The ANSS event ID is ak0177yd14jz and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0177yd14jz/executive.
2017/06/22 15:21:39 61.255 -146.824 9.8 4.1 Alaska
USGS/SLU Moment Tensor Solution ENS 2017/06/22 15:21:39:0 61.26 -146.82 9.8 4.1 Alaska Stations used: AK.CRQ AK.GHO AK.GLB AK.HIN AK.KNK AK.MCAR AK.PWL AK.SAW AK.SCM AK.VRDI AT.PMR TA.M22K TA.M24K TA.N25K Filtering commands used: cut o DIST/3.5 -30 o DIST/3.5 +40 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 1.17e+22 dyne-cm Mw = 3.98 Z = 31 km Plane Strike Dip Rake NP1 15 60 -125 NP2 250 45 -45 Principal Axes: Axis Value Plunge Azimuth T 1.17e+22 8 130 N 0.00e+00 30 35 P -1.17e+22 59 234 Moment Tensor: (dyne-cm) Component Value Mxx 3.56e+21 Mxy -7.17e+21 Mxz 2.01e+21 Myy 4.75e+21 Myz 5.52e+21 Mzz -8.31e+21 #############- ##################---- ######################------ #######################------- ###################------#-------- #############--------------######--- ##########------------------#########- #########--------------------########### #######----------------------########### ######-----------------------############# ####-------------------------############# ###--------------------------############# ###---------- ------------############## #----------- P ------------############# #----------- -----------############## ------------------------############## ----------------------######### ## --------------------########## T # -----------------########### --------------############## ---------############# ---########### Global CMT Convention Moment Tensor: R T P -8.31e+21 2.01e+21 -5.52e+21 2.01e+21 3.56e+21 7.17e+21 -5.52e+21 7.17e+21 4.75e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170622152139/index.html |
STK = 250 DIP = 45 RAKE = -45 MW = 3.98 HS = 31.0
The NDK file is 20170622152139.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/3.5 -30 o DIST/3.5 +40 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 205 45 -95 3.27 0.1781 WVFGRD96 2.0 35 50 95 3.44 0.2569 WVFGRD96 3.0 25 50 80 3.50 0.2799 WVFGRD96 4.0 5 65 40 3.44 0.2908 WVFGRD96 5.0 0 70 35 3.46 0.3042 WVFGRD96 6.0 0 70 30 3.49 0.3152 WVFGRD96 7.0 170 75 -30 3.52 0.3270 WVFGRD96 8.0 165 70 -40 3.58 0.3343 WVFGRD96 9.0 165 70 -40 3.61 0.3420 WVFGRD96 10.0 180 70 40 3.63 0.3458 WVFGRD96 11.0 265 55 20 3.65 0.3564 WVFGRD96 12.0 255 55 -20 3.67 0.3708 WVFGRD96 13.0 255 55 -20 3.69 0.3812 WVFGRD96 14.0 255 55 -25 3.71 0.3903 WVFGRD96 15.0 255 55 -25 3.73 0.3992 WVFGRD96 16.0 260 60 -25 3.75 0.4091 WVFGRD96 17.0 255 60 -30 3.76 0.4198 WVFGRD96 18.0 255 60 -30 3.78 0.4317 WVFGRD96 19.0 255 60 -30 3.80 0.4439 WVFGRD96 20.0 255 55 -30 3.82 0.4577 WVFGRD96 21.0 255 55 -30 3.84 0.4710 WVFGRD96 22.0 255 55 -35 3.86 0.4865 WVFGRD96 23.0 250 50 -40 3.88 0.5046 WVFGRD96 24.0 250 50 -40 3.89 0.5250 WVFGRD96 25.0 250 50 -40 3.91 0.5441 WVFGRD96 26.0 245 45 -45 3.93 0.5633 WVFGRD96 27.0 245 45 -45 3.94 0.5798 WVFGRD96 28.0 250 45 -45 3.95 0.5944 WVFGRD96 29.0 250 45 -45 3.96 0.6059 WVFGRD96 30.0 250 45 -45 3.97 0.6154 WVFGRD96 31.0 250 45 -45 3.98 0.6193 WVFGRD96 32.0 250 45 -45 3.99 0.6181 WVFGRD96 33.0 250 45 -45 3.99 0.6151 WVFGRD96 34.0 250 45 -45 4.00 0.6103 WVFGRD96 35.0 250 45 -45 4.00 0.6018 WVFGRD96 36.0 250 45 -40 4.00 0.5919 WVFGRD96 37.0 250 45 -40 4.01 0.5836 WVFGRD96 38.0 250 45 -40 4.02 0.5764 WVFGRD96 39.0 255 50 -40 4.03 0.5698 WVFGRD96 40.0 250 45 -45 4.10 0.5559 WVFGRD96 41.0 255 45 -40 4.11 0.5497 WVFGRD96 42.0 255 45 -40 4.12 0.5433 WVFGRD96 43.0 255 45 -40 4.13 0.5370 WVFGRD96 44.0 255 45 -40 4.13 0.5299 WVFGRD96 45.0 260 45 -35 4.14 0.5242 WVFGRD96 46.0 260 45 -35 4.15 0.5193 WVFGRD96 47.0 260 45 -35 4.15 0.5132 WVFGRD96 48.0 260 40 -30 4.16 0.5077 WVFGRD96 49.0 260 40 -30 4.16 0.5024
The best solution is
WVFGRD96 31.0 250 45 -45 3.98 0.6193
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/3.5 -30 o DIST/3.5 +40 rtr taper w 0.1 hp c 0.04 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