The ANSS event ID is aka2026lfrwki and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/aka2026lfrwki/executive.
2026/06/07 22:12:17 61.635 -150.515 28.7 3.8 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/06/07 22:12:17.0 61.63 -150.51 28.7 3.8 Alaska
Stations used:
AK.CAPN AK.CAST AK.CUT AK.FIRE AK.GHO AK.KNK AK.L22K AK.MCK
AK.RC01 AK.RND AK.SAW AK.SCM AK.SKN AK.SLK AT.PMR AV.SPCL
AV.STLK
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +30
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.20 n 3
Best Fitting Double Couple
Mo = 9.55e+21 dyne-cm
Mw = 3.92
Z = 74 km
Plane Strike Dip Rake
NP1 208 57 -130
NP2 85 50 -45
Principal Axes:
Axis Value Plunge Azimuth
T 9.55e+21 4 325
N 0.00e+00 33 232
P -9.55e+21 57 61
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.70e+21
Mxy -5.67e+21
Mxz -1.55e+21
Myy 9.49e+20
Myz -4.22e+21
Mzz -6.65e+21
##############
##################----
T ##############-----------
# ############--------------
################------------------
###############---------------------
##############------------------------
##############------------ -----------
#############------------- P -----------
#############-------------- ------------
############-----------------------------#
############----------------------------##
-##########---------------------------####
--########-------------------------#####
----#####------------------------#######
-------#--------------------##########
-------#############################
------############################
----##########################
---#########################
-#####################
##############
Global CMT Convention Moment Tensor:
R T P
-6.65e+21 -1.55e+21 4.22e+21
-1.55e+21 5.70e+21 5.67e+21
4.22e+21 5.67e+21 9.49e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260607221217/index.html
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STK = 85
DIP = 50
RAKE = -45
MW = 3.92
HS = 74.0
The NDK file is 20260607221217.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.
Map showing station locations used for computing the ML's. No distinction is made whether the vertical (Z) or horizontal (H) components were used.
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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 -30 o DIST/3.3 +30 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.20 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 245 35 -70 2.97 0.1273
WVFGRD96 4.0 280 80 60 3.07 0.1604
WVFGRD96 6.0 285 75 55 3.17 0.1727
WVFGRD96 8.0 90 80 -60 3.31 0.1802
WVFGRD96 10.0 95 80 -60 3.41 0.1840
WVFGRD96 12.0 265 65 -45 3.42 0.1794
WVFGRD96 14.0 265 60 -40 3.47 0.1804
WVFGRD96 16.0 100 75 60 3.57 0.1860
WVFGRD96 18.0 85 70 65 3.61 0.1959
WVFGRD96 20.0 90 55 60 3.63 0.2162
WVFGRD96 22.0 100 50 65 3.66 0.2476
WVFGRD96 24.0 90 40 60 3.69 0.2786
WVFGRD96 26.0 305 55 95 3.70 0.3089
WVFGRD96 28.0 300 55 80 3.71 0.3410
WVFGRD96 30.0 300 55 80 3.72 0.3655
WVFGRD96 32.0 85 65 -50 3.65 0.3859
WVFGRD96 34.0 80 60 -55 3.66 0.4053
WVFGRD96 36.0 80 60 -55 3.66 0.4170
WVFGRD96 38.0 80 60 -55 3.67 0.4277
WVFGRD96 40.0 80 60 -55 3.75 0.4226
WVFGRD96 42.0 85 80 -65 3.84 0.4241
WVFGRD96 44.0 85 75 -60 3.84 0.4376
WVFGRD96 46.0 85 75 -60 3.86 0.4432
WVFGRD96 48.0 80 60 -55 3.85 0.4482
WVFGRD96 50.0 80 60 -55 3.86 0.4557
WVFGRD96 52.0 80 60 -55 3.87 0.4650
WVFGRD96 54.0 80 55 -50 3.87 0.4715
WVFGRD96 56.0 80 55 -50 3.87 0.4801
WVFGRD96 58.0 80 55 -50 3.88 0.4847
WVFGRD96 60.0 80 55 -50 3.88 0.4895
WVFGRD96 62.0 80 50 -50 3.89 0.4929
WVFGRD96 64.0 80 50 -50 3.90 0.4963
WVFGRD96 66.0 80 50 -50 3.90 0.4970
WVFGRD96 68.0 80 50 -50 3.91 0.4952
WVFGRD96 70.0 80 50 -50 3.91 0.4929
WVFGRD96 72.0 85 50 -45 3.92 0.4974
WVFGRD96 74.0 85 50 -45 3.92 0.4990
WVFGRD96 76.0 85 50 -45 3.92 0.4944
WVFGRD96 78.0 85 50 -45 3.93 0.4875
WVFGRD96 80.0 85 50 -45 3.93 0.4937
WVFGRD96 82.0 85 50 -45 3.94 0.4919
WVFGRD96 84.0 85 50 -45 3.94 0.4815
WVFGRD96 86.0 85 50 -45 3.94 0.4836
WVFGRD96 88.0 85 50 -40 3.94 0.4817
WVFGRD96 90.0 85 50 -40 3.94 0.4745
WVFGRD96 92.0 85 50 -40 3.94 0.4750
WVFGRD96 94.0 85 50 -40 3.95 0.4670
WVFGRD96 96.0 85 50 -45 3.96 0.4681
WVFGRD96 98.0 85 50 -45 3.96 0.4624
The best solution is
WVFGRD96 74.0 85 50 -45 3.92 0.4990
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 -30 o DIST/3.3 +30 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.20 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