The ANSS event ID is ak025d8cqrw0 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak025d8cqrw0/executive.
2025/10/15 03:30:44 61.729 -147.456 27.0 4.0 Alaska
USGS/SLU Moment Tensor Solution
ENS 2025/10/15 03:30:44.0 61.73 -147.46 27.0 4.0 Alaska
Stations used:
AK.BAE AK.BMR AK.DHY AK.DIV AK.EYAK AK.FID AK.GHO AK.GLI
AK.HIN AK.K24K AK.KLU AK.KNK AK.KTH AK.L22K AK.MCK AK.O19K
AK.P23K AK.PAX AK.PIN AK.PPD AK.RC01 AK.RIDG AK.RND AK.SAW
AK.SKN AK.SWD AK.WAT6 AT.PMR 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 0.08 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 8.61e+21 dyne-cm
Mw = 3.89
Z = 45 km
Plane Strike Dip Rake
NP1 37 86 150
NP2 130 60 5
Principal Axes:
Axis Value Plunge Azimuth
T 8.61e+21 24 350
N 0.00e+00 60 210
P -8.61e+21 17 88
Moment Tensor: (dyne-cm)
Component Value
Mxx 6.93e+21
Mxy -1.61e+21
Mxz 3.04e+21
Myy -7.58e+21
Myz -3.04e+21
Mzz 6.50e+20
##############
####### ############
########## T #############--
########### ############----
-##########################-------
--#########################---------
----######################------------
------####################--------------
-------##################---------------
---------###############------------- --
----------#############-------------- P --
-----------###########--------------- --
-------------#######----------------------
--------------####----------------------
----------------------------------------
--------------###---------------------
-----------########-----------------
---------##############-----------
-----#########################
--##########################
######################
##############
Global CMT Convention Moment Tensor:
R T P
6.50e+20 3.04e+21 3.04e+21
3.04e+21 6.93e+21 1.61e+21
3.04e+21 1.61e+21 -7.58e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20251015033044/index.html
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STK = 130
DIP = 60
RAKE = 5
MW = 3.89
HS = 45.0
The NDK file is 20251015033044.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 0.08 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 1.0 310 90 0 3.16 0.3131
WVFGRD96 2.0 305 75 -20 3.32 0.4373
WVFGRD96 3.0 125 70 -20 3.37 0.4766
WVFGRD96 4.0 120 65 -35 3.43 0.5113
WVFGRD96 5.0 120 65 -35 3.46 0.5360
WVFGRD96 6.0 125 75 -30 3.45 0.5434
WVFGRD96 7.0 125 75 -25 3.46 0.5474
WVFGRD96 8.0 125 75 -30 3.50 0.5570
WVFGRD96 9.0 135 70 25 3.51 0.5621
WVFGRD96 10.0 135 70 25 3.52 0.5700
WVFGRD96 11.0 130 75 20 3.53 0.5775
WVFGRD96 12.0 130 75 20 3.54 0.5844
WVFGRD96 13.0 130 70 15 3.54 0.5899
WVFGRD96 14.0 130 75 20 3.56 0.5959
WVFGRD96 15.0 130 75 20 3.57 0.6017
WVFGRD96 16.0 130 75 20 3.58 0.6073
WVFGRD96 17.0 130 75 20 3.59 0.6134
WVFGRD96 18.0 130 75 20 3.60 0.6192
WVFGRD96 19.0 130 75 20 3.61 0.6246
WVFGRD96 20.0 130 75 15 3.62 0.6297
WVFGRD96 21.0 130 75 15 3.63 0.6344
WVFGRD96 22.0 130 75 15 3.64 0.6394
WVFGRD96 23.0 130 75 15 3.65 0.6442
WVFGRD96 24.0 130 75 15 3.65 0.6491
WVFGRD96 25.0 130 75 15 3.66 0.6534
WVFGRD96 26.0 130 75 15 3.67 0.6572
WVFGRD96 27.0 130 75 10 3.68 0.6610
WVFGRD96 28.0 130 75 10 3.69 0.6653
WVFGRD96 29.0 130 75 10 3.70 0.6695
WVFGRD96 30.0 130 75 10 3.71 0.6736
WVFGRD96 31.0 130 70 5 3.71 0.6776
WVFGRD96 32.0 130 70 5 3.72 0.6813
WVFGRD96 33.0 130 70 5 3.73 0.6848
WVFGRD96 34.0 130 70 5 3.74 0.6875
WVFGRD96 35.0 130 70 5 3.75 0.6904
WVFGRD96 36.0 130 65 5 3.76 0.6951
WVFGRD96 37.0 130 70 5 3.78 0.7004
WVFGRD96 38.0 130 70 5 3.79 0.7059
WVFGRD96 39.0 130 70 5 3.81 0.7131
WVFGRD96 40.0 130 60 5 3.85 0.7139
WVFGRD96 41.0 130 60 5 3.86 0.7176
WVFGRD96 42.0 130 60 5 3.87 0.7198
WVFGRD96 43.0 130 60 5 3.88 0.7217
WVFGRD96 44.0 130 60 5 3.88 0.7231
WVFGRD96 45.0 130 60 5 3.89 0.7238
WVFGRD96 46.0 130 60 5 3.90 0.7236
WVFGRD96 47.0 130 60 5 3.90 0.7230
WVFGRD96 48.0 130 60 5 3.91 0.7229
WVFGRD96 49.0 130 60 5 3.92 0.7217
WVFGRD96 50.0 130 60 5 3.92 0.7198
WVFGRD96 51.0 130 60 0 3.93 0.7182
WVFGRD96 52.0 130 60 0 3.93 0.7164
WVFGRD96 53.0 130 60 0 3.94 0.7141
WVFGRD96 54.0 125 60 -5 3.94 0.7126
WVFGRD96 55.0 125 60 -5 3.94 0.7101
WVFGRD96 56.0 125 60 -5 3.95 0.7088
WVFGRD96 57.0 125 60 -5 3.95 0.7071
WVFGRD96 58.0 125 60 -5 3.96 0.7042
WVFGRD96 59.0 125 60 -5 3.96 0.7022
The best solution is
WVFGRD96 45.0 130 60 5 3.89 0.7238
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 0.08 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