The ANSS event ID is ak02422ry0ln and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak02422ry0ln/executive.
2024/02/14 21:43:37 63.010 -150.616 109.3 4.7 Alaska
USGS/SLU Moment Tensor Solution
ENS 2024/02/14 21:43:37:0 63.01 -150.62 109.3 4.7 Alaska
Stations used:
AK.BAE AK.BPAW AK.CAST AK.CCB AK.CUT AK.DOT AK.GCSA AK.GHO
AK.GLI AK.H21K AK.H24K AK.HARP AK.HDA AK.I21K AK.I23K
AK.J19K AK.J20K AK.K20K AK.K24K AK.KLU AK.KNK AK.L20K
AK.M20K AK.MCK AK.MLY AK.NEA2 AK.PAX AK.PWL AK.RC01 AK.RIDG
AK.RND AK.SAW AK.SCM AK.SCRK AK.WRH AT.MENT 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 0.08 n 3
Best Fitting Double Couple
Mo = 1.23e+23 dyne-cm
Mw = 4.66
Z = 116 km
Plane Strike Dip Rake
NP1 220 85 -92
NP2 60 5 -70
Principal Axes:
Axis Value Plunge Azimuth
T 1.23e+23 40 312
N 0.00e+00 2 220
P -1.23e+23 50 128
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.19e+22
Mxy -1.05e+22
Mxz 7.76e+22
Myy 8.19e+21
Myz -9.32e+22
Mzz -2.01e+22
##############
######################
###########################-
##########################----
##########################--------
####### ###############-----------
######## T ##############-------------
######### ############----------------
######################------------------
######################-------------------#
####################---------------------#
###################----------------------#
#################------------------------#
###############------------ ----------
#############-------------- P ---------#
###########--------------- --------#
########---------------------------#
######---------------------------#
###--------------------------#
--------------------------##
#-------------------##
##---------###
Global CMT Convention Moment Tensor:
R T P
-2.01e+22 7.76e+22 9.32e+22
7.76e+22 1.19e+22 1.05e+22
9.32e+22 1.05e+22 8.19e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240214214337/index.html
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STK = 60
DIP = 5
RAKE = -70
MW = 4.66
HS = 116.0
The NDK file is 20240214214337.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 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 2.0 120 50 -65 3.77 0.2004
WVFGRD96 4.0 145 65 -10 3.75 0.2073
WVFGRD96 6.0 155 65 15 3.81 0.2266
WVFGRD96 8.0 60 75 -30 3.88 0.2438
WVFGRD96 10.0 240 75 -30 3.93 0.2641
WVFGRD96 12.0 240 75 -25 3.96 0.2806
WVFGRD96 14.0 240 75 -25 4.00 0.2935
WVFGRD96 16.0 240 75 -25 4.03 0.3032
WVFGRD96 18.0 240 75 -20 4.05 0.3112
WVFGRD96 20.0 240 75 -20 4.08 0.3183
WVFGRD96 22.0 240 80 -20 4.10 0.3245
WVFGRD96 24.0 240 80 -20 4.12 0.3312
WVFGRD96 26.0 240 80 -20 4.14 0.3371
WVFGRD96 28.0 65 80 25 4.16 0.3473
WVFGRD96 30.0 65 75 25 4.18 0.3546
WVFGRD96 32.0 65 75 25 4.20 0.3610
WVFGRD96 34.0 60 80 20 4.22 0.3676
WVFGRD96 36.0 60 80 20 4.24 0.3736
WVFGRD96 38.0 60 80 20 4.27 0.3816
WVFGRD96 40.0 60 75 25 4.33 0.3877
WVFGRD96 42.0 55 80 20 4.36 0.3932
WVFGRD96 44.0 55 80 20 4.37 0.3971
WVFGRD96 46.0 55 80 20 4.39 0.3987
WVFGRD96 48.0 55 80 20 4.40 0.4013
WVFGRD96 50.0 55 80 20 4.41 0.4027
WVFGRD96 52.0 55 85 25 4.43 0.4072
WVFGRD96 54.0 55 85 25 4.43 0.4105
WVFGRD96 56.0 55 80 30 4.44 0.4130
WVFGRD96 58.0 55 80 30 4.45 0.4216
WVFGRD96 60.0 235 85 -45 4.47 0.4387
WVFGRD96 62.0 235 85 -50 4.49 0.4559
WVFGRD96 64.0 60 90 50 4.49 0.4708
WVFGRD96 66.0 60 90 50 4.50 0.4842
WVFGRD96 68.0 240 90 -50 4.51 0.4953
WVFGRD96 70.0 55 90 55 4.52 0.5048
WVFGRD96 72.0 55 90 55 4.53 0.5140
WVFGRD96 74.0 235 85 -55 4.53 0.5230
WVFGRD96 76.0 60 90 55 4.54 0.5280
WVFGRD96 78.0 235 85 -60 4.55 0.5366
WVFGRD96 80.0 60 90 60 4.56 0.5382
WVFGRD96 82.0 60 90 60 4.56 0.5432
WVFGRD96 84.0 230 80 -70 4.57 0.5514
WVFGRD96 86.0 220 80 -80 4.59 0.5610
WVFGRD96 88.0 220 80 -85 4.60 0.5746
WVFGRD96 90.0 220 80 -85 4.60 0.5877
WVFGRD96 92.0 20 10 -110 4.61 0.5999
WVFGRD96 94.0 20 10 -110 4.62 0.6107
WVFGRD96 96.0 20 10 -110 4.62 0.6196
WVFGRD96 98.0 20 10 -110 4.62 0.6295
WVFGRD96 100.0 220 85 -90 4.64 0.6386
WVFGRD96 102.0 35 5 -95 4.65 0.6462
WVFGRD96 104.0 220 85 -90 4.65 0.6538
WVFGRD96 106.0 40 5 -90 4.65 0.6599
WVFGRD96 108.0 40 5 -90 4.65 0.6636
WVFGRD96 110.0 50 5 -80 4.66 0.6676
WVFGRD96 112.0 50 5 -80 4.66 0.6699
WVFGRD96 114.0 60 5 -70 4.66 0.6717
WVFGRD96 116.0 60 5 -70 4.66 0.6723
WVFGRD96 118.0 60 5 -70 4.66 0.6714
WVFGRD96 120.0 60 5 -70 4.66 0.6710
WVFGRD96 122.0 60 5 -70 4.66 0.6702
WVFGRD96 124.0 60 5 -70 4.66 0.6685
WVFGRD96 126.0 60 5 -70 4.66 0.6651
WVFGRD96 128.0 70 5 -60 4.67 0.6614
WVFGRD96 130.0 70 5 -60 4.67 0.6589
WVFGRD96 132.0 70 5 -60 4.67 0.6550
WVFGRD96 134.0 70 5 -60 4.67 0.6516
WVFGRD96 136.0 90 10 -35 4.67 0.6474
WVFGRD96 138.0 90 10 -35 4.67 0.6425
WVFGRD96 140.0 90 10 -35 4.67 0.6382
WVFGRD96 142.0 90 10 -35 4.67 0.6329
WVFGRD96 144.0 90 10 -35 4.67 0.6258
WVFGRD96 146.0 90 10 -35 4.67 0.6204
WVFGRD96 148.0 90 10 -35 4.67 0.6145
The best solution is
WVFGRD96 116.0 60 5 -70 4.66 0.6723
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