The ANSS event ID is ak0238gji26s and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0238gji26s/executive.
2023/07/03 14:47:29 61.289 -149.590 35.6 4.5 Alaska
USGS/SLU Moment Tensor Solution ENS 2023/07/03 14:47:29:0 61.29 -149.59 35.6 4.5 Alaska Stations used: AK.BARN AK.BMR AK.BPAW AK.CAST AK.CCB AK.CNP AK.CUT AK.DHY AK.DIV AK.EYAK AK.FID AK.FIRE AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HOM AK.I23K AK.J19K AK.J20K AK.J25K AK.K20K AK.K24K AK.KLU AK.KNK AK.L19K AK.L20K AK.L22K AK.M19K AK.M27K AK.MCAR AK.MCK AK.MLY AK.N18K AK.N19K AK.O18K AK.P23K AK.PAX AK.POKR AK.PPLA AK.PWL AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SLK AK.SWD AK.VRDI AK.WAT6 AK.WRH AT.PMR AV.SPCP AV.STLK IU.COLA Filtering commands used: cut o DIST/3.4 -40 o DIST/3.4 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 5.96e+22 dyne-cm Mw = 4.45 Z = 45 km Plane Strike Dip Rake NP1 190 60 -90 NP2 10 30 -90 Principal Axes: Axis Value Plunge Azimuth T 5.96e+22 15 280 N 0.00e+00 -0 190 P -5.96e+22 75 100 Moment Tensor: (dyne-cm) Component Value Mxx 1.56e+21 Mxy -8.82e+21 Mxz 5.17e+21 Myy 5.00e+22 Myz -2.93e+22 Mzz -5.16e+22 #########---## ###########--------### ############------------#### ############--------------#### #############----------------##### #############------------------##### #############--------------------##### ##############--------------------###### # #########----------------------##### ## T #########----------------------###### ## ########----------- ---------###### #############----------- P ---------###### #############----------- --------####### ############----------------------###### ############---------------------####### ###########---------------------###### ##########--------------------###### ##########-----------------####### ########----------------###### ########-------------####### ######----------###### ###-----###### Global CMT Convention Moment Tensor: R T P -5.16e+22 5.17e+21 2.93e+22 5.17e+21 1.56e+21 8.82e+21 2.93e+22 8.82e+21 5.00e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20230703144729/index.html |
STK = 10 DIP = 30 RAKE = -90 MW = 4.45 HS = 45.0
The NDK file is 20230703144729.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 2023/07/03 14:47:29:0 61.29 -149.59 35.6 4.5 Alaska Stations used: AK.BARN AK.BMR AK.BPAW AK.CAST AK.CCB AK.CNP AK.CUT AK.DHY AK.DIV AK.EYAK AK.FID AK.FIRE AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HOM AK.I23K AK.J19K AK.J20K AK.J25K AK.K20K AK.K24K AK.KLU AK.KNK AK.L19K AK.L20K AK.L22K AK.M19K AK.M27K AK.MCAR AK.MCK AK.MLY AK.N18K AK.N19K AK.O18K AK.P23K AK.PAX AK.POKR AK.PPLA AK.PWL AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SLK AK.SWD AK.VRDI AK.WAT6 AK.WRH AT.PMR AV.SPCP AV.STLK IU.COLA Filtering commands used: cut o DIST/3.4 -40 o DIST/3.4 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 5.96e+22 dyne-cm Mw = 4.45 Z = 45 km Plane Strike Dip Rake NP1 190 60 -90 NP2 10 30 -90 Principal Axes: Axis Value Plunge Azimuth T 5.96e+22 15 280 N 0.00e+00 -0 190 P -5.96e+22 75 100 Moment Tensor: (dyne-cm) Component Value Mxx 1.56e+21 Mxy -8.82e+21 Mxz 5.17e+21 Myy 5.00e+22 Myz -2.93e+22 Mzz -5.16e+22 #########---## ###########--------### ############------------#### ############--------------#### #############----------------##### #############------------------##### #############--------------------##### ##############--------------------###### # #########----------------------##### ## T #########----------------------###### ## ########----------- ---------###### #############----------- P ---------###### #############----------- --------####### ############----------------------###### ############---------------------####### ###########---------------------###### ##########--------------------###### ##########-----------------####### ########----------------###### ########-------------####### ######----------###### ###-----###### Global CMT Convention Moment Tensor: R T P -5.16e+22 5.17e+21 2.93e+22 5.17e+21 1.56e+21 8.82e+21 2.93e+22 8.82e+21 5.00e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20230703144729/index.html |
Regional Moment Tensor (Mwr) Moment 6.840e+15 N-m Magnitude 4.49 Mwr Depth 44.0 km Percent DC 95% Half Duration - Catalog US Data Source US 3 Contributor US 3 Nodal Planes Plane Strike Dip Rake NP1 12 28 -94 NP2 197 62 -88 Principal Axes Axis Value Plunge Azimuth T 6.922e+15 N-m 17 285 N -0.167e+15 N-m 2 16 P -6.755e+15 N-m 73 113 |
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/3.4 -40 o DIST/3.4 +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 1.0 180 50 90 3.63 0.1661 WVFGRD96 2.0 5 40 90 3.76 0.2164 WVFGRD96 3.0 185 55 85 3.83 0.2105 WVFGRD96 4.0 180 55 80 3.84 0.1976 WVFGRD96 5.0 95 30 -5 3.82 0.2121 WVFGRD96 6.0 100 30 5 3.83 0.2392 WVFGRD96 7.0 100 30 5 3.84 0.2616 WVFGRD96 8.0 105 25 15 3.91 0.2788 WVFGRD96 9.0 105 30 15 3.93 0.3002 WVFGRD96 10.0 105 30 15 3.94 0.3191 WVFGRD96 11.0 110 35 20 3.96 0.3361 WVFGRD96 12.0 110 35 20 3.97 0.3522 WVFGRD96 13.0 110 35 20 3.99 0.3658 WVFGRD96 14.0 110 35 20 4.00 0.3778 WVFGRD96 15.0 110 35 20 4.01 0.3879 WVFGRD96 16.0 110 35 20 4.03 0.3966 WVFGRD96 17.0 110 35 20 4.04 0.4038 WVFGRD96 18.0 110 40 15 4.06 0.4099 WVFGRD96 19.0 105 40 10 4.07 0.4162 WVFGRD96 20.0 105 40 10 4.09 0.4212 WVFGRD96 21.0 105 40 10 4.10 0.4247 WVFGRD96 22.0 105 40 10 4.12 0.4282 WVFGRD96 23.0 105 35 5 4.13 0.4307 WVFGRD96 24.0 65 35 -20 4.12 0.4365 WVFGRD96 25.0 65 35 -20 4.14 0.4474 WVFGRD96 26.0 65 35 -25 4.15 0.4582 WVFGRD96 27.0 65 35 -25 4.17 0.4689 WVFGRD96 28.0 60 35 -30 4.18 0.4793 WVFGRD96 29.0 55 30 -40 4.19 0.4919 WVFGRD96 30.0 50 25 -50 4.20 0.5049 WVFGRD96 31.0 45 25 -55 4.21 0.5192 WVFGRD96 32.0 40 25 -60 4.22 0.5330 WVFGRD96 33.0 35 25 -65 4.23 0.5475 WVFGRD96 34.0 30 25 -75 4.24 0.5609 WVFGRD96 35.0 10 25 -100 4.26 0.5753 WVFGRD96 36.0 10 25 -100 4.27 0.5892 WVFGRD96 37.0 10 25 -100 4.28 0.6003 WVFGRD96 38.0 5 25 -100 4.28 0.6087 WVFGRD96 39.0 5 30 -100 4.30 0.6179 WVFGRD96 40.0 195 65 -85 4.41 0.6205 WVFGRD96 41.0 195 65 -85 4.42 0.6255 WVFGRD96 42.0 10 25 -95 4.43 0.6284 WVFGRD96 43.0 190 60 -90 4.44 0.6289 WVFGRD96 44.0 10 30 -90 4.44 0.6294 WVFGRD96 45.0 10 30 -90 4.45 0.6305 WVFGRD96 46.0 10 30 -90 4.46 0.6279 WVFGRD96 47.0 10 30 -90 4.46 0.6254 WVFGRD96 48.0 190 60 -90 4.47 0.6209 WVFGRD96 49.0 10 30 -90 4.47 0.6155 WVFGRD96 50.0 10 30 -90 4.48 0.6090 WVFGRD96 51.0 190 60 -90 4.48 0.6008 WVFGRD96 52.0 15 30 -85 4.49 0.5936 WVFGRD96 53.0 15 30 -85 4.49 0.5839 WVFGRD96 54.0 190 60 -90 4.49 0.5743 WVFGRD96 55.0 15 30 -85 4.49 0.5647 WVFGRD96 56.0 20 30 -80 4.50 0.5530 WVFGRD96 57.0 15 30 -85 4.50 0.5431 WVFGRD96 58.0 15 30 -80 4.50 0.5313 WVFGRD96 59.0 15 30 -80 4.50 0.5201
The best solution is
WVFGRD96 45.0 10 30 -90 4.45 0.6305
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/3.4 -40 o DIST/3.4 +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