Location
Location ANSS
The ANSS event ID is aka2026jfsvox and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/aka2026jfsvox/executive.
2026/05/10 18:59:49 59.731 -152.397 94.9 4.1 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2026/05/10 18:59:49.0 59.73 -152.40 94.9 4.1 Alaska
Stations used:
AK.BAE AK.BRLK AK.CAPN AK.FIRE AK.L19K AK.N18K AK.O19K
AK.Q19K AK.RC01 AK.SWD AV.ACH AV.RED AV.SPCL AV.STLK
II.KDAK
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 = 3.09e+22 dyne-cm
Mw = 4.26
Z = 102 km
Plane Strike Dip Rake
NP1 60 55 50
NP2 296 51 133
Principal Axes:
Axis Value Plunge Azimuth
T 3.09e+22 58 271
N 0.00e+00 32 86
P -3.09e+22 2 177
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.08e+22
Mxy 1.50e+21
Mxz 1.32e+21
Myy 8.53e+21
Myz -1.39e+22
Mzz 2.22e+22
--------------
----------------------
----------------------------
------------------------------
----------------------------------
--#################-----------------
########################-------------#
############################---------###
###############################-----####
########### ####################--######
########### T ############################
########### ####################---#####
################################------####
#############################---------##
##########################------------##
######################----------------
#################-------------------
----------------------------------
------------------------------
----------------------------
----------- --------
------- P ----
Global CMT Convention Moment Tensor:
R T P
2.22e+22 1.32e+21 1.39e+22
1.32e+21 -3.08e+22 -1.50e+21
1.39e+22 -1.50e+21 8.53e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260510185949/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 60
DIP = 55
RAKE = 50
MW = 4.26
HS = 102.0
The NDK file is 20260510185949.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
| SLU |
USGSMWR |
USGS/SLU Moment Tensor Solution
ENS 2026/05/10 18:59:49.0 59.73 -152.40 94.9 4.1 Alaska
Stations used:
AK.BAE AK.BRLK AK.CAPN AK.FIRE AK.L19K AK.N18K AK.O19K
AK.Q19K AK.RC01 AK.SWD AV.ACH AV.RED AV.SPCL AV.STLK
II.KDAK
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 = 3.09e+22 dyne-cm
Mw = 4.26
Z = 102 km
Plane Strike Dip Rake
NP1 60 55 50
NP2 296 51 133
Principal Axes:
Axis Value Plunge Azimuth
T 3.09e+22 58 271
N 0.00e+00 32 86
P -3.09e+22 2 177
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.08e+22
Mxy 1.50e+21
Mxz 1.32e+21
Myy 8.53e+21
Myz -1.39e+22
Mzz 2.22e+22
--------------
----------------------
----------------------------
------------------------------
----------------------------------
--#################-----------------
########################-------------#
############################---------###
###############################-----####
########### ####################--######
########### T ############################
########### ####################---#####
################################------####
#############################---------##
##########################------------##
######################----------------
#################-------------------
----------------------------------
------------------------------
----------------------------
----------- --------
------- P ----
Global CMT Convention Moment Tensor:
R T P
2.22e+22 1.32e+21 1.39e+22
1.32e+21 -3.08e+22 -1.50e+21
1.39e+22 -1.50e+21 8.53e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260510185949/index.html
|
Regional Moment Tensor (Mwr)
Moment 3.007e+15 N-m
Magnitude 4.25 Mwr
Depth 89.0 km
Percent DC 87%
Half Duration -
Catalog US
Data Source US
Contributor US
Nodal Planes
Plane Strike Dip Rake
NP1 295 46 109
NP2 89 47 71
Principal Axes
Axis Value Plunge Azimuth
T 2.898e+15 76 286
N 0.208e+15 14 102
P -3.106e+15 1 192
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Magnitudes
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.
ML Magnitude
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.
Context
The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.
Waveform Inversion using wvfgrd96
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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Location of broadband stations used for waveform inversion
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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 3
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 270 35 -80 3.47 0.1952
WVFGRD96 4.0 295 45 -35 3.47 0.1945
WVFGRD96 6.0 305 40 -10 3.48 0.2026
WVFGRD96 8.0 310 40 -10 3.56 0.2169
WVFGRD96 10.0 320 55 25 3.61 0.2331
WVFGRD96 12.0 50 55 40 3.66 0.2439
WVFGRD96 14.0 50 55 40 3.69 0.2471
WVFGRD96 16.0 50 60 40 3.71 0.2452
WVFGRD96 18.0 50 60 35 3.74 0.2380
WVFGRD96 20.0 235 65 40 3.76 0.2273
WVFGRD96 22.0 235 65 40 3.79 0.2255
WVFGRD96 24.0 230 70 30 3.82 0.2269
WVFGRD96 26.0 230 70 25 3.83 0.2265
WVFGRD96 28.0 45 85 -45 3.85 0.2261
WVFGRD96 30.0 35 80 -40 3.86 0.2325
WVFGRD96 32.0 35 80 -35 3.88 0.2376
WVFGRD96 34.0 35 80 -35 3.89 0.2396
WVFGRD96 36.0 40 80 -25 3.91 0.2398
WVFGRD96 38.0 40 70 -10 3.94 0.2427
WVFGRD96 40.0 40 70 -10 4.00 0.2460
WVFGRD96 42.0 40 70 -10 4.03 0.2472
WVFGRD96 44.0 40 70 -10 4.05 0.2460
WVFGRD96 46.0 40 85 -25 4.07 0.2475
WVFGRD96 48.0 35 70 -35 4.09 0.2535
WVFGRD96 50.0 35 70 -35 4.11 0.2597
WVFGRD96 52.0 35 70 -30 4.12 0.2651
WVFGRD96 54.0 35 70 -30 4.13 0.2699
WVFGRD96 56.0 35 65 -25 4.15 0.2747
WVFGRD96 58.0 60 45 40 4.17 0.2861
WVFGRD96 60.0 60 45 40 4.18 0.3033
WVFGRD96 62.0 65 45 40 4.20 0.3194
WVFGRD96 64.0 60 50 35 4.21 0.3348
WVFGRD96 66.0 60 50 35 4.22 0.3496
WVFGRD96 68.0 65 50 40 4.23 0.3632
WVFGRD96 70.0 65 50 40 4.23 0.3761
WVFGRD96 72.0 65 50 40 4.24 0.3857
WVFGRD96 74.0 65 50 40 4.24 0.3954
WVFGRD96 76.0 60 55 35 4.25 0.4032
WVFGRD96 78.0 55 50 40 4.24 0.4108
WVFGRD96 80.0 55 50 40 4.24 0.4179
WVFGRD96 82.0 55 50 40 4.24 0.4228
WVFGRD96 84.0 60 50 50 4.24 0.4279
WVFGRD96 86.0 60 50 45 4.25 0.4334
WVFGRD96 88.0 60 50 45 4.25 0.4387
WVFGRD96 90.0 60 50 45 4.26 0.4422
WVFGRD96 92.0 60 50 45 4.26 0.4462
WVFGRD96 94.0 60 50 50 4.25 0.4489
WVFGRD96 96.0 60 50 50 4.25 0.4506
WVFGRD96 98.0 60 50 50 4.25 0.4523
WVFGRD96 100.0 60 50 45 4.27 0.4537
WVFGRD96 102.0 60 55 50 4.26 0.4543
WVFGRD96 104.0 60 55 50 4.26 0.4539
WVFGRD96 106.0 60 50 50 4.26 0.4538
WVFGRD96 108.0 60 55 50 4.26 0.4533
WVFGRD96 110.0 60 55 50 4.26 0.4525
WVFGRD96 112.0 60 55 50 4.26 0.4511
WVFGRD96 114.0 60 55 50 4.27 0.4500
WVFGRD96 116.0 60 55 50 4.27 0.4479
WVFGRD96 118.0 60 55 50 4.27 0.4457
WVFGRD96 120.0 60 55 50 4.27 0.4442
WVFGRD96 122.0 60 55 50 4.27 0.4419
WVFGRD96 124.0 60 55 50 4.27 0.4402
WVFGRD96 126.0 60 55 50 4.27 0.4374
WVFGRD96 128.0 55 60 35 4.29 0.4361
The best solution is
WVFGRD96 102.0 60 55 50 4.26 0.4543
The mechanism corresponding to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
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Figure 2. Depth sensitivity for waveform mechanism
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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.
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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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
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.
Velocity Model
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
Last Changed Sun May 10 22:42:26 CEST 2026
