The ANSS event ID is aka2026nfzhjl and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/aka2026nfzhjl/executive.
2026/07/06 05:36:22 60.014 -152.525 108.0 4.0 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/07/06 05:36:22.0 60.01 -152.52 108.0 4.0 Alaska
Stations used:
AK.BRLK AK.CAPN AK.CNP AK.FIRE AK.HOM AK.L19K AK.L22K
AK.N18K AK.O18K AK.O19K AK.P17K AK.PPLA AK.RC01 AK.SKN
AK.SLK AK.SSN AT.PMR AV.RED AV.SPCL AV.STLK
Filtering commands used:
cut o DIST/3.5 -30 o DIST/3.5 +30
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.15 n 3
Best Fitting Double Couple
Mo = 1.17e+22 dyne-cm
Mw = 3.98
Z = 98 km
Plane Strike Dip Rake
NP1 304 76 154
NP2 40 65 15
Principal Axes:
Axis Value Plunge Azimuth
T 1.17e+22 28 260
N 0.00e+00 61 98
P -1.17e+22 8 354
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.11e+22
Mxy 2.93e+21
Mxz -2.42e+21
Myy 8.76e+21
Myz -4.58e+21
Mzz 2.33e+21
--- P --------
------- ------------
---------------------------#
----------------------------##
------------------------------####
######-------------------------#####
###########--------------------#######
################---------------#########
###################------------#########
#######################--------###########
##########################----############
##### ##################################
##### T ###################---############
#### #################--------########
#######################----------#######
####################--------------####
#################-----------------##
#############---------------------
########----------------------
##--------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.33e+21 -2.42e+21 4.58e+21
-2.42e+21 -1.11e+22 -2.93e+21
4.58e+21 -2.93e+21 8.76e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260706053622/index.html
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STK = 40
DIP = 65
RAKE = 15
MW = 3.98
HS = 98.0
The NDK file is 20260706053622.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/3.5 -30 o DIST/3.5 +30 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.15 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 310 85 -10 3.01 0.2018
WVFGRD96 4.0 130 80 15 3.15 0.2433
WVFGRD96 6.0 130 80 15 3.25 0.2628
WVFGRD96 8.0 130 80 15 3.35 0.2703
WVFGRD96 10.0 130 80 10 3.41 0.2631
WVFGRD96 12.0 130 80 15 3.46 0.2446
WVFGRD96 14.0 125 85 15 3.49 0.2193
WVFGRD96 16.0 305 80 -15 3.51 0.1933
WVFGRD96 18.0 305 80 15 3.51 0.1668
WVFGRD96 20.0 305 80 25 3.53 0.1467
WVFGRD96 22.0 215 75 30 3.56 0.1588
WVFGRD96 24.0 215 75 30 3.59 0.1768
WVFGRD96 26.0 215 70 25 3.61 0.1952
WVFGRD96 28.0 215 55 15 3.64 0.2129
WVFGRD96 30.0 215 50 10 3.66 0.2304
WVFGRD96 32.0 215 55 15 3.65 0.2344
WVFGRD96 34.0 215 55 15 3.65 0.2306
WVFGRD96 36.0 215 65 20 3.63 0.2225
WVFGRD96 38.0 30 85 -20 3.63 0.2195
WVFGRD96 40.0 30 70 -25 3.72 0.2444
WVFGRD96 42.0 30 70 -25 3.76 0.2605
WVFGRD96 44.0 30 70 -20 3.78 0.2810
WVFGRD96 46.0 35 70 -10 3.80 0.3076
WVFGRD96 48.0 35 70 -10 3.83 0.3405
WVFGRD96 50.0 40 70 10 3.85 0.3752
WVFGRD96 52.0 40 70 10 3.87 0.4110
WVFGRD96 54.0 40 65 15 3.89 0.4350
WVFGRD96 56.0 40 65 15 3.90 0.4433
WVFGRD96 58.0 40 65 15 3.90 0.4515
WVFGRD96 60.0 40 65 15 3.91 0.4620
WVFGRD96 62.0 40 65 15 3.91 0.4670
WVFGRD96 64.0 40 65 15 3.92 0.4752
WVFGRD96 66.0 40 65 15 3.92 0.4803
WVFGRD96 68.0 40 65 15 3.93 0.4842
WVFGRD96 70.0 40 65 15 3.93 0.4854
WVFGRD96 72.0 45 65 20 3.95 0.4892
WVFGRD96 74.0 45 65 20 3.95 0.4948
WVFGRD96 76.0 45 65 20 3.95 0.4968
WVFGRD96 78.0 45 65 20 3.96 0.4993
WVFGRD96 80.0 45 65 20 3.96 0.4998
WVFGRD96 82.0 45 65 20 3.96 0.4999
WVFGRD96 84.0 45 65 20 3.97 0.5027
WVFGRD96 86.0 45 60 20 3.97 0.5023
WVFGRD96 88.0 45 60 20 3.97 0.4994
WVFGRD96 90.0 45 60 20 3.97 0.5015
WVFGRD96 92.0 40 65 15 3.97 0.5031
WVFGRD96 94.0 40 65 15 3.97 0.5015
WVFGRD96 96.0 40 65 15 3.98 0.5055
WVFGRD96 98.0 40 65 15 3.98 0.5063
WVFGRD96 100.0 40 65 15 3.98 0.5045
WVFGRD96 102.0 40 65 15 3.99 0.5055
WVFGRD96 104.0 40 65 15 3.99 0.5031
WVFGRD96 106.0 40 65 15 3.99 0.5049
WVFGRD96 108.0 40 65 15 4.00 0.5051
WVFGRD96 110.0 40 65 15 4.00 0.5035
WVFGRD96 112.0 40 65 15 4.00 0.5040
WVFGRD96 114.0 40 65 15 4.01 0.5031
WVFGRD96 116.0 45 60 20 4.01 0.5050
WVFGRD96 118.0 40 65 15 4.01 0.5012
WVFGRD96 120.0 45 60 20 4.02 0.5039
WVFGRD96 122.0 45 60 20 4.02 0.4995
WVFGRD96 124.0 40 60 15 4.02 0.4991
WVFGRD96 126.0 40 60 15 4.02 0.5002
WVFGRD96 128.0 40 60 15 4.03 0.5013
WVFGRD96 130.0 40 60 15 4.03 0.4984
WVFGRD96 132.0 40 60 15 4.03 0.5009
WVFGRD96 134.0 40 60 15 4.04 0.4965
WVFGRD96 136.0 40 60 15 4.04 0.4994
WVFGRD96 138.0 40 60 15 4.04 0.4979
WVFGRD96 140.0 40 60 15 4.04 0.4939
WVFGRD96 142.0 40 60 15 4.05 0.4966
WVFGRD96 144.0 45 60 10 4.06 0.4925
WVFGRD96 146.0 45 60 10 4.06 0.4949
WVFGRD96 148.0 45 60 10 4.06 0.4915
The best solution is
WVFGRD96 98.0 40 65 15 3.98 0.5063
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 -30 o DIST/3.5 +30 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.15 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