The ANSS event ID is ak014fb2i27g and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak014fb2i27g/executive.
2014/11/29 21:06:49 62.544 -148.058 62.1 4.6 Alaska
USGS/SLU Moment Tensor Solution ENS 2014/11/29 21:06:49:0 62.54 -148.06 62.1 4.6 Alaska Stations used: AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CNP AK.CRQ AK.CTG AK.DHY AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT AK.ISLE AK.KLU AK.KNK AK.KTH AK.MDM AK.MESA AK.PAX AK.PPLA AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.SUCK AK.SWD AK.TGL AK.TRF AK.WRH AK.YAH AT.PMR AT.TTA CN.HYT IM.IL31 IU.COLA TA.I23K TA.M24K TA.N25K TA.POKR US.EGAK Filtering commands used: cut o DIST/3.3 -50 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.19e+23 dyne-cm Mw = 4.65 Z = 74 km Plane Strike Dip Rake NP1 220 73 -148 NP2 120 60 -20 Principal Axes: Axis Value Plunge Azimuth T 1.19e+23 8 348 N 0.00e+00 54 246 P -1.19e+23 34 84 Moment Tensor: (dyne-cm) Component Value Mxx 1.10e+23 Mxy -3.31e+22 Mxz 1.03e+22 Myy -7.50e+22 Myz -5.85e+22 Mzz -3.52e+22 # T ########## ##### ############## ###########################- ########################------ #######################----------- ######################-------------- --###################----------------- ---#################-------------------- ----##############---------------------- ------############--------------- ------ --------########----------------- P ------ ----------#####------------------ ------ ------------#----------------------------- -----------##--------------------------- ----------######------------------------ --------###########------------------- ------#################------------- -----############################# --############################ -########################### ###################### ############## Global CMT Convention Moment Tensor: R T P -3.52e+22 1.03e+22 5.85e+22 1.03e+22 1.10e+23 3.31e+22 5.85e+22 3.31e+22 -7.50e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141129210649/index.html |
STK = 120 DIP = 60 RAKE = -20 MW = 4.65 HS = 74.0
The NDK file is 20141129210649.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 2014/11/29 21:06:49:0 62.54 -148.06 62.1 4.6 Alaska Stations used: AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CNP AK.CRQ AK.CTG AK.DHY AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT AK.ISLE AK.KLU AK.KNK AK.KTH AK.MDM AK.MESA AK.PAX AK.PPLA AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.SUCK AK.SWD AK.TGL AK.TRF AK.WRH AK.YAH AT.PMR AT.TTA CN.HYT IM.IL31 IU.COLA TA.I23K TA.M24K TA.N25K TA.POKR US.EGAK Filtering commands used: cut o DIST/3.3 -50 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.19e+23 dyne-cm Mw = 4.65 Z = 74 km Plane Strike Dip Rake NP1 220 73 -148 NP2 120 60 -20 Principal Axes: Axis Value Plunge Azimuth T 1.19e+23 8 348 N 0.00e+00 54 246 P -1.19e+23 34 84 Moment Tensor: (dyne-cm) Component Value Mxx 1.10e+23 Mxy -3.31e+22 Mxz 1.03e+22 Myy -7.50e+22 Myz -5.85e+22 Mzz -3.52e+22 # T ########## ##### ############## ###########################- ########################------ #######################----------- ######################-------------- --###################----------------- ---#################-------------------- ----##############---------------------- ------############--------------- ------ --------########----------------- P ------ ----------#####------------------ ------ ------------#----------------------------- -----------##--------------------------- ----------######------------------------ --------###########------------------- ------#################------------- -----############################# --############################ -########################### ###################### ############## Global CMT Convention Moment Tensor: R T P -3.52e+22 1.03e+22 5.85e+22 1.03e+22 1.10e+23 3.31e+22 5.85e+22 3.31e+22 -7.50e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141129210649/index.html |
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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 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 2.0 225 60 45 3.90 0.2799 WVFGRD96 4.0 290 55 -35 3.97 0.2928 WVFGRD96 6.0 295 70 -20 3.99 0.3268 WVFGRD96 8.0 295 70 -20 4.05 0.3567 WVFGRD96 10.0 110 70 -20 4.09 0.3687 WVFGRD96 12.0 125 65 25 4.11 0.3794 WVFGRD96 14.0 125 65 25 4.13 0.3905 WVFGRD96 16.0 125 70 25 4.15 0.4008 WVFGRD96 18.0 125 70 20 4.17 0.4098 WVFGRD96 20.0 305 70 20 4.19 0.4219 WVFGRD96 22.0 305 70 20 4.21 0.4342 WVFGRD96 24.0 305 75 20 4.23 0.4452 WVFGRD96 26.0 305 75 20 4.25 0.4557 WVFGRD96 28.0 120 75 -15 4.27 0.4684 WVFGRD96 30.0 120 75 -15 4.29 0.4821 WVFGRD96 32.0 120 75 -15 4.31 0.4937 WVFGRD96 34.0 115 75 -20 4.33 0.5068 WVFGRD96 36.0 115 75 -20 4.36 0.5203 WVFGRD96 38.0 120 80 -15 4.39 0.5340 WVFGRD96 40.0 115 65 -20 4.45 0.5469 WVFGRD96 42.0 115 65 -20 4.47 0.5549 WVFGRD96 44.0 115 65 -25 4.49 0.5656 WVFGRD96 46.0 115 65 -20 4.51 0.5809 WVFGRD96 48.0 115 60 -25 4.53 0.5976 WVFGRD96 50.0 115 60 -25 4.54 0.6169 WVFGRD96 52.0 115 60 -25 4.56 0.6358 WVFGRD96 54.0 115 60 -25 4.57 0.6531 WVFGRD96 56.0 115 60 -25 4.59 0.6699 WVFGRD96 58.0 115 60 -25 4.60 0.6850 WVFGRD96 60.0 115 55 -30 4.61 0.6982 WVFGRD96 62.0 115 55 -30 4.62 0.7109 WVFGRD96 64.0 115 55 -30 4.63 0.7196 WVFGRD96 66.0 115 55 -30 4.64 0.7258 WVFGRD96 68.0 115 55 -25 4.64 0.7300 WVFGRD96 70.0 115 55 -25 4.65 0.7325 WVFGRD96 72.0 120 60 -20 4.65 0.7336 WVFGRD96 74.0 120 60 -20 4.65 0.7347 WVFGRD96 76.0 120 60 -20 4.66 0.7338 WVFGRD96 78.0 120 60 -20 4.66 0.7315 WVFGRD96 80.0 120 60 -20 4.66 0.7279 WVFGRD96 82.0 120 60 -20 4.66 0.7237 WVFGRD96 84.0 120 60 -20 4.66 0.7189 WVFGRD96 86.0 120 60 -15 4.67 0.7140 WVFGRD96 88.0 120 60 -15 4.67 0.7095 WVFGRD96 90.0 120 60 -15 4.67 0.7041 WVFGRD96 92.0 120 65 -15 4.67 0.6989 WVFGRD96 94.0 125 65 -10 4.68 0.6936 WVFGRD96 96.0 125 65 -10 4.68 0.6899 WVFGRD96 98.0 125 65 -10 4.68 0.6860
The best solution is
WVFGRD96 74.0 120 60 -20 4.65 0.7347
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 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.06 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