The ANSS event ID is ak022djyj1sr and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak022djyj1sr/executive.
2022/10/22 05:02:35 61.818 -151.101 68.3 4.4 Alaska
USGS/SLU Moment Tensor Solution ENS 2022/10/22 05:02:35:0 61.82 -151.10 68.3 4.4 Alaska Stations used: AK.CAST AK.CUT AK.DHY AK.DIV AK.FID AK.GHO AK.GLI AK.K20K AK.KNK AK.KTH AK.L19K AK.L20K AK.L22K AK.N19K AK.O19K AK.RC01 AK.SAW AK.SCM AK.SLK AK.SSN AT.PMR AV.RED AV.SPCP AV.STLK Filtering commands used: cut o DIST/3.3 -50 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 4.84e+22 dyne-cm Mw = 4.39 Z = 74 km Plane Strike Dip Rake NP1 185 70 -80 NP2 338 22 -116 Principal Axes: Axis Value Plunge Azimuth T 4.84e+22 24 267 N 0.00e+00 9 2 P -4.84e+22 64 111 Moment Tensor: (dyne-cm) Component Value Mxx -1.14e+21 Mxy 5.12e+21 Mxz 6.05e+21 Myy 3.18e+22 Myz -3.61e+22 Mzz -3.06e+22 #####---###### ###########----####### #############---------###### #############------------##### ##############---------------##### ###############----------------##### ###############------------------##### ################-------------------##### ###############---------------------#### ################---------------------##### #### #########----------------------#### #### T #########---------- ---------#### #### #########---------- P ---------#### ###############---------- ---------### ###############---------------------#### ##############---------------------### #############--------------------### ############-------------------### ###########-----------------## ##########----------------## ########-------------# #####--------- Global CMT Convention Moment Tensor: R T P -3.06e+22 6.05e+21 3.61e+22 6.05e+21 -1.14e+21 -5.12e+21 3.61e+22 -5.12e+21 3.18e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20221022050235/index.html |
STK = 185 DIP = 70 RAKE = -80 MW = 4.39 HS = 74.0
The NDK file is 20221022050235.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 2022/10/22 05:02:35:0 61.82 -151.10 68.3 4.4 Alaska Stations used: AK.CAST AK.CUT AK.DHY AK.DIV AK.FID AK.GHO AK.GLI AK.K20K AK.KNK AK.KTH AK.L19K AK.L20K AK.L22K AK.N19K AK.O19K AK.RC01 AK.SAW AK.SCM AK.SLK AK.SSN AT.PMR AV.RED AV.SPCP AV.STLK Filtering commands used: cut o DIST/3.3 -50 o DIST/3.3 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 4.84e+22 dyne-cm Mw = 4.39 Z = 74 km Plane Strike Dip Rake NP1 185 70 -80 NP2 338 22 -116 Principal Axes: Axis Value Plunge Azimuth T 4.84e+22 24 267 N 0.00e+00 9 2 P -4.84e+22 64 111 Moment Tensor: (dyne-cm) Component Value Mxx -1.14e+21 Mxy 5.12e+21 Mxz 6.05e+21 Myy 3.18e+22 Myz -3.61e+22 Mzz -3.06e+22 #####---###### ###########----####### #############---------###### #############------------##### ##############---------------##### ###############----------------##### ###############------------------##### ################-------------------##### ###############---------------------#### ################---------------------##### #### #########----------------------#### #### T #########---------- ---------#### #### #########---------- P ---------#### ###############---------- ---------### ###############---------------------#### ##############---------------------### #############--------------------### ############-------------------### ###########-----------------## ##########----------------## ########-------------# #####--------- Global CMT Convention Moment Tensor: R T P -3.06e+22 6.05e+21 3.61e+22 6.05e+21 -1.14e+21 -5.12e+21 3.61e+22 -5.12e+21 3.18e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20221022050235/index.html |
Regional Moment Tensor (Mwr) Moment 5.377e+15 N-m Magnitude 4.42 Mwr Depth 76.0 km Percent DC 92% Half Duration - Catalog US Data Source US 3 Contributor US 3 Nodal Planes Plane Strike Dip Rake NP1 347 21 -98 NP2 175 70 -87 Principal Axes Axis Value Plunge Azimuth T 5.270e+15 N-m 25 263 N 0.209e+15 N-m 3 354 P -5.479e+15 N-m 65 91 |
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 -50 o DIST/3.3 +40 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 2.0 335 45 90 3.59 0.1931 WVFGRD96 4.0 5 55 -55 3.65 0.2073 WVFGRD96 6.0 35 40 5 3.67 0.2462 WVFGRD96 8.0 25 35 -15 3.76 0.2790 WVFGRD96 10.0 25 40 -20 3.79 0.3020 WVFGRD96 12.0 25 45 -15 3.81 0.3121 WVFGRD96 14.0 25 45 -15 3.83 0.3152 WVFGRD96 16.0 25 45 -15 3.85 0.3147 WVFGRD96 18.0 215 60 40 3.87 0.3148 WVFGRD96 20.0 210 60 35 3.89 0.3206 WVFGRD96 22.0 215 60 40 3.91 0.3253 WVFGRD96 24.0 210 65 35 3.93 0.3294 WVFGRD96 26.0 210 65 35 3.95 0.3322 WVFGRD96 28.0 40 50 35 3.99 0.3358 WVFGRD96 30.0 35 50 30 4.01 0.3391 WVFGRD96 32.0 35 50 25 4.02 0.3398 WVFGRD96 34.0 35 50 20 4.04 0.3435 WVFGRD96 36.0 30 55 20 4.05 0.3500 WVFGRD96 38.0 30 55 20 4.07 0.3565 WVFGRD96 40.0 350 30 -80 4.18 0.3798 WVFGRD96 42.0 160 60 -90 4.21 0.3980 WVFGRD96 44.0 165 60 -90 4.23 0.4129 WVFGRD96 46.0 165 60 -85 4.25 0.4255 WVFGRD96 48.0 175 60 -75 4.27 0.4382 WVFGRD96 50.0 170 65 -85 4.28 0.4574 WVFGRD96 52.0 170 65 -85 4.30 0.4759 WVFGRD96 54.0 175 65 -80 4.31 0.4949 WVFGRD96 56.0 180 65 -75 4.32 0.5129 WVFGRD96 58.0 180 65 -75 4.33 0.5306 WVFGRD96 60.0 180 65 -75 4.34 0.5443 WVFGRD96 62.0 180 65 -75 4.35 0.5552 WVFGRD96 64.0 180 65 -75 4.35 0.5643 WVFGRD96 66.0 180 65 -75 4.36 0.5710 WVFGRD96 68.0 185 65 -75 4.37 0.5758 WVFGRD96 70.0 185 65 -75 4.37 0.5778 WVFGRD96 72.0 185 70 -80 4.39 0.5798 WVFGRD96 74.0 185 70 -80 4.39 0.5816 WVFGRD96 76.0 185 70 -80 4.39 0.5815 WVFGRD96 78.0 185 70 -80 4.40 0.5803 WVFGRD96 80.0 185 70 -80 4.40 0.5778 WVFGRD96 82.0 180 70 -80 4.40 0.5738 WVFGRD96 84.0 185 70 -75 4.40 0.5691 WVFGRD96 86.0 185 70 -75 4.40 0.5627 WVFGRD96 88.0 185 70 -75 4.40 0.5572 WVFGRD96 90.0 185 70 -75 4.40 0.5498 WVFGRD96 92.0 185 70 -75 4.41 0.5432 WVFGRD96 94.0 180 65 -75 4.40 0.5375 WVFGRD96 96.0 180 65 -75 4.40 0.5319 WVFGRD96 98.0 180 65 -70 4.40 0.5272
The best solution is
WVFGRD96 74.0 185 70 -80 4.39 0.5816
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 -50 o DIST/3.3 +40 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