The ANSS event ID is us2000apcc and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us2000apcc/executive.
2017/09/16 23:38:03 59.866 -136.794 6.5 5 Yukon, Canada
USGS/SLU Moment Tensor Solution ENS 2017/09/16 23:38:03:0 59.87 -136.79 6.5 5.0 Yukon, Canada Stations used: AK.BARN AK.BCP AK.BERG AK.BESE AK.CRQ AK.CTG AK.GLB AK.GRNC AK.LOGN AK.MCAR AK.MESA AK.PIN AK.SSP AK.TGL AK.VRDI AK.YAH AT.SIT AT.SKAG AT.YKU2 CN.DLBC CN.HYT CN.WHY NY.FARO NY.MAYO NY.MMPY NY.WTLY TA.K29M TA.L27K TA.M26K TA.M27K TA.M29M TA.M30M TA.M31M TA.N30M TA.N31M TA.O29M TA.O30N TA.P29M TA.P32M TA.P33M TA.Q32M TA.R33M TA.S31K TA.S32K TA.S34M TA.T33K 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 0.10 n 3 Best Fitting Double Couple Mo = 4.57e+23 dyne-cm Mw = 5.04 Z = 10 km Plane Strike Dip Rake NP1 115 60 55 NP2 349 45 135 Principal Axes: Axis Value Plunge Azimuth T 4.57e+23 59 333 N 0.00e+00 30 134 P -4.57e+23 9 229 Moment Tensor: (dyne-cm) Component Value Mxx -9.24e+22 Mxy -2.70e+23 Mxz 2.25e+23 Myy -2.32e+23 Myz -3.97e+22 Mzz 3.24e+23 ######-------- #############--------- ##################---------- #####################--------- ########################---------- ##########################---------- ############## ###########---------- --############# T ############---------- ---############ ############---------- -----###########################---------- -------#########################---------- ---------#######################---------- -----------######################--------- -------------###################-------- ----------------###############--------- -------------------###########-------- -- ----------------------##--##### - P -----------------------####### ----------------------###### ----------------------###### ------------------#### ------------## Global CMT Convention Moment Tensor: R T P 3.24e+23 2.25e+23 3.97e+22 2.25e+23 -9.24e+22 2.70e+23 3.97e+22 2.70e+23 -2.32e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170916233803/index.html |
STK = 115 DIP = 60 RAKE = 55 MW = 5.04 HS = 10.0
The NDK file is 20170916233803.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 2017/09/16 23:38:03:0 59.87 -136.79 6.5 5.0 Yukon, Canada Stations used: AK.BARN AK.BCP AK.BERG AK.BESE AK.CRQ AK.CTG AK.GLB AK.GRNC AK.LOGN AK.MCAR AK.MESA AK.PIN AK.SSP AK.TGL AK.VRDI AK.YAH AT.SIT AT.SKAG AT.YKU2 CN.DLBC CN.HYT CN.WHY NY.FARO NY.MAYO NY.MMPY NY.WTLY TA.K29M TA.L27K TA.M26K TA.M27K TA.M29M TA.M30M TA.M31M TA.N30M TA.N31M TA.O29M TA.O30N TA.P29M TA.P32M TA.P33M TA.Q32M TA.R33M TA.S31K TA.S32K TA.S34M TA.T33K 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 0.10 n 3 Best Fitting Double Couple Mo = 4.57e+23 dyne-cm Mw = 5.04 Z = 10 km Plane Strike Dip Rake NP1 115 60 55 NP2 349 45 135 Principal Axes: Axis Value Plunge Azimuth T 4.57e+23 59 333 N 0.00e+00 30 134 P -4.57e+23 9 229 Moment Tensor: (dyne-cm) Component Value Mxx -9.24e+22 Mxy -2.70e+23 Mxz 2.25e+23 Myy -2.32e+23 Myz -3.97e+22 Mzz 3.24e+23 ######-------- #############--------- ##################---------- #####################--------- ########################---------- ##########################---------- ############## ###########---------- --############# T ############---------- ---############ ############---------- -----###########################---------- -------#########################---------- ---------#######################---------- -----------######################--------- -------------###################-------- ----------------###############--------- -------------------###########-------- -- ----------------------##--##### - P -----------------------####### ----------------------###### ----------------------###### ------------------#### ------------## Global CMT Convention Moment Tensor: R T P 3.24e+23 2.25e+23 3.97e+22 2.25e+23 -9.24e+22 2.70e+23 3.97e+22 2.70e+23 -2.32e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170916233803/index.html |
Regional Moment Tensor (Mwr) Moment 4.649e+16 N-m Magnitude 5.0 Mwr Depth 10.0 km Percent DC 75 % Half Duration – Catalog US Data Source US3 Contributor US3 Nodal Planes Plane Strike Dip Rake NP1 336 42 109 NP2 131 51 74 Principal Axes Axis Value Plunge Azimuth T 4.305e+16 N-m 77 341 N 0.624e+16 N-m 12 142 P -4.929e+16 N-m 4 233 |
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:
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 280 55 10 4.88 0.4081 WVFGRD96 2.0 280 90 -50 4.95 0.4123 WVFGRD96 3.0 280 90 -50 4.95 0.4304 WVFGRD96 4.0 105 75 50 4.96 0.4537 WVFGRD96 5.0 125 60 70 5.01 0.4928 WVFGRD96 6.0 130 55 75 5.02 0.5222 WVFGRD96 7.0 120 60 60 5.00 0.5374 WVFGRD96 8.0 120 60 60 5.01 0.5439 WVFGRD96 9.0 115 60 55 5.01 0.5433 WVFGRD96 10.0 115 60 55 5.04 0.5485 WVFGRD96 11.0 115 60 50 5.04 0.5410 WVFGRD96 12.0 110 65 45 5.04 0.5326 WVFGRD96 13.0 110 65 45 5.04 0.5209 WVFGRD96 14.0 105 65 35 5.04 0.5079 WVFGRD96 15.0 105 65 35 5.05 0.4947 WVFGRD96 16.0 105 65 35 5.05 0.4802 WVFGRD96 17.0 105 65 35 5.06 0.4651 WVFGRD96 18.0 105 65 35 5.06 0.4488 WVFGRD96 19.0 105 65 35 5.07 0.4329 WVFGRD96 20.0 105 60 35 5.09 0.4187 WVFGRD96 21.0 100 65 30 5.09 0.4042 WVFGRD96 22.0 100 65 30 5.10 0.3902 WVFGRD96 23.0 100 65 30 5.10 0.3762 WVFGRD96 24.0 100 65 30 5.10 0.3624 WVFGRD96 25.0 100 65 30 5.11 0.3491 WVFGRD96 26.0 100 60 25 5.11 0.3369 WVFGRD96 27.0 100 60 25 5.11 0.3253 WVFGRD96 28.0 100 60 25 5.11 0.3142 WVFGRD96 29.0 100 60 25 5.11 0.3034
The best solution is
WVFGRD96 10.0 115 60 55 5.04 0.5485
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 0.10 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 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