The ANSS event ID is ak017d1s8a1m and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak017d1s8a1m/executive.
2017/10/11 06:05:21 61.587 -141.081 10.3 3.9 Yukon, Canada
USGS/SLU Moment Tensor Solution ENS 2017/10/11 06:05:21:0 61.59 -141.08 10.3 3.9 Yukon, Canada Stations used: AK.BARN AK.BCP AK.BERG AK.BMR AK.CRQ AK.CTG AK.DHY AK.DIV AK.FID AK.GLB AK.GLI AK.GRNC AK.HDA AK.HMT AK.KAI AK.KLU AK.KNK AK.LOGN AK.MCAR AK.MESA AK.PIN AK.SCRK AK.SSP AK.SUCK AK.TGL AK.VRDI AT.MENT AT.SKAG CN.HYT CN.WHY NY.MAYO TA.I26K TA.I28M TA.J25K TA.J26L TA.J30M TA.K29M TA.L26K TA.L27K 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.P30M 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 = 9.89e+21 dyne-cm Mw = 3.93 Z = 8 km Plane Strike Dip Rake NP1 255 50 70 NP2 105 44 112 Principal Axes: Axis Value Plunge Azimuth T 9.89e+21 74 100 N 0.00e+00 15 268 P -9.89e+21 3 359 Moment Tensor: (dyne-cm) Component Value Mxx -9.83e+21 Mxy 4.40e+19 Mxz -9.96e+20 Myy 6.82e+20 Myz 2.52e+21 Mzz 9.15e+21 ----- P ------ --------- ---------- ---------------------------- ------------------------------ ---------------------------------- -----------------############------- ------------#######################--- ----------#############################- -------################################# ##----#################################### ##--#################### ############### ######################## T ############### ##---################### ############### -----################################### --------###############################- ---------###########################-- ------------###################----- ---------------------------------- ------------------------------ ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 9.15e+21 -9.96e+20 -2.52e+21 -9.96e+20 -9.83e+21 -4.40e+19 -2.52e+21 -4.40e+19 6.82e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20171011060521/index.html |
STK = 255 DIP = 50 RAKE = 70 MW = 3.93 HS = 8.0
The NDK file is 20171011060521.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: 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.
![]() |
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.
![]() |
|
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 1.0 215 15 0 4.03 0.4113 WVFGRD96 2.0 215 25 -5 3.90 0.4530 WVFGRD96 3.0 215 30 -5 3.86 0.4800 WVFGRD96 4.0 230 30 25 3.85 0.4969 WVFGRD96 5.0 255 35 70 3.92 0.5355 WVFGRD96 6.0 260 45 75 3.94 0.5908 WVFGRD96 7.0 260 45 75 3.94 0.6139 WVFGRD96 8.0 255 50 70 3.93 0.6169 WVFGRD96 9.0 260 50 70 3.93 0.6090 WVFGRD96 10.0 260 50 70 3.95 0.5989 WVFGRD96 11.0 255 50 65 3.95 0.5793 WVFGRD96 12.0 250 55 55 3.94 0.5566 WVFGRD96 13.0 250 55 55 3.94 0.5333 WVFGRD96 14.0 245 60 50 3.94 0.5086 WVFGRD96 15.0 60 50 40 3.93 0.4834 WVFGRD96 16.0 60 50 40 3.93 0.4609 WVFGRD96 17.0 60 55 35 3.94 0.4391 WVFGRD96 18.0 60 55 35 3.94 0.4181 WVFGRD96 19.0 55 60 30 3.95 0.3977 WVFGRD96 20.0 55 55 30 3.96 0.3781 WVFGRD96 21.0 55 55 30 3.97 0.3588 WVFGRD96 22.0 55 55 30 3.97 0.3403 WVFGRD96 23.0 55 60 30 3.97 0.3225 WVFGRD96 24.0 55 60 30 3.98 0.3058 WVFGRD96 25.0 55 60 30 3.98 0.2901 WVFGRD96 26.0 50 60 25 3.98 0.2755 WVFGRD96 27.0 50 60 25 3.98 0.2631 WVFGRD96 28.0 220 65 -25 3.99 0.2538 WVFGRD96 29.0 220 65 -25 4.00 0.2483
The best solution is
WVFGRD96 8.0 255 50 70 3.93 0.6169
The mechanism corresponding to the best fit is
![]() |
|
The best fit as a function of depth is given in the following figure:
![]() |
|
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
![]() |
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. |
![]() |
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