The ANSS event ID is nn00512427 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00512427/executive.
2015/09/27 02:44:00 41.871 -119.612 10.2 4.2 Nevada
USGS/SLU Moment Tensor Solution ENS 2015/09/27 02:44:00:0 41.87 -119.61 10.2 4.2 Nevada Stations used: BK.WDC IM.NV31 IW.MFID IW.PLID LB.BMN NC.KCPB NC.KHMB NC.KMR NC.KRMB NC.MDPB NN.BEK NN.COLR NN.CTC NN.KVN NN.LCH NN.LHV NN.PAH NN.PNT NN.REDF NN.RUB NN.RYN NN.SPR3 NN.VCN NN.WDEM NN.YER TA.R11A UO.BUCK UO.DBO UO.PINE US.BMO US.ELK US.HAWA US.HLID US.WVOR UW.BABR UW.BLOW UW.CCRK UW.DDRF UW.IRON UW.IZEE UW.JEDS UW.PHIN UW.TREE UW.UMAT UW.YACT Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.84e+22 dyne-cm Mw = 4.11 Z = 5 km Plane Strike Dip Rake NP1 3 56 -113 NP2 220 40 -60 Principal Axes: Axis Value Plunge Azimuth T 1.84e+22 9 109 N 0.00e+00 19 16 P -1.84e+22 69 222 Moment Tensor: (dyne-cm) Component Value Mxx 6.60e+20 Mxy -6.70e+21 Mxz 3.62e+21 Myy 1.50e+22 Myz 6.65e+21 Mzz -1.57e+22 #########----- ###############------- ################---######### #############--------######### ############------------########## ###########--------------########### ##########-----------------########### #########-------------------############ ########--------------------############ ########----------------------############ #######-----------------------############ #######---------- ----------############ ######----------- P ---------############# #####----------- ---------######### #####-----------------------######### T ####----------------------########## ###----------------------########### ##---------------------########### #-------------------########## #-----------------########## -------------######### --------###### Global CMT Convention Moment Tensor: R T P -1.57e+22 3.62e+21 -6.65e+21 3.62e+21 6.60e+20 6.70e+21 -6.65e+21 6.70e+21 1.50e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150927024400/index.html |
STK = 220 DIP = 40 RAKE = -60 MW = 4.11 HS = 5.0
The NDK file is 20150927024400.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 2015/09/27 02:44:00:0 41.87 -119.61 10.2 4.2 Nevada Stations used: BK.WDC IM.NV31 IW.MFID IW.PLID LB.BMN NC.KCPB NC.KHMB NC.KMR NC.KRMB NC.MDPB NN.BEK NN.COLR NN.CTC NN.KVN NN.LCH NN.LHV NN.PAH NN.PNT NN.REDF NN.RUB NN.RYN NN.SPR3 NN.VCN NN.WDEM NN.YER TA.R11A UO.BUCK UO.DBO UO.PINE US.BMO US.ELK US.HAWA US.HLID US.WVOR UW.BABR UW.BLOW UW.CCRK UW.DDRF UW.IRON UW.IZEE UW.JEDS UW.PHIN UW.TREE UW.UMAT UW.YACT Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.84e+22 dyne-cm Mw = 4.11 Z = 5 km Plane Strike Dip Rake NP1 3 56 -113 NP2 220 40 -60 Principal Axes: Axis Value Plunge Azimuth T 1.84e+22 9 109 N 0.00e+00 19 16 P -1.84e+22 69 222 Moment Tensor: (dyne-cm) Component Value Mxx 6.60e+20 Mxy -6.70e+21 Mxz 3.62e+21 Myy 1.50e+22 Myz 6.65e+21 Mzz -1.57e+22 #########----- ###############------- ################---######### #############--------######### ############------------########## ###########--------------########### ##########-----------------########### #########-------------------############ ########--------------------############ ########----------------------############ #######-----------------------############ #######---------- ----------############ ######----------- P ---------############# #####----------- ---------######### #####-----------------------######### T ####----------------------########## ###----------------------########### ##---------------------########### #-------------------########## #-----------------########## -------------######### --------###### Global CMT Convention Moment Tensor: R T P -1.57e+22 3.62e+21 -6.65e+21 3.62e+21 6.60e+20 6.70e+21 -6.65e+21 6.70e+21 1.50e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150927024400/index.html |
Mw Moment 1.771e+15 N-m Magnitude 4.10 Depth 6.0 km Percent DC 100% Half Duration – Catalog NN (nn00512427) Data Source NN1 Contributor NN1 Nodal Planes Plane Strike Dip Rake NP1 36 56 -64 NP2 174 42 -124 Principal Axes Axis Value Plunge Azimuth T 1.768 8 107 N -0.003 22 200 P -1.775 67 359 |
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 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 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 1.0 255 65 -5 3.84 0.5074 WVFGRD96 2.0 250 50 -10 3.97 0.6486 WVFGRD96 3.0 240 40 -25 4.04 0.7453 WVFGRD96 4.0 230 45 -45 4.07 0.7949 WVFGRD96 5.0 220 40 -60 4.11 0.8172 WVFGRD96 6.0 250 65 -5 4.04 0.7966 WVFGRD96 7.0 250 80 15 4.04 0.7919 WVFGRD96 8.0 250 75 20 4.07 0.7867 WVFGRD96 9.0 250 70 15 4.09 0.7857 WVFGRD96 10.0 250 70 15 4.10 0.7806 WVFGRD96 11.0 250 75 15 4.11 0.7709 WVFGRD96 12.0 250 75 15 4.12 0.7567 WVFGRD96 13.0 250 75 15 4.13 0.7428 WVFGRD96 14.0 250 70 15 4.14 0.7269 WVFGRD96 15.0 250 70 15 4.15 0.7109 WVFGRD96 16.0 250 70 15 4.16 0.6925 WVFGRD96 17.0 250 70 15 4.17 0.6759 WVFGRD96 18.0 250 70 15 4.18 0.6580 WVFGRD96 19.0 250 70 20 4.18 0.6410 WVFGRD96 20.0 250 70 20 4.19 0.6248 WVFGRD96 21.0 250 70 20 4.20 0.6079 WVFGRD96 22.0 250 70 20 4.21 0.5905 WVFGRD96 23.0 250 70 20 4.22 0.5731 WVFGRD96 24.0 250 70 20 4.23 0.5566 WVFGRD96 25.0 250 70 25 4.23 0.5413 WVFGRD96 26.0 250 70 25 4.24 0.5256 WVFGRD96 27.0 250 70 25 4.24 0.5105 WVFGRD96 28.0 250 70 25 4.25 0.4956 WVFGRD96 29.0 250 70 25 4.26 0.4816
The best solution is
WVFGRD96 5.0 220 40 -60 4.11 0.8172
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 +60 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 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