USGS/SLU Moment Tensor Solution ENS 2020/08/22 22:25:53:0 59.51 -152.47 59.6 3.7 Alaska Stations used: AK.BRLK AK.CAPN AK.CNP AK.GLI AK.HOM AK.KNK AK.N18K AK.N19K AK.O18K AK.O19K AK.P17K AK.Q19K AK.RC01 AK.SKN AK.SLK AK.SWD AT.PMR AV.ILSW AV.SPU AV.STLK II.KDAK TA.O22K 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 = 1.55e+22 dyne-cm Mw = 4.06 Z = 82 km Plane Strike Dip Rake NP1 303 71 159 NP2 40 70 20 Principal Axes: Axis Value Plunge Azimuth T 1.55e+22 28 261 N 0.00e+00 62 83 P -1.55e+22 1 352 Moment Tensor: (dyne-cm) Component Value Mxx -1.49e+22 Mxy 4.05e+21 Mxz -1.20e+21 Myy 1.15e+22 Myz -6.31e+21 Mzz 3.41e+21 --- P -------- ------- ------------ ---------------------------# ----------------------------## ------------------------------#### ########----------------------###### ##############----------------######## ##################------------########## ######################-------########### #########################----############# ########################################## ##### ###################---############ ##### T #################-------########## #### ################----------####### #####################--------------##### ##################-----------------### ###############--------------------# ############---------------------- #######----------------------- #--------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 3.41e+21 -1.20e+21 6.31e+21 -1.20e+21 -1.49e+22 -4.05e+21 6.31e+21 -4.05e+21 1.15e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200822222553/index.html |
STK = 40 DIP = 70 RAKE = 20 MW = 4.06 HS = 82.0
The NDK file is 20200822222553.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2020/08/22 22:25:53:0 59.51 -152.47 59.6 3.7 Alaska Stations used: AK.BRLK AK.CAPN AK.CNP AK.GLI AK.HOM AK.KNK AK.N18K AK.N19K AK.O18K AK.O19K AK.P17K AK.Q19K AK.RC01 AK.SKN AK.SLK AK.SWD AT.PMR AV.ILSW AV.SPU AV.STLK II.KDAK TA.O22K 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 = 1.55e+22 dyne-cm Mw = 4.06 Z = 82 km Plane Strike Dip Rake NP1 303 71 159 NP2 40 70 20 Principal Axes: Axis Value Plunge Azimuth T 1.55e+22 28 261 N 0.00e+00 62 83 P -1.55e+22 1 352 Moment Tensor: (dyne-cm) Component Value Mxx -1.49e+22 Mxy 4.05e+21 Mxz -1.20e+21 Myy 1.15e+22 Myz -6.31e+21 Mzz 3.41e+21 --- P -------- ------- ------------ ---------------------------# ----------------------------## ------------------------------#### ########----------------------###### ##############----------------######## ##################------------########## ######################-------########### #########################----############# ########################################## ##### ###################---############ ##### T #################-------########## #### ################----------####### #####################--------------##### ##################-----------------### ###############--------------------# ############---------------------- #######----------------------- #--------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 3.41e+21 -1.20e+21 6.31e+21 -1.20e+21 -1.49e+22 -4.05e+21 6.31e+21 -4.05e+21 1.15e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20200822222553/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 2.0 305 90 -10 3.05 0.1614 WVFGRD96 4.0 125 90 25 3.18 0.1966 WVFGRD96 6.0 130 60 20 3.27 0.2231 WVFGRD96 8.0 130 60 20 3.36 0.2512 WVFGRD96 10.0 130 65 20 3.40 0.2631 WVFGRD96 12.0 125 65 15 3.45 0.2612 WVFGRD96 14.0 40 75 -30 3.45 0.2549 WVFGRD96 16.0 40 75 -30 3.49 0.2619 WVFGRD96 18.0 40 75 -30 3.52 0.2708 WVFGRD96 20.0 35 70 -25 3.55 0.2822 WVFGRD96 22.0 35 70 -25 3.58 0.2943 WVFGRD96 24.0 35 70 -20 3.61 0.3063 WVFGRD96 26.0 35 70 -20 3.63 0.3172 WVFGRD96 28.0 35 70 -10 3.64 0.3268 WVFGRD96 30.0 40 70 -5 3.65 0.3345 WVFGRD96 32.0 40 70 0 3.67 0.3408 WVFGRD96 34.0 40 65 5 3.69 0.3452 WVFGRD96 36.0 40 70 5 3.71 0.3480 WVFGRD96 38.0 40 70 5 3.74 0.3524 WVFGRD96 40.0 45 55 15 3.82 0.3678 WVFGRD96 42.0 40 65 10 3.83 0.3748 WVFGRD96 44.0 40 65 10 3.86 0.3858 WVFGRD96 46.0 40 65 10 3.88 0.3960 WVFGRD96 48.0 40 65 10 3.90 0.4074 WVFGRD96 50.0 40 65 10 3.92 0.4180 WVFGRD96 52.0 40 70 15 3.93 0.4302 WVFGRD96 54.0 40 70 15 3.95 0.4416 WVFGRD96 56.0 40 70 15 3.96 0.4548 WVFGRD96 58.0 40 70 20 3.98 0.4661 WVFGRD96 60.0 40 70 20 3.99 0.4795 WVFGRD96 62.0 40 70 20 4.00 0.4896 WVFGRD96 64.0 40 70 20 4.01 0.4992 WVFGRD96 66.0 40 70 20 4.02 0.5092 WVFGRD96 68.0 40 70 20 4.03 0.5163 WVFGRD96 70.0 40 70 20 4.03 0.5212 WVFGRD96 72.0 40 70 20 4.04 0.5260 WVFGRD96 74.0 40 70 20 4.05 0.5308 WVFGRD96 76.0 40 70 20 4.05 0.5321 WVFGRD96 78.0 40 70 20 4.06 0.5351 WVFGRD96 80.0 40 70 20 4.06 0.5350 WVFGRD96 82.0 40 70 20 4.06 0.5353 WVFGRD96 84.0 40 70 20 4.07 0.5341 WVFGRD96 86.0 40 70 20 4.07 0.5332 WVFGRD96 88.0 40 70 20 4.07 0.5313 WVFGRD96 90.0 40 70 20 4.08 0.5286 WVFGRD96 92.0 45 65 20 4.08 0.5267 WVFGRD96 94.0 45 65 20 4.09 0.5246 WVFGRD96 96.0 45 65 20 4.09 0.5217 WVFGRD96 98.0 45 65 20 4.09 0.5196 WVFGRD96 100.0 45 65 20 4.09 0.5165 WVFGRD96 102.0 45 65 20 4.10 0.5139 WVFGRD96 104.0 45 65 20 4.10 0.5110 WVFGRD96 106.0 45 65 20 4.10 0.5088 WVFGRD96 108.0 45 70 20 4.09 0.5065
The best solution is
WVFGRD96 82.0 40 70 20 4.06 0.5353
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: