The ANSS event ID is us10008mel and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us10008mel/executive.
2017/05/01 12:31:54 59.821 -136.711 10.0 6.2 Alaska
USGS/SLU Moment Tensor Solution ENS 2017/05/01 12:31:54:0 59.82 -136.71 10.0 6.2 Alaska Stations used: AK.BARN AK.BESE AK.CTG AK.CYK AK.DOT AK.GLB AK.JIS AK.KIAG AK.LOGN AK.MCAR AK.PAX AK.PIN AK.PNL AK.PTPK AK.RIDG AK.SAMH AK.SAW AK.SCRK AK.VRDI AT.CRAG AT.SIT AT.SKAG AV.WACK CN.BVCY CN.DAWY CN.HYT CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 CN.YUK8 NY.FARO NY.MAYO NY.WTLY TA.HARP TA.I29M TA.J26L TA.J29M TA.K29M TA.L26K TA.L27K TA.L29M TA.M23K TA.M26K TA.M27K TA.M29M TA.M30M TA.M31M TA.N25K TA.N30M TA.N31M TA.O28M TA.O29M TA.O30N TA.P29M TA.P32M TA.P33M TA.Q32M TA.R31K TA.R32K TA.R33M TA.S31K TA.S32K TA.S34M TA.T33K TA.T35M TA.U33K TA.U35K TA.V35K US.EGAK US.WRAK YO.BEAV YO.LIRD Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.50e+25 dyne-cm Mw = 6.05 Z = 18 km Plane Strike Dip Rake NP1 170 70 142 NP2 275 55 25 Principal Axes: Axis Value Plunge Azimuth T 1.50e+25 41 127 N 0.00e+00 48 326 P -1.50e+25 9 225 Moment Tensor: (dyne-cm) Component Value Mxx -3.97e+24 Mxy -1.15e+25 Mxz -2.83e+24 Myy -1.97e+24 Myz 7.56e+24 Mzz 5.94e+24 ###----------- ######---------------- #########------------------- #########--------------------- ###########----------------------- ############------------------------ ##########---##########--------------- ######--------################---------- ##------------####################------ #--------------#######################---- ----------------########################-- ----------------#########################- ----------------########################## ----------------######################## ----------------############ ######### ----------------########### T ######## ---------------########### ####### -- ----------################### P -----------################ ------------############## ------------########## ----------#### Global CMT Convention Moment Tensor: R T P 5.94e+24 -2.83e+24 -7.56e+24 -2.83e+24 -3.97e+24 1.15e+25 -7.56e+24 1.15e+25 -1.97e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170501123154/index.html |
STK = 275 DIP = 55 RAKE = 25 MW = 6.05 HS = 18.0
The NDK file is 20170501123154.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 2017/05/01 12:31:54:0 59.82 -136.71 10.0 6.2 Alaska Stations used: AK.BARN AK.BESE AK.CTG AK.CYK AK.DOT AK.GLB AK.JIS AK.KIAG AK.LOGN AK.MCAR AK.PAX AK.PIN AK.PNL AK.PTPK AK.RIDG AK.SAMH AK.SAW AK.SCRK AK.VRDI AT.CRAG AT.SIT AT.SKAG AV.WACK CN.BVCY CN.DAWY CN.HYT CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 CN.YUK8 NY.FARO NY.MAYO NY.WTLY TA.HARP TA.I29M TA.J26L TA.J29M TA.K29M TA.L26K TA.L27K TA.L29M TA.M23K TA.M26K TA.M27K TA.M29M TA.M30M TA.M31M TA.N25K TA.N30M TA.N31M TA.O28M TA.O29M TA.O30N TA.P29M TA.P32M TA.P33M TA.Q32M TA.R31K TA.R32K TA.R33M TA.S31K TA.S32K TA.S34M TA.T33K TA.T35M TA.U33K TA.U35K TA.V35K US.EGAK US.WRAK YO.BEAV YO.LIRD Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 1.50e+25 dyne-cm Mw = 6.05 Z = 18 km Plane Strike Dip Rake NP1 170 70 142 NP2 275 55 25 Principal Axes: Axis Value Plunge Azimuth T 1.50e+25 41 127 N 0.00e+00 48 326 P -1.50e+25 9 225 Moment Tensor: (dyne-cm) Component Value Mxx -3.97e+24 Mxy -1.15e+25 Mxz -2.83e+24 Myy -1.97e+24 Myz 7.56e+24 Mzz 5.94e+24 ###----------- ######---------------- #########------------------- #########--------------------- ###########----------------------- ############------------------------ ##########---##########--------------- ######--------################---------- ##------------####################------ #--------------#######################---- ----------------########################-- ----------------#########################- ----------------########################## ----------------######################## ----------------############ ######### ----------------########### T ######## ---------------########### ####### -- ----------################### P -----------################ ------------############## ------------########## ----------#### Global CMT Convention Moment Tensor: R T P 5.94e+24 -2.83e+24 -7.56e+24 -2.83e+24 -3.97e+24 1.15e+25 -7.56e+24 1.15e+25 -1.97e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170501123154/index.html |
CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C201705011231A DATA: II LD IU DK CU MN G IC GE KP L.P.BODY WAVES:162S, 350C, T= 40 MANTLE WAVES: 129S, 193C, T=125 SURFACE WAVES: 166S, 407C, T= 50 TIMESTAMP: Q-20170501130642 CENTROID LOCATION: ORIGIN TIME: 12:31:59.7 0.1 LAT:59.94N 0.00;LON:136.56W 0.01 DEP: 17.4 0.3;TRIANG HDUR: 3.1 MOMENT TENSOR: SCALE 10**25 D-CM RR= 1.710 0.021; TT=-0.923 0.018 PP=-0.790 0.017; RT= 1.030 0.054 RP=-1.630 0.059; TP= 2.050 0.015 PRINCIPAL AXES: 1.(T) VAL= 2.514;PLG=64;AZM= 89 2.(N) 1.060; 16; 322 3.(P) -3.577; 20; 226 BEST DBLE.COUPLE:M0= 3.05*10**25 NP1: STRIKE=290;DIP=29;SLIP= 55 NP2: STRIKE=149;DIP=67;SLIP= 108 ----------- #------------------ ###---#######---------- ###--###############------- #-----##################----- #-------###################---- --------####################--- ----------########## #######--- -----------######### T ########-- ------------######## #########- -------------###################- -------------################## --------------################# --- ---------############## -- P ----------############ -------------####### -----------------## ----------- |
W-phase Moment Tensor (Mww) Moment 2.570e+18 N-m Magnitude 6.2 Mww Depth 15.5 km Percent DC 88 % Half Duration 6 s Catalog US Data Source US3 Contributor US3 Nodal Planes Plane Strike Dip Rake NP1 282 46 35 NP2 165 66 130 Principal Axes Axis Value Plunge Azimuth T 2.489e+18 N-m 52 122 N 0.156e+18 N-m 36 326 P -2.645e+18 N-m 12 228 |
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 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 270 90 0 5.60 0.3317 WVFGRD96 2.0 315 45 90 5.84 0.4186 WVFGRD96 3.0 85 70 -15 5.76 0.4394 WVFGRD96 4.0 85 65 -15 5.80 0.4582 WVFGRD96 5.0 85 55 -10 5.84 0.4759 WVFGRD96 6.0 90 55 5 5.86 0.5009 WVFGRD96 7.0 90 55 5 5.88 0.5285 WVFGRD96 8.0 90 50 10 5.93 0.5539 WVFGRD96 9.0 275 50 20 5.95 0.5779 WVFGRD96 10.0 275 50 25 5.97 0.6056 WVFGRD96 11.0 275 50 25 5.98 0.6289 WVFGRD96 12.0 275 50 25 5.99 0.6473 WVFGRD96 13.0 275 50 25 6.00 0.6614 WVFGRD96 14.0 275 55 25 6.01 0.6727 WVFGRD96 15.0 275 55 25 6.02 0.6807 WVFGRD96 16.0 275 55 25 6.03 0.6860 WVFGRD96 17.0 275 55 25 6.04 0.6886 WVFGRD96 18.0 275 55 25 6.05 0.6889 WVFGRD96 19.0 275 55 25 6.05 0.6873 WVFGRD96 20.0 275 55 25 6.06 0.6836 WVFGRD96 21.0 275 55 25 6.08 0.6816 WVFGRD96 22.0 275 55 25 6.08 0.6752 WVFGRD96 23.0 275 55 25 6.09 0.6674 WVFGRD96 24.0 275 55 25 6.10 0.6584 WVFGRD96 25.0 275 55 25 6.10 0.6482 WVFGRD96 26.0 275 55 25 6.11 0.6367 WVFGRD96 27.0 275 60 20 6.12 0.6245 WVFGRD96 28.0 275 60 20 6.12 0.6117 WVFGRD96 29.0 275 60 20 6.13 0.5981
The best solution is
WVFGRD96 18.0 275 55 25 6.05 0.6889
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 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 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