0 60 -25 3.83 0.2657
WVFGRD96 31.0 0 60 -25 3.84 0.2746
WVFGRD96 32.0 0 60 -25 3.86 0.2818
WVFGRD96 33.0 0 60 -25 3.87 0.2872
WVFGRD96 34.0 0 60 -20 3.88 0.2929
WVFGRD96 35.0 0 65 -20 3.92 0.2991
WVFGRD96 36.0 5 70 -15 3.95 0.3068
WVFGRD96 37.0 5 70 -10 3.97 0.3166
WVFGRD96 38.0 5 75 -5 4.01 0.3277
WVFGRD96 39.0 5 75 -5 4.03 0.3412
WVFGRD96 40.0 5 70 -10 4.08 0.3573
WVFGRD96 41.0 5 70 -5 4.10 0.3644
WVFGRD96 42.0 5 70 -5 4.11 0.3702
WVFGRD96 43.0 5 65 -5 4.11 0.3761
WVFGRD96 44.0 5 65 -5 4.12 0.3827
WVFGRD96 45.0 5 65 -5 4.13 0.3883
WVFGRD96 46.0 5 65 -5 4.14 0.3934
WVFGRD96 47.0 5 65 -5 4.15 0.3970
WVFGRD96 48.0 5 65 -5 4.16 0.3995
WVFGRD96 49.0 5 60 -5 4.14 0.4017
WVFGRD96 50.0 10 65 15 4.16 0.4059
WVFGRD96 51.0 10 65 15 4.17 0.4103
WVFGRD96 52.0 15 60 25 4.15 0.4165
WVFGRD96 53.0 15 60 25 4.15 0.4216
WVFGRD96 54.0 15 60 25 4.16 0.4257
WVFGRD96 55.0 15 65 25 4.19 0.4286
WVFGRD96 56.0 80 85 -30 4.15 0.4346
WVFGRD96 57.0 260 90 30 4.14 0.4373
WVFGRD96 58.0 80 85 -30 4.15 0.4484
WVFGRD96 59.0 80 85 -30 4.16 0.4541
WVFGRD96 60.0 260 90 30 4.15 0.4569
WVFGRD96 61.0 80 85 -30 4.16 0.4635
WVFGRD96 62.0 80 45 45 4.13 0.4787
WVFGRD96 63.0 80 45 45 4.13 0.4917
WVFGRD96 64.0 80 45 45 4.13 0.5028
WVFGRD96 65.0 80 45 40 4.15 0.5143
WVFGRD96 66.0 80 50 40 4.16 0.5247
WVFGRD96 67.0 80 50 40 4.16 0.5355
WVFGRD96 68.0 80 50 40 4.17 0.5455
WVFGRD96 69.0 80 50 40 4.17 0.5545
WVFGRD96 70.0 75 50 35 4.17 0.5624
WVFGRD96 71.0 75 50 35 4.17 0.5703
WVFGRD96 72.0 80 50 40 4.18 0.5769
WVFGRD96 73.0 80 50 40 4.18 0.5855
WVFGRD96 74.0 75 50 35 4.18 0.5918
WVFGRD96 75.0 75 50 35 4.18 0.5982
WVFGRD96 76.0 75 50 35 4.18 0.6048
WVFGRD96 77.0 75 50 35 4.18 0.6104
WVFGRD96 78.0 75 50 35 4.19 0.6170
WVFGRD96 79.0 75 50 35 4.19 0.6215
WVFGRD96 80.0 75 50 35 4.19 0.6276
WVFGRD96 81.0 75 50 35 4.20 0.6323
WVFGRD96 82.0 75 50 35 4.20 0.6388
WVFGRD96 83.0 75 50 35 4.20 0.6414
WVFGRD96 84.0 75 50 35 4.20 0.6473
WVFGRD96 85.0 75 50 35 4.21 0.6517
WVFGRD96 86.0 75 50 35 4.21 0.6564
WVFGRD96 87.0 75 50 40 4.20 0.6591
WVFGRD96 88.0 75 50 40 4.20 0.6657
WVFGRD96 89.0 75 50 40 4.21 0.6697
WVFGRD96 90.0 75 50 40 4.21 0.6734
WVFGRD96 91.0 75 50 40 4.21 0.6784
WVFGRD96 92.0 75 50 40 4.21 0.6816
WVFGRD96 93.0 75 50 40 4.22 0.6854
WVFGRD96 94.0 75 50 40 4.22 0.6889
WVFGRD96 95.0 75 50 40 4.22 0.6924
WVFGRD96 96.0 75 50 40 4.22 0.6945
WVFGRD96 97.0 75 50 40 4.23 0.6997
WVFGRD96 98.0 75 50 40 4.23 0.6995
WVFGRD96 99.0 75 50 40 4.23 0.7037
WVFGRD96 100.0 75 50 40 4.23 0.7063
WVFGRD96 101.0 75 50 40 4.23 0.7071
WVFGRD96 102.0 75 50 40 4.24 0.7103
WVFGRD96 103.0 75 50 40 4.24 0.7112
WVFGRD96 104.0 75 50 40 4.24 0.7131
WVFGRD96 105.0 75 50 40 4.24 0.7134
WVFGRD96 106.0 75 50 40 4.24 0.7161
WVFGRD96 107.0 75 50 40 4.24 0.7158
WVFGRD96 108.0 80 55 40 4.26 0.7188
WVFGRD96 109.0 80 55 40 4.26 0.7196
WVFGRD96 110.0 80 55 40 4.26 0.7201
WVFGRD96 111.0 80 55 40 4.26 0.7223
WVFGRD96 112.0 80 55 40 4.26 0.7219
WVFGRD96 113.0 80 55 40 4.27 0.7227
WVFGRD96 114.0 80 55 40 4.27 0.7242
WVFGRD96 115.0 80 55 40 4.27 0.7236
WVFGRD96 116.0 80 55 40 4.27 0.7248
WVFGRD96 117.0 80 55 40 4.27 0.7259
WVFGRD96 118.0 80 55 40 4.27 0.7243
WVFGRD96 119.0 80 55 40 4.27 0.7264
WVFGRD96 120.0 80 55 40 4.27 0.7266
WVFGRD96 121.0 80 55 40 4.27 0.7257
WVFGRD96 122.0 80 55 40 4.28 0.7272
WVFGRD96 123.0 80 55 40 4.28 0.7255
WVFGRD96 124.0 80 55 40 4.28 0.7266
WVFGRD96 125.0 80 55 40 4.28 0.7264
WVFGRD96 126.0 80 55 40 4.28 0.7269
WVFGRD96 127.0 80 55 40 4.28 0.7256
WVFGRD96 128.0 80 55 40 4.28 0.7256
WVFGRD96 129.0 80 55 40 4.28 0.7258
The best solution is
WVFGRD96 122.0 80 55 40 4.28 0.7272
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
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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