The ANSS event ID is ak02556vvgv8 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak02556vvgv8/executive.
2025/04/23 00:24:51 61.807 -150.061 26.1 4.5 Alaska
USGS/SLU Moment Tensor Solution ENS 2025/04/23 00:24:51:0 61.81 -150.06 26.1 4.5 Alaska Stations used: AK.BAE AK.BMR AK.BPAW AK.CAPN AK.CAST AK.FID AK.FIRE AK.GHO AK.HIN AK.KNK AK.L22K AK.MCK AK.O19K AK.PAX AK.PWL AK.RAG AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SLK AK.SSN AK.SWD AT.PMR AT.TTA AV.RED AV.SPCL AV.STLK Filtering commands used: cut o DIST/3.5 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 5.75e+22 dyne-cm Mw = 4.44 Z = 46 km Plane Strike Dip Rake NP1 30 65 -50 NP2 147 46 -144 Principal Axes: Axis Value Plunge Azimuth T 5.75e+22 11 92 N 0.00e+00 36 190 P -5.75e+22 52 348 Moment Tensor: (dyne-cm) Component Value Mxx -2.06e+22 Mxy 2.14e+21 Mxz -2.77e+22 Myy 5.44e+22 Myz 1.67e+22 Mzz -3.38e+22 -------------- ---------------------# ##-----------------------### ##------------------------#### ####--------- ------------###### ####---------- P -----------######## #####---------- -----------######### ######------------------------########## #######----------------------########### ########---------------------############# ########---------------------######### # #########-------------------########## T # ##########-----------------########### # ##########---------------############### ###########------------################# ###########----------################# ############-------################# #############---################## ############--################ ########--------############ ##-------------------- -------------- Global CMT Convention Moment Tensor: R T P -3.38e+22 -2.77e+22 -1.67e+22 -2.77e+22 -2.06e+22 -2.14e+21 -1.67e+22 -2.14e+21 5.44e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250423002451/index.html |
STK = 30 DIP = 65 RAKE = -50 MW = 4.44 HS = 46.0
The NDK file is 20250423002451.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 2025/04/23 00:24:51:0 61.81 -150.06 26.1 4.5 Alaska Stations used: AK.BAE AK.BMR AK.BPAW AK.CAPN AK.CAST AK.FID AK.FIRE AK.GHO AK.HIN AK.KNK AK.L22K AK.MCK AK.O19K AK.PAX AK.PWL AK.RAG AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SLK AK.SSN AK.SWD AT.PMR AT.TTA AV.RED AV.SPCL AV.STLK Filtering commands used: cut o DIST/3.5 -40 o DIST/3.5 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 5.75e+22 dyne-cm Mw = 4.44 Z = 46 km Plane Strike Dip Rake NP1 30 65 -50 NP2 147 46 -144 Principal Axes: Axis Value Plunge Azimuth T 5.75e+22 11 92 N 0.00e+00 36 190 P -5.75e+22 52 348 Moment Tensor: (dyne-cm) Component Value Mxx -2.06e+22 Mxy 2.14e+21 Mxz -2.77e+22 Myy 5.44e+22 Myz 1.67e+22 Mzz -3.38e+22 -------------- ---------------------# ##-----------------------### ##------------------------#### ####--------- ------------###### ####---------- P -----------######## #####---------- -----------######### ######------------------------########## #######----------------------########### ########---------------------############# ########---------------------######### # #########-------------------########## T # ##########-----------------########### # ##########---------------############### ###########------------################# ###########----------################# ############-------################# #############---################## ############--################ ########--------############ ##-------------------- -------------- Global CMT Convention Moment Tensor: R T P -3.38e+22 -2.77e+22 -1.67e+22 -2.77e+22 -2.06e+22 -2.14e+21 -1.67e+22 -2.14e+21 5.44e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250423002451/index.html |
Regional Moment Tensor (Mwr) Moment 6.556e+15 N-m Magnitude 4.48 Mwr Depth 51.0 km Percent DC 90% Half Duration - Catalog US Data Source US Contributor US Nodal Planes Plane Strike Dip Rake NP1 21 51 -63 NP2 162 47 -119 Principal Axes Axis Value Plunge Azimuth T 6.714e+15 2 92 N -0.328e+15 21 183 P -6.386e+15 69 356 |
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/3.5 -40 o DIST/3.5 +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 1.0 145 50 40 3.58 0.1482 WVFGRD96 2.0 340 45 70 3.76 0.1951 WVFGRD96 3.0 320 55 30 3.76 0.1908 WVFGRD96 4.0 125 50 -10 3.78 0.2032 WVFGRD96 5.0 125 55 -15 3.81 0.2190 WVFGRD96 6.0 125 55 -15 3.84 0.2310 WVFGRD96 7.0 125 60 -20 3.87 0.2397 WVFGRD96 8.0 125 55 -15 3.92 0.2431 WVFGRD96 9.0 50 65 35 3.95 0.2481 WVFGRD96 10.0 50 65 30 3.98 0.2563 WVFGRD96 11.0 50 65 30 4.00 0.2630 WVFGRD96 12.0 50 65 30 4.01 0.2682 WVFGRD96 13.0 50 65 30 4.03 0.2717 WVFGRD96 14.0 215 70 -30 4.04 0.2771 WVFGRD96 15.0 215 70 -25 4.06 0.2813 WVFGRD96 16.0 215 70 -25 4.08 0.2844 WVFGRD96 17.0 215 70 -25 4.09 0.2872 WVFGRD96 18.0 215 70 -25 4.10 0.2895 WVFGRD96 19.0 215 70 -25 4.11 0.2911 WVFGRD96 20.0 215 70 -25 4.13 0.2916 WVFGRD96 21.0 215 70 -25 4.14 0.2913 WVFGRD96 22.0 215 70 -25 4.15 0.2902 WVFGRD96 23.0 220 75 -20 4.16 0.2888 WVFGRD96 24.0 225 80 25 4.18 0.2922 WVFGRD96 25.0 225 75 25 4.19 0.2977 WVFGRD96 26.0 225 80 30 4.20 0.3043 WVFGRD96 27.0 40 80 -30 4.20 0.3095 WVFGRD96 28.0 40 80 -30 4.21 0.3187 WVFGRD96 29.0 40 80 -30 4.22 0.3300 WVFGRD96 30.0 40 80 -35 4.23 0.3407 WVFGRD96 31.0 40 75 -35 4.24 0.3515 WVFGRD96 32.0 40 75 -35 4.25 0.3639 WVFGRD96 33.0 40 75 -35 4.26 0.3745 WVFGRD96 34.0 35 70 -40 4.27 0.3857 WVFGRD96 35.0 35 70 -40 4.28 0.3936 WVFGRD96 36.0 35 70 -40 4.29 0.4016 WVFGRD96 37.0 35 70 -40 4.29 0.4068 WVFGRD96 38.0 35 70 -40 4.30 0.4119 WVFGRD96 39.0 35 70 -35 4.32 0.4168 WVFGRD96 40.0 35 70 -45 4.39 0.4225 WVFGRD96 41.0 35 70 -45 4.40 0.4274 WVFGRD96 42.0 35 70 -45 4.41 0.4289 WVFGRD96 43.0 30 65 -50 4.42 0.4326 WVFGRD96 44.0 30 65 -50 4.43 0.4347 WVFGRD96 45.0 30 65 -50 4.43 0.4350 WVFGRD96 46.0 30 65 -50 4.44 0.4364 WVFGRD96 47.0 30 65 -50 4.45 0.4359 WVFGRD96 48.0 30 65 -50 4.45 0.4348 WVFGRD96 49.0 30 65 -50 4.45 0.4344 WVFGRD96 50.0 30 60 -45 4.46 0.4316 WVFGRD96 51.0 30 60 -45 4.46 0.4319 WVFGRD96 52.0 30 60 -45 4.47 0.4292 WVFGRD96 53.0 30 60 -45 4.47 0.4292 WVFGRD96 54.0 30 65 -45 4.47 0.4266 WVFGRD96 55.0 30 65 -45 4.47 0.4260 WVFGRD96 56.0 30 65 -45 4.47 0.4233 WVFGRD96 57.0 30 65 -45 4.47 0.4224 WVFGRD96 58.0 30 65 -45 4.47 0.4195 WVFGRD96 59.0 35 70 -45 4.48 0.4190
The best solution is
WVFGRD96 46.0 30 65 -50 4.44 0.4364
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/3.5 -40 o DIST/3.5 +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