Location
Location ANSS
The ANSS event ID is us6000rt6y and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/us6000rt6y/executive.
2025/12/07 18:04:08 60.479 -139.651 8.2 4.6 Alaska-Yukon
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2025/12/07 18:04:08.0 60.48 -139.65 8.2 4.6 Alaska-Yukon
Stations used:
AK.BAE AK.BAGL AK.BAL AK.BERG AK.BESE AK.BGLC AK.CRQ AK.CYK
AK.DHY AK.FID AK.GHO AK.GLI AK.GREN AK.GRES AK.GRIN AK.GRNC
AK.HDA AK.ISLE AK.J25K AK.KHIT AK.KIAG AK.KNK AK.L26K
AK.LOGN AK.M26K AK.MCAR AK.MESA AK.PIN AK.PNL AK.PS09
AK.PS10 AK.PS12 AK.PTPK AK.PWL AK.R32K AK.RAG AK.RC01
AK.RKAV AK.SWD AK.TGL AK.VRDI AT.PMR AV.N25K AV.WACK
CN.BRWY CN.DAWY CN.HYT CN.PLBC CN.WHY CN.YUK3 PQ.KLONY
PQ.OGILY
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 = 8.13e+22 dyne-cm
Mw = 4.54
Z = 12 km
Plane Strike Dip Rake
NP1 10 75 20
NP2 275 71 164
Principal Axes:
Axis Value Plunge Azimuth
T 8.13e+22 25 233
N 0.00e+00 65 45
P -8.13e+22 3 142
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.57e+22
Mxy 7.17e+22
Mxz -1.53e+22
Myy 1.18e+22
Myz -2.71e+22
Mzz 1.39e+22
-----------###
---------------#######
-------------------#########
--------------------##########
----------------------############
-----------------------#############
------------------------##############
-------------------------###############
---------##############--###############
---######################--------#########
#########################-------------####
#########################----------------#
########################------------------
#######################-----------------
#######################-----------------
##### #############-----------------
#### T ############-----------------
### ############----------------
###############----------- -
#############------------ P
#########-------------
####----------
Global CMT Convention Moment Tensor:
R T P
1.39e+22 -1.53e+22 2.71e+22
-1.53e+22 -2.57e+22 -7.17e+22
2.71e+22 -7.17e+22 1.18e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20251207180408/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 = 10
DIP = 75
RAKE = 20
MW = 4.54
HS = 12.0
The NDK file is 20251207180408.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 2025/12/07 18:04:08.0 60.48 -139.65 8.2 4.6 Alaska-Yukon
Stations used:
AK.BAE AK.BAGL AK.BAL AK.BERG AK.BESE AK.BGLC AK.CRQ AK.CYK
AK.DHY AK.FID AK.GHO AK.GLI AK.GREN AK.GRES AK.GRIN AK.GRNC
AK.HDA AK.ISLE AK.J25K AK.KHIT AK.KIAG AK.KNK AK.L26K
AK.LOGN AK.M26K AK.MCAR AK.MESA AK.PIN AK.PNL AK.PS09
AK.PS10 AK.PS12 AK.PTPK AK.PWL AK.R32K AK.RAG AK.RC01
AK.RKAV AK.SWD AK.TGL AK.VRDI AT.PMR AV.N25K AV.WACK
CN.BRWY CN.DAWY CN.HYT CN.PLBC CN.WHY CN.YUK3 PQ.KLONY
PQ.OGILY
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 = 8.13e+22 dyne-cm
Mw = 4.54
Z = 12 km
Plane Strike Dip Rake
NP1 10 75 20
NP2 275 71 164
Principal Axes:
Axis Value Plunge Azimuth
T 8.13e+22 25 233
N 0.00e+00 65 45
P -8.13e+22 3 142
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.57e+22
Mxy 7.17e+22
Mxz -1.53e+22
Myy 1.18e+22
Myz -2.71e+22
Mzz 1.39e+22
-----------###
---------------#######
-------------------#########
--------------------##########
----------------------############
-----------------------#############
------------------------##############
-------------------------###############
---------##############--###############
---######################--------#########
#########################-------------####
#########################----------------#
########################------------------
#######################-----------------
#######################-----------------
##### #############-----------------
#### T ############-----------------
### ############----------------
###############----------- -
#############------------ P
#########-------------
####----------
Global CMT Convention Moment Tensor:
R T P
1.39e+22 -1.53e+22 2.71e+22
-1.53e+22 -2.57e+22 -7.17e+22
2.71e+22 -7.17e+22 1.18e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20251207180408/index.html
|
W-phase Moment Tensor (Mww)
Moment 9.686e+15 N-m
Magnitude 4.59 Mww
Depth 11.5 km
Percent DC 95%
Half Duration 0.50 s
Catalog US
Data Source US
Contributor US
Nodal Planes
Plane Strike Dip Rake
NP1 284 90 156
NP2 14 66 0
Principal Axes
Axis Value Plunge Azimuth
T 9.805e+15 17 236
N -0.241e+15 66 103
P -9.564e+15 16 331
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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 1.0 5 65 -25 4.40 0.5002
WVFGRD96 2.0 0 55 -30 4.45 0.5079
WVFGRD96 3.0 10 70 30 4.44 0.5262
WVFGRD96 4.0 10 70 30 4.45 0.5499
WVFGRD96 5.0 10 70 25 4.46 0.5689
WVFGRD96 6.0 10 70 25 4.47 0.5844
WVFGRD96 7.0 10 70 25 4.48 0.5949
WVFGRD96 8.0 10 70 25 4.49 0.6019
WVFGRD96 9.0 10 75 20 4.50 0.6094
WVFGRD96 10.0 10 75 20 4.52 0.6112
WVFGRD96 11.0 10 75 20 4.53 0.6135
WVFGRD96 12.0 10 75 20 4.54 0.6135
WVFGRD96 13.0 10 75 20 4.55 0.6116
WVFGRD96 14.0 5 70 -20 4.56 0.6113
WVFGRD96 15.0 5 70 -20 4.57 0.6092
WVFGRD96 16.0 5 75 -20 4.58 0.6056
WVFGRD96 17.0 5 75 -20 4.59 0.6008
WVFGRD96 18.0 5 75 -20 4.60 0.5947
WVFGRD96 19.0 5 75 -20 4.61 0.5876
WVFGRD96 20.0 5 75 -20 4.62 0.5801
WVFGRD96 21.0 5 75 -20 4.63 0.5724
WVFGRD96 22.0 5 75 -20 4.63 0.5645
WVFGRD96 23.0 5 75 -20 4.64 0.5566
WVFGRD96 24.0 5 75 -20 4.64 0.5475
WVFGRD96 25.0 5 80 -25 4.65 0.5378
WVFGRD96 26.0 5 80 -25 4.65 0.5277
WVFGRD96 27.0 5 80 -25 4.66 0.5172
WVFGRD96 28.0 5 80 -25 4.66 0.5065
WVFGRD96 29.0 5 80 -25 4.66 0.4958
The best solution is
WVFGRD96 12.0 10 75 20 4.54 0.6135
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 CUS.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
CUS Model with Q from simple gamma values
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
1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00
9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00
10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00
20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00
0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00
Last Changed Tue Dec 9 14:03:43 CST 2025
