The ANSS event ID is ak2026ccwsww and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak2026ccwsww/executive.
2026/01/30 21:27:22 63.054 -149.608 95.2 4.1 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/01/30 21:27:22.0 63.05 -149.61 95.2 4.1 Alaska
Stations used:
AK.BAE AK.BPAW AK.CCB AK.CUT AK.DHY AK.DIV AK.GHO AK.HDA
AK.I21K AK.J25K AK.K24K AK.KNK AK.L22K AK.MCK AK.NEA2
AK.PAX AK.POKR AK.PPLA AK.PWL AK.RC01 AK.RND AK.SAW AK.SCM
AK.WAT6 AK.WRH AV.STLK IM.IL31 IU.COLA
Filtering commands used:
cut o DIST/3.5 -40 o DIST/3.5 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 3.55e+22 dyne-cm
Mw = 4.30
Z = 96 km
Plane Strike Dip Rake
NP1 334 64 146
NP2 80 60 30
Principal Axes:
Axis Value Plunge Azimuth
T 3.55e+22 41 295
N 0.00e+00 49 121
P -3.55e+22 3 28
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.40e+22
Mxy -2.24e+22
Mxz 6.07e+21
Myy 8.64e+21
Myz -1.67e+22
Mzz 1.54e+22
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####--------------- P
##########------------ ---
#############-----------------
#################-----------------
###################-----------------
######################----------------
######## #############----------------
######## T ##############---------------
######### ###############--------------#
############################-----------###
#############################--------#####
#############################------#######
-############################--#########
-----#####################---###########
-----------------------------#########
----------------------------########
---------------------------#######
-------------------------#####
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--------------------##
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Global CMT Convention Moment Tensor:
R T P
1.54e+22 6.07e+21 1.67e+22
6.07e+21 -2.40e+22 2.24e+22
1.67e+22 2.24e+22 8.64e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260130212722/index.html
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STK = 80
DIP = 60
RAKE = 30
MW = 4.30
HS = 96.0
The NDK file is 20260130212722.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/3.5 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 40.0 80 80 25 4.09 0.4298
WVFGRD96 42.0 80 80 25 4.12 0.4253
WVFGRD96 44.0 80 80 25 4.14 0.4237
WVFGRD96 46.0 80 80 30 4.16 0.4272
WVFGRD96 48.0 80 85 35 4.18 0.4348
WVFGRD96 50.0 85 75 40 4.19 0.4462
WVFGRD96 52.0 85 75 40 4.20 0.4593
WVFGRD96 54.0 85 70 40 4.21 0.4736
WVFGRD96 56.0 90 60 40 4.21 0.4909
WVFGRD96 58.0 85 60 40 4.22 0.5153
WVFGRD96 60.0 85 60 40 4.23 0.5390
WVFGRD96 62.0 85 60 40 4.23 0.5614
WVFGRD96 64.0 85 60 40 4.24 0.5822
WVFGRD96 66.0 85 60 40 4.25 0.6021
WVFGRD96 68.0 85 60 40 4.25 0.6202
WVFGRD96 70.0 85 60 40 4.25 0.6360
WVFGRD96 72.0 85 60 40 4.26 0.6493
WVFGRD96 74.0 85 60 35 4.27 0.6622
WVFGRD96 76.0 85 60 35 4.27 0.6744
WVFGRD96 78.0 80 60 30 4.28 0.6851
WVFGRD96 80.0 80 60 30 4.28 0.6931
WVFGRD96 82.0 80 60 30 4.28 0.7021
WVFGRD96 84.0 80 60 30 4.29 0.7088
WVFGRD96 86.0 80 60 30 4.29 0.7138
WVFGRD96 88.0 80 60 30 4.29 0.7188
WVFGRD96 90.0 80 60 30 4.29 0.7216
WVFGRD96 92.0 80 60 30 4.30 0.7251
WVFGRD96 94.0 80 60 30 4.30 0.7263
WVFGRD96 96.0 80 60 30 4.30 0.7276
WVFGRD96 98.0 80 60 30 4.30 0.7273
WVFGRD96 100.0 85 55 35 4.30 0.7263
WVFGRD96 102.0 80 60 30 4.31 0.7261
WVFGRD96 104.0 80 60 30 4.31 0.7240
WVFGRD96 106.0 85 55 35 4.31 0.7216
WVFGRD96 108.0 85 55 35 4.31 0.7193
WVFGRD96 110.0 85 55 35 4.31 0.7183
WVFGRD96 112.0 85 55 35 4.31 0.7145
WVFGRD96 114.0 85 55 35 4.31 0.7128
WVFGRD96 116.0 85 55 35 4.32 0.7104
WVFGRD96 118.0 85 55 35 4.32 0.7072
WVFGRD96 120.0 85 55 35 4.32 0.7043
WVFGRD96 122.0 85 55 35 4.32 0.7022
WVFGRD96 124.0 85 55 35 4.32 0.6987
WVFGRD96 126.0 85 60 35 4.33 0.6969
WVFGRD96 128.0 85 60 35 4.33 0.6945
WVFGRD96 130.0 85 60 35 4.33 0.6909
WVFGRD96 132.0 85 60 35 4.34 0.6902
WVFGRD96 134.0 85 60 35 4.34 0.6863
WVFGRD96 136.0 85 60 35 4.34 0.6854
WVFGRD96 138.0 85 60 35 4.34 0.6827
WVFGRD96 140.0 85 60 35 4.35 0.6815
WVFGRD96 142.0 85 60 35 4.35 0.6801
WVFGRD96 144.0 85 60 35 4.35 0.6770
WVFGRD96 146.0 85 60 35 4.35 0.6758
WVFGRD96 148.0 85 60 35 4.36 0.6684
The best solution is
WVFGRD96 96.0 80 60 30 4.30 0.7276
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/3.5 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 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