The ANSS event ID is us10007s20 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us10007s20/executive.
2017/01/08 23:47:12 74.386 -92.416 31.0 6 Canada
USGS/SLU Moment Tensor Solution ENS 2017/01/08 23:47:12:0 74.39 -92.42 31.0 6.0 Canada Stations used: CN.EUNU CN.FRB CN.INK CN.RES CN.YKAW3 DK.NEEM DK.NOR DK.TULEG NY.WGLY TA.A36M TA.C36M TA.E25K TA.E27K TA.EPYK TA.F31M TA.G26K TA.G27K TA.G30M TA.H27K TA.I29M Filtering commands used: cut o DIST/3.3 -100 o DIST/3.3 +150 rtr taper w 0.1 hp c 0.01 n 3 lp c 0.04 n 3 Best Fitting Double Couple Mo = 7.76e+24 dyne-cm Mw = 5.86 Z = 34 km Plane Strike Dip Rake NP1 312 56 97 NP2 120 35 80 Principal Axes: Axis Value Plunge Azimuth T 7.76e+24 78 247 N 0.00e+00 6 128 P -7.76e+24 10 37 Moment Tensor: (dyne-cm) Component Value Mxx -4.72e+24 Mxy -3.50e+24 Mxz -1.71e+24 Myy -2.47e+24 Myz -2.26e+24 Mzz 7.18e+24 -------------- -------------------- ----------------------- P -- #######----------------- --- ##############-------------------- ###################----------------- -######################--------------- --########################-------------- --##########################------------ ---###########################------------ ----############# ############---------- ----############# T #############--------- -----############ ##############-------- -----#############################------ -------############################----- --------##########################---- ---------########################--- -----------#####################-# -------------##############--- ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 7.18e+24 -1.71e+24 2.26e+24 -1.71e+24 -4.72e+24 3.50e+24 2.26e+24 3.50e+24 -2.47e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170108234712/index.html |
STK = 120 DIP = 35 RAKE = 80 MW = 5.86 HS = 34.0
The NDK file is 20170108234712.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 2017/01/08 23:47:12:0 74.39 -92.42 31.0 6.0 Canada Stations used: CN.EUNU CN.FRB CN.INK CN.RES CN.YKAW3 DK.NEEM DK.NOR DK.TULEG NY.WGLY TA.A36M TA.C36M TA.E25K TA.E27K TA.EPYK TA.F31M TA.G26K TA.G27K TA.G30M TA.H27K TA.I29M Filtering commands used: cut o DIST/3.3 -100 o DIST/3.3 +150 rtr taper w 0.1 hp c 0.01 n 3 lp c 0.04 n 3 Best Fitting Double Couple Mo = 7.76e+24 dyne-cm Mw = 5.86 Z = 34 km Plane Strike Dip Rake NP1 312 56 97 NP2 120 35 80 Principal Axes: Axis Value Plunge Azimuth T 7.76e+24 78 247 N 0.00e+00 6 128 P -7.76e+24 10 37 Moment Tensor: (dyne-cm) Component Value Mxx -4.72e+24 Mxy -3.50e+24 Mxz -1.71e+24 Myy -2.47e+24 Myz -2.26e+24 Mzz 7.18e+24 -------------- -------------------- ----------------------- P -- #######----------------- --- ##############-------------------- ###################----------------- -######################--------------- --########################-------------- --##########################------------ ---###########################------------ ----############# ############---------- ----############# T #############--------- -----############ ##############-------- -----#############################------ -------############################----- --------##########################---- ---------########################--- -----------#####################-# -------------##############--- ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 7.18e+24 -1.71e+24 2.26e+24 -1.71e+24 -4.72e+24 3.50e+24 2.26e+24 3.50e+24 -2.47e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170108234712/index.html |
Body-wave Moment Tensor (Mwb) Moment 9.868e+17 N-m Magnitude 5.9 Mwb Depth 21.0 km Percent DC 58 % Half Duration – Catalog US Data Source US2 Contributor US2 Nodal Planes Plane Strike Dip Rake NP1 326 59 125 NP2 92 46 47 Principal Axes Axis Value Plunge Azimuth T 8.519e+17 N-m 60 289 N 2.294e+17 N-m 29 126 P -10.813e+17 N-m 7 32 |
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.
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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 -100 o DIST/3.3 +150 rtr taper w 0.1 hp c 0.01 n 3 lp c 0.04 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 125 50 -90 5.66 0.4391 WVFGRD96 2.0 320 40 -90 5.68 0.4466 WVFGRD96 3.0 165 45 -75 5.66 0.4212 WVFGRD96 4.0 160 90 10 5.53 0.4012 WVFGRD96 5.0 340 90 -10 5.55 0.3908 WVFGRD96 6.0 70 55 -5 5.57 0.3795 WVFGRD96 7.0 70 55 -5 5.58 0.3787 WVFGRD96 8.0 320 80 -50 5.66 0.3756 WVFGRD96 9.0 320 80 -50 5.66 0.3849 WVFGRD96 10.0 325 80 -55 5.66 0.3975 WVFGRD96 11.0 325 85 -60 5.67 0.4083 WVFGRD96 12.0 325 85 -60 5.67 0.4207 WVFGRD96 13.0 285 75 70 5.76 0.4393 WVFGRD96 14.0 285 75 70 5.76 0.4600 WVFGRD96 15.0 285 75 70 5.76 0.4771 WVFGRD96 16.0 285 75 70 5.76 0.4925 WVFGRD96 17.0 290 70 65 5.76 0.5064 WVFGRD96 18.0 290 70 70 5.77 0.5234 WVFGRD96 19.0 290 70 70 5.77 0.5374 WVFGRD96 20.0 290 70 70 5.81 0.5469 WVFGRD96 21.0 290 70 70 5.81 0.5565 WVFGRD96 22.0 290 70 70 5.81 0.5636 WVFGRD96 23.0 295 65 70 5.80 0.5708 WVFGRD96 24.0 295 65 75 5.81 0.5776 WVFGRD96 25.0 295 65 75 5.81 0.5828 WVFGRD96 26.0 295 65 75 5.81 0.5860 WVFGRD96 27.0 300 65 75 5.82 0.5882 WVFGRD96 28.0 300 65 75 5.82 0.5899 WVFGRD96 29.0 135 30 100 5.83 0.5916 WVFGRD96 30.0 130 30 95 5.83 0.5932 WVFGRD96 31.0 120 35 85 5.84 0.5942 WVFGRD96 32.0 125 35 85 5.84 0.5951 WVFGRD96 33.0 120 35 80 5.85 0.5955 WVFGRD96 34.0 120 35 80 5.86 0.5957 WVFGRD96 35.0 115 40 75 5.87 0.5955 WVFGRD96 36.0 115 40 75 5.87 0.5952 WVFGRD96 37.0 115 45 75 5.88 0.5940 WVFGRD96 38.0 120 50 70 5.90 0.5938 WVFGRD96 39.0 120 50 70 5.91 0.5930
The best solution is
WVFGRD96 34.0 120 35 80 5.86 0.5957
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 -100 o DIST/3.3 +150 rtr taper w 0.1 hp c 0.01 n 3 lp c 0.04 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