The ANSS event ID is ak022crxd45r and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak022crxd45r/executive.
2022/10/05 10:01:40 61.748 -149.768 42.5 3.7 Alaska
USGS/SLU Moment Tensor Solution
ENS 2022/10/05 10:01:40:0 61.75 -149.77 42.5 3.7 Alaska
Stations used:
AK.CUT AK.DHY AK.FIRE AK.GHO AK.GLI AK.KNK AK.RC01 AK.SAW
AK.SCM AK.SSN AT.PMR
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 7.00e+21 dyne-cm
Mw = 3.83
Z = 49 km
Plane Strike Dip Rake
NP1 275 55 -50
NP2 39 51 -133
Principal Axes:
Axis Value Plunge Azimuth
T 7.00e+21 2 338
N 0.00e+00 32 69
P -7.00e+21 58 244
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.64e+21
Mxy -3.19e+21
Mxz 1.60e+21
Myy -6.02e+20
Myz 2.73e+21
Mzz -5.04e+21
T ############
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###############################---
################################----
##########-------------##########-----
######------------------------####------
##-------------------------------#------
#---------------------------------####----
---------------------------------#######--
------------ -----------------#########-
------------ P ----------------###########
----------- ---------------###########
---------------------------#############
-------------------------#############
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------------------################
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Global CMT Convention Moment Tensor:
R T P
-5.04e+21 1.60e+21 -2.73e+21
1.60e+21 5.64e+21 3.19e+21
-2.73e+21 3.19e+21 -6.02e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20221005100140/index.html
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STK = 275
DIP = 55
RAKE = -50
MW = 3.83
HS = 49.0
The NDK file is 20221005100140.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 o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 160 45 90 3.07 0.1743
WVFGRD96 2.0 340 45 90 3.23 0.2529
WVFGRD96 3.0 310 45 40 3.23 0.2674
WVFGRD96 4.0 300 50 15 3.23 0.2947
WVFGRD96 5.0 300 50 15 3.26 0.3182
WVFGRD96 6.0 300 55 15 3.28 0.3388
WVFGRD96 7.0 295 60 0 3.30 0.3568
WVFGRD96 8.0 300 55 10 3.36 0.3725
WVFGRD96 9.0 295 55 0 3.37 0.3828
WVFGRD96 10.0 295 60 0 3.39 0.3922
WVFGRD96 11.0 295 60 0 3.41 0.3995
WVFGRD96 12.0 295 60 0 3.42 0.4048
WVFGRD96 13.0 295 60 0 3.44 0.4084
WVFGRD96 14.0 295 60 0 3.45 0.4108
WVFGRD96 15.0 295 60 5 3.46 0.4127
WVFGRD96 16.0 295 60 5 3.48 0.4149
WVFGRD96 17.0 295 60 5 3.49 0.4165
WVFGRD96 18.0 295 60 5 3.50 0.4182
WVFGRD96 19.0 295 60 5 3.51 0.4211
WVFGRD96 20.0 295 60 5 3.52 0.4248
WVFGRD96 21.0 295 60 5 3.53 0.4286
WVFGRD96 22.0 295 60 0 3.54 0.4328
WVFGRD96 23.0 295 65 -5 3.55 0.4375
WVFGRD96 24.0 295 65 -5 3.56 0.4413
WVFGRD96 25.0 295 65 -10 3.57 0.4462
WVFGRD96 26.0 290 60 -15 3.58 0.4505
WVFGRD96 27.0 290 60 -15 3.59 0.4557
WVFGRD96 28.0 290 60 -15 3.60 0.4598
WVFGRD96 29.0 290 60 -20 3.61 0.4641
WVFGRD96 30.0 290 60 -20 3.62 0.4679
WVFGRD96 31.0 290 60 -20 3.63 0.4711
WVFGRD96 32.0 290 60 -20 3.63 0.4726
WVFGRD96 33.0 285 60 -30 3.64 0.4747
WVFGRD96 34.0 285 60 -30 3.65 0.4760
WVFGRD96 35.0 285 60 -30 3.66 0.4780
WVFGRD96 36.0 285 60 -30 3.66 0.4781
WVFGRD96 37.0 285 60 -30 3.67 0.4771
WVFGRD96 38.0 285 60 -30 3.68 0.4757
WVFGRD96 39.0 285 65 -35 3.69 0.4734
WVFGRD96 40.0 280 50 -35 3.77 0.4828
WVFGRD96 41.0 280 55 -40 3.77 0.4820
WVFGRD96 42.0 280 55 -40 3.78 0.4818
WVFGRD96 43.0 280 55 -45 3.80 0.4820
WVFGRD96 44.0 275 55 -50 3.80 0.4841
WVFGRD96 45.0 275 55 -50 3.81 0.4848
WVFGRD96 46.0 275 55 -50 3.82 0.4857
WVFGRD96 47.0 275 55 -50 3.82 0.4862
WVFGRD96 48.0 275 55 -50 3.83 0.4863
WVFGRD96 49.0 275 55 -50 3.83 0.4863
WVFGRD96 50.0 275 55 -50 3.83 0.4851
WVFGRD96 51.0 275 55 -50 3.84 0.4862
WVFGRD96 52.0 275 55 -50 3.84 0.4861
WVFGRD96 53.0 275 55 -50 3.85 0.4846
WVFGRD96 54.0 275 55 -50 3.85 0.4846
WVFGRD96 55.0 270 55 -60 3.86 0.4837
WVFGRD96 56.0 270 55 -60 3.86 0.4836
WVFGRD96 57.0 270 55 -60 3.86 0.4829
WVFGRD96 58.0 270 55 -60 3.87 0.4820
WVFGRD96 59.0 270 55 -60 3.87 0.4822
WVFGRD96 60.0 270 55 -60 3.87 0.4806
WVFGRD96 61.0 270 55 -60 3.87 0.4800
WVFGRD96 62.0 275 60 -55 3.86 0.4791
WVFGRD96 63.0 275 60 -55 3.87 0.4776
WVFGRD96 64.0 275 60 -55 3.87 0.4772
WVFGRD96 65.0 275 60 -55 3.87 0.4757
WVFGRD96 66.0 275 60 -55 3.87 0.4751
WVFGRD96 67.0 270 60 -65 3.88 0.4736
WVFGRD96 68.0 270 60 -65 3.88 0.4735
WVFGRD96 69.0 270 60 -65 3.88 0.4728
WVFGRD96 70.0 270 60 -65 3.88 0.4709
WVFGRD96 71.0 270 60 -65 3.88 0.4706
WVFGRD96 72.0 270 60 -65 3.89 0.4694
WVFGRD96 73.0 265 60 -70 3.88 0.4681
WVFGRD96 74.0 265 60 -70 3.89 0.4669
WVFGRD96 75.0 265 60 -70 3.89 0.4660
WVFGRD96 76.0 265 60 -70 3.89 0.4651
WVFGRD96 77.0 265 60 -70 3.89 0.4632
WVFGRD96 78.0 265 60 -70 3.89 0.4626
WVFGRD96 79.0 265 60 -70 3.89 0.4611
WVFGRD96 80.0 265 60 -70 3.90 0.4597
WVFGRD96 81.0 265 60 -70 3.90 0.4580
WVFGRD96 82.0 265 60 -75 3.90 0.4566
WVFGRD96 83.0 260 60 -80 3.90 0.4561
WVFGRD96 84.0 260 60 -80 3.91 0.4537
WVFGRD96 85.0 260 60 -80 3.91 0.4528
WVFGRD96 86.0 260 60 -80 3.91 0.4512
WVFGRD96 87.0 260 60 -80 3.91 0.4502
WVFGRD96 88.0 260 60 -80 3.91 0.4484
WVFGRD96 89.0 260 60 -80 3.91 0.4461
WVFGRD96 90.0 260 60 -80 3.91 0.4452
WVFGRD96 91.0 260 60 -80 3.92 0.4434
WVFGRD96 92.0 260 60 -80 3.92 0.4416
WVFGRD96 93.0 260 60 -80 3.92 0.4397
WVFGRD96 94.0 260 60 -80 3.92 0.4377
WVFGRD96 95.0 260 60 -80 3.92 0.4366
WVFGRD96 96.0 260 60 -80 3.92 0.4341
WVFGRD96 97.0 260 60 -80 3.92 0.4322
WVFGRD96 98.0 260 60 -80 3.92 0.4306
WVFGRD96 99.0 260 60 -80 3.93 0.4286
The best solution is
WVFGRD96 49.0 275 55 -50 3.83 0.4863
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 o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 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