USGS/SLU Moment Tensor Solution ENS 2020/03/24 17:01:32:0 69.56 -144.24 5.0 4.0 Alaska Stations used: AK.COLD AK.H24K TA.C24K TA.C26K TA.C27K TA.D23K TA.D24K TA.D25K TA.D27M TA.D28M TA.E21K TA.E23K TA.E24K TA.E25K TA.E27K TA.E28M TA.E29M TA.F24K TA.F25K TA.F26K TA.F28M TA.F30M TA.G23K TA.G24K TA.G26K TA.G27K TA.G29M TA.H27K 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 0.07 n 3 Best Fitting Double Couple Mo = 4.79e+21 dyne-cm Mw = 3.72 Z = 8 km Plane Strike Dip Rake NP1 225 80 25 NP2 130 65 169 Principal Axes: Axis Value Plunge Azimuth T 4.79e+21 25 90 N 0.00e+00 63 245 P -4.79e+21 10 356 Moment Tensor: (dyne-cm) Component Value Mxx -4.62e+21 Mxy 3.46e+20 Mxz -8.11e+20 Myy 3.93e+21 Myz 1.88e+21 Mzz 6.92e+20 ---- P ------- -------- ----------- ---------------------------- ----------------------------## #--------------------------####### ###-----------------------########## #####-------------------############## #######----------------################# ########-------------################### ##########----------###################### ###########-------################# #### #############----################## T #### ################################### #### ############----######################## ###########-------###################### ########------------################## ######----------------############## ####---------------------######### #----------------------------- ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 6.92e+20 -8.11e+20 -1.88e+21 -8.11e+20 -4.62e+21 -3.46e+20 -1.88e+21 -3.46e+20 3.93e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200324170132/index.html |
STK = 225 DIP = 80 RAKE = 25 MW = 3.72 HS = 8.0
The NDK file is 20200324170132.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/03/24 17:01:32:0 69.56 -144.24 5.0 4.0 Alaska Stations used: AK.COLD AK.H24K TA.C24K TA.C26K TA.C27K TA.D23K TA.D24K TA.D25K TA.D27M TA.D28M TA.E21K TA.E23K TA.E24K TA.E25K TA.E27K TA.E28M TA.E29M TA.F24K TA.F25K TA.F26K TA.F28M TA.F30M TA.G23K TA.G24K TA.G26K TA.G27K TA.G29M TA.H27K 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 0.07 n 3 Best Fitting Double Couple Mo = 4.79e+21 dyne-cm Mw = 3.72 Z = 8 km Plane Strike Dip Rake NP1 225 80 25 NP2 130 65 169 Principal Axes: Axis Value Plunge Azimuth T 4.79e+21 25 90 N 0.00e+00 63 245 P -4.79e+21 10 356 Moment Tensor: (dyne-cm) Component Value Mxx -4.62e+21 Mxy 3.46e+20 Mxz -8.11e+20 Myy 3.93e+21 Myz 1.88e+21 Mzz 6.92e+20 ---- P ------- -------- ----------- ---------------------------- ----------------------------## #--------------------------####### ###-----------------------########## #####-------------------############## #######----------------################# ########-------------################### ##########----------###################### ###########-------################# #### #############----################## T #### ################################### #### ############----######################## ###########-------###################### ########------------################## ######----------------############## ####---------------------######### #----------------------------- ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 6.92e+20 -8.11e+20 -1.88e+21 -8.11e+20 -4.62e+21 -3.46e+20 -1.88e+21 -3.46e+20 3.93e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200324170132/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 0.07 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 40 90 0 3.42 0.4084 WVFGRD96 2.0 220 80 10 3.53 0.4936 WVFGRD96 3.0 40 90 -15 3.57 0.5183 WVFGRD96 4.0 40 90 -15 3.60 0.5250 WVFGRD96 5.0 225 80 20 3.64 0.5298 WVFGRD96 6.0 40 90 -20 3.65 0.5255 WVFGRD96 7.0 40 90 -20 3.68 0.5264 WVFGRD96 8.0 225 80 25 3.72 0.5392 WVFGRD96 9.0 225 80 25 3.74 0.5319 WVFGRD96 10.0 225 80 25 3.75 0.5240 WVFGRD96 11.0 225 80 20 3.76 0.5173 WVFGRD96 12.0 40 90 -25 3.77 0.5085 WVFGRD96 13.0 40 90 -25 3.78 0.5025 WVFGRD96 14.0 40 90 -20 3.79 0.4975 WVFGRD96 15.0 40 90 -20 3.80 0.4913 WVFGRD96 16.0 40 90 -20 3.81 0.4852 WVFGRD96 17.0 40 90 -20 3.82 0.4786 WVFGRD96 18.0 40 90 -15 3.83 0.4729 WVFGRD96 19.0 40 90 -15 3.84 0.4666 WVFGRD96 20.0 220 90 15 3.84 0.4600 WVFGRD96 21.0 40 90 -15 3.85 0.4538 WVFGRD96 22.0 40 90 -10 3.86 0.4467 WVFGRD96 23.0 40 80 -5 3.86 0.4409 WVFGRD96 24.0 40 80 -5 3.86 0.4361 WVFGRD96 25.0 40 80 0 3.87 0.4317 WVFGRD96 26.0 45 80 10 3.86 0.4289 WVFGRD96 27.0 45 80 10 3.87 0.4261 WVFGRD96 28.0 45 80 10 3.88 0.4226 WVFGRD96 29.0 310 90 0 3.90 0.4165
The best solution is
WVFGRD96 8.0 225 80 25 3.72 0.5392
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 0.07 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 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: