The ANSS event ID is ak2026belrda and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak2026belrda/executive.
2026/01/17 14:06:00 60.936 -147.165 16.0 3.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/01/17 14:06:00.0 60.94 -147.16 16.0 3.8 Alaska
Stations used:
AK.BAE AK.CUT AK.DIV AK.EYAK AK.FID AK.GHO AK.HIN AK.KNK
AK.L22K AK.PWL AK.SAW AK.SCM AK.SKN AK.VRDI AK.WAT6 AV.WAZA
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
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 3.27e+21 dyne-cm
Mw = 3.61
Z = 31 km
Plane Strike Dip Rake
NP1 205 55 -80
NP2 8 36 -104
Principal Axes:
Axis Value Plunge Azimuth
T 3.27e+21 9 288
N 0.00e+00 8 19
P -3.27e+21 77 149
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.84e+20
Mxy -8.61e+20
Mxz 7.61e+20
Myy 2.84e+21
Myz -8.61e+20
Mzz -3.03e+21
############--
################--####
################-------#####
##############-----------#####
##############--------------######
##############----------------######
###########-----------------#######
# T #########--------------------#######
# ########---------------------#######
#############---------------------########
############----------------------########
###########---------- ----------########
###########---------- P ----------########
#########----------- ----------#######
#########-----------------------########
########----------------------########
#######---------------------########
######--------------------########
####-------------------#######
####----------------########
##-------------#######
--------######
Global CMT Convention Moment Tensor:
R T P
-3.03e+21 7.61e+20 8.61e+20
7.61e+20 1.84e+20 8.61e+20
8.61e+20 8.61e+20 2.84e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260117140600/index.html
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STK = 205
DIP = 55
RAKE = -80
MW = 3.61
HS = 31.0
The NDK file is 20260117140600.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 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 20 45 90 3.12 0.2972
WVFGRD96 2.0 20 45 90 3.26 0.4204
WVFGRD96 3.0 25 50 95 3.32 0.3843
WVFGRD96 4.0 190 40 70 3.35 0.3350
WVFGRD96 5.0 175 20 60 3.38 0.3503
WVFGRD96 6.0 175 20 60 3.38 0.3765
WVFGRD96 7.0 175 20 65 3.36 0.3868
WVFGRD96 8.0 175 20 60 3.42 0.3996
WVFGRD96 9.0 170 20 55 3.40 0.4014
WVFGRD96 10.0 225 90 -60 3.39 0.4129
WVFGRD96 11.0 220 85 -65 3.39 0.4246
WVFGRD96 12.0 215 80 -65 3.40 0.4371
WVFGRD96 13.0 220 80 -60 3.40 0.4497
WVFGRD96 14.0 220 80 -60 3.41 0.4617
WVFGRD96 15.0 215 75 -65 3.42 0.4731
WVFGRD96 16.0 220 75 -60 3.44 0.4850
WVFGRD96 17.0 220 75 -60 3.45 0.4962
WVFGRD96 18.0 220 75 -60 3.46 0.5067
WVFGRD96 19.0 215 70 -65 3.47 0.5169
WVFGRD96 20.0 215 70 -65 3.48 0.5270
WVFGRD96 21.0 215 70 -65 3.50 0.5353
WVFGRD96 22.0 215 70 -65 3.51 0.5438
WVFGRD96 23.0 215 65 -65 3.53 0.5522
WVFGRD96 24.0 215 65 -65 3.54 0.5613
WVFGRD96 25.0 215 65 -70 3.55 0.5696
WVFGRD96 26.0 210 60 -75 3.56 0.5775
WVFGRD96 27.0 210 60 -75 3.57 0.5841
WVFGRD96 28.0 210 60 -75 3.58 0.5891
WVFGRD96 29.0 210 60 -75 3.59 0.5923
WVFGRD96 30.0 210 60 -75 3.60 0.5936
WVFGRD96 31.0 205 55 -80 3.61 0.5937
WVFGRD96 32.0 205 55 -80 3.62 0.5918
WVFGRD96 33.0 205 55 -80 3.63 0.5874
WVFGRD96 34.0 205 55 -80 3.64 0.5801
WVFGRD96 35.0 205 50 -75 3.65 0.5697
WVFGRD96 36.0 205 50 -75 3.66 0.5601
WVFGRD96 37.0 205 50 -75 3.67 0.5490
WVFGRD96 38.0 205 55 -75 3.67 0.5395
WVFGRD96 39.0 205 55 -75 3.69 0.5330
WVFGRD96 40.0 205 65 -85 3.77 0.5181
WVFGRD96 41.0 205 65 -85 3.78 0.5160
WVFGRD96 42.0 10 25 -100 3.78 0.5121
WVFGRD96 43.0 10 30 -100 3.79 0.5087
WVFGRD96 44.0 10 30 -100 3.79 0.5053
WVFGRD96 45.0 10 30 -100 3.80 0.5002
WVFGRD96 46.0 10 30 -100 3.80 0.4945
WVFGRD96 47.0 10 30 -100 3.80 0.4879
WVFGRD96 48.0 10 30 -100 3.81 0.4809
WVFGRD96 49.0 10 30 -100 3.81 0.4736
WVFGRD96 50.0 10 30 -100 3.81 0.4652
WVFGRD96 51.0 15 35 -95 3.82 0.4576
WVFGRD96 52.0 15 35 -95 3.82 0.4516
WVFGRD96 53.0 15 35 -95 3.82 0.4449
WVFGRD96 54.0 200 55 -85 3.82 0.4377
WVFGRD96 55.0 15 35 -90 3.82 0.4307
WVFGRD96 56.0 20 40 -80 3.83 0.4231
WVFGRD96 57.0 20 40 -80 3.83 0.4188
WVFGRD96 58.0 20 40 -80 3.83 0.4149
WVFGRD96 59.0 20 40 -80 3.83 0.4106
The best solution is
WVFGRD96 31.0 205 55 -80 3.61 0.5937
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 br c 0.12 0.25 n 4 p 2
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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