The ANSS event ID is ak025qufoy6 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak025qufoy6/executive.
2025/01/16 23:24:12 61.337 -146.958 4.0 4.1 Alaska
USGS/SLU Moment Tensor Solution
ENS 2025/01/16 23:24:12:0 61.34 -146.96 4.0 4.1 Alaska
Stations used:
AK.DHY AK.DIV AK.EYAK AK.FID AK.GHO AK.GLB AK.HIN AK.KLU
AK.L22K AK.PWL AK.RC01 AK.SAW AK.SCM AK.SSN AK.SWD AK.WAT6
AT.PMR AV.WAZA
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
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 8.04e+21 dyne-cm
Mw = 3.87
Z = 29 km
Plane Strike Dip Rake
NP1 60 85 50
NP2 324 40 172
Principal Axes:
Axis Value Plunge Azimuth
T 8.04e+21 37 295
N 0.00e+00 40 64
P -8.04e+21 29 181
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.26e+21
Mxy -2.11e+21
Mxz 5.02e+21
Myy 4.19e+21
Myz -3.42e+21
Mzz 1.07e+21
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----------------------
#############---------------
##################------------
#######################-----------
##########################----------
###### ###################------####
####### T #####################--#######
####### ####################--########
############################------########
#########################---------########
######################-------------#######
###################----------------#######
##############---------------------#####
###########------------------------#####
######----------------------------####
#--------------------------------###
-------------------------------###
------------- -------------#
------------ P ------------#
--------- ----------
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Global CMT Convention Moment Tensor:
R T P
1.07e+21 5.02e+21 3.42e+21
5.02e+21 -5.26e+21 2.11e+21
3.42e+21 2.11e+21 4.19e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250116232412/index.html
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STK = 60
DIP = 85
RAKE = 50
MW = 3.87
HS = 29.0
The NDK file is 20250116232412.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 0.10 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 50 45 -75 3.27 0.2273
WVFGRD96 2.0 35 45 -80 3.47 0.3905
WVFGRD96 3.0 60 60 25 3.48 0.3914
WVFGRD96 4.0 240 90 -50 3.54 0.4273
WVFGRD96 5.0 65 85 55 3.59 0.5006
WVFGRD96 6.0 65 85 55 3.61 0.5514
WVFGRD96 7.0 65 85 50 3.61 0.5806
WVFGRD96 8.0 65 85 55 3.66 0.5967
WVFGRD96 9.0 70 80 55 3.67 0.6094
WVFGRD96 10.0 65 80 50 3.67 0.6205
WVFGRD96 11.0 65 80 50 3.68 0.6289
WVFGRD96 12.0 60 90 45 3.68 0.6376
WVFGRD96 13.0 60 90 45 3.69 0.6456
WVFGRD96 14.0 240 90 -45 3.70 0.6528
WVFGRD96 15.0 60 90 45 3.71 0.6597
WVFGRD96 16.0 240 90 -45 3.72 0.6664
WVFGRD96 17.0 240 90 -45 3.73 0.6731
WVFGRD96 18.0 240 90 -45 3.74 0.6793
WVFGRD96 19.0 60 90 45 3.75 0.6851
WVFGRD96 20.0 60 90 45 3.76 0.6904
WVFGRD96 21.0 240 90 -45 3.78 0.6950
WVFGRD96 22.0 60 90 45 3.79 0.6992
WVFGRD96 23.0 60 90 45 3.80 0.7026
WVFGRD96 24.0 240 90 -50 3.81 0.7052
WVFGRD96 25.0 60 90 50 3.82 0.7073
WVFGRD96 26.0 60 85 50 3.84 0.7109
WVFGRD96 27.0 60 85 50 3.85 0.7154
WVFGRD96 28.0 60 85 50 3.86 0.7182
WVFGRD96 29.0 60 85 50 3.87 0.7189
WVFGRD96 30.0 60 85 50 3.88 0.7188
WVFGRD96 31.0 60 85 50 3.88 0.7172
WVFGRD96 32.0 60 85 50 3.89 0.7140
WVFGRD96 33.0 60 85 50 3.90 0.7091
WVFGRD96 34.0 55 90 50 3.90 0.7030
WVFGRD96 35.0 235 90 -50 3.91 0.6971
WVFGRD96 36.0 55 90 50 3.92 0.6902
WVFGRD96 37.0 55 90 50 3.92 0.6840
WVFGRD96 38.0 235 90 -50 3.93 0.6781
WVFGRD96 39.0 235 85 -50 3.93 0.6735
WVFGRD96 40.0 55 90 60 4.04 0.6688
WVFGRD96 41.0 230 85 -60 4.05 0.6650
WVFGRD96 42.0 230 85 -55 4.05 0.6589
WVFGRD96 43.0 230 85 -55 4.05 0.6554
WVFGRD96 44.0 230 85 -55 4.06 0.6517
WVFGRD96 45.0 225 80 -55 4.07 0.6489
WVFGRD96 46.0 225 80 -55 4.07 0.6458
WVFGRD96 47.0 225 80 -55 4.08 0.6431
WVFGRD96 48.0 225 80 -55 4.08 0.6405
WVFGRD96 49.0 225 80 -55 4.09 0.6363
WVFGRD96 50.0 225 80 -55 4.09 0.6321
WVFGRD96 51.0 225 80 -50 4.09 0.6283
WVFGRD96 52.0 225 80 -50 4.10 0.6242
WVFGRD96 53.0 225 80 -50 4.10 0.6195
WVFGRD96 54.0 225 80 -50 4.10 0.6152
WVFGRD96 55.0 225 80 -50 4.11 0.6102
WVFGRD96 56.0 225 80 -50 4.11 0.6046
WVFGRD96 57.0 225 80 -50 4.11 0.5993
WVFGRD96 58.0 225 80 -50 4.12 0.5941
WVFGRD96 59.0 225 80 -50 4.12 0.5884
The best solution is
WVFGRD96 29.0 60 85 50 3.87 0.7189
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 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