Left: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated. Right: residuals as a function of distance and azimuth.
The ANSS event ID is ak02546r3kto and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak02546r3kto/executive.
2025/04/01 15:44:30 63.060 -150.361 106.2 3.7 Alaska
USGS/SLU Moment Tensor Solution
ENS 2025/04/01 15:44:30:0 63.06 -150.36 106.2 3.7 Alaska
Stations used:
AK.CUT AK.GHO AK.K24K AK.KNK AK.L19K AK.L22K AK.MCK AK.PAX
AK.RC01 AK.SSN AK.WRH AT.PMR IU.COLA
Filtering commands used:
cut o DIST/3.5 -40 o DIST/3.5 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 7.00e+21 dyne-cm
Mw = 3.83
Z = 112 km
Plane Strike Dip Rake
NP1 333 85 155
NP2 65 65 5
Principal Axes:
Axis Value Plunge Azimuth
T 7.00e+21 21 286
N 0.00e+00 65 143
P -7.00e+21 14 22
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.22e+21
Mxy -3.88e+21
Mxz -8.90e+20
Myy 4.76e+21
Myz -2.84e+21
Mzz 4.67e+20
------------
##-------------- P ---
######------------- ------
#########---------------------
############----------------------
##############----------------------
################----------------------
## #############--------------------##
## T ##############-----------------####
### ###############---------------######
######################------------########
#######################---------##########
########################-----#############
########################-###############
#####################---################
###############---------##############
------------------------############
------------------------##########
-----------------------#######
----------------------######
--------------------##
--------------
Global CMT Convention Moment Tensor:
R T P
4.67e+20 -8.90e+20 2.84e+21
-8.90e+20 -5.22e+21 3.88e+21
2.84e+21 3.88e+21 4.76e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250401154430/index.html
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STK = 65
DIP = 65
RAKE = 5
MW = 3.83
HS = 112.0
The NDK file is 20250401154430.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: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
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/3.5 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 150 65 -35 3.01 0.2750
WVFGRD96 4.0 345 70 30 3.10 0.2976
WVFGRD96 6.0 165 55 20 3.14 0.3305
WVFGRD96 8.0 165 55 20 3.21 0.3532
WVFGRD96 10.0 160 60 10 3.23 0.3600
WVFGRD96 12.0 340 80 30 3.28 0.3583
WVFGRD96 14.0 335 90 30 3.30 0.3568
WVFGRD96 16.0 155 85 -30 3.32 0.3529
WVFGRD96 18.0 335 90 30 3.34 0.3392
WVFGRD96 20.0 240 55 -25 3.39 0.3416
WVFGRD96 22.0 240 50 -20 3.42 0.3517
WVFGRD96 24.0 240 50 -15 3.44 0.3638
WVFGRD96 26.0 245 55 -15 3.46 0.3786
WVFGRD96 28.0 245 60 -15 3.48 0.3956
WVFGRD96 30.0 245 65 -15 3.50 0.4120
WVFGRD96 32.0 245 65 -5 3.51 0.4271
WVFGRD96 34.0 245 65 -5 3.54 0.4443
WVFGRD96 36.0 245 70 -5 3.56 0.4557
WVFGRD96 38.0 245 80 -10 3.58 0.4634
WVFGRD96 40.0 240 70 -15 3.65 0.4907
WVFGRD96 42.0 245 65 -5 3.67 0.4914
WVFGRD96 44.0 240 70 -10 3.69 0.4933
WVFGRD96 46.0 245 65 -5 3.71 0.4959
WVFGRD96 48.0 245 65 -5 3.73 0.4980
WVFGRD96 50.0 245 65 -5 3.75 0.5027
WVFGRD96 52.0 245 70 -5 3.75 0.5082
WVFGRD96 54.0 245 70 -5 3.76 0.5144
WVFGRD96 56.0 245 70 -5 3.78 0.5229
WVFGRD96 58.0 245 70 0 3.79 0.5297
WVFGRD96 60.0 245 85 -15 3.77 0.5361
WVFGRD96 62.0 245 85 -15 3.78 0.5433
WVFGRD96 64.0 245 75 0 3.81 0.5501
WVFGRD96 66.0 245 90 -15 3.78 0.5596
WVFGRD96 68.0 65 75 15 3.77 0.5689
WVFGRD96 70.0 65 75 15 3.77 0.5775
WVFGRD96 72.0 65 75 15 3.77 0.5861
WVFGRD96 74.0 65 70 15 3.78 0.5944
WVFGRD96 76.0 65 70 15 3.78 0.6012
WVFGRD96 78.0 65 70 15 3.78 0.6074
WVFGRD96 80.0 65 75 10 3.79 0.6127
WVFGRD96 82.0 65 70 10 3.79 0.6194
WVFGRD96 84.0 65 70 10 3.79 0.6248
WVFGRD96 86.0 65 70 10 3.80 0.6299
WVFGRD96 88.0 65 70 10 3.80 0.6322
WVFGRD96 90.0 65 70 10 3.80 0.6362
WVFGRD96 92.0 65 70 10 3.81 0.6393
WVFGRD96 94.0 65 70 10 3.81 0.6420
WVFGRD96 96.0 65 70 5 3.82 0.6446
WVFGRD96 98.0 65 70 5 3.82 0.6461
WVFGRD96 100.0 65 70 5 3.82 0.6483
WVFGRD96 102.0 65 70 5 3.82 0.6494
WVFGRD96 104.0 65 70 5 3.83 0.6488
WVFGRD96 106.0 65 70 5 3.83 0.6510
WVFGRD96 108.0 65 65 5 3.82 0.6507
WVFGRD96 110.0 65 65 5 3.83 0.6506
WVFGRD96 112.0 65 65 5 3.83 0.6510
WVFGRD96 114.0 65 65 5 3.83 0.6507
WVFGRD96 116.0 65 65 5 3.83 0.6507
WVFGRD96 118.0 65 60 10 3.82 0.6499
WVFGRD96 120.0 65 65 5 3.84 0.6482
WVFGRD96 122.0 65 60 10 3.83 0.6486
WVFGRD96 124.0 65 60 10 3.83 0.6468
WVFGRD96 126.0 65 60 10 3.83 0.6465
WVFGRD96 128.0 65 60 10 3.83 0.6448
WVFGRD96 130.0 65 60 10 3.84 0.6442
WVFGRD96 132.0 65 60 10 3.84 0.6430
WVFGRD96 134.0 65 60 10 3.84 0.6408
WVFGRD96 136.0 65 60 10 3.84 0.6402
WVFGRD96 138.0 65 60 10 3.84 0.6386
WVFGRD96 140.0 65 60 10 3.85 0.6375
WVFGRD96 142.0 65 55 15 3.84 0.6358
WVFGRD96 144.0 65 55 15 3.84 0.6353
WVFGRD96 146.0 65 55 15 3.85 0.6332
WVFGRD96 148.0 65 55 15 3.85 0.6322
The best solution is
WVFGRD96 112.0 65 65 5 3.83 0.6510
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/3.5 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 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. |
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