USGS/SLU Moment Tensor Solution ENS 2020/03/18 15:31:33:0 66.32 -157.21 10.0 4.8 Alaska Stations used: AK.ANM AK.BPAW AK.COLD AK.H21K AK.H22K AK.H24K AK.I21K AK.I23K AK.J19K AK.J20K AK.KTH AK.MLY AK.NEA2 AK.RDOG TA.E18K TA.E22K TA.F15K TA.F17K TA.G16K TA.G24K TA.H17K TA.H18K TA.I17K TA.I20K TA.J18K 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 0.10 n 3 Best Fitting Double Couple Mo = 1.27e+23 dyne-cm Mw = 4.67 Z = 12 km Plane Strike Dip Rake NP1 175 85 -20 NP2 267 70 -175 Principal Axes: Axis Value Plunge Azimuth T 1.27e+23 10 223 N 0.00e+00 69 342 P -1.27e+23 18 129 Moment Tensor: (dyne-cm) Component Value Mxx 2.08e+22 Mxy 1.18e+23 Mxz 6.65e+21 Myy -1.32e+22 Myz -4.36e+22 Mzz -7.56e+21 -----######### ---------############# ------------################ -------------################# ---------------################### ----------------#################### -----------------##################### ------------------###################### ---------------###------------########## --------###########--------------------### ---#################---------------------- -###################---------------------- ####################---------------------- ###################--------------------- ###################--------------------- ###################------------ ---- ##################------------ P --- ### ###########------------ -- # T ###########--------------- ############------------- ############---------- ########------ Global CMT Convention Moment Tensor: R T P -7.56e+21 6.65e+21 4.36e+22 6.65e+21 2.08e+22 -1.18e+23 4.36e+22 -1.18e+23 -1.32e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200318153133/index.html |
STK = 175 DIP = 85 RAKE = -20 MW = 4.67 HS = 12.0
The NDK file is 20200318153133.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/03/18 15:31:33:0 66.32 -157.21 10.0 4.8 Alaska Stations used: AK.ANM AK.BPAW AK.COLD AK.H21K AK.H22K AK.H24K AK.I21K AK.I23K AK.J19K AK.J20K AK.KTH AK.MLY AK.NEA2 AK.RDOG TA.E18K TA.E22K TA.F15K TA.F17K TA.G16K TA.G24K TA.H17K TA.H18K TA.I17K TA.I20K TA.J18K 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 0.10 n 3 Best Fitting Double Couple Mo = 1.27e+23 dyne-cm Mw = 4.67 Z = 12 km Plane Strike Dip Rake NP1 175 85 -20 NP2 267 70 -175 Principal Axes: Axis Value Plunge Azimuth T 1.27e+23 10 223 N 0.00e+00 69 342 P -1.27e+23 18 129 Moment Tensor: (dyne-cm) Component Value Mxx 2.08e+22 Mxy 1.18e+23 Mxz 6.65e+21 Myy -1.32e+22 Myz -4.36e+22 Mzz -7.56e+21 -----######### ---------############# ------------################ -------------################# ---------------################### ----------------#################### -----------------##################### ------------------###################### ---------------###------------########## --------###########--------------------### ---#################---------------------- -###################---------------------- ####################---------------------- ###################--------------------- ###################--------------------- ###################------------ ---- ##################------------ P --- ### ###########------------ -- # T ###########--------------- ############------------- ############---------- ########------ Global CMT Convention Moment Tensor: R T P -7.56e+21 6.65e+21 4.36e+22 6.65e+21 2.08e+22 -1.18e+23 4.36e+22 -1.18e+23 -1.32e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200318153133/index.html |
(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.
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 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 170 90 0 4.22 0.3039 WVFGRD96 2.0 355 80 10 4.33 0.3776 WVFGRD96 3.0 355 80 5 4.39 0.4138 WVFGRD96 4.0 355 80 10 4.44 0.4297 WVFGRD96 5.0 350 70 -15 4.48 0.4448 WVFGRD96 6.0 350 70 -20 4.51 0.4686 WVFGRD96 7.0 175 85 -20 4.54 0.4953 WVFGRD96 8.0 170 80 -25 4.59 0.5293 WVFGRD96 9.0 170 75 -25 4.61 0.5511 WVFGRD96 10.0 170 80 -25 4.64 0.5666 WVFGRD96 11.0 175 85 -20 4.66 0.5778 WVFGRD96 12.0 175 85 -20 4.67 0.5838 WVFGRD96 13.0 175 85 -20 4.69 0.5834 WVFGRD96 14.0 175 85 -20 4.70 0.5779 WVFGRD96 15.0 175 85 -20 4.72 0.5678 WVFGRD96 16.0 175 85 -20 4.73 0.5547 WVFGRD96 17.0 175 85 -20 4.74 0.5378 WVFGRD96 18.0 175 85 -20 4.74 0.5178 WVFGRD96 19.0 175 85 -20 4.75 0.4981 WVFGRD96 20.0 175 85 -20 4.76 0.4779 WVFGRD96 21.0 175 80 -20 4.76 0.4570 WVFGRD96 22.0 175 80 -25 4.76 0.4367 WVFGRD96 23.0 175 85 -25 4.77 0.4175 WVFGRD96 24.0 175 85 -25 4.77 0.3986 WVFGRD96 25.0 175 85 -25 4.77 0.3806 WVFGRD96 26.0 175 85 -25 4.78 0.3632 WVFGRD96 27.0 175 85 -25 4.78 0.3460 WVFGRD96 28.0 175 85 -25 4.78 0.3301 WVFGRD96 29.0 170 80 -25 4.79 0.3147
The best solution is
WVFGRD96 12.0 175 85 -20 4.67 0.5838
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 0.10 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 Bureau of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Oklahoma Geological Survey, TexNet, the Iris stations, the Transportable Array of EarthScope and other networks.
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: