The ANSS event ID is usp000jwtz and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000jwtz/executive.
2012/12/11 05:12:20 68.093 -136.372 10.0 4.9 Yukon, Canada
USGS/SLU Moment Tensor Solution ENS 2012/12/11 05:12:20:0 68.09 -136.37 10.0 4.9 Yukon, Canada Stations used: AK.CCB AK.COLD AK.DOT AK.FYU AK.GLM AK.MDM AK.PAX AK.PPD AK.WRH CN.DAWY CN.INK IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.51e+23 dyne-cm Mw = 4.72 Z = 8 km Plane Strike Dip Rake NP1 230 60 -50 NP2 351 48 -138 Principal Axes: Axis Value Plunge Azimuth T 1.51e+23 7 293 N 0.00e+00 34 27 P -1.51e+23 55 193 Moment Tensor: (dyne-cm) Component Value Mxx -2.41e+22 Mxy -6.41e+22 Mxz 7.57e+22 Myy 1.24e+23 Myz 4.51e+15 Mzz -1.00e+23 ######-------- #############--------- ##################---------- ####################---------- ################################## #################-------########## T ##############----------########### # ############-------------########### ##############----------------########## #############------------------########### ###########--------------------########### ##########----------------------########## #########-----------------------########## #######------------------------######### ######---------- -----------########## ####----------- P -----------######### ##------------ -----------######## #-------------------------######## -----------------------####### ---------------------####### -----------------##### ------------## Global CMT Convention Moment Tensor: R T P -1.00e+23 7.57e+22 -4.51e+15 7.57e+22 -2.41e+22 6.41e+22 -4.51e+15 6.41e+22 1.24e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121211051220/index.html |
STK = 230 DIP = 60 RAKE = -50 MW = 4.72 HS = 8.0
The NDK file is 20121211051220.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution ENS 2012/12/11 05:12:20:0 68.09 -136.37 10.0 4.9 Yukon, Canada Stations used: AK.CCB AK.COLD AK.DOT AK.FYU AK.GLM AK.MDM AK.PAX AK.PPD AK.WRH CN.DAWY CN.INK IU.COLA US.EGAK Filtering commands used: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.51e+23 dyne-cm Mw = 4.72 Z = 8 km Plane Strike Dip Rake NP1 230 60 -50 NP2 351 48 -138 Principal Axes: Axis Value Plunge Azimuth T 1.51e+23 7 293 N 0.00e+00 34 27 P -1.51e+23 55 193 Moment Tensor: (dyne-cm) Component Value Mxx -2.41e+22 Mxy -6.41e+22 Mxz 7.57e+22 Myy 1.24e+23 Myz 4.51e+15 Mzz -1.00e+23 ######-------- #############--------- ##################---------- ####################---------- ################################## #################-------########## T ##############----------########### # ############-------------########### ##############----------------########## #############------------------########### ###########--------------------########### ##########----------------------########## #########-----------------------########## #######------------------------######### ######---------- -----------########## ####----------- P -----------######### ##------------ -----------######## #-------------------------######## -----------------------####### ---------------------####### -----------------##### ------------## Global CMT Convention Moment Tensor: R T P -1.00e+23 7.57e+22 -4.51e+15 7.57e+22 -2.41e+22 6.41e+22 -4.51e+15 6.41e+22 1.24e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20121211051220/index.html |
USGS/SLU Regional Moment Solution NORTHERN YUKON TERRITORY, CANADA 12/12/11 05:12:20.69 Epicenter: 68.135 -136.451 MW 4.8 USGS/SLU REGIONAL MOMENT TENSOR Depth 5 No. of sta: 17 Moment Tensor; Scale 10**16 Nm Mrr=-1.85 Mtt= 0.33 Mpp= 1.51 Mrt= 0.44 Mrp=-0.04 Mtp= 0.94 Principal axes: T Val= 2.04 Plg= 3 Azm=299 N -0.09 13 30 P -1.94 77 198 Best Double Couple:Mo=2.0*10**16 NP1:Strike= 16 Dip=44 Slip=-109 NP2: 221 49 -73 |
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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:
hp c 0.02 n 3 lp c 0.05 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 60 45 -25 4.43 0.4085 WVFGRD96 1.0 60 45 -35 4.46 0.4412 WVFGRD96 2.0 60 45 -40 4.56 0.5599 WVFGRD96 3.0 230 45 -65 4.62 0.6276 WVFGRD96 4.0 225 50 -65 4.65 0.6827 WVFGRD96 5.0 225 50 -65 4.67 0.7033 WVFGRD96 6.0 230 60 -50 4.67 0.6988 WVFGRD96 7.0 230 65 -40 4.67 0.6894 WVFGRD96 8.0 230 60 -50 4.72 0.7088 WVFGRD96 9.0 235 70 -35 4.69 0.6770 WVFGRD96 10.0 245 65 -10 4.64 0.6511 WVFGRD96 11.0 250 65 -5 4.64 0.6564 WVFGRD96 12.0 250 65 -5 4.65 0.6630 WVFGRD96 13.0 250 65 -5 4.66 0.6682 WVFGRD96 14.0 250 70 5 4.68 0.6727 WVFGRD96 15.0 250 70 5 4.69 0.6768 WVFGRD96 16.0 250 70 5 4.69 0.6792 WVFGRD96 17.0 250 70 5 4.70 0.6803 WVFGRD96 18.0 250 70 0 4.71 0.6799 WVFGRD96 19.0 250 70 0 4.72 0.6785 WVFGRD96 20.0 250 70 5 4.73 0.6764 WVFGRD96 21.0 250 70 5 4.73 0.6735 WVFGRD96 22.0 250 70 5 4.74 0.6698 WVFGRD96 23.0 250 70 0 4.75 0.6650 WVFGRD96 24.0 250 70 0 4.75 0.6596 WVFGRD96 25.0 240 90 50 4.85 0.6554 WVFGRD96 26.0 60 85 -55 4.86 0.6543 WVFGRD96 27.0 60 85 -55 4.87 0.6529 WVFGRD96 28.0 240 90 50 4.87 0.6489 WVFGRD96 29.0 60 85 -55 4.88 0.6476
The best solution is
WVFGRD96 8.0 230 60 -50 4.72 0.7088
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
hp c 0.02 n 3 lp c 0.05 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