Location
Location ANSS
The ANSS event ID is ak025dxe5mlz and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/ak025dxe5mlz/executive.
2025/10/30 17:33:14 59.631 -150.233 23.6 5.4 Alaska
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2025/10/30 17:33:14.0 59.63 -150.23 23.6 5.4 Alaska
Stations used:
AK.BRLK AK.CAPN AK.DHY AK.DIV AK.EYAK AK.FID AK.GHO AK.GLI
AK.HIN AK.KLU AK.KNK AK.L22K AK.O18K AK.O19K AK.P23K AK.PWL
AK.RC01 AK.SAW AK.SCM AK.SKN AK.SLK AK.SSN AK.SWD AK.WAT6
AT.PMR AV.RED AV.SPCL AV.WAZA 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 = 8.81e+23 dyne-cm
Mw = 5.23
Z = 39 km
Plane Strike Dip Rake
NP1 165 60 -50
NP2 286 48 -138
Principal Axes:
Axis Value Plunge Azimuth
T 8.81e+23 7 228
N 0.00e+00 34 322
P -8.81e+23 55 128
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.84e+23
Mxy 5.71e+23
Mxz 1.86e+23
Myy 3.00e+23
Myz -3.99e+23
Mzz -5.84e+23
-#############
----##################
-------#####################
-------#######################
---------#########################
------###-----------################
---#######----------------############
-##########--------------------#########
###########----------------------#######
#############-----------------------######
#############-------------------------####
#############--------------------------###
##############------------ -----------##
#############------------ P ------------
##############----------- ------------
##############------------------------
##############----------------------
# ##########--------------------
T ###########-----------------
#############--------------
#############---------
###########---
Global CMT Convention Moment Tensor:
R T P
-5.84e+23 1.86e+23 3.99e+23
1.86e+23 2.84e+23 -5.71e+23
3.99e+23 -5.71e+23 3.00e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20251030173314/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 = 165
DIP = 60
RAKE = -50
MW = 5.23
HS = 39.0
The NDK file is 20251030173314.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 |
USGSW |
USGS/SLU Moment Tensor Solution
ENS 2025/10/30 17:33:14.0 59.63 -150.23 23.6 5.4 Alaska
Stations used:
AK.BRLK AK.CAPN AK.DHY AK.DIV AK.EYAK AK.FID AK.GHO AK.GLI
AK.HIN AK.KLU AK.KNK AK.L22K AK.O18K AK.O19K AK.P23K AK.PWL
AK.RC01 AK.SAW AK.SCM AK.SKN AK.SLK AK.SSN AK.SWD AK.WAT6
AT.PMR AV.RED AV.SPCL AV.WAZA 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 = 8.81e+23 dyne-cm
Mw = 5.23
Z = 39 km
Plane Strike Dip Rake
NP1 165 60 -50
NP2 286 48 -138
Principal Axes:
Axis Value Plunge Azimuth
T 8.81e+23 7 228
N 0.00e+00 34 322
P -8.81e+23 55 128
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.84e+23
Mxy 5.71e+23
Mxz 1.86e+23
Myy 3.00e+23
Myz -3.99e+23
Mzz -5.84e+23
-#############
----##################
-------#####################
-------#######################
---------#########################
------###-----------################
---#######----------------############
-##########--------------------#########
###########----------------------#######
#############-----------------------######
#############-------------------------####
#############--------------------------###
##############------------ -----------##
#############------------ P ------------
##############----------- ------------
##############------------------------
##############----------------------
# ##########--------------------
T ###########-----------------
#############--------------
#############---------
###########---
Global CMT Convention Moment Tensor:
R T P
-5.84e+23 1.86e+23 3.99e+23
1.86e+23 2.84e+23 -5.71e+23
3.99e+23 -5.71e+23 3.00e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20251030173314/index.html
|
W-phase Moment Tensor (Mww)
Moment 1.412e+17 N-m
Magnitude 5.37 Mww
Depth 35.5 km
Percent DC 92%
Half Duration 0.50 s
Catalog US
Data Source US
Contributor US
Nodal Planes
Plane Strike Dip Rake
NP1 291 46 -133
NP2 164 58 -54
Principal Axes
Axis Value Plunge Azimuth
T 1.382e+17 7 230
N 0.057e+17 30 324
P -1.439e+17 59 128
|
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 45 45 -90 4.51 0.1503
WVFGRD96 2.0 45 45 -90 4.66 0.2079
WVFGRD96 3.0 310 35 75 4.70 0.2037
WVFGRD96 4.0 290 40 50 4.69 0.2048
WVFGRD96 5.0 20 80 65 4.71 0.2150
WVFGRD96 6.0 15 80 65 4.73 0.2433
WVFGRD96 7.0 15 80 60 4.75 0.2682
WVFGRD96 8.0 20 75 65 4.83 0.2855
WVFGRD96 9.0 20 75 65 4.85 0.3060
WVFGRD96 10.0 20 75 60 4.87 0.3222
WVFGRD96 11.0 15 70 55 4.89 0.3375
WVFGRD96 12.0 15 70 55 4.91 0.3510
WVFGRD96 13.0 15 65 50 4.92 0.3621
WVFGRD96 14.0 15 65 50 4.94 0.3704
WVFGRD96 15.0 15 70 50 4.95 0.3772
WVFGRD96 16.0 15 70 50 4.97 0.3832
WVFGRD96 17.0 15 70 50 4.98 0.3877
WVFGRD96 18.0 15 70 50 5.00 0.3908
WVFGRD96 19.0 15 70 50 5.01 0.3935
WVFGRD96 20.0 15 80 55 5.02 0.3975
WVFGRD96 21.0 15 80 55 5.04 0.4022
WVFGRD96 22.0 175 70 -40 5.05 0.4161
WVFGRD96 23.0 175 70 -40 5.06 0.4297
WVFGRD96 24.0 175 70 -40 5.07 0.4424
WVFGRD96 25.0 170 65 -40 5.08 0.4548
WVFGRD96 26.0 170 65 -40 5.10 0.4671
WVFGRD96 27.0 170 65 -40 5.11 0.4794
WVFGRD96 28.0 170 65 -45 5.12 0.4919
WVFGRD96 29.0 165 55 -40 5.13 0.5030
WVFGRD96 30.0 165 55 -40 5.14 0.5155
WVFGRD96 31.0 165 60 -45 5.15 0.5263
WVFGRD96 32.0 165 60 -45 5.16 0.5362
WVFGRD96 33.0 165 60 -50 5.17 0.5438
WVFGRD96 34.0 165 60 -50 5.18 0.5512
WVFGRD96 35.0 165 60 -50 5.19 0.5555
WVFGRD96 36.0 165 60 -50 5.19 0.5585
WVFGRD96 37.0 165 60 -50 5.20 0.5599
WVFGRD96 38.0 165 60 -50 5.21 0.5596
WVFGRD96 39.0 165 60 -50 5.23 0.5600
WVFGRD96 40.0 160 60 -60 5.31 0.5326
WVFGRD96 41.0 160 60 -55 5.32 0.5358
WVFGRD96 42.0 160 60 -60 5.34 0.5376
WVFGRD96 43.0 160 60 -60 5.35 0.5352
WVFGRD96 44.0 160 60 -60 5.35 0.5324
WVFGRD96 45.0 160 60 -60 5.36 0.5271
WVFGRD96 46.0 160 60 -60 5.37 0.5215
WVFGRD96 47.0 160 60 -60 5.37 0.5146
WVFGRD96 48.0 155 55 -60 5.37 0.5068
WVFGRD96 49.0 160 60 -60 5.38 0.4989
WVFGRD96 50.0 160 60 -60 5.38 0.4900
WVFGRD96 51.0 160 60 -60 5.39 0.4812
WVFGRD96 52.0 160 60 -60 5.39 0.4717
WVFGRD96 53.0 160 60 -60 5.39 0.4618
WVFGRD96 54.0 160 60 -60 5.39 0.4523
WVFGRD96 55.0 160 60 -60 5.39 0.4423
WVFGRD96 56.0 160 60 -60 5.39 0.4334
WVFGRD96 57.0 160 60 -60 5.39 0.4236
WVFGRD96 58.0 160 60 -65 5.39 0.4157
WVFGRD96 59.0 155 55 -65 5.38 0.4079
The best solution is
WVFGRD96 39.0 165 60 -50 5.23 0.5600
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 Fri Oct 31 06:48:19 CDT 2025
