The ANSS event ID is ak024em2arnr and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak024em2arnr/executive.
2024/11/13 09:07:03 60.945 -147.361 16.2 4.5 Alaska
USGS/SLU Moment Tensor Solution ENS 2024/11/13 09:07:03:0 60.94 -147.36 16.2 4.5 Alaska Stations used: AK.BAE AK.BAT AK.BGLC AK.BRSE AK.EYAK AK.FID AK.GHO AK.GRIN AK.HIN AK.KHIT AK.KIAG AK.KNK AK.L22K AK.M23K AK.M26K AK.MCAR AK.P23K AK.PAX AK.PS11 AK.PS12 AK.PWL AK.SAW AK.SCM AK.SLK AK.SWD AK.VMT AK.VRDI AT.DORN AT.NSHR AT.PMR AV.N25K AV.STLK 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 = 3.31e+22 dyne-cm Mw = 4.28 Z = 30 km Plane Strike Dip Rake NP1 85 80 50 NP2 343 41 165 Principal Axes: Axis Value Plunge Azimuth T 3.31e+22 41 318 N 0.00e+00 39 93 P -3.31e+22 24 205 Moment Tensor: (dyne-cm) Component Value Mxx -1.22e+22 Mxy -1.99e+22 Mxz 2.34e+22 Myy 3.57e+21 Myz -5.76e+21 Mzz 8.68e+21 ###----------- ############---------- ##################---------- #####################--------- ########################---------- ######### ###############--------- ########## T ################--------- ########### #################--------- ###############################--------- #################################--------- #################################------### #################################-######## -------###########----------------######## ---------------------------------####### ---------------------------------####### -------------------------------####### ------------------------------###### --------- ----------------###### ------- P ----------------#### ------ ---------------#### -------------------### -------------# Global CMT Convention Moment Tensor: R T P 8.68e+21 2.34e+22 5.76e+21 2.34e+22 -1.22e+22 1.99e+22 5.76e+21 1.99e+22 3.57e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20241113090703/index.html |
STK = 85 DIP = 80 RAKE = 50 MW = 4.28 HS = 30.0
The NDK file is 20241113090703.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 2024/11/13 09:07:03:0 60.94 -147.36 16.2 4.5 Alaska Stations used: AK.BAE AK.BAT AK.BGLC AK.BRSE AK.EYAK AK.FID AK.GHO AK.GRIN AK.HIN AK.KHIT AK.KIAG AK.KNK AK.L22K AK.M23K AK.M26K AK.MCAR AK.P23K AK.PAX AK.PS11 AK.PS12 AK.PWL AK.SAW AK.SCM AK.SLK AK.SWD AK.VMT AK.VRDI AT.DORN AT.NSHR AT.PMR AV.N25K AV.STLK 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 = 3.31e+22 dyne-cm Mw = 4.28 Z = 30 km Plane Strike Dip Rake NP1 85 80 50 NP2 343 41 165 Principal Axes: Axis Value Plunge Azimuth T 3.31e+22 41 318 N 0.00e+00 39 93 P -3.31e+22 24 205 Moment Tensor: (dyne-cm) Component Value Mxx -1.22e+22 Mxy -1.99e+22 Mxz 2.34e+22 Myy 3.57e+21 Myz -5.76e+21 Mzz 8.68e+21 ###----------- ############---------- ##################---------- #####################--------- ########################---------- ######### ###############--------- ########## T ################--------- ########### #################--------- ###############################--------- #################################--------- #################################------### #################################-######## -------###########----------------######## ---------------------------------####### ---------------------------------####### -------------------------------####### ------------------------------###### --------- ----------------###### ------- P ----------------#### ------ ---------------#### -------------------### -------------# Global CMT Convention Moment Tensor: R T P 8.68e+21 2.34e+22 5.76e+21 2.34e+22 -1.22e+22 1.99e+22 5.76e+21 1.99e+22 3.57e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20241113090703/index.html |
Regional Moment Tensor (Mwr) Moment 3.943e+15 N-m Magnitude 4.33 Mwr Depth 33.0 km Percent DC 88% Half Duration - Catalog US Data Source US 3 Contributor US 3 Nodal Planes Plane Strike Dip Rake NP1 344 40 168 NP2 83 82 51 Principal Axes Axis Value Plunge Azimuth T 4.054e+15 40 317 N -0.234e+15 39 90 P -3.821e+15 26 203 |
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 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 20 50 55 3.52 0.1762 WVFGRD96 2.0 25 50 65 3.69 0.2432 WVFGRD96 3.0 10 55 40 3.72 0.2420 WVFGRD96 4.0 340 50 -25 3.74 0.2524 WVFGRD96 5.0 345 55 -20 3.77 0.2744 WVFGRD96 6.0 345 55 -20 3.80 0.2932 WVFGRD96 7.0 345 55 -15 3.82 0.3101 WVFGRD96 8.0 345 50 -15 3.89 0.3248 WVFGRD96 9.0 90 70 45 3.92 0.3435 WVFGRD96 10.0 90 70 45 3.95 0.3670 WVFGRD96 11.0 85 75 40 3.96 0.3893 WVFGRD96 12.0 85 75 40 3.99 0.4102 WVFGRD96 13.0 85 75 40 4.01 0.4307 WVFGRD96 14.0 85 75 40 4.03 0.4506 WVFGRD96 15.0 85 75 40 4.05 0.4699 WVFGRD96 16.0 85 75 40 4.07 0.4891 WVFGRD96 17.0 85 75 40 4.09 0.5081 WVFGRD96 18.0 85 75 40 4.11 0.5270 WVFGRD96 19.0 85 75 40 4.13 0.5456 WVFGRD96 20.0 85 75 40 4.14 0.5638 WVFGRD96 21.0 85 75 45 4.17 0.5819 WVFGRD96 22.0 85 80 45 4.18 0.5989 WVFGRD96 23.0 85 80 45 4.20 0.6163 WVFGRD96 24.0 85 80 45 4.21 0.6321 WVFGRD96 25.0 85 80 50 4.23 0.6474 WVFGRD96 26.0 85 80 50 4.24 0.6609 WVFGRD96 27.0 85 80 50 4.25 0.6718 WVFGRD96 28.0 85 80 50 4.26 0.6795 WVFGRD96 29.0 85 80 50 4.27 0.6850 WVFGRD96 30.0 85 80 50 4.28 0.6862 WVFGRD96 31.0 85 80 55 4.29 0.6857 WVFGRD96 32.0 85 80 55 4.30 0.6829 WVFGRD96 33.0 85 80 55 4.30 0.6769 WVFGRD96 34.0 85 80 55 4.31 0.6705 WVFGRD96 35.0 85 80 55 4.31 0.6619 WVFGRD96 36.0 85 80 50 4.31 0.6545 WVFGRD96 37.0 85 80 50 4.31 0.6470 WVFGRD96 38.0 85 80 50 4.32 0.6399 WVFGRD96 39.0 85 80 45 4.32 0.6334 WVFGRD96 40.0 85 80 60 4.43 0.6235 WVFGRD96 41.0 85 80 55 4.42 0.6229 WVFGRD96 42.0 85 80 55 4.43 0.6198 WVFGRD96 43.0 85 80 55 4.43 0.6146 WVFGRD96 44.0 85 80 55 4.44 0.6091 WVFGRD96 45.0 85 80 50 4.43 0.6044 WVFGRD96 46.0 85 80 50 4.44 0.5984 WVFGRD96 47.0 85 75 50 4.45 0.5930 WVFGRD96 48.0 85 75 50 4.45 0.5884 WVFGRD96 49.0 85 75 45 4.45 0.5828 WVFGRD96 50.0 85 75 45 4.45 0.5791 WVFGRD96 51.0 85 75 45 4.46 0.5743 WVFGRD96 52.0 85 75 45 4.46 0.5689 WVFGRD96 53.0 85 75 45 4.46 0.5639 WVFGRD96 54.0 85 75 45 4.47 0.5579 WVFGRD96 55.0 85 75 45 4.47 0.5528 WVFGRD96 56.0 85 75 45 4.47 0.5452 WVFGRD96 57.0 85 75 45 4.47 0.5394 WVFGRD96 58.0 85 75 45 4.48 0.5324 WVFGRD96 59.0 85 75 40 4.47 0.5268
The best solution is
WVFGRD96 30.0 85 80 50 4.28 0.6862
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 0.10 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