The ANSS event ID is ak0228vb1a7q and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0228vb1a7q/executive.
2022/07/12 07:24:58 60.971 -150.945 68.5 4.8 Alaska
USGS/SLU Moment Tensor Solution ENS 2022/07/12 07:24:58:0 60.97 -150.95 68.5 4.8 Alaska Stations used: AK.CAPN AK.FID AK.FIRE AK.GHO AK.GLI AK.HIN AK.K20K AK.KNK AK.M19K AK.N18K AK.N19K AK.P23K AK.Q19K AK.RC01 AK.SAW AK.SCM AK.SKN AK.SSN AK.SWD AV.ILS AV.RED AV.SPCP 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 0.08 n 3 Best Fitting Double Couple Mo = 2.72e+23 dyne-cm Mw = 4.89 Z = 72 km Plane Strike Dip Rake NP1 195 84 -98 NP2 70 10 -35 Principal Axes: Axis Value Plunge Azimuth T 2.72e+23 39 292 N 0.00e+00 8 195 P -2.72e+23 50 96 Moment Tensor: (dyne-cm) Component Value Mxx 2.23e+22 Mxy -4.68e+22 Mxz 6.28e+22 Myy 3.11e+22 Myz -2.57e+23 Mzz -5.34e+22 ############-- ###############------- #################----------- ##################------------ ###################--------------- ###################----------------- ####################------------------ ####### ##########-------------------- ####### T ##########-------------------- ######## #########---------------------# ####################--------- ---------# ###################---------- P ---------# ###################---------- ---------# #################----------------------# #################---------------------## ################---------------------# ##############--------------------## -############-------------------## -##########-----------------## --#######----------------### ---###------------#### --############ Global CMT Convention Moment Tensor: R T P -5.34e+22 6.28e+22 2.57e+23 6.28e+22 2.23e+22 4.68e+22 2.57e+23 4.68e+22 3.11e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220712072458/index.html |
STK = 70 DIP = 10 RAKE = -35 MW = 4.89 HS = 72.0
The NDK file is 20220712072458.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution ENS 2022/07/12 07:24:58:0 60.97 -150.95 68.5 4.8 Alaska Stations used: AK.CAPN AK.FID AK.FIRE AK.GHO AK.GLI AK.HIN AK.K20K AK.KNK AK.M19K AK.N18K AK.N19K AK.P23K AK.Q19K AK.RC01 AK.SAW AK.SCM AK.SKN AK.SSN AK.SWD AV.ILS AV.RED AV.SPCP 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 0.08 n 3 Best Fitting Double Couple Mo = 2.72e+23 dyne-cm Mw = 4.89 Z = 72 km Plane Strike Dip Rake NP1 195 84 -98 NP2 70 10 -35 Principal Axes: Axis Value Plunge Azimuth T 2.72e+23 39 292 N 0.00e+00 8 195 P -2.72e+23 50 96 Moment Tensor: (dyne-cm) Component Value Mxx 2.23e+22 Mxy -4.68e+22 Mxz 6.28e+22 Myy 3.11e+22 Myz -2.57e+23 Mzz -5.34e+22 ############-- ###############------- #################----------- ##################------------ ###################--------------- ###################----------------- ####################------------------ ####### ##########-------------------- ####### T ##########-------------------- ######## #########---------------------# ####################--------- ---------# ###################---------- P ---------# ###################---------- ---------# #################----------------------# #################---------------------## ################---------------------# ##############--------------------## -############-------------------## -##########-----------------## --#######----------------### ---###------------#### --############ Global CMT Convention Moment Tensor: R T P -5.34e+22 6.28e+22 2.57e+23 6.28e+22 2.23e+22 4.68e+22 2.57e+23 4.68e+22 3.11e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220712072458/index.html |
-phase Moment Tensor (Mww) Moment 2.062e+16 N-m Magnitude 4.81 Mww Depth 60.5 km Percent DC 67% Half Duration 0.66 s Catalog US Data Source US 3 Contributor US 3 Nodal Planes Plane Strike Dip Rake NP1 350 11 -110 NP2 191 80 -86 Principal Axes Axis Value Plunge Azimuth T 2.222e+16 N-m 35 278 N -0.371e+16 N-m 4 10 P -1.851e+16 N-m 55 106 |
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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.
Right: Residuals from new relation as a function of distance and azimuth.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 2.0 125 65 15 4.07 0.2505 WVFGRD96 4.0 120 80 -5 4.17 0.2928 WVFGRD96 6.0 120 75 -5 4.24 0.3086 WVFGRD96 8.0 280 90 -5 4.32 0.3225 WVFGRD96 10.0 100 70 -5 4.35 0.3194 WVFGRD96 12.0 100 70 -5 4.37 0.3177 WVFGRD96 14.0 100 70 5 4.39 0.3168 WVFGRD96 16.0 100 70 5 4.41 0.3200 WVFGRD96 18.0 100 65 5 4.42 0.3253 WVFGRD96 20.0 100 65 5 4.44 0.3324 WVFGRD96 22.0 100 60 5 4.46 0.3386 WVFGRD96 24.0 100 60 10 4.48 0.3480 WVFGRD96 26.0 105 55 10 4.49 0.3602 WVFGRD96 28.0 105 55 10 4.52 0.3747 WVFGRD96 30.0 105 50 10 4.53 0.3887 WVFGRD96 32.0 100 45 -5 4.55 0.4047 WVFGRD96 34.0 105 50 10 4.57 0.4186 WVFGRD96 36.0 110 50 15 4.58 0.4299 WVFGRD96 38.0 100 5 -25 4.56 0.4443 WVFGRD96 40.0 105 5 -20 4.73 0.4655 WVFGRD96 42.0 110 5 -15 4.74 0.4865 WVFGRD96 44.0 75 10 -40 4.75 0.5057 WVFGRD96 46.0 205 80 -90 4.76 0.5255 WVFGRD96 48.0 200 80 -90 4.77 0.5428 WVFGRD96 50.0 200 80 -90 4.79 0.5611 WVFGRD96 52.0 200 80 -90 4.80 0.5772 WVFGRD96 54.0 15 10 -95 4.81 0.5925 WVFGRD96 56.0 200 80 -90 4.82 0.6069 WVFGRD96 58.0 35 10 -70 4.83 0.6177 WVFGRD96 60.0 40 10 -65 4.84 0.6298 WVFGRD96 62.0 45 10 -60 4.85 0.6373 WVFGRD96 64.0 50 10 -55 4.86 0.6455 WVFGRD96 66.0 55 10 -50 4.87 0.6506 WVFGRD96 68.0 60 10 -45 4.87 0.6570 WVFGRD96 70.0 65 10 -40 4.88 0.6582 WVFGRD96 72.0 70 10 -35 4.89 0.6613 WVFGRD96 74.0 70 10 -35 4.90 0.6612 WVFGRD96 76.0 70 10 -35 4.90 0.6605 WVFGRD96 78.0 70 10 -35 4.91 0.6582 WVFGRD96 80.0 75 10 -30 4.91 0.6536 WVFGRD96 82.0 75 10 -30 4.92 0.6504 WVFGRD96 84.0 75 10 -30 4.92 0.6432 WVFGRD96 86.0 80 10 -25 4.92 0.6381 WVFGRD96 88.0 80 10 -25 4.93 0.6317 WVFGRD96 90.0 80 10 -25 4.93 0.6240 WVFGRD96 92.0 85 15 -20 4.94 0.6165 WVFGRD96 94.0 85 15 -20 4.94 0.6074 WVFGRD96 96.0 85 15 -20 4.94 0.5999 WVFGRD96 98.0 90 15 -15 4.95 0.5923
The best solution is
WVFGRD96 72.0 70 10 -35 4.89 0.6613
The mechanism corresponding 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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 0.08 n 3
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Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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