The ANSS event ID is ak0193wxcfea and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/ak0193wxcfea/executive.
2019/03/26 21:27:19 66.306 -157.247 8.5 5 Alaska
USGS/SLU Moment Tensor Solution ENS 2019/03/26 21:27:19:0 66.31 -157.25 8.5 5.0 Alaska Stations used: AK.ANM AK.BPAW AK.BWN AK.CAST AK.CCB AK.CHUM AK.COLD AK.CUT AK.FA01 AK.FA02 AK.GCSA AK.HDA AK.KTH AK.PPD AK.PPLA AK.RDOG AK.RND AK.SKN AK.TNA AK.TRF AV.STLK IU.COLA TA.B18K TA.C17K TA.D17K TA.D23K TA.E23K TA.E25K TA.F14K TA.F17K TA.F18K TA.F19K TA.F21K TA.F22K TA.F24K TA.F25K TA.F26K TA.G17K TA.G18K TA.G23K TA.G24K TA.G26K TA.H16K TA.H17K TA.H19K TA.H20K TA.H21K TA.H24K TA.I17K TA.I20K TA.I23K TA.J14K TA.J16K TA.J17K TA.J18K TA.J19K TA.J20K TA.J25K TA.K13K TA.K15K TA.K17K TA.L16K TA.L17K TA.L18K TA.L19K TA.L20K TA.M16K TA.M17K TA.M18K TA.M20K TA.POKR TA.TOLK XV.F1TN XV.F2TN XV.F3TN XV.F4TN XV.F6TP XV.F7TV XV.F8KN XV.FAPT XV.FNN1 XV.FNN2 XV.FPAP 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 0.07 n 3 Best Fitting Double Couple Mo = 3.59e+23 dyne-cm Mw = 4.97 Z = 12 km Plane Strike Dip Rake NP1 350 85 20 NP2 258 70 175 Principal Axes: Axis Value Plunge Azimuth T 3.59e+23 18 216 N 0.00e+00 69 3 P -3.59e+23 10 122 Moment Tensor: (dyne-cm) Component Value Mxx 1.14e+23 Mxy 3.12e+23 Mxz -4.99e+22 Myy -1.36e+23 Myz -1.14e+23 Mzz 2.13e+22 ----########## --------############## ------------################ -------------################# ----------------################## -----------------################### -------------------################### --------------------#################### -----------------###-------------------# ------------##########-------------------- --------##############-------------------- -----#################-------------------- --#####################------------------- ######################------------------ ######################------------------ ######################----------- -- #####################----------- P - ##### ############----------- ### T ############------------ ## ############----------- ###############------- ###########--- Global CMT Convention Moment Tensor: R T P 2.13e+22 -4.99e+22 1.14e+23 -4.99e+22 1.14e+23 -3.12e+23 1.14e+23 -3.12e+23 -1.36e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190326212719/index.html |
STK = 350 DIP = 85 RAKE = 20 MW = 4.97 HS = 12.0
The NDK file is 20190326212719.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 2019/03/26 21:27:19:0 66.31 -157.25 8.5 5.0 Alaska Stations used: AK.ANM AK.BPAW AK.BWN AK.CAST AK.CCB AK.CHUM AK.COLD AK.CUT AK.FA01 AK.FA02 AK.GCSA AK.HDA AK.KTH AK.PPD AK.PPLA AK.RDOG AK.RND AK.SKN AK.TNA AK.TRF AV.STLK IU.COLA TA.B18K TA.C17K TA.D17K TA.D23K TA.E23K TA.E25K TA.F14K TA.F17K TA.F18K TA.F19K TA.F21K TA.F22K TA.F24K TA.F25K TA.F26K TA.G17K TA.G18K TA.G23K TA.G24K TA.G26K TA.H16K TA.H17K TA.H19K TA.H20K TA.H21K TA.H24K TA.I17K TA.I20K TA.I23K TA.J14K TA.J16K TA.J17K TA.J18K TA.J19K TA.J20K TA.J25K TA.K13K TA.K15K TA.K17K TA.L16K TA.L17K TA.L18K TA.L19K TA.L20K TA.M16K TA.M17K TA.M18K TA.M20K TA.POKR TA.TOLK XV.F1TN XV.F2TN XV.F3TN XV.F4TN XV.F6TP XV.F7TV XV.F8KN XV.FAPT XV.FNN1 XV.FNN2 XV.FPAP 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 0.07 n 3 Best Fitting Double Couple Mo = 3.59e+23 dyne-cm Mw = 4.97 Z = 12 km Plane Strike Dip Rake NP1 350 85 20 NP2 258 70 175 Principal Axes: Axis Value Plunge Azimuth T 3.59e+23 18 216 N 0.00e+00 69 3 P -3.59e+23 10 122 Moment Tensor: (dyne-cm) Component Value Mxx 1.14e+23 Mxy 3.12e+23 Mxz -4.99e+22 Myy -1.36e+23 Myz -1.14e+23 Mzz 2.13e+22 ----########## --------############## ------------################ -------------################# ----------------################## -----------------################### -------------------################### --------------------#################### -----------------###-------------------# ------------##########-------------------- --------##############-------------------- -----#################-------------------- --#####################------------------- ######################------------------ ######################------------------ ######################----------- -- #####################----------- P - ##### ############----------- ### T ############------------ ## ############----------- ###############------- ###########--- Global CMT Convention Moment Tensor: R T P 2.13e+22 -4.99e+22 1.14e+23 -4.99e+22 1.14e+23 -3.12e+23 1.14e+23 -3.12e+23 -1.36e+23 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190326212719/index.html |
egional Moment Tensor (Mwr) Moment 3.085e+16 N-m Magnitude 4.93 Mwr Depth 5.0 km Percent DC 37% Half Duration - Catalog US Data Source US 2 Contributor US 2 Nodal Planes Plane Strike Dip Rake NP1 159 41 -37 NP2 278 67 -125 Principal Axes Axis Value Plunge Azimuth T 3.482e+16 N-m 15 33 N -1.092e+16 N-m 31 294 P -2.390e+16 N-m 55 145 |
W-phase Moment Tensor (Mww) Moment 4.616e+16 N-m Magnitude 5.04 Mww Depth 11.5 km Percent DC 25% Half Duration 0.84 s Catalog US Data Source US 2 Contributor US 2 Nodal Planes Plane Strike Dip Rake NP1 132 39 -77 NP2 295 53 -100 Principal Axes Axis Value Plunge Azimuth T 5.276e+16 N-m 7 32 N -1.982e+16 N-m 8 301 P -3.294e+16 N-m 79 163 |
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: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
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 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 350 75 -15 4.62 0.4195 WVFGRD96 2.0 345 65 -25 4.75 0.5384 WVFGRD96 3.0 345 65 -25 4.80 0.5815 WVFGRD96 4.0 350 75 -15 4.81 0.6049 WVFGRD96 5.0 350 80 -15 4.83 0.6187 WVFGRD96 6.0 165 75 -25 4.86 0.6348 WVFGRD96 7.0 170 85 -20 4.88 0.6497 WVFGRD96 8.0 165 75 -30 4.92 0.6691 WVFGRD96 9.0 170 85 -25 4.93 0.6728 WVFGRD96 10.0 350 90 25 4.95 0.6727 WVFGRD96 11.0 350 85 20 4.96 0.6749 WVFGRD96 12.0 350 85 20 4.97 0.6750 WVFGRD96 13.0 350 85 20 4.98 0.6714 WVFGRD96 14.0 350 85 20 4.99 0.6655 WVFGRD96 15.0 350 80 20 5.00 0.6575 WVFGRD96 16.0 350 80 15 5.01 0.6484 WVFGRD96 17.0 350 80 15 5.02 0.6388 WVFGRD96 18.0 350 80 15 5.02 0.6285 WVFGRD96 19.0 350 80 15 5.03 0.6176 WVFGRD96 20.0 350 80 15 5.04 0.6064 WVFGRD96 21.0 350 80 15 5.04 0.5949 WVFGRD96 22.0 350 80 15 5.05 0.5840 WVFGRD96 23.0 350 80 15 5.05 0.5729 WVFGRD96 24.0 350 80 15 5.06 0.5616 WVFGRD96 25.0 350 80 15 5.07 0.5500 WVFGRD96 26.0 350 80 15 5.07 0.5383 WVFGRD96 27.0 350 80 15 5.08 0.5268 WVFGRD96 28.0 350 75 10 5.08 0.5153 WVFGRD96 29.0 350 75 10 5.09 0.5038
The best solution is
WVFGRD96 12.0 350 85 20 4.97 0.6750
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 0.07 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