The ANSS event ID is ak0118i0juhl and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0118i0juhl/executive.
2011/07/04 03:57:55 60.238 -152.802 111.9 4.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2011/07/04 03:57:55:0 60.24 -152.80 111.9 4.2 Alaska
Stations used:
AK.BPAW AK.CAST AK.CNP AK.KTH AK.PPLA AK.RC01 AK.SSN AK.TRF
AT.OHAK AT.PMR AT.SVW2 II.KDAK
Filtering commands used:
hp c 0.02 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 2.43e+22 dyne-cm
Mw = 4.19
Z = 124 km
Plane Strike Dip Rake
NP1 259 71 114
NP2 25 30 40
Principal Axes:
Axis Value Plunge Azimuth
T 2.43e+22 57 201
N 0.00e+00 23 71
P -2.43e+22 23 331
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.53e+21
Mxy 1.11e+22
Mxz -1.79e+22
Myy -3.98e+21
Myz 2.65e+20
Mzz 1.35e+22
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---- -------------------##
----- P --------------------##
------- ---------------------###
--------------------------------####
----------------------------------####
-----------------------------------#####
-------------------################----#
-------------#######################------
--------############################------
-----###############################------
--##################################------
##################################------
############### ###############-------
############## T ##############-------
############# #############-------
##########################--------
#######################-------
###################---------
#############---------
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Global CMT Convention Moment Tensor:
R T P
1.35e+22 -1.79e+22 -2.65e+20
-1.79e+22 -9.53e+21 -1.11e+22
-2.65e+20 -1.11e+22 -3.98e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110704035755/index.html
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STK = 25
DIP = 30
RAKE = 40
MW = 4.19
HS = 124.0
The NDK file is 20110704035755.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 85 50 -70 3.27 0.1748
WVFGRD96 1.0 75 50 -85 3.31 0.1880
WVFGRD96 2.0 5 45 -95 3.39 0.2345
WVFGRD96 3.0 165 45 -95 3.44 0.2554
WVFGRD96 4.0 5 50 -60 3.46 0.2598
WVFGRD96 5.0 20 80 5 3.43 0.2736
WVFGRD96 6.0 20 80 5 3.46 0.2873
WVFGRD96 7.0 20 80 5 3.48 0.3008
WVFGRD96 8.0 20 80 5 3.52 0.3141
WVFGRD96 9.0 20 80 10 3.54 0.3218
WVFGRD96 10.0 20 70 -20 3.54 0.3301
WVFGRD96 11.0 210 70 25 3.54 0.3416
WVFGRD96 12.0 210 70 25 3.56 0.3533
WVFGRD96 13.0 210 70 25 3.57 0.3639
WVFGRD96 14.0 210 70 25 3.58 0.3735
WVFGRD96 15.0 210 70 25 3.60 0.3825
WVFGRD96 16.0 210 70 25 3.61 0.3918
WVFGRD96 17.0 210 70 25 3.62 0.4001
WVFGRD96 18.0 210 70 25 3.63 0.4075
WVFGRD96 19.0 210 70 25 3.64 0.4143
WVFGRD96 20.0 210 70 25 3.65 0.4220
WVFGRD96 21.0 210 70 25 3.66 0.4283
WVFGRD96 22.0 210 75 30 3.68 0.4342
WVFGRD96 23.0 205 70 25 3.71 0.4408
WVFGRD96 24.0 210 75 35 3.71 0.4475
WVFGRD96 25.0 210 75 35 3.72 0.4533
WVFGRD96 26.0 205 75 30 3.74 0.4585
WVFGRD96 27.0 205 75 30 3.75 0.4644
WVFGRD96 28.0 205 75 30 3.76 0.4688
WVFGRD96 29.0 205 75 30 3.77 0.4716
WVFGRD96 30.0 205 75 30 3.78 0.4748
WVFGRD96 31.0 205 75 30 3.79 0.4778
WVFGRD96 32.0 205 75 30 3.80 0.4794
WVFGRD96 33.0 210 75 35 3.80 0.4796
WVFGRD96 34.0 205 75 30 3.82 0.4806
WVFGRD96 35.0 205 75 30 3.83 0.4820
WVFGRD96 36.0 210 75 30 3.82 0.4830
WVFGRD96 37.0 210 75 30 3.83 0.4840
WVFGRD96 38.0 210 80 35 3.85 0.4839
WVFGRD96 39.0 210 75 30 3.86 0.4857
WVFGRD96 40.0 210 75 45 3.95 0.4823
WVFGRD96 41.0 210 75 45 3.96 0.4813
WVFGRD96 42.0 210 75 45 3.97 0.4795
WVFGRD96 43.0 210 75 45 3.98 0.4771
WVFGRD96 44.0 210 75 45 3.99 0.4745
WVFGRD96 45.0 210 75 45 4.00 0.4715
WVFGRD96 46.0 210 75 45 4.00 0.4681
WVFGRD96 47.0 210 75 45 4.01 0.4643
WVFGRD96 48.0 210 75 45 4.02 0.4602
WVFGRD96 49.0 215 70 45 4.01 0.4559
WVFGRD96 50.0 215 70 45 4.01 0.4518
WVFGRD96 51.0 215 70 45 4.02 0.4476
WVFGRD96 52.0 215 70 45 4.02 0.4435
WVFGRD96 53.0 215 70 45 4.03 0.4392
WVFGRD96 54.0 215 70 45 4.03 0.4347
WVFGRD96 55.0 215 70 40 4.02 0.4302
WVFGRD96 56.0 215 70 40 4.02 0.4257
WVFGRD96 57.0 20 70 25 4.03 0.4286
WVFGRD96 58.0 20 70 25 4.04 0.4344
WVFGRD96 59.0 25 65 30 4.03 0.4401
WVFGRD96 60.0 25 65 30 4.03 0.4458
WVFGRD96 61.0 25 65 30 4.03 0.4511
WVFGRD96 62.0 25 65 30 4.04 0.4560
WVFGRD96 63.0 25 65 35 4.06 0.4608
WVFGRD96 64.0 25 65 35 4.06 0.4657
WVFGRD96 65.0 25 65 35 4.06 0.4713
WVFGRD96 66.0 25 65 35 4.07 0.4762
WVFGRD96 67.0 20 65 30 4.09 0.4802
WVFGRD96 68.0 20 65 30 4.09 0.4837
WVFGRD96 69.0 20 65 30 4.09 0.4883
WVFGRD96 70.0 20 65 35 4.11 0.4924
WVFGRD96 71.0 20 65 35 4.11 0.4959
WVFGRD96 72.0 20 65 35 4.11 0.4985
WVFGRD96 73.0 20 65 35 4.12 0.5027
WVFGRD96 74.0 20 65 35 4.12 0.5055
WVFGRD96 75.0 20 65 35 4.12 0.5073
WVFGRD96 76.0 20 65 35 4.12 0.5116
WVFGRD96 77.0 20 65 35 4.12 0.5146
WVFGRD96 78.0 20 65 35 4.12 0.5159
WVFGRD96 79.0 15 45 10 4.10 0.5201
WVFGRD96 80.0 20 40 20 4.09 0.5265
WVFGRD96 81.0 15 40 15 4.12 0.5327
WVFGRD96 82.0 15 40 15 4.12 0.5404
WVFGRD96 83.0 15 40 15 4.12 0.5463
WVFGRD96 84.0 15 40 15 4.12 0.5528
WVFGRD96 85.0 20 35 25 4.12 0.5588
WVFGRD96 86.0 15 40 20 4.14 0.5638
WVFGRD96 87.0 15 40 20 4.15 0.5709
WVFGRD96 88.0 15 35 20 4.15 0.5760
WVFGRD96 89.0 15 35 20 4.15 0.5823
WVFGRD96 90.0 15 35 20 4.15 0.5874
WVFGRD96 91.0 15 35 20 4.15 0.5923
WVFGRD96 92.0 15 35 20 4.15 0.5976
WVFGRD96 93.0 15 35 20 4.16 0.6013
WVFGRD96 94.0 20 35 30 4.16 0.6066
WVFGRD96 95.0 20 35 30 4.16 0.6095
WVFGRD96 96.0 20 30 30 4.16 0.6148
WVFGRD96 97.0 20 30 30 4.17 0.6171
WVFGRD96 98.0 15 35 25 4.18 0.6223
WVFGRD96 99.0 20 30 30 4.17 0.6246
WVFGRD96 100.0 20 30 30 4.17 0.6291
WVFGRD96 101.0 15 35 25 4.18 0.6307
WVFGRD96 102.0 15 35 25 4.18 0.6347
WVFGRD96 103.0 15 35 25 4.18 0.6360
WVFGRD96 104.0 15 35 25 4.19 0.6397
WVFGRD96 105.0 15 35 25 4.19 0.6403
WVFGRD96 106.0 20 30 30 4.17 0.6439
WVFGRD96 107.0 25 30 40 4.18 0.6445
WVFGRD96 108.0 25 30 40 4.19 0.6477
WVFGRD96 109.0 25 30 40 4.19 0.6483
WVFGRD96 110.0 25 30 40 4.19 0.6512
WVFGRD96 111.0 25 30 40 4.19 0.6520
WVFGRD96 112.0 25 30 40 4.19 0.6536
WVFGRD96 113.0 25 30 40 4.19 0.6547
WVFGRD96 114.0 25 30 40 4.19 0.6557
WVFGRD96 115.0 25 30 40 4.19 0.6571
WVFGRD96 116.0 25 30 40 4.19 0.6568
WVFGRD96 117.0 25 30 40 4.19 0.6588
WVFGRD96 118.0 25 30 40 4.19 0.6580
WVFGRD96 119.0 25 30 40 4.19 0.6598
WVFGRD96 120.0 25 30 40 4.19 0.6597
WVFGRD96 121.0 25 30 40 4.19 0.6601
WVFGRD96 122.0 25 30 40 4.19 0.6607
WVFGRD96 123.0 25 30 40 4.19 0.6596
WVFGRD96 124.0 25 30 40 4.19 0.6611
WVFGRD96 125.0 25 30 40 4.19 0.6599
WVFGRD96 126.0 25 30 40 4.19 0.6605
WVFGRD96 127.0 25 30 40 4.20 0.6605
WVFGRD96 128.0 25 30 40 4.20 0.6593
WVFGRD96 129.0 25 30 40 4.20 0.6600
WVFGRD96 130.0 25 30 40 4.20 0.6586
WVFGRD96 131.0 25 30 40 4.20 0.6591
WVFGRD96 132.0 25 30 40 4.20 0.6585
WVFGRD96 133.0 25 30 40 4.20 0.6567
WVFGRD96 134.0 25 30 40 4.20 0.6578
WVFGRD96 135.0 25 30 40 4.20 0.6561
WVFGRD96 136.0 25 30 40 4.20 0.6556
WVFGRD96 137.0 25 30 40 4.20 0.6556
WVFGRD96 138.0 25 30 40 4.20 0.6531
WVFGRD96 139.0 25 30 40 4.20 0.6537
The best solution is
WVFGRD96 124.0 25 30 40 4.19 0.6611
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