The ANSS event ID is aka2026nrcfxi and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/aka2026nrcfxi/executive.
2026/07/12 06:00:44 59.720 -153.026 106.8 4.2 Alaska
USGS/SLU Moment Tensor Solution
ENS 2026/07/12 06:00:44.0 59.72 -153.03 106.8 4.2 Alaska
Stations used:
AK.BRLK AK.CAST AK.CNP AK.DIV AK.FIRE AK.GHO AK.HOM AK.KNK
AK.M16K AK.N18K AK.O18K AK.O19K AK.P17K AK.P23K AK.PPLA
AK.Q19K AK.RC01 AK.SCM AK.SKN AK.SSN AK.SWD AT.PMR AV.ACH
AV.RED AV.SPCL AV.STLK II.KDAK
Filtering commands used:
cut o DIST/3.5 -40 o DIST/3.5 +40
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.26e+22 dyne-cm
Mw = 4.17
Z = 114 km
Plane Strike Dip Rake
NP1 292 61 132
NP2 50 50 40
Principal Axes:
Axis Value Plunge Azimuth
T 2.26e+22 53 255
N 0.00e+00 36 87
P -2.26e+22 6 353
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.15e+22
Mxy 4.75e+21
Mxz -5.23e+21
Myy 7.16e+21
Myz -1.02e+22
Mzz 1.43e+22
--- P --------
------- ------------
----------------------------
------------------------------
---------------------------------#
----------------------------------##
-#################-----------------###
########################------------####
############################-------#####
################################---#######
##################################-#######
########## ####################---######
########## T ###################------####
######### ##################--------##
############################-----------#
#########################-------------
#####################---------------
#################-----------------
-########---------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
1.43e+22 -5.23e+21 1.02e+22
-5.23e+21 -2.15e+22 -4.75e+21
1.02e+22 -4.75e+21 7.16e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260712060044/index.html
|
STK = 50
DIP = 50
RAKE = 40
MW = 4.17
HS = 114.0
The NDK file is 20260712060044.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.
 |
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.
|
|
|
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 -40 o DIST/3.5 +40 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 2.0 75 40 -85 3.32 0.2235
WVFGRD96 4.0 250 80 -55 3.34 0.1999
WVFGRD96 6.0 280 75 -50 3.35 0.2369
WVFGRD96 8.0 280 70 -50 3.44 0.2580
WVFGRD96 10.0 300 65 50 3.47 0.2728
WVFGRD96 12.0 300 65 50 3.51 0.2835
WVFGRD96 14.0 30 50 40 3.55 0.2902
WVFGRD96 16.0 30 50 35 3.58 0.2960
WVFGRD96 18.0 30 50 35 3.61 0.2981
WVFGRD96 20.0 210 50 35 3.63 0.3008
WVFGRD96 22.0 210 50 35 3.66 0.3023
WVFGRD96 24.0 180 50 -30 3.67 0.3062
WVFGRD96 26.0 180 50 -30 3.69 0.3072
WVFGRD96 28.0 180 55 -30 3.70 0.3059
WVFGRD96 30.0 210 50 35 3.73 0.3050
WVFGRD96 32.0 350 55 -30 3.75 0.3094
WVFGRD96 34.0 350 55 -30 3.76 0.3194
WVFGRD96 36.0 350 55 -30 3.78 0.3260
WVFGRD96 38.0 155 50 -70 3.80 0.3298
WVFGRD96 40.0 150 50 -80 3.90 0.3574
WVFGRD96 42.0 325 40 -85 3.93 0.3628
WVFGRD96 44.0 330 40 -80 3.95 0.3648
WVFGRD96 46.0 330 40 -80 3.97 0.3653
WVFGRD96 48.0 335 40 -75 3.98 0.3639
WVFGRD96 50.0 335 40 -75 3.99 0.3603
WVFGRD96 52.0 145 50 -90 4.00 0.3578
WVFGRD96 54.0 35 35 25 3.99 0.3659
WVFGRD96 56.0 40 35 30 4.01 0.3758
WVFGRD96 58.0 40 35 30 4.01 0.3850
WVFGRD96 60.0 40 35 25 4.03 0.3973
WVFGRD96 62.0 45 35 30 4.04 0.4092
WVFGRD96 64.0 45 35 30 4.05 0.4213
WVFGRD96 66.0 45 35 30 4.06 0.4308
WVFGRD96 68.0 45 40 30 4.06 0.4397
WVFGRD96 70.0 45 40 30 4.07 0.4481
WVFGRD96 72.0 45 40 30 4.07 0.4555
WVFGRD96 74.0 50 45 45 4.07 0.4665
WVFGRD96 76.0 50 45 45 4.08 0.4779
WVFGRD96 78.0 50 45 40 4.09 0.4891
WVFGRD96 80.0 50 50 40 4.10 0.4998
WVFGRD96 82.0 50 50 40 4.11 0.5109
WVFGRD96 84.0 50 50 40 4.11 0.5221
WVFGRD96 86.0 50 50 40 4.12 0.5327
WVFGRD96 88.0 50 50 40 4.12 0.5420
WVFGRD96 90.0 50 50 40 4.13 0.5504
WVFGRD96 92.0 50 50 40 4.13 0.5572
WVFGRD96 94.0 50 50 35 4.15 0.5632
WVFGRD96 96.0 50 50 35 4.15 0.5700
WVFGRD96 98.0 50 50 35 4.15 0.5759
WVFGRD96 100.0 50 50 35 4.16 0.5805
WVFGRD96 102.0 50 50 35 4.16 0.5847
WVFGRD96 104.0 50 50 35 4.17 0.5890
WVFGRD96 106.0 50 50 35 4.17 0.5926
WVFGRD96 108.0 50 50 35 4.17 0.5934
WVFGRD96 110.0 50 50 40 4.17 0.5958
WVFGRD96 112.0 50 50 40 4.17 0.5975
WVFGRD96 114.0 50 50 40 4.17 0.5975
WVFGRD96 116.0 50 50 40 4.17 0.5972
WVFGRD96 118.0 50 50 40 4.18 0.5963
WVFGRD96 120.0 50 50 40 4.18 0.5958
WVFGRD96 122.0 50 50 40 4.18 0.5952
WVFGRD96 124.0 50 50 40 4.19 0.5924
WVFGRD96 126.0 50 50 40 4.19 0.5910
WVFGRD96 128.0 50 50 40 4.19 0.5883
The best solution is
WVFGRD96 114.0 50 50 40 4.17 0.5975
The mechanism corresponding to the best fit is
|
|
|
The best fit as a function of depth is given in the following figure:
|
|
|
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 -40 o DIST/3.5 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3
|
| 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. |
|
| 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