The ANSS event ID is ak0247zzhfxj and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0247zzhfxj/executive.
2024/06/22 13:39:28 63.131 -150.424 107.4 4.0 Alaska
USGS/SLU Moment Tensor Solution
ENS 2024/06/22 13:39:28:0 63.13 -150.42 107.4 4.0 Alaska
Stations used:
AK.BPAW AK.CAST AK.CCB AK.CUT AK.DOT AK.GHO AK.H21K AK.H24K
AK.HDA AK.I23K AK.J19K AK.J20K AK.K20K AK.K24K AK.KNK
AK.L19K AK.L20K AK.L22K AK.MCK AK.MLY AK.PAX AK.RC01
AK.RIDG AK.RND AK.SAW AK.SCM AK.WRH AT.PMR AT.TTA IM.IL31
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 0.10 n 3
Best Fitting Double Couple
Mo = 1.45e+22 dyne-cm
Mw = 4.04
Z = 110 km
Plane Strike Dip Rake
NP1 326 64 134
NP2 80 50 35
Principal Axes:
Axis Value Plunge Azimuth
T 1.45e+22 50 286
N 0.00e+00 39 123
P -1.45e+22 8 26
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.10e+22
Mxy -7.13e+21
Mxz 9.62e+19
Myy 2.86e+21
Myz -7.75e+21
Mzz 8.16e+21
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------------------ P -
######--------------- ----
###########-------------------
###############-------------------
##################------------------
#####################-----------------
#######################-----------------
######### #############---------------
########## T ##############--------------#
########## ###############------------##
#############################----------###
##############################-------#####
-#############################----######
---#####################################
-----#####################----########
-----------#######------------######
-----------------------------#####
---------------------------###
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Global CMT Convention Moment Tensor:
R T P
8.16e+21 9.62e+19 7.75e+21
9.62e+19 -1.10e+22 7.13e+21
7.75e+21 7.13e+21 2.86e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240622133928/index.html
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STK = 80
DIP = 50
RAKE = 35
MW = 4.04
HS = 110.0
The NDK file is 20240622133928.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/3.5 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 120 40 -80 3.21 0.1863
WVFGRD96 4.0 340 45 -10 3.22 0.1844
WVFGRD96 6.0 165 60 25 3.27 0.2097
WVFGRD96 8.0 165 60 25 3.35 0.2310
WVFGRD96 10.0 165 60 25 3.40 0.2441
WVFGRD96 12.0 165 60 25 3.43 0.2490
WVFGRD96 14.0 155 60 -20 3.46 0.2501
WVFGRD96 16.0 155 60 -20 3.49 0.2502
WVFGRD96 18.0 155 60 -20 3.51 0.2456
WVFGRD96 20.0 155 55 -20 3.53 0.2387
WVFGRD96 22.0 260 60 30 3.56 0.2324
WVFGRD96 24.0 260 65 30 3.58 0.2400
WVFGRD96 26.0 80 70 35 3.61 0.2508
WVFGRD96 28.0 250 80 -30 3.64 0.2628
WVFGRD96 30.0 250 85 -30 3.66 0.2809
WVFGRD96 32.0 255 90 -30 3.68 0.2976
WVFGRD96 34.0 75 85 35 3.70 0.3129
WVFGRD96 36.0 75 85 30 3.71 0.3224
WVFGRD96 38.0 75 80 30 3.74 0.3289
WVFGRD96 40.0 75 80 40 3.81 0.3365
WVFGRD96 42.0 75 75 40 3.84 0.3431
WVFGRD96 44.0 75 75 40 3.86 0.3506
WVFGRD96 46.0 75 75 40 3.87 0.3589
WVFGRD96 48.0 80 70 45 3.89 0.3681
WVFGRD96 50.0 80 70 45 3.90 0.3781
WVFGRD96 52.0 75 70 40 3.91 0.3853
WVFGRD96 54.0 75 65 40 3.92 0.3941
WVFGRD96 56.0 75 65 40 3.93 0.4072
WVFGRD96 58.0 80 60 45 3.94 0.4197
WVFGRD96 60.0 80 60 45 3.95 0.4325
WVFGRD96 62.0 75 60 40 3.96 0.4463
WVFGRD96 64.0 75 60 40 3.96 0.4591
WVFGRD96 66.0 75 60 40 3.97 0.4717
WVFGRD96 68.0 75 55 40 3.97 0.4854
WVFGRD96 70.0 75 55 35 3.98 0.4983
WVFGRD96 72.0 75 55 35 3.98 0.5101
WVFGRD96 74.0 75 55 35 3.99 0.5213
WVFGRD96 76.0 75 55 35 3.99 0.5327
WVFGRD96 78.0 75 55 35 3.99 0.5430
WVFGRD96 80.0 75 50 35 4.00 0.5523
WVFGRD96 82.0 75 50 35 4.00 0.5603
WVFGRD96 84.0 75 55 35 4.00 0.5678
WVFGRD96 86.0 75 50 35 4.01 0.5746
WVFGRD96 88.0 75 50 35 4.01 0.5799
WVFGRD96 90.0 75 50 35 4.02 0.5863
WVFGRD96 92.0 75 50 35 4.02 0.5922
WVFGRD96 94.0 75 50 35 4.02 0.5962
WVFGRD96 96.0 75 50 35 4.02 0.5996
WVFGRD96 98.0 75 50 35 4.03 0.6022
WVFGRD96 100.0 75 50 35 4.03 0.6053
WVFGRD96 102.0 75 50 35 4.03 0.6079
WVFGRD96 104.0 75 50 35 4.04 0.6089
WVFGRD96 106.0 80 50 35 4.04 0.6094
WVFGRD96 108.0 80 50 35 4.04 0.6113
WVFGRD96 110.0 80 50 35 4.04 0.6124
WVFGRD96 112.0 80 50 35 4.04 0.6119
WVFGRD96 114.0 80 50 35 4.05 0.6113
WVFGRD96 116.0 80 50 35 4.05 0.6104
WVFGRD96 118.0 80 50 35 4.05 0.6086
WVFGRD96 120.0 80 50 35 4.05 0.6085
WVFGRD96 122.0 80 50 35 4.06 0.6065
WVFGRD96 124.0 80 50 35 4.06 0.6034
WVFGRD96 126.0 80 50 35 4.06 0.6029
WVFGRD96 128.0 80 50 35 4.06 0.5998
WVFGRD96 130.0 80 50 35 4.07 0.5981
WVFGRD96 132.0 80 50 35 4.07 0.5957
WVFGRD96 134.0 80 50 35 4.07 0.5939
WVFGRD96 136.0 80 50 35 4.07 0.5908
WVFGRD96 138.0 80 50 35 4.07 0.5883
WVFGRD96 140.0 80 50 35 4.08 0.5866
WVFGRD96 142.0 80 50 35 4.08 0.5829
WVFGRD96 144.0 80 50 35 4.08 0.5817
WVFGRD96 146.0 80 50 35 4.08 0.5790
WVFGRD96 148.0 80 50 35 4.09 0.5767
The best solution is
WVFGRD96 110.0 80 50 35 4.04 0.6124
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 0.10 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. |
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