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 us7000csxi and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us7000csxi/executive.
2020/12/21 12:16:18 66.339 -135.693 23.4 4.2 Yukon, Canada
USGS/SLU Moment Tensor Solution
ENS 2020/12/21 12:16:18:0 66.34 -135.69 23.4 4.2 Yukon, Canada
Stations used:
AK.G27K AK.I27K CN.INK TA.E29M TA.EPYK TA.G30M TA.G31M
TA.H27K TA.H29M TA.H31M TA.I28M TA.I29M TA.I30M TA.J29N
TA.J30M TA.K29M
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 0.07 n 3
Best Fitting Double Couple
Mo = 2.79e+22 dyne-cm
Mw = 4.23
Z = 34 km
Plane Strike Dip Rake
NP1 80 90 10
NP2 350 80 180
Principal Axes:
Axis Value Plunge Azimuth
T 2.79e+22 7 305
N 0.00e+00 80 80
P -2.79e+22 7 215
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.38e+21
Mxy -2.58e+22
Mxz 4.76e+21
Myy 9.38e+21
Myz -8.40e+20
Mzz -4.23e+14
####----------
#########-------------
#############---------------
#############----------------
T ##############-----------------
# ##############------------------
####################------------------
#####################-------------------
######################------------------
#######################--------------#####
#######################---################
################--------##################
#####-------------------##################
-----------------------#################
------------------------################
-----------------------###############
----------------------##############
---------------------#############
-- --------------###########
- P --------------##########
--------------#######
-----------###
Global CMT Convention Moment Tensor:
R T P
-4.23e+14 4.76e+21 8.40e+20
4.76e+21 -9.38e+21 2.58e+22
8.40e+20 2.58e+22 9.38e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20201221121618/index.html
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STK = 80
DIP = 90
RAKE = 10
MW = 4.23
HS = 34.0
The NDK file is 20201221121618.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 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 255 75 -5 3.90 0.5538
WVFGRD96 2.0 255 90 5 3.92 0.5913
WVFGRD96 3.0 255 90 10 3.95 0.6081
WVFGRD96 4.0 75 90 15 3.97 0.6187
WVFGRD96 5.0 255 85 -15 3.98 0.6367
WVFGRD96 6.0 75 90 15 3.99 0.6461
WVFGRD96 7.0 75 90 15 4.00 0.6563
WVFGRD96 8.0 255 85 -15 4.01 0.6677
WVFGRD96 9.0 255 85 -15 4.02 0.6749
WVFGRD96 10.0 75 90 15 4.03 0.6808
WVFGRD96 11.0 75 90 15 4.04 0.6870
WVFGRD96 12.0 75 90 15 4.05 0.6938
WVFGRD96 13.0 75 90 10 4.05 0.7006
WVFGRD96 14.0 75 90 10 4.06 0.7075
WVFGRD96 15.0 255 90 -10 4.07 0.7138
WVFGRD96 16.0 75 90 10 4.08 0.7204
WVFGRD96 17.0 255 90 -10 4.08 0.7270
WVFGRD96 18.0 255 90 -10 4.09 0.7328
WVFGRD96 19.0 75 90 10 4.10 0.7393
WVFGRD96 20.0 75 90 10 4.11 0.7472
WVFGRD96 21.0 255 90 -10 4.12 0.7535
WVFGRD96 22.0 260 90 -10 4.13 0.7595
WVFGRD96 23.0 80 90 10 4.14 0.7660
WVFGRD96 24.0 80 90 10 4.15 0.7716
WVFGRD96 25.0 80 90 10 4.15 0.7764
WVFGRD96 26.0 80 90 10 4.16 0.7810
WVFGRD96 27.0 80 90 10 4.17 0.7853
WVFGRD96 28.0 260 90 -10 4.18 0.7903
WVFGRD96 29.0 80 90 10 4.19 0.7946
WVFGRD96 30.0 80 90 10 4.19 0.7971
WVFGRD96 31.0 80 90 10 4.20 0.7993
WVFGRD96 32.0 80 90 10 4.21 0.8013
WVFGRD96 33.0 80 90 10 4.22 0.8023
WVFGRD96 34.0 80 90 10 4.23 0.8036
WVFGRD96 35.0 80 90 10 4.24 0.8031
WVFGRD96 36.0 260 85 -10 4.25 0.8029
WVFGRD96 37.0 80 90 10 4.27 0.8017
WVFGRD96 38.0 80 90 10 4.28 0.8001
WVFGRD96 39.0 260 90 -10 4.30 0.7977
WVFGRD96 40.0 260 90 -10 4.32 0.7948
WVFGRD96 41.0 260 85 -10 4.33 0.7911
WVFGRD96 42.0 80 90 10 4.34 0.7882
WVFGRD96 43.0 80 90 10 4.34 0.7839
WVFGRD96 44.0 80 90 10 4.35 0.7788
WVFGRD96 45.0 80 90 10 4.36 0.7728
WVFGRD96 46.0 80 90 10 4.37 0.7665
WVFGRD96 47.0 80 90 10 4.37 0.7614
WVFGRD96 48.0 260 90 -10 4.38 0.7555
WVFGRD96 49.0 260 90 -10 4.39 0.7487
WVFGRD96 50.0 260 90 -10 4.39 0.7421
The best solution is
WVFGRD96 34.0 80 90 10 4.23 0.8036
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 0.07 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