The ANSS event ID is ak0198go5nyc and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0198go5nyc/executive.
2019/07/03 22:29:26 60.326 -151.305 61.0 4.7 Alaska
USGS/SLU Moment Tensor Solution ENS 2019/07/03 22:29:26:0 60.33 -151.30 61.0 4.7 Alaska Stations used: AK.BRLK AK.CAPN AK.CNP AK.DIV AK.EYAK AK.FIRE AK.GHO AK.HIN AK.HOM AK.KLU AK.KNK AK.PPLA AK.PWL AK.RC01 AK.SKN AK.SLK AK.SWD AT.PMR AV.ILSW AV.RED AV.SPU AV.STLK II.KDAK TA.K20K TA.L19K TA.M20K TA.M24K TA.N19K TA.O18K TA.O19K TA.O22K TA.P18K TA.P19K TA.P23K TA.Q19K 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 = 1.27e+23 dyne-cm Mw = 4.67 Z = 76 km Plane Strike Dip Rake NP1 324 76 154 NP2 60 65 15 Principal Axes: Axis Value Plunge Azimuth T 1.27e+23 28 280 N 0.00e+00 61 118 P -1.27e+23 8 14 Moment Tensor: (dyne-cm) Component Value Mxx -1.15e+23 Mxy -4.48e+22 Mxz -7.65e+21 Myy 9.02e+22 Myz -5.56e+22 Mzz 2.52e+22 ---------- P - -------------- ----- ###------------------------- #######----------------------- ###########----------------------- ##############---------------------- #################-------------------## ###################-----------------#### ### ###############--------------##### #### T ################-----------######## #### ##################--------######### ##########################-----########### ###########################-############## #########################--############# #####################-------############ ################------------########## #########-------------------######## ----------------------------###### ---------------------------### --------------------------## ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 2.52e+22 -7.65e+21 5.56e+22 -7.65e+21 -1.15e+23 4.48e+22 5.56e+22 4.48e+22 9.02e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190703222926/index.html |
STK = 60 DIP = 65 RAKE = 15 MW = 4.67 HS = 76.0
The NDK file is 20190703222926.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 2019/07/03 22:29:26:0 60.33 -151.30 61.0 4.7 Alaska Stations used: AK.BRLK AK.CAPN AK.CNP AK.DIV AK.EYAK AK.FIRE AK.GHO AK.HIN AK.HOM AK.KLU AK.KNK AK.PPLA AK.PWL AK.RC01 AK.SKN AK.SLK AK.SWD AT.PMR AV.ILSW AV.RED AV.SPU AV.STLK II.KDAK TA.K20K TA.L19K TA.M20K TA.M24K TA.N19K TA.O18K TA.O19K TA.O22K TA.P18K TA.P19K TA.P23K TA.Q19K 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 = 1.27e+23 dyne-cm Mw = 4.67 Z = 76 km Plane Strike Dip Rake NP1 324 76 154 NP2 60 65 15 Principal Axes: Axis Value Plunge Azimuth T 1.27e+23 28 280 N 0.00e+00 61 118 P -1.27e+23 8 14 Moment Tensor: (dyne-cm) Component Value Mxx -1.15e+23 Mxy -4.48e+22 Mxz -7.65e+21 Myy 9.02e+22 Myz -5.56e+22 Mzz 2.52e+22 ---------- P - -------------- ----- ###------------------------- #######----------------------- ###########----------------------- ##############---------------------- #################-------------------## ###################-----------------#### ### ###############--------------##### #### T ################-----------######## #### ##################--------######### ##########################-----########### ###########################-############## #########################--############# #####################-------############ ################------------########## #########-------------------######## ----------------------------###### ---------------------------### --------------------------## ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 2.52e+22 -7.65e+21 5.56e+22 -7.65e+21 -1.15e+23 4.48e+22 5.56e+22 4.48e+22 9.02e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190703222926/index.html |
Regional Moment Tensor (Mwr) Moment 1.137e+16 N-m Magnitude 4.64 Mwr Depth 67.0 km Percent DC 82% Half Duration - Catalog US Data Source US 3 Contributor US 3 Nodal Planes Plane Strike Dip Rake NP1 330 79 159 NP2 64 69 12 Principal Axes Axis Value Plunge Azimuth T 1.186e+16 N-m 23 286 N -0.106e+16 N-m 66 125 P -1.081e+16 N-m 7 19 |
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 2.0 315 55 -50 3.85 0.2396 WVFGRD96 4.0 140 90 15 3.89 0.2613 WVFGRD96 6.0 325 70 20 3.97 0.2829 WVFGRD96 8.0 340 55 15 4.04 0.3061 WVFGRD96 10.0 340 60 15 4.08 0.3184 WVFGRD96 12.0 340 65 15 4.11 0.3216 WVFGRD96 14.0 335 75 15 4.14 0.3162 WVFGRD96 16.0 245 75 20 4.18 0.3213 WVFGRD96 18.0 245 75 10 4.20 0.3321 WVFGRD96 20.0 245 75 5 4.23 0.3453 WVFGRD96 22.0 245 75 0 4.25 0.3614 WVFGRD96 24.0 245 75 0 4.28 0.3766 WVFGRD96 26.0 245 80 0 4.29 0.3878 WVFGRD96 28.0 245 80 5 4.31 0.3956 WVFGRD96 30.0 245 75 -5 4.32 0.4010 WVFGRD96 32.0 65 85 0 4.33 0.4076 WVFGRD96 34.0 65 75 0 4.35 0.4210 WVFGRD96 36.0 65 75 -5 4.37 0.4369 WVFGRD96 38.0 55 75 5 4.42 0.4589 WVFGRD96 40.0 55 70 15 4.49 0.4907 WVFGRD96 42.0 55 70 15 4.52 0.5000 WVFGRD96 44.0 55 70 15 4.54 0.5063 WVFGRD96 46.0 55 70 15 4.56 0.5138 WVFGRD96 48.0 55 70 10 4.57 0.5221 WVFGRD96 50.0 55 70 15 4.58 0.5316 WVFGRD96 52.0 55 70 15 4.60 0.5422 WVFGRD96 54.0 60 65 15 4.60 0.5552 WVFGRD96 56.0 60 65 15 4.61 0.5671 WVFGRD96 58.0 60 65 15 4.62 0.5775 WVFGRD96 60.0 60 65 15 4.63 0.5876 WVFGRD96 62.0 60 65 15 4.63 0.5945 WVFGRD96 64.0 60 65 15 4.64 0.6023 WVFGRD96 66.0 60 65 15 4.65 0.6070 WVFGRD96 68.0 60 65 15 4.65 0.6121 WVFGRD96 70.0 60 65 15 4.66 0.6156 WVFGRD96 72.0 60 65 15 4.66 0.6185 WVFGRD96 74.0 60 65 15 4.67 0.6206 WVFGRD96 76.0 60 65 15 4.67 0.6226 WVFGRD96 78.0 60 65 15 4.68 0.6221 WVFGRD96 80.0 60 65 15 4.68 0.6218 WVFGRD96 82.0 60 65 15 4.69 0.6208 WVFGRD96 84.0 60 65 15 4.69 0.6189 WVFGRD96 86.0 60 65 15 4.69 0.6179 WVFGRD96 88.0 60 65 15 4.70 0.6150 WVFGRD96 90.0 60 65 15 4.70 0.6109 WVFGRD96 92.0 60 65 15 4.70 0.6087 WVFGRD96 94.0 60 65 15 4.71 0.6052 WVFGRD96 96.0 60 70 20 4.70 0.6012 WVFGRD96 98.0 60 70 20 4.71 0.5986
The best solution is
WVFGRD96 76.0 60 65 15 4.67 0.6226
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