The ANSS event ID is aka2026nyxoap and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/aka2026nyxoap/executive.
2026/07/16 11:37:21 60.569 -141.508 8.5 5.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/07/16 11:37:21.0 60.57 -141.51 8.5 5.2 Alaska
Stations used:
AK.BAE AK.BAGL AK.BAL AK.BAT AK.BERG AK.BESE AK.CRQ AK.CUT
AK.CYK AK.DIV AK.DOT AK.FID AK.GLI AK.GREN AK.GRES AK.GRIN
AK.HDA AK.ISLE AK.J25K AK.J26L AK.KHIT AK.KIAG AK.KNK
AK.M23K AK.MCAR AK.MESA AK.P23K AK.PAX AK.PS09 AK.PS10
AK.PS12 AK.PTPK AK.R32K AK.RAG AK.RC01 AK.RIDG AK.RKAV
AK.RND AK.SAW AK.SCM AK.TGL AK.VMT AK.VRDI AT.ESTR AT.PMR
AV.N25K AV.WACK AV.WAZA CN.BRWY CN.BVCY CN.HYT CN.PLBC
CN.YUK3 EO.KLRS NY.MAYO
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 0.10 n 3
Best Fitting Double Couple
Mo = 5.82e+23 dyne-cm
Mw = 5.11
Z = 22 km
Plane Strike Dip Rake
NP1 85 82 96
NP2 225 10 50
Principal Axes:
Axis Value Plunge Azimuth
T 5.82e+23 52 3
N 0.00e+00 6 265
P -5.82e+23 37 170
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.41e+23
Mxy 7.63e+22
Mxz 5.57e+23
Myy -1.13e+22
Myz -3.57e+22
Mzz 1.53e+23
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--############## ###############
--############### T ################
--################ #################
--######################################
-#######################################
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------------------ -------------
---------------- P -----------
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Global CMT Convention Moment Tensor:
R T P
1.53e+23 5.57e+23 3.57e+22
5.57e+23 -1.41e+23 -7.63e+22
3.57e+22 -7.63e+22 -1.13e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260716113721/index.html
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STK = 225
DIP = 10
RAKE = 50
MW = 5.11
HS = 22.0
The NDK file is 20260716113721.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 -40 o DIST/3.3 +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 1.0 60 45 90 4.49 0.1982
WVFGRD96 2.0 60 45 90 4.66 0.2926
WVFGRD96 3.0 245 45 95 4.69 0.2395
WVFGRD96 4.0 255 75 70 4.67 0.2154
WVFGRD96 5.0 90 90 80 4.72 0.2717
WVFGRD96 6.0 265 85 -95 4.74 0.3292
WVFGRD96 7.0 120 5 -55 4.75 0.3770
WVFGRD96 8.0 125 5 -50 4.85 0.4108
WVFGRD96 9.0 130 10 -50 4.88 0.4546
WVFGRD96 10.0 145 15 -35 4.90 0.4937
WVFGRD96 11.0 140 15 -40 4.92 0.5274
WVFGRD96 12.0 145 15 -35 4.94 0.5557
WVFGRD96 13.0 150 15 -30 4.96 0.5795
WVFGRD96 14.0 150 15 -30 4.98 0.5989
WVFGRD96 15.0 175 15 0 4.99 0.6164
WVFGRD96 16.0 185 15 10 5.01 0.6325
WVFGRD96 17.0 200 15 25 5.03 0.6454
WVFGRD96 18.0 205 15 30 5.04 0.6569
WVFGRD96 19.0 205 15 30 5.06 0.6655
WVFGRD96 20.0 205 15 30 5.07 0.6709
WVFGRD96 21.0 225 10 50 5.09 0.6741
WVFGRD96 22.0 225 10 50 5.11 0.6751
WVFGRD96 23.0 225 10 50 5.12 0.6734
WVFGRD96 24.0 230 10 55 5.13 0.6701
WVFGRD96 25.0 225 10 50 5.14 0.6652
WVFGRD96 26.0 230 10 55 5.15 0.6586
WVFGRD96 27.0 240 10 70 5.15 0.6517
WVFGRD96 28.0 245 10 75 5.16 0.6448
WVFGRD96 29.0 250 10 80 5.17 0.6365
WVFGRD96 30.0 80 80 90 5.17 0.6283
WVFGRD96 31.0 80 80 90 5.18 0.6196
WVFGRD96 32.0 80 80 90 5.18 0.6096
WVFGRD96 33.0 280 10 110 5.19 0.5998
WVFGRD96 34.0 75 80 85 5.19 0.5890
WVFGRD96 35.0 75 80 85 5.19 0.5783
WVFGRD96 36.0 275 15 110 5.19 0.5661
WVFGRD96 37.0 275 15 110 5.19 0.5552
WVFGRD96 38.0 75 75 85 5.18 0.5417
WVFGRD96 39.0 75 75 85 5.18 0.5293
The best solution is
WVFGRD96 22.0 225 10 50 5.11 0.6751
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 0.10 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