USGS/SLU Moment Tensor Solution ENS 2017/07/18 23:42:39:0 60.24 -150.88 74.0 4.0 Alaska Stations used: AK.CNP AK.GHO AK.GLI AK.KNK AK.PWL AK.RC01 AK.SSN AK.SWD AT.PMR TA.M22K TA.N19K TA.O22K TA.P19K Filtering commands used: cut o DIST/3.4 -30 o DIST/3.4 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 6.31e+21 dyne-cm Mw = 3.80 Z = 66 km Plane Strike Dip Rake NP1 315 86 87 NP2 170 5 125 Principal Axes: Axis Value Plunge Azimuth T 6.31e+21 49 222 N 0.00e+00 3 315 P -6.31e+21 41 48 Moment Tensor: (dyne-cm) Component Value Mxx -1.35e+20 Mxy -4.50e+20 Mxz -4.43e+21 Myy -7.63e+20 Myz -4.39e+21 Mzz 8.97e+20 -------------- #--------------------- #--------------------------- #----------------------------- -#####---------------------------- -########----------------- ------- -###########--------------- P -------- -##############------------- --------- -################----------------------- -###################---------------------- -#####################-------------------- -######################------------------- -########################----------------- -#########################-------------- -########## ##############------------ -######### T ###############---------- -######## #################------- -#############################---- -############################- --########################## -##################### -############# Global CMT Convention Moment Tensor: R T P 8.97e+20 -4.43e+21 4.39e+21 -4.43e+21 -1.35e+20 4.50e+20 4.39e+21 4.50e+20 -7.63e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170718234239/index.html |
STK = -10 DIP = -5 RAKE = -55 MW = 3.80 HS = 66.0
The NDK file is 20170718234239.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2017/07/18 23:42:39:0 60.24 -150.88 74.0 4.0 Alaska Stations used: AK.CNP AK.GHO AK.GLI AK.KNK AK.PWL AK.RC01 AK.SSN AK.SWD AT.PMR TA.M22K TA.N19K TA.O22K TA.P19K Filtering commands used: cut o DIST/3.4 -30 o DIST/3.4 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 6.31e+21 dyne-cm Mw = 3.80 Z = 66 km Plane Strike Dip Rake NP1 315 86 87 NP2 170 5 125 Principal Axes: Axis Value Plunge Azimuth T 6.31e+21 49 222 N 0.00e+00 3 315 P -6.31e+21 41 48 Moment Tensor: (dyne-cm) Component Value Mxx -1.35e+20 Mxy -4.50e+20 Mxz -4.43e+21 Myy -7.63e+20 Myz -4.39e+21 Mzz 8.97e+20 -------------- #--------------------- #--------------------------- #----------------------------- -#####---------------------------- -########----------------- ------- -###########--------------- P -------- -##############------------- --------- -################----------------------- -###################---------------------- -#####################-------------------- -######################------------------- -########################----------------- -#########################-------------- -########## ##############------------ -######### T ###############---------- -######## #################------- -#############################---- -############################- --########################## -##################### -############# Global CMT Convention Moment Tensor: R T P 8.97e+20 -4.43e+21 4.39e+21 -4.43e+21 -1.35e+20 4.50e+20 4.39e+21 4.50e+20 -7.63e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170718234239/index.html |
Regional Moment Tensor (Mwr) Moment 6.810e+14 N-m Magnitude 3.8 Mwr Depth 63.0 km Percent DC 67 % Half Duration – Catalog US Data Source US2 Contributor US2 Nodal Planes Plane Strike Dip Rake NP1 307 84 74 NP2 198 17 160 Principal Axes Axis Value Plunge Azimuth T 7.338e+14 N-m 48 201 N -1.222e+14 N-m 16 309 P -6.116e+14 N-m 37 51 |
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/3.4 -30 o DIST/3.4 +40 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 2.0 325 40 -90 3.02 0.2553 WVFGRD96 4.0 225 40 -5 3.08 0.2241 WVFGRD96 6.0 220 35 -20 3.08 0.2854 WVFGRD96 8.0 195 25 -45 3.16 0.3219 WVFGRD96 10.0 190 25 -50 3.18 0.3439 WVFGRD96 12.0 220 45 -5 3.25 0.3538 WVFGRD96 14.0 135 70 60 3.24 0.3627 WVFGRD96 16.0 135 70 50 3.29 0.3697 WVFGRD96 18.0 45 60 10 3.38 0.3737 WVFGRD96 20.0 45 60 5 3.40 0.3757 WVFGRD96 22.0 45 60 5 3.43 0.3735 WVFGRD96 24.0 45 60 5 3.45 0.3675 WVFGRD96 26.0 45 55 0 3.45 0.3602 WVFGRD96 28.0 45 50 0 3.46 0.3567 WVFGRD96 30.0 45 50 0 3.48 0.3528 WVFGRD96 32.0 30 30 -25 3.46 0.3570 WVFGRD96 34.0 20 20 -30 3.47 0.3755 WVFGRD96 36.0 20 20 -30 3.49 0.3967 WVFGRD96 38.0 10 15 -45 3.50 0.4212 WVFGRD96 40.0 350 10 -65 3.66 0.4431 WVFGRD96 42.0 140 90 -80 3.67 0.4979 WVFGRD96 44.0 75 5 20 3.68 0.5450 WVFGRD96 46.0 85 5 30 3.69 0.5882 WVFGRD96 48.0 100 5 50 3.70 0.6230 WVFGRD96 50.0 100 5 50 3.71 0.6504 WVFGRD96 52.0 100 5 50 3.73 0.6705 WVFGRD96 54.0 100 5 50 3.74 0.6855 WVFGRD96 56.0 100 5 50 3.75 0.6979 WVFGRD96 58.0 100 5 50 3.76 0.7063 WVFGRD96 60.0 100 5 50 3.77 0.7098 WVFGRD96 62.0 100 5 50 3.78 0.7115 WVFGRD96 64.0 90 5 40 3.79 0.7117 WVFGRD96 66.0 -10 -5 -55 3.80 0.7120 WVFGRD96 68.0 315 85 85 3.80 0.7094 WVFGRD96 70.0 315 85 85 3.81 0.7037 WVFGRD96 72.0 135 90 -85 3.84 0.6863 WVFGRD96 74.0 310 85 80 3.83 0.6883 WVFGRD96 76.0 130 90 -80 3.85 0.6663 WVFGRD96 78.0 130 90 -80 3.86 0.6545 WVFGRD96 80.0 125 90 -75 3.87 0.6403 WVFGRD96 82.0 305 85 80 3.87 0.6409 WVFGRD96 84.0 140 5 100 3.87 0.6133 WVFGRD96 86.0 135 10 100 3.86 0.6014 WVFGRD96 88.0 305 85 75 3.88 0.5921 WVFGRD96 90.0 300 80 80 3.88 0.5810 WVFGRD96 92.0 300 80 80 3.88 0.5704 WVFGRD96 94.0 300 80 80 3.89 0.5580 WVFGRD96 96.0 300 80 80 3.89 0.5459 WVFGRD96 98.0 300 80 75 3.89 0.5321
The best solution is
WVFGRD96 66.0 -10 -5 -55 3.80 0.7120
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/3.4 -30 o DIST/3.4 +40 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 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: