The ANSS event ID is us20009x32 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us20009x32/executive.
2017/07/17 21:52:36 60.969 -138.324 10.0 3.7 Yukon, Canada
USGS/SLU Moment Tensor Solution
ENS 2017/07/17 21:52:36:0 60.97 -138.32 10.0 3.7 Yukon, Canada
Stations used:
AK.BCP AK.BESE AK.JIS AK.MCK AK.MDM AK.MESA AK.PAX AK.PIN
AK.PNL AK.PPD AK.SAMH AK.SCRK AK.TABL AT.MENT AT.SIT
AT.SKAG AV.WACK CN.BVCY CN.HYT CN.YUK2 CN.YUK3 CN.YUK4
CN.YUK5 CN.YUK7 IU.COLA NY.MAYO TA.EPYK TA.H27K TA.HARP
TA.I27K TA.I28M TA.J25K TA.J26L TA.J29M TA.K24K TA.K29M
TA.L26K TA.L27K TA.L29M TA.M26K TA.M27K TA.M29M TA.M31M
TA.N30M TA.N31M TA.O28M TA.O29M TA.O30N TA.P29M TA.P33M
TA.POKR TA.Q32M TA.R32K TA.R33M TA.S31K TA.S34M TA.T35M
TA.U33K US.EGAK
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +40
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 5.13e+21 dyne-cm
Mw = 3.74
Z = 1 km
Plane Strike Dip Rake
NP1 292 51 124
NP2 65 50 55
Principal Axes:
Axis Value Plunge Azimuth
T 5.13e+21 64 268
N 0.00e+00 26 89
P -5.13e+21 1 359
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.12e+21
Mxy 1.36e+20
Mxz -1.38e+20
Myy 9.87e+20
Myz -2.02e+21
Mzz 4.14e+21
----- P ------
--------- ----------
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----------------------------------
---###############------------------
########################--------------
#############################---------##
###############################-------##
##################################----####
############# ####################-#####
############# T ####################-#####
############# ##################----####
###############################-------##
#############################----------#
#########################-------------
--##################----------------
----------------------------------
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Global CMT Convention Moment Tensor:
R T P
4.14e+21 -1.38e+20 2.02e+21
-1.38e+20 -5.12e+21 -1.36e+20
2.02e+21 -1.36e+20 9.87e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170717215236/index.html
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STK = 65
DIP = 50
RAKE = 55
MW = 3.74
HS = 1.0
The NDK file is 20170717215236.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 -30 o DIST/3.3 +40 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 1.0 65 50 55 3.74 0.7139
WVFGRD96 2.0 75 50 70 3.82 0.6968
WVFGRD96 3.0 95 30 100 3.84 0.6086
WVFGRD96 4.0 100 30 105 3.81 0.5528
WVFGRD96 5.0 40 75 -35 3.75 0.5438
WVFGRD96 6.0 40 70 -30 3.76 0.5534
WVFGRD96 7.0 40 70 -30 3.76 0.5657
WVFGRD96 8.0 40 70 -30 3.77 0.5738
WVFGRD96 9.0 40 70 -30 3.78 0.5792
WVFGRD96 10.0 35 65 -35 3.80 0.5718
WVFGRD96 11.0 35 65 -35 3.81 0.5696
WVFGRD96 12.0 40 65 -35 3.82 0.5651
WVFGRD96 13.0 40 65 -35 3.82 0.5587
WVFGRD96 14.0 40 65 -35 3.83 0.5512
WVFGRD96 15.0 40 65 -35 3.84 0.5420
WVFGRD96 16.0 40 65 -35 3.84 0.5317
WVFGRD96 17.0 40 65 -35 3.85 0.5213
WVFGRD96 18.0 40 65 -40 3.86 0.5106
WVFGRD96 19.0 215 60 -40 3.86 0.5001
WVFGRD96 20.0 100 30 -75 3.88 0.4832
WVFGRD96 21.0 105 30 -65 3.89 0.4827
WVFGRD96 22.0 105 30 -65 3.90 0.4807
WVFGRD96 23.0 105 30 -65 3.91 0.4769
WVFGRD96 24.0 105 30 -65 3.92 0.4712
WVFGRD96 25.0 110 30 -60 3.92 0.4640
WVFGRD96 26.0 110 30 -60 3.93 0.4562
WVFGRD96 27.0 110 30 -60 3.94 0.4473
WVFGRD96 28.0 115 35 -50 3.95 0.4368
WVFGRD96 29.0 90 70 -75 3.95 0.4297
The best solution is
WVFGRD96 1.0 65 50 55 3.74 0.7139
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 -30 o DIST/3.3 +40 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 CUS.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 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00