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 us1000eme9 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us1000eme9/executive.
2018/06/10 00:29:17 61.153 -140.517 5.0 3.9 Yukon, Canada
USGS/SLU Moment Tensor Solution
ENS 2018/06/10 00:29:17:0 61.15 -140.52 5.0 3.9 Yukon, Canada
Stations used:
AK.BARN AK.BCP AK.BESE AK.BMR AK.CTG AK.DIV AK.GLB AK.GLI
AK.HIN AK.HMT AK.ISLE AK.KLU AK.KNK AK.LOGN AK.MCAR AK.MESA
AK.SCM AK.SCRK AK.SSP AK.VRDI AK.WAX AT.MENT AT.SKAG
CN.DAWY CN.WHY NY.FARO NY.MAYO TA.J26L TA.J29N TA.K27K
TA.K29M TA.L26K TA.L27K TA.L29M TA.M26K TA.M27K TA.M29M
TA.M30M TA.M31M TA.N25K TA.N30M TA.N31M TA.N32M TA.O29M
TA.O30N TA.P29M TA.P33M US.EGAK
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 7.24e+21 dyne-cm
Mw = 3.84
Z = 9 km
Plane Strike Dip Rake
NP1 245 75 -25
NP2 342 66 -164
Principal Axes:
Axis Value Plunge Azimuth
T 7.24e+21 6 295
N 0.00e+00 61 36
P -7.24e+21 28 202
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.60e+21
Mxy -4.66e+21
Mxz 3.12e+21
Myy 5.13e+21
Myz 4.20e+20
Mzz -1.53e+21
#-------------
#######---------------
############----------------
###############---------------
##################----------------
##################----------------
T ###################----------######
# ####################--##############
#####################----###############
##################---------###############
##############-------------###############
###########-----------------##############
#########-------------------##############
#####----------------------#############
###-------------------------############
#--------------------------###########
--------------------------##########
---------- ------------#########
-------- P ------------#######
------- ------------######
------------------####
--------------
Global CMT Convention Moment Tensor:
R T P
-1.53e+21 3.12e+21 -4.20e+20
3.12e+21 -3.60e+21 4.66e+21
-4.20e+20 4.66e+21 5.13e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180610002917/index.html
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STK = 245
DIP = 75
RAKE = -25
MW = 3.84
HS = 9.0
The NDK file is 20180610002917.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 -30 o DIST/3.3 +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 1.0 250 75 -20 3.73 0.5864
WVFGRD96 2.0 250 75 -25 3.77 0.6008
WVFGRD96 3.0 245 70 -30 3.80 0.6137
WVFGRD96 4.0 245 70 -30 3.80 0.6272
WVFGRD96 5.0 245 70 -30 3.81 0.6389
WVFGRD96 6.0 245 75 -30 3.82 0.6469
WVFGRD96 7.0 245 75 -25 3.82 0.6524
WVFGRD96 8.0 245 75 -25 3.83 0.6567
WVFGRD96 9.0 245 75 -25 3.84 0.6583
WVFGRD96 10.0 245 75 -25 3.86 0.6571
WVFGRD96 11.0 245 75 -25 3.87 0.6538
WVFGRD96 12.0 245 75 -25 3.88 0.6477
WVFGRD96 13.0 245 75 -25 3.89 0.6397
WVFGRD96 14.0 245 75 -25 3.90 0.6306
WVFGRD96 15.0 245 75 -25 3.91 0.6208
WVFGRD96 16.0 245 75 -25 3.92 0.6097
WVFGRD96 17.0 245 75 -25 3.93 0.5983
WVFGRD96 18.0 245 75 -25 3.93 0.5860
WVFGRD96 19.0 245 75 -25 3.94 0.5750
WVFGRD96 20.0 245 75 -25 3.96 0.5639
WVFGRD96 21.0 245 75 -25 3.97 0.5521
WVFGRD96 22.0 245 75 -25 3.97 0.5412
WVFGRD96 23.0 245 75 -25 3.98 0.5322
WVFGRD96 24.0 245 75 -25 3.99 0.5229
WVFGRD96 25.0 245 75 -25 3.99 0.5137
WVFGRD96 26.0 245 75 -25 4.00 0.5062
WVFGRD96 27.0 245 75 -25 4.01 0.4995
WVFGRD96 28.0 245 75 -25 4.02 0.4927
WVFGRD96 29.0 245 75 -25 4.02 0.4866
The best solution is
WVFGRD96 9.0 245 75 -25 3.84 0.6583
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 +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 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