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 us7000kvgv and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us7000kvgv/executive.
2023/09/13 06:46:43 61.352 -139.944 4.0 4 Yukon, Canada
USGS/SLU Moment Tensor Solution
ENS 2023/09/13 06:46:43:0 61.35 -139.94 4.0 4.0 Yukon, Canada
Stations used:
AK.BAE AK.BARK AK.BARN AK.BAT AK.BERG AK.BESE AK.BGLC
AK.BMR AK.BRLK AK.CCB AK.CRQ AK.CUT AK.CYK AK.DHY AK.DIV
AK.EYAK AK.FIRE AK.GHO AK.GLB AK.GLI AK.GRIN AK.H24K AK.HDA
AK.HIN AK.I23K AK.I26K AK.I27K AK.ISLE AK.J25K AK.J26L
AK.JIS AK.K24K AK.K27K AK.KHIT AK.KIAG AK.KLU AK.KNK
AK.L22K AK.LOGN AK.M23K AK.M27K AK.MCAR AK.MCK AK.MDM
AK.MESA AK.NEA2 AK.PAX AK.PNL AK.POKR AK.PS08 AK.PS09
AK.PS10 AK.PS12 AK.PTPK AK.PWL AK.RC01 AK.RIDG AK.RND
AK.S31K AK.S32K AK.SAMH AK.SAW AK.SCM AK.SCRK AK.TGL AK.VMT
AK.VRDI AK.WAX AK.WRH AT.MENT AT.PMR AT.SIT AV.EDES AV.EDSO
AV.N25K AV.WACK CN.ATLI CN.BRWY CN.BVCY CN.DAWY CN.HYT
CN.PLBC CN.WHY CN.YUK3 CN.YUK4 CN.YUK6 CN.YUK7 CN.YUK8
EO.KLRS IM.IL31 IU.COLA NY.MAYO US.EGAK
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 0.08 n 3
Best Fitting Double Couple
Mo = 1.17e+22 dyne-cm
Mw = 3.98
Z = 14 km
Plane Strike Dip Rake
NP1 146 60 145
NP2 255 60 35
Principal Axes:
Axis Value Plunge Azimuth
T 1.17e+22 45 110
N 0.00e+00 45 291
P -1.17e+22 0 200
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.61e+21
Mxy -5.76e+21
Mxz -2.01e+21
Myy 3.78e+21
Myz 5.52e+21
Mzz 5.84e+21
--------------
----------------------
##--------------------------
###---------------------------
#####-----------------------------
######------------------------------
#######---------------#########-------
#########------#######################--
#########--#############################
#########--###############################
######------##############################
####---------#############################
###-----------################ #########
--------------############### T ########
---------------############## ########
----------------######################
-----------------###################
------------------################
------------------############
---------------------#######
--- ----------------
P ------------
Global CMT Convention Moment Tensor:
R T P
5.84e+21 -2.01e+21 -5.52e+21
-2.01e+21 -9.61e+21 5.76e+21
-5.52e+21 5.76e+21 3.78e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20230913064643/index.html
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STK = 255
DIP = 60
RAKE = 35
MW = 3.98
HS = 14.0
The NDK file is 20230913064643.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/3.3 -40 o DIST/3.3 +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 1.0 160 55 50 3.59 0.3211
WVFGRD96 2.0 170 50 60 3.71 0.3769
WVFGRD96 3.0 340 90 50 3.77 0.3988
WVFGRD96 4.0 155 85 -50 3.79 0.4463
WVFGRD96 5.0 150 80 -50 3.81 0.4844
WVFGRD96 6.0 150 75 -45 3.82 0.5130
WVFGRD96 7.0 145 70 -45 3.84 0.5334
WVFGRD96 8.0 140 65 -50 3.91 0.5410
WVFGRD96 9.0 135 60 -55 3.93 0.5508
WVFGRD96 10.0 135 60 -55 3.94 0.5514
WVFGRD96 11.0 260 55 45 3.95 0.5533
WVFGRD96 12.0 260 55 45 3.96 0.5634
WVFGRD96 13.0 260 60 45 3.98 0.5684
WVFGRD96 14.0 255 60 35 3.98 0.5710
WVFGRD96 15.0 255 60 35 3.99 0.5698
WVFGRD96 16.0 255 60 35 4.00 0.5656
WVFGRD96 17.0 255 60 35 4.01 0.5588
WVFGRD96 18.0 255 60 35 4.02 0.5498
WVFGRD96 19.0 255 60 35 4.03 0.5393
WVFGRD96 20.0 255 60 35 4.04 0.5279
WVFGRD96 21.0 255 60 35 4.05 0.5158
WVFGRD96 22.0 255 60 30 4.06 0.5026
WVFGRD96 23.0 255 60 30 4.07 0.4891
WVFGRD96 24.0 255 60 30 4.07 0.4758
WVFGRD96 25.0 255 60 30 4.08 0.4631
WVFGRD96 26.0 255 60 30 4.08 0.4503
WVFGRD96 27.0 255 60 30 4.09 0.4372
WVFGRD96 28.0 255 60 30 4.10 0.4240
WVFGRD96 29.0 255 60 30 4.10 0.4112
The best solution is
WVFGRD96 14.0 255 60 35 3.98 0.5710
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 0.08 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