The ANSS event ID is us10008mgu and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us10008mgu/executive.
2017/05/01 14:18:15 59.830 -136.704 2.5 6.3 Alaska
USGS/SLU Moment Tensor Solution ENS 2017/05/01 14:18:15:0 59.83 -136.70 2.5 6.3 Alaska Stations used: AK.BARN AK.BCP AK.BESE AK.CTG AK.GLB AK.JIS AK.LOGN AK.MCAR AK.PIN AK.VRDI AT.SIT AT.YKU2 CN.DLBC CN.HYT NY.FARO NY.MAYO NY.WTLY TA.M27K TA.M30M TA.M31M TA.N31M TA.P33M Filtering commands used: cut o DIST/3.3 -40 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 = 1.91e+25 dyne-cm Mw = 6.12 Z = 14 km Plane Strike Dip Rake NP1 5 90 -155 NP2 275 65 0 Principal Axes: Axis Value Plunge Azimuth T 1.91e+25 17 137 N 0.00e+00 65 5 P -1.91e+25 17 233 Moment Tensor: (dyne-cm) Component Value Mxx 3.00e+24 Mxy -1.70e+25 Mxz -7.02e+23 Myy -3.00e+24 Myz 8.02e+24 Mzz 0.00e+00 #########----- #############--------- ###############------------- ################-------------- ##################---------------- ###################----------------- ####################------------------ ###############---###------------------- #####---------------##########---------- ##-------------------##############------- ---------------------##################--- ---------------------####################- ---------------------##################### --------------------#################### -------------------##################### ---- -----------#################### --- P -----------############ #### -- -----------############ T ### --------------############ # -------------############### ---------############# -----######### Global CMT Convention Moment Tensor: R T P 0.00e+00 -7.02e+23 -8.02e+24 -7.02e+23 3.00e+24 1.70e+25 -8.02e+24 1.70e+25 -3.00e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170501141815/index.html |
STK = 275 DIP = 65 RAKE = 0 MW = 6.12 HS = 14.0
The NDK file is 20170501141815.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 14:18:15:0 59.83 -136.70 2.5 6.3 Alaska Stations used: AK.BARN AK.BCP AK.BESE AK.CTG AK.GLB AK.JIS AK.LOGN AK.MCAR AK.PIN AK.VRDI AT.SIT AT.YKU2 CN.DLBC CN.HYT NY.FARO NY.MAYO NY.WTLY TA.M27K TA.M30M TA.M31M TA.N31M TA.P33M Filtering commands used: cut o DIST/3.3 -40 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 = 1.91e+25 dyne-cm Mw = 6.12 Z = 14 km Plane Strike Dip Rake NP1 5 90 -155 NP2 275 65 0 Principal Axes: Axis Value Plunge Azimuth T 1.91e+25 17 137 N 0.00e+00 65 5 P -1.91e+25 17 233 Moment Tensor: (dyne-cm) Component Value Mxx 3.00e+24 Mxy -1.70e+25 Mxz -7.02e+23 Myy -3.00e+24 Myz 8.02e+24 Mzz 0.00e+00 #########----- #############--------- ###############------------- ################-------------- ##################---------------- ###################----------------- ####################------------------ ###############---###------------------- #####---------------##########---------- ##-------------------##############------- ---------------------##################--- ---------------------####################- ---------------------##################### --------------------#################### -------------------##################### ---- -----------#################### --- P -----------############ #### -- -----------############ T ### --------------############ # -------------############### ---------############# -----######### Global CMT Convention Moment Tensor: R T P 0.00e+00 -7.02e+23 -8.02e+24 -7.02e+23 3.00e+24 1.70e+25 -8.02e+24 1.70e+25 -3.00e+24 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170501141815/index.html |
May 1, 2017, SOUTHEASTERN ALASKA, MW=6.3 Howard Koss CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: C201705011418A DATA: II IU CU IC G DK MN GE LD KP L.P.BODY WAVES:109S, 263C, T= 40 MANTLE WAVES: 127S, 213C, T=125 SURFACE WAVES: 123S, 282C, T= 50 TIMESTAMP: Q-20170501185838 CENTROID LOCATION: ORIGIN TIME: 14:18:22.0 0.1 LAT:59.88N 0.00;LON:136.64W 0.01 DEP: 15.7 0.4;TRIANG HDUR: 3.3 MOMENT TENSOR: SCALE 10**25 D-CM RR= 0.495 0.015; TT= 0.728 0.017 PP=-1.220 0.015; RT=-0.195 0.048 RP=-0.992 0.054; TP= 2.660 0.015 PRINCIPAL AXES: 1.(T) VAL= 2.823;PLG=18;AZM=143 2.(N) 0.395; 69; 356 3.(P) -3.215; 11; 236 BEST DBLE.COUPLE:M0= 3.02*10**25 NP1: STRIKE=281;DIP=69;SLIP= 5 NP2: STRIKE=189;DIP=85;SLIP= 159 ########--- ###########-------- #############---------- ##############------------- ###############-------------- ################--------------- #####--------##---------------- ----------------#######---------- ----------------###########------ ---------------###############--- ---------------#################- --------------################# -- ---------################# - P --------######### ##### --------######### T #### ---------######### ## -------############ ---######## |
W-phase Moment Tensor (Mww) Moment 3.459e+18 N-m Magnitude 6.3 Mww Depth 17.5 km Percent DC 88 % Half Duration 7 s Catalog US Data Source US3 Contributor US3 Nodal Planes Plane Strike Dip Rake NP1 282 76 23 NP2 186 68 165 Principal Axes Axis Value Plunge Azimuth T 3.557e+18 N-m 26 145 N -0.205e+18 N-m 63 312 P -3.352e+18 N-m 5 53 |
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 +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 1.0 285 65 25 5.80 0.3082 WVFGRD96 2.0 285 65 25 5.89 0.3852 WVFGRD96 3.0 280 70 10 5.89 0.4057 WVFGRD96 4.0 275 60 -5 5.93 0.4307 WVFGRD96 5.0 275 60 -5 5.96 0.4599 WVFGRD96 6.0 275 60 -5 5.98 0.4850 WVFGRD96 7.0 275 65 -5 6.00 0.5084 WVFGRD96 8.0 275 60 -5 6.04 0.5292 WVFGRD96 9.0 275 60 -5 6.06 0.5435 WVFGRD96 10.0 275 60 0 6.07 0.5541 WVFGRD96 11.0 275 65 0 6.08 0.5622 WVFGRD96 12.0 275 65 0 6.10 0.5673 WVFGRD96 13.0 275 65 0 6.11 0.5694 WVFGRD96 14.0 275 65 0 6.12 0.5695 WVFGRD96 15.0 275 65 0 6.13 0.5679 WVFGRD96 16.0 275 70 0 6.14 0.5644 WVFGRD96 17.0 275 70 0 6.15 0.5596 WVFGRD96 18.0 275 70 0 6.15 0.5530 WVFGRD96 19.0 275 70 5 6.16 0.5447 WVFGRD96 20.0 275 70 5 6.17 0.5354 WVFGRD96 21.0 275 70 5 6.18 0.5251 WVFGRD96 22.0 275 70 5 6.18 0.5136 WVFGRD96 23.0 275 70 5 6.19 0.5015 WVFGRD96 24.0 275 70 5 6.20 0.4885 WVFGRD96 25.0 275 70 5 6.20 0.4750 WVFGRD96 26.0 275 70 5 6.21 0.4614 WVFGRD96 27.0 275 70 5 6.21 0.4477 WVFGRD96 28.0 275 70 5 6.22 0.4337 WVFGRD96 29.0 275 70 5 6.22 0.4194
The best solution is
WVFGRD96 14.0 275 65 0 6.12 0.5695
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 +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