The ANSS event ID is uw62079456 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uw62079456/executive.
2025/03/06 00:18:24 47.924 -123.141 42.4 3.9 Washington
USGS/SLU Moment Tensor Solution
ENS 2025/03/06 00:18:24:0 47.92 -123.14 42.4 3.9 Washington
Stations used:
CN.CLRS CN.PGC US.NLWA UW.BHW UW.EQUIL UW.GNW UW.HILL
UW.KALA UW.LON UW.LRIV UW.WATCH
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 = 9.23e+21 dyne-cm
Mw = 3.91
Z = 51 km
Plane Strike Dip Rake
NP1 170 80 55
NP2 66 36 163
Principal Axes:
Axis Value Plunge Azimuth
T 9.23e+21 44 46
N 0.00e+00 34 177
P -9.23e+21 27 287
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.70e+21
Mxy 4.45e+21
Mxz 2.14e+21
Myy -4.29e+21
Myz 6.83e+21
Mzz 2.58e+21
---###########
-------###############
----------##################
-----------###################
-------------#####################
--------------########### ########
---------------########### T #########
---- ---------########### #########-
---- P ----------######################-
----- ----------#####################---
------------------#####################---
-------------------###################----
-------------------##################-----
------------------#################-----
-------------------##############-------
------------------############--------
#-----------------#########---------
###--------------######-----------
######---------#--------------
###############-------------
#############---------
##########----
Global CMT Convention Moment Tensor:
R T P
2.58e+21 2.14e+21 -6.83e+21
2.14e+21 1.70e+21 -4.45e+21
-6.83e+21 -4.45e+21 -4.29e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250306001824/index.html
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STK = 170
DIP = 80
RAKE = 55
MW = 3.91
HS = 51.0
The NDK file is 20250306001824.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 1.0 160 55 50 3.02 0.1838
WVFGRD96 2.0 25 50 -65 3.25 0.3213
WVFGRD96 3.0 160 65 40 3.26 0.3363
WVFGRD96 4.0 160 70 45 3.31 0.3543
WVFGRD96 5.0 330 85 -50 3.35 0.3739
WVFGRD96 6.0 320 75 -65 3.43 0.4152
WVFGRD96 7.0 315 70 -65 3.44 0.4436
WVFGRD96 8.0 315 70 -70 3.52 0.4586
WVFGRD96 9.0 315 70 -70 3.52 0.4756
WVFGRD96 10.0 315 65 -70 3.53 0.4865
WVFGRD96 11.0 305 55 -70 3.55 0.4985
WVFGRD96 12.0 305 55 -70 3.55 0.5079
WVFGRD96 13.0 300 55 -70 3.56 0.5143
WVFGRD96 14.0 295 50 -75 3.58 0.5203
WVFGRD96 15.0 295 50 -75 3.59 0.5253
WVFGRD96 16.0 295 50 -75 3.60 0.5279
WVFGRD96 17.0 300 55 -75 3.60 0.5294
WVFGRD96 18.0 295 55 -75 3.62 0.5307
WVFGRD96 19.0 300 55 -75 3.62 0.5306
WVFGRD96 20.0 300 55 -75 3.63 0.5285
WVFGRD96 21.0 160 80 60 3.58 0.5291
WVFGRD96 22.0 160 80 60 3.59 0.5337
WVFGRD96 23.0 160 80 60 3.60 0.5366
WVFGRD96 24.0 165 75 60 3.61 0.5394
WVFGRD96 25.0 165 75 60 3.62 0.5409
WVFGRD96 26.0 165 80 55 3.63 0.5419
WVFGRD96 27.0 165 80 55 3.64 0.5422
WVFGRD96 28.0 165 80 55 3.65 0.5410
WVFGRD96 29.0 170 70 60 3.66 0.5396
WVFGRD96 30.0 170 70 60 3.67 0.5409
WVFGRD96 31.0 170 70 55 3.67 0.5410
WVFGRD96 32.0 170 70 55 3.68 0.5390
WVFGRD96 33.0 170 80 50 3.69 0.5415
WVFGRD96 34.0 170 80 50 3.70 0.5441
WVFGRD96 35.0 170 80 50 3.70 0.5468
WVFGRD96 36.0 170 80 50 3.71 0.5483
WVFGRD96 37.0 170 80 50 3.72 0.5515
WVFGRD96 38.0 170 80 45 3.73 0.5545
WVFGRD96 39.0 170 80 45 3.74 0.5583
WVFGRD96 40.0 170 80 60 3.83 0.5662
WVFGRD96 41.0 170 80 55 3.84 0.5726
WVFGRD96 42.0 170 80 55 3.85 0.5786
WVFGRD96 43.0 170 80 55 3.86 0.5839
WVFGRD96 44.0 170 80 55 3.86 0.5895
WVFGRD96 45.0 170 80 55 3.87 0.5919
WVFGRD96 46.0 170 80 55 3.88 0.5963
WVFGRD96 47.0 170 80 55 3.89 0.5992
WVFGRD96 48.0 170 80 55 3.89 0.6006
WVFGRD96 49.0 170 80 55 3.90 0.6018
WVFGRD96 50.0 170 80 55 3.91 0.6019
WVFGRD96 51.0 170 80 55 3.91 0.6026
WVFGRD96 52.0 170 80 55 3.92 0.6013
WVFGRD96 53.0 170 80 55 3.92 0.6005
WVFGRD96 54.0 170 80 55 3.93 0.5967
WVFGRD96 55.0 170 80 55 3.93 0.5958
WVFGRD96 56.0 170 80 55 3.94 0.5928
WVFGRD96 57.0 170 80 50 3.94 0.5902
WVFGRD96 58.0 170 80 50 3.95 0.5871
WVFGRD96 59.0 170 80 50 3.95 0.5830
The best solution is
WVFGRD96 51.0 170 80 55 3.91 0.6026
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