USGS/SLU Moment Tensor Solution ENS 2018/08/12 21:31:04:0 69.46 -144.25 5.7 5.9 Alaska Stations used: AK.FYU AK.PPD TA.D24K TA.D25K TA.D27M TA.E24K TA.E27K TA.E28M TA.E29M TA.F24K TA.F28M TA.G23K TA.G24K TA.G27K TA.G29M TA.H29M TA.TOLK Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 Best Fitting Double Couple Mo = 3.59e+23 dyne-cm Mw = 4.97 Z = 16 km Plane Strike Dip Rake NP1 107 77 149 NP2 205 60 15 Principal Axes: Axis Value Plunge Azimuth T 3.59e+23 31 62 N 0.00e+00 57 267 P -3.59e+23 11 159 Moment Tensor: (dyne-cm) Component Value Mxx -2.44e+23 Mxy 2.24e+23 Mxz 1.37e+23 Myy 1.64e+23 Myz 1.15e+23 Mzz 8.05e+22 -------------- -----------------##### -----------------########### ----------------############## ----------------################## ---------------##################### ---------------############### ##### ---------------################ T ###### ##------------################# ###### ######--------############################ ##########---############################# ############--############################ ############-------####################### ##########--------------################ ##########------------------------------ #########----------------------------- ########---------------------------- #######--------------------------- #####------------------------- ####--------------- ------ ##-------------- P --- ------------ Global CMT Convention Moment Tensor: R T P 8.05e+22 1.37e+23 -1.15e+23 1.37e+23 -2.44e+23 -2.24e+23 -1.15e+23 -2.24e+23 1.64e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180812213104/index.html |
STK = 205 DIP = 60 RAKE = 15 MW = 4.97 HS = 16.0
The NDK file is 20180812213104.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2018/08/12 21:31:04:0 69.46 -144.25 5.7 5.9 Alaska Stations used: AK.FYU AK.PPD TA.D24K TA.D25K TA.D27M TA.E24K TA.E27K TA.E28M TA.E29M TA.F24K TA.F28M TA.G23K TA.G24K TA.G27K TA.G29M TA.H29M TA.TOLK Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 n 3 Best Fitting Double Couple Mo = 3.59e+23 dyne-cm Mw = 4.97 Z = 16 km Plane Strike Dip Rake NP1 107 77 149 NP2 205 60 15 Principal Axes: Axis Value Plunge Azimuth T 3.59e+23 31 62 N 0.00e+00 57 267 P -3.59e+23 11 159 Moment Tensor: (dyne-cm) Component Value Mxx -2.44e+23 Mxy 2.24e+23 Mxz 1.37e+23 Myy 1.64e+23 Myz 1.15e+23 Mzz 8.05e+22 -------------- -----------------##### -----------------########### ----------------############## ----------------################## ---------------##################### ---------------############### ##### ---------------################ T ###### ##------------################# ###### ######--------############################ ##########---############################# ############--############################ ############-------####################### ##########--------------################ ##########------------------------------ #########----------------------------- ########---------------------------- #######--------------------------- #####------------------------- ####--------------- ------ ##-------------- P --- ------------ Global CMT Convention Moment Tensor: R T P 8.05e+22 1.37e+23 -1.15e+23 1.37e+23 -2.44e+23 -2.24e+23 -1.15e+23 -2.24e+23 1.64e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180812213104/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 -30 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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 25 85 -5 4.54 0.3830 WVFGRD96 2.0 25 85 -5 4.64 0.4770 WVFGRD96 3.0 205 85 -10 4.69 0.5115 WVFGRD96 4.0 205 90 -10 4.72 0.5280 WVFGRD96 5.0 25 80 15 4.75 0.5417 WVFGRD96 6.0 25 75 15 4.78 0.5567 WVFGRD96 7.0 205 75 20 4.80 0.5716 WVFGRD96 8.0 20 90 -30 4.84 0.5880 WVFGRD96 9.0 210 50 20 4.90 0.6036 WVFGRD96 10.0 210 50 20 4.92 0.6206 WVFGRD96 11.0 210 55 20 4.92 0.6345 WVFGRD96 12.0 205 60 15 4.92 0.6456 WVFGRD96 13.0 205 60 15 4.94 0.6537 WVFGRD96 14.0 205 60 15 4.95 0.6586 WVFGRD96 15.0 205 60 15 4.96 0.6615 WVFGRD96 16.0 205 60 15 4.97 0.6616 WVFGRD96 17.0 205 60 15 4.98 0.6588 WVFGRD96 18.0 205 60 15 4.99 0.6546 WVFGRD96 19.0 205 60 15 5.00 0.6490 WVFGRD96 20.0 205 60 15 5.01 0.6411 WVFGRD96 21.0 205 60 15 5.02 0.6316 WVFGRD96 22.0 205 60 15 5.03 0.6221 WVFGRD96 23.0 205 60 15 5.03 0.6112 WVFGRD96 24.0 205 60 15 5.04 0.6011 WVFGRD96 25.0 205 60 15 5.05 0.5895 WVFGRD96 26.0 20 45 -10 5.09 0.5783 WVFGRD96 27.0 20 45 -10 5.10 0.5694 WVFGRD96 28.0 20 50 -10 5.10 0.5600 WVFGRD96 29.0 20 50 -10 5.11 0.5505
The best solution is
WVFGRD96 16.0 205 60 15 4.97 0.6616
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 -30 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.07 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: