USGS/SLU Moment Tensor Solution ENS 2019/02/22 09:52:56:0 65.49 -166.78 15.7 3.7 Alaska Stations used: AK.ANM AK.GAMB AK.RDOG AK.TNA TA.C18K TA.E18K TA.F17K TA.F19K TA.G16K TA.G18K TA.H17K TA.H18K TA.I17K TA.J14K TA.J16K Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 6.10e+21 dyne-cm Mw = 3.79 Z = 15 km Plane Strike Dip Rake NP1 95 71 -120 NP2 335 35 -35 Principal Axes: Axis Value Plunge Azimuth T 6.10e+21 20 207 N 0.00e+00 28 105 P -6.10e+21 54 328 Moment Tensor: (dyne-cm) Component Value Mxx 2.78e+21 Mxy 3.10e+21 Mxz -4.21e+21 Myy 5.05e+20 Myz 6.45e+20 Mzz -3.29e+21 ############## -----------########### ------------------########## ---------------------######### -------------------------######### ----------- --------------######## ------------ P ---------------######## ------------- ----------------######## ---------------------------------####### ----------------------------------######## #----------------------------------####### #####------------------------------####### #########---------------------------####-- #################--------------####----- ##################################------ #################################----- ################################---- ##############################---- ###### ##################--- ##### T #################--- ## ################- ############## Global CMT Convention Moment Tensor: R T P -3.29e+21 -4.21e+21 -6.45e+20 -4.21e+21 2.78e+21 -3.10e+21 -6.45e+20 -3.10e+21 5.05e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190222095256/index.html |
STK = 335 DIP = 35 RAKE = -35 MW = 3.79 HS = 15.0
The NDK file is 20190222095256.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2019/02/22 09:52:56:0 65.49 -166.78 15.7 3.7 Alaska Stations used: AK.ANM AK.GAMB AK.RDOG AK.TNA TA.C18K TA.E18K TA.F17K TA.F19K TA.G16K TA.G18K TA.H17K TA.H18K TA.I17K TA.J14K TA.J16K Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 6.10e+21 dyne-cm Mw = 3.79 Z = 15 km Plane Strike Dip Rake NP1 95 71 -120 NP2 335 35 -35 Principal Axes: Axis Value Plunge Azimuth T 6.10e+21 20 207 N 0.00e+00 28 105 P -6.10e+21 54 328 Moment Tensor: (dyne-cm) Component Value Mxx 2.78e+21 Mxy 3.10e+21 Mxz -4.21e+21 Myy 5.05e+20 Myz 6.45e+20 Mzz -3.29e+21 ############## -----------########### ------------------########## ---------------------######### -------------------------######### ----------- --------------######## ------------ P ---------------######## ------------- ----------------######## ---------------------------------####### ----------------------------------######## #----------------------------------####### #####------------------------------####### #########---------------------------####-- #################--------------####----- ##################################------ #################################----- ################################---- ##############################---- ###### ##################--- ##### T #################--- ## ################- ############## Global CMT Convention Moment Tensor: R T P -3.29e+21 -4.21e+21 -6.45e+20 -4.21e+21 2.78e+21 -3.10e+21 -6.45e+20 -3.10e+21 5.05e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190222095256/index.html |
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for 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 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 20 70 5 3.43 0.3585 WVFGRD96 2.0 30 65 25 3.54 0.4079 WVFGRD96 3.0 85 60 -20 3.54 0.4163 WVFGRD96 4.0 90 75 70 3.63 0.4197 WVFGRD96 5.0 95 70 70 3.64 0.4612 WVFGRD96 6.0 95 70 70 3.64 0.4840 WVFGRD96 7.0 345 40 -20 3.63 0.5093 WVFGRD96 8.0 340 35 -30 3.71 0.5379 WVFGRD96 9.0 335 35 -35 3.72 0.5724 WVFGRD96 10.0 335 35 -35 3.74 0.5993 WVFGRD96 11.0 335 35 -35 3.75 0.6189 WVFGRD96 12.0 335 35 -35 3.76 0.6328 WVFGRD96 13.0 335 35 -35 3.77 0.6415 WVFGRD96 14.0 335 35 -35 3.78 0.6456 WVFGRD96 15.0 335 35 -35 3.79 0.6471 WVFGRD96 16.0 335 35 -35 3.80 0.6463 WVFGRD96 17.0 335 35 -35 3.81 0.6427 WVFGRD96 18.0 335 35 -35 3.82 0.6379 WVFGRD96 19.0 340 35 -25 3.82 0.6319 WVFGRD96 20.0 340 35 -25 3.83 0.6252 WVFGRD96 21.0 340 35 -25 3.85 0.6191 WVFGRD96 22.0 340 35 -25 3.86 0.6101 WVFGRD96 23.0 340 35 -25 3.87 0.6001 WVFGRD96 24.0 340 35 -25 3.88 0.5883 WVFGRD96 25.0 340 35 -25 3.89 0.5764 WVFGRD96 26.0 340 35 -25 3.90 0.5629 WVFGRD96 27.0 340 35 -25 3.90 0.5486 WVFGRD96 28.0 335 30 -25 3.90 0.5324 WVFGRD96 29.0 335 30 -25 3.91 0.5154
The best solution is
WVFGRD96 15.0 335 35 -35 3.79 0.6471
The mechanism correspond 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 and because the velocity model used in the predictions may not be perfect. 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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. 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.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: