The ANSS event ID is us100078uz and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us100078uz/executive.
2016/11/16 14:25:35 59.613 -137.648 1.5 4.6 Alaska
USGS/SLU Moment Tensor Solution ENS 2016/11/16 14:25:35:0 59.61 -137.65 1.5 4.6 Alaska Stations used: AK.BARN AK.BCP AK.BESE AK.GLB AK.JIS AK.MCAR AK.MESA AK.PIN AK.TABL AK.VRDI AK.WAX AK.YAH AT.SIT AT.SKAG AT.YKU2 CN.HYT CN.WHY NY.FARO TA.L27K TA.M26K TA.M27K TA.M30M TA.M31M TA.N25K TA.N31M TA.P33M Filtering commands used: cut o DIST/3.3 -25 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.025 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 6.84e+22 dyne-cm Mw = 4.49 Z = 15 km Plane Strike Dip Rake NP1 348 54 127 NP2 115 50 50 Principal Axes: Axis Value Plunge Azimuth T 6.84e+22 60 318 N 0.00e+00 29 143 P -6.84e+22 2 52 Moment Tensor: (dyne-cm) Component Value Mxx -1.66e+22 Mxy -4.14e+22 Mxz 2.02e+22 Myy -3.50e+22 Myz -2.18e+22 Mzz 5.16e+22 ####---------- ###########----------- ################------------ ##################------------ ######################---------- P ########################--------- ############ ###########------------ --########### T ############------------ --########### ############------------ ----##########################------------ -----#########################------------ ------########################------------ --------#######################----------- ---------#####################---------- -----------###################---------- -------------###############---------- ----------------###########-------## --------------------------######## -----------------------####### ---------------------####### ------------------#### ------------## Global CMT Convention Moment Tensor: R T P 5.16e+22 2.02e+22 2.18e+22 2.02e+22 -1.66e+22 4.14e+22 2.18e+22 4.14e+22 -3.50e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20161116142535/index.html |
STK = 115 DIP = 50 RAKE = 50 MW = 4.49 HS = 15.0
The NDK file is 20161116142535.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 2016/11/16 14:25:35:0 59.61 -137.65 1.5 4.6 Alaska Stations used: AK.BARN AK.BCP AK.BESE AK.GLB AK.JIS AK.MCAR AK.MESA AK.PIN AK.TABL AK.VRDI AK.WAX AK.YAH AT.SIT AT.SKAG AT.YKU2 CN.HYT CN.WHY NY.FARO TA.L27K TA.M26K TA.M27K TA.M30M TA.M31M TA.N25K TA.N31M TA.P33M Filtering commands used: cut o DIST/3.3 -25 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.025 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 6.84e+22 dyne-cm Mw = 4.49 Z = 15 km Plane Strike Dip Rake NP1 348 54 127 NP2 115 50 50 Principal Axes: Axis Value Plunge Azimuth T 6.84e+22 60 318 N 0.00e+00 29 143 P -6.84e+22 2 52 Moment Tensor: (dyne-cm) Component Value Mxx -1.66e+22 Mxy -4.14e+22 Mxz 2.02e+22 Myy -3.50e+22 Myz -2.18e+22 Mzz 5.16e+22 ####---------- ###########----------- ################------------ ##################------------ ######################---------- P ########################--------- ############ ###########------------ --########### T ############------------ --########### ############------------ ----##########################------------ -----#########################------------ ------########################------------ --------#######################----------- ---------#####################---------- -----------###################---------- -------------###############---------- ----------------###########-------## --------------------------######## -----------------------####### ---------------------####### ------------------#### ------------## Global CMT Convention Moment Tensor: R T P 5.16e+22 2.02e+22 2.18e+22 2.02e+22 -1.66e+22 4.14e+22 2.18e+22 4.14e+22 -3.50e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20161116142535/index.html |
Regional Moment Tensor (Mwr) Moment 5.601e+15 N-m Magnitude 4.4 Mwr Depth 17.0 km Percent DC 88 % Half Duration – Catalog US Data Source US3 Contributor US3 Nodal Planes Plane Strike Dip Rake NP1 352 57 112 NP2 136 39 60 Principal Axes Axis Value Plunge Azimuth T 5.427e+15 N-m 69 310 N 0.334e+15 N-m 18 160 P -5.761e+15 N-m 10 67 |
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 -25 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.025 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 60 65 -20 4.17 0.3206 WVFGRD96 2.0 65 60 -20 4.25 0.3535 WVFGRD96 3.0 65 50 -20 4.32 0.3567 WVFGRD96 4.0 255 45 -10 4.34 0.3751 WVFGRD96 5.0 255 45 -10 4.36 0.3969 WVFGRD96 6.0 260 45 0 4.36 0.4126 WVFGRD96 7.0 85 45 15 4.37 0.4264 WVFGRD96 8.0 85 40 15 4.43 0.4377 WVFGRD96 9.0 90 40 20 4.43 0.4491 WVFGRD96 10.0 100 45 30 4.43 0.4582 WVFGRD96 11.0 110 45 50 4.47 0.4734 WVFGRD96 12.0 115 45 55 4.48 0.4869 WVFGRD96 13.0 115 50 55 4.49 0.4954 WVFGRD96 14.0 115 50 55 4.50 0.4993 WVFGRD96 15.0 115 50 50 4.49 0.5002 WVFGRD96 16.0 115 50 50 4.50 0.4983 WVFGRD96 17.0 115 50 50 4.50 0.4941 WVFGRD96 18.0 115 50 45 4.50 0.4891 WVFGRD96 19.0 115 50 45 4.50 0.4830 WVFGRD96 20.0 110 55 40 4.51 0.4764 WVFGRD96 21.0 110 50 40 4.52 0.4699 WVFGRD96 22.0 110 50 35 4.52 0.4626 WVFGRD96 23.0 110 50 35 4.52 0.4547 WVFGRD96 24.0 110 55 35 4.53 0.4461 WVFGRD96 25.0 110 55 35 4.53 0.4374 WVFGRD96 26.0 110 55 35 4.54 0.4282 WVFGRD96 27.0 105 55 30 4.55 0.4188 WVFGRD96 28.0 105 55 30 4.55 0.4093 WVFGRD96 29.0 105 55 30 4.55 0.3992
The best solution is
WVFGRD96 15.0 115 50 50 4.49 0.5002
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 -25 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.025 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