The ANSS event ID is us10006g6y and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us10006g6y/executive.
2016/08/23 23:36:23 62.292 -133.493 4.0 4.1 Yukon, Canada
USGS/SLU Moment Tensor Solution ENS 2016/08/23 23:36:23:0 62.29 -133.49 4.0 4.1 Yukon, Canada Stations used: AK.BCP AK.LOGN AK.PIN AK.PNL CN.DAWY CN.WHY CN.YUK2 CN.YUK3 CN.YUK4 NY.MAYO NY.WGLY TA.I27K TA.J26L TA.K29M TA.L27K TA.M30M TA.M31M TA.N30M TA.N31M TA.N32M TA.O28M TA.O29M TA.O30N TA.P29M TA.P30M TA.P33M TA.R33M TA.T35M Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 Best Fitting Double Couple Mo = 4.32e+21 dyne-cm Mw = 3.69 Z = 14 km Plane Strike Dip Rake NP1 328 69 -148 NP2 225 60 -25 Principal Axes: Axis Value Plunge Azimuth T 4.32e+21 5 95 N 0.00e+00 52 358 P -4.32e+21 38 189 Moment Tensor: (dyne-cm) Component Value Mxx -2.60e+21 Mxy -7.90e+20 Mxz 2.03e+21 Myy 4.18e+21 Myz 7.38e+20 Mzz -1.58e+21 -------------- ---------------------- #######--------------------- ##########-------------####### ##############-------############# #################-################## #################---################## ################------################## ##############----------################ #############-------------################ ############---------------############ ###########-----------------########### T #########--------------------########## #######----------------------########### #######----------------------########### #####------------------------######### ####---------- -----------######## ##----------- P ------------###### ----------- ------------#### -------------------------### ---------------------- -------------- Global CMT Convention Moment Tensor: R T P -1.58e+21 2.03e+21 -7.38e+20 2.03e+21 -2.60e+21 7.90e+20 -7.38e+20 7.90e+20 4.18e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160823233623/index.html |
STK = 225 DIP = 60 RAKE = -25 MW = 3.69 HS = 14.0
The NDK file is 20160823233623.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 +70 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 1.0 135 80 -5 3.29 0.3164 WVFGRD96 2.0 310 65 -35 3.44 0.3826 WVFGRD96 3.0 305 60 -40 3.51 0.4124 WVFGRD96 4.0 310 65 -35 3.51 0.4250 WVFGRD96 5.0 315 75 -30 3.50 0.4308 WVFGRD96 6.0 230 70 0 3.51 0.4405 WVFGRD96 7.0 230 70 -10 3.53 0.4576 WVFGRD96 8.0 225 65 -20 3.59 0.4750 WVFGRD96 9.0 225 65 -25 3.61 0.4880 WVFGRD96 10.0 225 65 -25 3.63 0.4981 WVFGRD96 11.0 225 60 -25 3.65 0.5064 WVFGRD96 12.0 225 60 -25 3.67 0.5149 WVFGRD96 13.0 225 60 -25 3.68 0.5205 WVFGRD96 14.0 225 60 -25 3.69 0.5227 WVFGRD96 15.0 225 60 -25 3.70 0.5225 WVFGRD96 16.0 230 65 -20 3.70 0.5205 WVFGRD96 17.0 230 65 -20 3.71 0.5179 WVFGRD96 18.0 230 65 -15 3.72 0.5139 WVFGRD96 19.0 230 65 -15 3.73 0.5089 WVFGRD96 20.0 230 65 -15 3.74 0.5022 WVFGRD96 21.0 230 60 -10 3.75 0.4941 WVFGRD96 22.0 230 60 -10 3.76 0.4863 WVFGRD96 23.0 230 60 -10 3.77 0.4773 WVFGRD96 24.0 235 70 25 3.78 0.4737 WVFGRD96 25.0 235 70 30 3.79 0.4670 WVFGRD96 26.0 235 70 30 3.80 0.4602 WVFGRD96 27.0 235 70 30 3.80 0.4522 WVFGRD96 28.0 235 70 30 3.81 0.4435 WVFGRD96 29.0 235 70 30 3.82 0.4352
The best solution is
WVFGRD96 14.0 225 60 -25 3.69 0.5227
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 +70 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 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