The ANSS event ID is aka2026eyfank and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/aka2026eyfank/executive.
2026/03/11 20:04:19 61.630 -149.609 27.2 3.7 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/03/11 20:04:19.0 61.63 -149.61 27.2 3.7 Alaska
Stations used:
AK.BAE AK.CUT AK.DHY AK.DOT AK.EYAK AK.FID AK.GHO AK.GLI
AK.K24K AK.KNK AK.L19K AK.L22K AK.PAX AK.RND AK.SAW AK.SCM
AK.SKN AK.SLK AK.VRDI AK.WAT6 AT.PMR AV.RED AV.STLK
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 0.07 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 6.31e+21 dyne-cm
Mw = 3.80
Z = 46 km
Plane Strike Dip Rake
NP1 210 50 -65
NP2 354 46 -117
Principal Axes:
Axis Value Plunge Azimuth
T 6.31e+21 2 283
N 0.00e+00 19 13
P -6.31e+21 71 187
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.61e+20
Mxy -1.42e+21
Mxz 1.98e+21
Myy 5.99e+21
Myz -2.95e+18
Mzz -5.63e+21
#######-------
##############----####
################---#########
##############-------#########
##############----------##########
#############-------------##########
#############---------------##########
##########------------------##########
T #########-------------------##########
########---------------------##########
##########----------------------##########
##########----------------------##########
#########---------- ----------##########
########---------- P ----------#########
########---------- ----------#########
######-----------------------#########
#####-----------------------########
#####---------------------########
###--------------------#######
###------------------#######
-----------------#####
-----------###
Global CMT Convention Moment Tensor:
R T P
-5.63e+21 1.98e+21 2.95e+18
1.98e+21 -3.61e+20 1.42e+21
2.95e+18 1.42e+21 5.99e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260311200419/index.html
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STK = 210
DIP = 50
RAKE = -65
MW = 3.80
HS = 46.0
The NDK file is 20260311200419.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 0.07 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 0 45 75 3.12 0.3078
WVFGRD96 2.0 5 45 80 3.23 0.3986
WVFGRD96 3.0 170 55 60 3.29 0.3906
WVFGRD96 4.0 45 55 -50 3.33 0.4014
WVFGRD96 5.0 235 50 -40 3.37 0.4069
WVFGRD96 6.0 270 40 25 3.37 0.4155
WVFGRD96 7.0 265 40 20 3.36 0.4255
WVFGRD96 8.0 265 35 20 3.42 0.4303
WVFGRD96 9.0 265 40 20 3.41 0.4358
WVFGRD96 10.0 265 40 15 3.40 0.4402
WVFGRD96 11.0 260 40 10 3.40 0.4455
WVFGRD96 12.0 260 45 15 3.42 0.4510
WVFGRD96 13.0 255 40 -10 3.40 0.4572
WVFGRD96 14.0 250 40 -15 3.41 0.4658
WVFGRD96 15.0 250 40 -15 3.41 0.4747
WVFGRD96 16.0 245 40 -25 3.42 0.4828
WVFGRD96 17.0 245 40 -25 3.43 0.4917
WVFGRD96 18.0 245 40 -25 3.44 0.4996
WVFGRD96 19.0 240 40 -30 3.45 0.5067
WVFGRD96 20.0 245 45 -20 3.47 0.5143
WVFGRD96 21.0 240 40 -30 3.47 0.5211
WVFGRD96 22.0 240 40 -30 3.48 0.5274
WVFGRD96 23.0 240 45 -25 3.50 0.5346
WVFGRD96 24.0 240 45 -25 3.51 0.5410
WVFGRD96 25.0 240 45 -25 3.52 0.5467
WVFGRD96 26.0 235 45 -35 3.53 0.5526
WVFGRD96 27.0 235 45 -35 3.53 0.5588
WVFGRD96 28.0 235 45 -35 3.54 0.5641
WVFGRD96 29.0 230 45 -35 3.56 0.5696
WVFGRD96 30.0 230 45 -35 3.56 0.5745
WVFGRD96 31.0 225 45 -40 3.57 0.5787
WVFGRD96 32.0 225 50 -35 3.59 0.5858
WVFGRD96 33.0 225 50 -40 3.60 0.5922
WVFGRD96 34.0 220 50 -45 3.61 0.5991
WVFGRD96 35.0 220 50 -45 3.62 0.6061
WVFGRD96 36.0 215 50 -50 3.63 0.6120
WVFGRD96 37.0 215 50 -50 3.64 0.6183
WVFGRD96 38.0 215 50 -50 3.65 0.6211
WVFGRD96 39.0 210 50 -55 3.67 0.6232
WVFGRD96 30.0 230 45 -35 3.56 0.5745
WVFGRD96 31.0 225 45 -40 3.57 0.5787
WVFGRD96 32.0 225 50 -35 3.59 0.5858
WVFGRD96 33.0 225 50 -40 3.60 0.5922
WVFGRD96 34.0 220 50 -45 3.61 0.5991
WVFGRD96 35.0 220 50 -45 3.62 0.6061
WVFGRD96 36.0 215 50 -50 3.63 0.6120
WVFGRD96 37.0 215 50 -50 3.64 0.6183
WVFGRD96 38.0 215 50 -50 3.65 0.6211
WVFGRD96 39.0 210 50 -55 3.67 0.6232
WVFGRD96 40.0 215 50 -55 3.75 0.6132
WVFGRD96 41.0 215 50 -55 3.76 0.6216
WVFGRD96 42.0 215 50 -55 3.77 0.6274
WVFGRD96 43.0 210 50 -60 3.78 0.6325
WVFGRD96 44.0 210 50 -60 3.79 0.6359
WVFGRD96 45.0 210 50 -60 3.80 0.6381
WVFGRD96 46.0 210 50 -65 3.80 0.6388
WVFGRD96 47.0 210 50 -65 3.81 0.6385
WVFGRD96 48.0 210 50 -65 3.81 0.6366
WVFGRD96 49.0 210 50 -65 3.82 0.6335
WVFGRD96 50.0 210 50 -65 3.82 0.6295
WVFGRD96 51.0 210 55 -65 3.83 0.6251
WVFGRD96 52.0 210 55 -65 3.83 0.6211
WVFGRD96 53.0 210 55 -65 3.83 0.6162
WVFGRD96 54.0 210 55 -65 3.84 0.6109
WVFGRD96 55.0 210 55 -65 3.84 0.6043
WVFGRD96 56.0 210 55 -65 3.84 0.5973
WVFGRD96 57.0 210 55 -65 3.84 0.5897
WVFGRD96 58.0 210 55 -65 3.84 0.5813
WVFGRD96 59.0 205 55 -70 3.85 0.5733
The best solution is
WVFGRD96 46.0 210 50 -65 3.80 0.6388
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 0.07 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