The ANSS event ID is nn00373580 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00373580/executive.
2011/04/27 19:19:20 38.410 -118.723 0.0 2.8 Nevada
USGS/SLU Moment Tensor Solution ENS 2011/04/27 19:19:20:0 38.41 -118.72 0.0 2.8 Nevada Stations used: BK.CMB BK.HUMO BK.JCC BK.ORV BK.WDC BK.YBH CI.GSC CI.ISA CI.LDF CI.MWC CI.OSI CI.PASC II.PFO LB.DAC NC.AFD NC.KHMB NC.MDPB UU.BGU UU.KNB UU.LCMT UU.MTPU UU.NLU UU.PSUT UU.SZCU UU.TCRU Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 9.55e+21 dyne-cm Mw = 3.92 Z = 3 km Plane Strike Dip Rake NP1 55 75 -30 NP2 153 61 -163 Principal Axes: Axis Value Plunge Azimuth T 9.55e+21 9 107 N 0.00e+00 57 211 P -9.55e+21 32 11 Moment Tensor: (dyne-cm) Component Value Mxx -5.90e+21 Mxy -3.85e+21 Mxz -4.62e+21 Myy 8.29e+21 Myz 6.18e+20 Mzz -2.39e+21 -------------- #--------------------- ####----------- ---------- #####----------- P ----------- #######----------- ------------- ########--------------------------## #########-------------------------#### ##########-----------------------####### ###########--------------------######### ############-------------------########### #############---------------############## #############-------------################ ##############----------############## # ##############------################# T ###############--#################### #############--####################### #######---------#################### ----------------################## ----------------############## ------------------########## ------------------#### -------------- Global CMT Convention Moment Tensor: R T P -2.39e+21 -4.62e+21 -6.18e+20 -4.62e+21 -5.90e+21 3.85e+21 -6.18e+20 3.85e+21 8.29e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110427191920/index.html |
STK = 55 DIP = 75 RAKE = -30 MW = 3.92 HS = 3.0
The NDK file is 20110427191920.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 2011/04/27 19:19:20:0 38.41 -118.72 0.0 2.8 Nevada Stations used: BK.CMB BK.HUMO BK.JCC BK.ORV BK.WDC BK.YBH CI.GSC CI.ISA CI.LDF CI.MWC CI.OSI CI.PASC II.PFO LB.DAC NC.AFD NC.KHMB NC.MDPB UU.BGU UU.KNB UU.LCMT UU.MTPU UU.NLU UU.PSUT UU.SZCU UU.TCRU Filtering commands used: hp c 0.02 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 9.55e+21 dyne-cm Mw = 3.92 Z = 3 km Plane Strike Dip Rake NP1 55 75 -30 NP2 153 61 -163 Principal Axes: Axis Value Plunge Azimuth T 9.55e+21 9 107 N 0.00e+00 57 211 P -9.55e+21 32 11 Moment Tensor: (dyne-cm) Component Value Mxx -5.90e+21 Mxy -3.85e+21 Mxz -4.62e+21 Myy 8.29e+21 Myz 6.18e+20 Mzz -2.39e+21 -------------- #--------------------- ####----------- ---------- #####----------- P ----------- #######----------- ------------- ########--------------------------## #########-------------------------#### ##########-----------------------####### ###########--------------------######### ############-------------------########### #############---------------############## #############-------------################ ##############----------############## # ##############------################# T ###############--#################### #############--####################### #######---------#################### ----------------################## ----------------############## ------------------########## ------------------#### -------------- Global CMT Convention Moment Tensor: R T P -2.39e+21 -4.62e+21 -6.18e+20 -4.62e+21 -5.90e+21 3.85e+21 -6.18e+20 3.85e+21 8.29e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110427191920/index.html |
REVIEWED BY NSL STAFF Event ID:335238 Origin ID:792727 Algorithm: Ichinose (2003) Long Period, Regional-Distance Waves Seismic Moment Tensor Solution 2011/04/27 (117) 19:19:21.00 38.4141 -118.7180 792727 Depth = 2.0 (km) Mw = 4.00 Mo = 1.23x10^22 (dyne x cm) Percent Double Couple = 92 % Percent CLVD = 8 % no ISO calculated Epsilon=-0.04 Percent Variance Reduction = 58.81 % Total Fit = 6.72 Major Double Couple strike dip rake Nodal Plane 1: 62 46 -14 Nodal Plane 2: 162 80 -135 DEVIATORIC MOMENT TENSOR Moment Tensor Elements: Spherical Coordinates Mrr= -0.31 Mtt= -0.49 Mff= 0.81 Mrt= -0.37 Mrf= 0.73 Mtf= 0.59 EXP=22 Moment Tensor Elements: Cartesian Coordinates -0.49 -0.59 -0.37 -0.59 0.81 -0.73 -0.37 -0.73 -0.31 Eigenvalues: T-axis eigenvalue= 1.25 N-axis eigenvalue= -0.05 P-axis eigenvalue= -1.20 Eigenvalues and eigenvectors of the Major Double Couple: T-axis ev= 1.25 trend=284 plunge=21 N-axis ev= 0.00 trend=172 plunge=44 P-axis ev=-1.25 trend=32 plunge=38 Maximum Azmuithal Gap=248 Distance to Nearest Station= 87.8 (km) Number of Stations (D=Displacement/V=Velocity) Used=5 (defining only) MLAC.CI.D CMB.BK.D TIN.CI.D HELL.BK.D GRA.CI.D ##--------------- ######------------------- ########------------- ----- ###########------------ P ------- ############------------ -------- #############------------------------ -###############-----------------------## ################-----------------------## ################----------------------### T ################---------------------#### #################-------------------###### ###################-------------------###### ####################----------------######## ####################---------------######### #####################------------########## ######################---------############ #####################-------############# #####################---################ -###################################### ---##############--################# -------------------############## ------------------########### -----------------######## ---------------### All Stations defining and nondefining: Station.Net Def Distance Azi Bazi lo-f hi-f vmodel (km) (deg) (deg) (Hz) (Hz) MLAC.CI (D) Y 87.8 187 7 0.020 0.080 MLAC.CI.wus.glib CMB.BK (D) Y 152.1 254 73 0.020 0.080 CMB.BK.wus.glib TIN.CI (D) Y 157.5 164 344 0.020 0.080 TIN.CI.wus.glib HELL.BK (D) Y 194.5 188 8 0.020 0.080 HELL.BK.wus.glib GRA.CI (D) Y 196.8 143 323 0.020 0.080 GRA.CI.wus.glib (V)-velocity (D)-Displacement Author: www-data Date: 2011/04/27 20:21:18 mtinv Version 2.1_DEVEL OCT2008 |
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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:
hp c 0.02 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 60 70 -25 3.79 0.6556 WVFGRD96 1.0 60 75 -15 3.80 0.6762 WVFGRD96 2.0 60 70 -25 3.87 0.7533 WVFGRD96 3.0 55 75 -30 3.92 0.7631 WVFGRD96 4.0 55 75 -30 3.94 0.7587 WVFGRD96 5.0 60 85 35 3.96 0.7458 WVFGRD96 6.0 240 90 -40 3.98 0.7463 WVFGRD96 7.0 60 85 35 3.98 0.7519 WVFGRD96 8.0 60 85 45 4.03 0.7493 WVFGRD96 9.0 60 85 40 4.02 0.7498 WVFGRD96 10.0 240 90 -40 4.02 0.7482 WVFGRD96 11.0 240 90 -40 4.03 0.7500 WVFGRD96 12.0 240 90 -40 4.03 0.7507 WVFGRD96 13.0 240 90 -40 4.04 0.7508 WVFGRD96 14.0 60 85 40 4.05 0.7513 WVFGRD96 15.0 60 85 35 4.05 0.7510 WVFGRD96 16.0 60 85 35 4.06 0.7501 WVFGRD96 17.0 60 85 35 4.07 0.7488 WVFGRD96 18.0 240 90 -35 4.07 0.7457 WVFGRD96 19.0 60 85 35 4.08 0.7430 WVFGRD96 20.0 60 85 35 4.09 0.7393 WVFGRD96 21.0 60 85 35 4.10 0.7346 WVFGRD96 22.0 60 85 35 4.11 0.7292 WVFGRD96 23.0 240 90 -35 4.11 0.7223 WVFGRD96 24.0 65 80 35 4.12 0.7170 WVFGRD96 25.0 65 80 35 4.13 0.7104 WVFGRD96 26.0 240 90 -35 4.13 0.6999 WVFGRD96 27.0 240 90 -35 4.14 0.6915 WVFGRD96 28.0 65 80 35 4.15 0.6867 WVFGRD96 29.0 65 80 30 4.16 0.6788
The best solution is
WVFGRD96 3.0 55 75 -30 3.92 0.7631
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
hp c 0.02 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2
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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