USGS/SLU Moment Tensor Solution ENS 2020/07/09 16:44:19:0 62.33 -148.73 18.5 3.6 Alaska Stations used: AK.CUT AK.DHY AK.DIV AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.K24K AK.KLU AK.KNK AK.L22K AK.RC01 AK.RND AK.SAW AK.SCM AK.SLK AK.TRF AT.PMR TA.M22K TA.M24K 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 = 5.13e+21 dyne-cm Mw = 3.74 Z = 51 km Plane Strike Dip Rake NP1 246 52 -117 NP2 105 45 -60 Principal Axes: Axis Value Plunge Azimuth T 5.13e+21 4 354 N 0.00e+00 21 263 P -5.13e+21 69 94 Moment Tensor: (dyne-cm) Component Value Mxx 5.05e+21 Mxy -4.60e+20 Mxz 4.69e+20 Myy -6.09e+20 Myz -1.75e+21 Mzz -4.44e+21 ### T ######## ####### ############ ############################ ############################## ################################## ##################----------------## ##############------------------------ ############---------------------------- #########------------------------------- --######---------------------------------- ---####------------------ -------------- ----#-------------------- P -------------- ----#-------------------- -------------- --####---------------------------------- --######-------------------------------# ##########--------------------------## #############------------------##### ################################## ############################## ############################ ###################### ############## Global CMT Convention Moment Tensor: R T P -4.44e+21 4.69e+20 1.75e+21 4.69e+20 5.05e+21 4.60e+20 1.75e+21 4.60e+20 -6.09e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200709164419/index.html |
STK = 105 DIP = 45 RAKE = -60 MW = 3.74 HS = 51.0
The NDK file is 20200709164419.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/07/09 16:44:19:0 62.33 -148.73 18.5 3.6 Alaska Stations used: AK.CUT AK.DHY AK.DIV AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.K24K AK.KLU AK.KNK AK.L22K AK.RC01 AK.RND AK.SAW AK.SCM AK.SLK AK.TRF AT.PMR TA.M22K TA.M24K 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 = 5.13e+21 dyne-cm Mw = 3.74 Z = 51 km Plane Strike Dip Rake NP1 246 52 -117 NP2 105 45 -60 Principal Axes: Axis Value Plunge Azimuth T 5.13e+21 4 354 N 0.00e+00 21 263 P -5.13e+21 69 94 Moment Tensor: (dyne-cm) Component Value Mxx 5.05e+21 Mxy -4.60e+20 Mxz 4.69e+20 Myy -6.09e+20 Myz -1.75e+21 Mzz -4.44e+21 ### T ######## ####### ############ ############################ ############################## ################################## ##################----------------## ##############------------------------ ############---------------------------- #########------------------------------- --######---------------------------------- ---####------------------ -------------- ----#-------------------- P -------------- ----#-------------------- -------------- --####---------------------------------- --######-------------------------------# ##########--------------------------## #############------------------##### ################################## ############################## ############################ ###################### ############## Global CMT Convention Moment Tensor: R T P -4.44e+21 4.69e+20 1.75e+21 4.69e+20 5.05e+21 4.60e+20 1.75e+21 4.60e+20 -6.09e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200709164419/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 70 45 85 2.82 0.1468 WVFGRD96 2.0 255 45 95 2.97 0.1862 WVFGRD96 3.0 265 65 50 3.06 0.1963 WVFGRD96 4.0 260 65 45 3.07 0.2093 WVFGRD96 5.0 70 90 55 3.07 0.2232 WVFGRD96 6.0 75 85 50 3.10 0.2412 WVFGRD96 7.0 235 60 75 3.10 0.2556 WVFGRD96 8.0 80 80 50 3.19 0.2627 WVFGRD96 9.0 75 60 95 3.20 0.2729 WVFGRD96 10.0 75 60 95 3.21 0.2804 WVFGRD96 11.0 240 35 75 3.22 0.2841 WVFGRD96 12.0 240 35 75 3.23 0.2835 WVFGRD96 13.0 240 35 75 3.24 0.2803 WVFGRD96 14.0 65 60 80 3.25 0.2761 WVFGRD96 15.0 65 60 80 3.26 0.2718 WVFGRD96 16.0 65 60 80 3.27 0.2684 WVFGRD96 17.0 65 60 80 3.28 0.2638 WVFGRD96 18.0 290 55 -35 3.29 0.2645 WVFGRD96 19.0 285 55 -40 3.31 0.2739 WVFGRD96 20.0 285 55 -40 3.33 0.2828 WVFGRD96 21.0 285 55 -40 3.35 0.2913 WVFGRD96 22.0 285 55 -40 3.36 0.2990 WVFGRD96 23.0 285 60 -40 3.37 0.3061 WVFGRD96 24.0 285 60 -40 3.39 0.3127 WVFGRD96 25.0 285 60 -40 3.40 0.3172 WVFGRD96 26.0 285 60 -40 3.41 0.3203 WVFGRD96 27.0 120 50 -20 3.42 0.3203 WVFGRD96 28.0 120 50 -20 3.43 0.3212 WVFGRD96 29.0 280 50 -45 3.44 0.3216 WVFGRD96 30.0 115 70 -35 3.45 0.3403 WVFGRD96 31.0 115 70 -40 3.47 0.3557 WVFGRD96 32.0 115 65 -40 3.48 0.3727 WVFGRD96 33.0 115 65 -40 3.49 0.3907 WVFGRD96 34.0 100 55 -60 3.51 0.4094 WVFGRD96 35.0 100 55 -60 3.52 0.4280 WVFGRD96 36.0 105 55 -55 3.53 0.4459 WVFGRD96 37.0 105 55 -55 3.54 0.4596 WVFGRD96 38.0 100 50 -55 3.55 0.4699 WVFGRD96 39.0 100 50 -60 3.57 0.4770 WVFGRD96 40.0 100 50 -60 3.64 0.4864 WVFGRD96 41.0 100 50 -60 3.66 0.4899 WVFGRD96 42.0 100 50 -60 3.67 0.4918 WVFGRD96 43.0 105 50 -60 3.69 0.4963 WVFGRD96 44.0 105 50 -60 3.70 0.5003 WVFGRD96 45.0 95 45 -65 3.71 0.5058 WVFGRD96 46.0 95 45 -65 3.72 0.5092 WVFGRD96 47.0 100 45 -65 3.73 0.5134 WVFGRD96 48.0 100 45 -65 3.73 0.5144 WVFGRD96 49.0 100 45 -60 3.73 0.5166 WVFGRD96 50.0 100 45 -60 3.74 0.5161 WVFGRD96 51.0 105 45 -60 3.74 0.5166 WVFGRD96 52.0 95 40 -65 3.75 0.5151 WVFGRD96 53.0 95 40 -65 3.75 0.5138 WVFGRD96 54.0 95 40 -65 3.75 0.5118 WVFGRD96 55.0 100 40 -60 3.75 0.5086 WVFGRD96 56.0 100 40 -60 3.76 0.5077 WVFGRD96 57.0 100 40 -60 3.76 0.5043 WVFGRD96 58.0 100 40 -60 3.76 0.5013 WVFGRD96 59.0 100 40 -60 3.76 0.4982
The best solution is
WVFGRD96 51.0 105 45 -60 3.74 0.5166
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: