The ANSS event ID is nc72592705 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nc72592705/executive.
2016/02/16 23:27:30 37.202 -118.400 15.1 4.31 California
USGS/SLU Moment Tensor Solution ENS 2016/02/16 23:27:30:0 37.20 -118.40 15.1 4.3 California Stations used: AZ.CRY AZ.KNW AZ.PFO AZ.SND AZ.TMSP BK.BKS BK.BRK BK.CMB BK.HELL BK.JRSC BK.KCC BK.MHC BK.PACP BK.PKD BK.SAO BK.SUTB BK.VAK BK.WENL CI.ADO CI.ARV CI.BAK CI.BBR CI.BCW CI.BEL CI.CCC CI.CGO CI.CHF CI.CIA CI.CWC CI.DAN CI.DEC CI.DGR CI.DJJ CI.EDW2 CI.FMP CI.FOX2 CI.FUR CI.GMR CI.GRA CI.GSC CI.HEC CI.IRM CI.ISA CI.LMR2 CI.LPC CI.LRL CI.MLAC CI.MOP CI.MPM CI.MPP CI.MTP CI.MUR CI.MWC CI.NEE2 CI.OAT CI.OSI CI.PASC CI.RRX CI.RVR CI.SBC CI.SLA CI.SMM CI.SPG2 CI.SVD CI.TFT CI.TUQ CI.VCS CI.VOG CI.VTV CI.WAS2 CI.WCS2 CI.WLH2 CI.WOR IM.NV31 LB.BMN LB.TPH NC.BBGB NC.MCB NC.MDY NC.MINS NC.MMLB NC.PMPB NN.BEK NN.CMK6 NN.CTC NN.DSP NN.EMB NN.GWY NN.LCH NN.LHV NN.MOHS NN.MPK NN.OUT1 NN.PAH NN.PNT NN.PRN NN.Q09A NN.Q12A NN.QSM NN.REDF NN.RUB NN.RYN NN.S11A NN.SHP NN.SPR3 NN.UNVG NN.V12A NN.VCN NN.WDEM NN.WTNK NN.YER NP.PLA PB.B082A SN.HEL TA.R11A US.TPNV UU.CCUT UU.VRUT YN.BCCC YN.GVAR1 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 = 2.79e+22 dyne-cm Mw = 4.23 Z = 18 km Plane Strike Dip Rake NP1 30 90 10 NP2 300 80 180 Principal Axes: Axis Value Plunge Azimuth T 2.79e+22 7 255 N 0.00e+00 80 30 P -2.79e+22 7 165 Moment Tensor: (dyne-cm) Component Value Mxx -2.38e+22 Mxy 1.37e+22 Mxz 2.42e+21 Myy 2.38e+22 Myz -4.19e+21 Mzz -4.23e+14 -------------- ---------------------# -----------------------##### -----------------------####### ------------------------########## #-----------------------############ ########----------------############## #############-----------################ #################------################# #####################--################### ######################--################## ####################-------############### # ###############-----------############ T ##############---------------######## #############------------------###### ##############---------------------### ############------------------------ ##########------------------------ #######----------------------- #####----------------------- #-------------- ---- ----------- P Global CMT Convention Moment Tensor: R T P -4.23e+14 2.42e+21 4.19e+21 2.42e+21 -2.38e+22 -1.37e+22 4.19e+21 -1.37e+22 2.38e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160216232730/index.html |
STK = 30 DIP = 90 RAKE = 10 MW = 4.23 HS = 18.0
The NDK file is 20160216232730.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 2016/02/16 23:27:30:0 37.20 -118.40 15.1 4.3 California Stations used: AZ.CRY AZ.KNW AZ.PFO AZ.SND AZ.TMSP BK.BKS BK.BRK BK.CMB BK.HELL BK.JRSC BK.KCC BK.MHC BK.PACP BK.PKD BK.SAO BK.SUTB BK.VAK BK.WENL CI.ADO CI.ARV CI.BAK CI.BBR CI.BCW CI.BEL CI.CCC CI.CGO CI.CHF CI.CIA CI.CWC CI.DAN CI.DEC CI.DGR CI.DJJ CI.EDW2 CI.FMP CI.FOX2 CI.FUR CI.GMR CI.GRA CI.GSC CI.HEC CI.IRM CI.ISA CI.LMR2 CI.LPC CI.LRL CI.MLAC CI.MOP CI.MPM CI.MPP CI.MTP CI.MUR CI.MWC CI.NEE2 CI.OAT CI.OSI CI.PASC CI.RRX CI.RVR CI.SBC CI.SLA CI.SMM CI.SPG2 CI.SVD CI.TFT CI.TUQ CI.VCS CI.VOG CI.VTV CI.WAS2 CI.WCS2 CI.WLH2 CI.WOR IM.NV31 LB.BMN LB.TPH NC.BBGB NC.MCB NC.MDY NC.MINS NC.MMLB NC.PMPB NN.BEK NN.CMK6 NN.CTC NN.DSP NN.EMB NN.GWY NN.LCH NN.LHV NN.MOHS NN.MPK NN.OUT1 NN.PAH NN.PNT NN.PRN NN.Q09A NN.Q12A NN.QSM NN.REDF NN.RUB NN.RYN NN.S11A NN.SHP NN.SPR3 NN.UNVG NN.V12A NN.VCN NN.WDEM NN.WTNK NN.YER NP.PLA PB.B082A SN.HEL TA.R11A US.TPNV UU.CCUT UU.VRUT YN.BCCC YN.GVAR1 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 = 2.79e+22 dyne-cm Mw = 4.23 Z = 18 km Plane Strike Dip Rake NP1 30 90 10 NP2 300 80 180 Principal Axes: Axis Value Plunge Azimuth T 2.79e+22 7 255 N 0.00e+00 80 30 P -2.79e+22 7 165 Moment Tensor: (dyne-cm) Component Value Mxx -2.38e+22 Mxy 1.37e+22 Mxz 2.42e+21 Myy 2.38e+22 Myz -4.19e+21 Mzz -4.23e+14 -------------- ---------------------# -----------------------##### -----------------------####### ------------------------########## #-----------------------############ ########----------------############## #############-----------################ #################------################# #####################--################### ######################--################## ####################-------############### # ###############-----------############ T ##############---------------######## #############------------------###### ##############---------------------### ############------------------------ ##########------------------------ #######----------------------- #####----------------------- #-------------- ---- ----------- P Global CMT Convention Moment Tensor: R T P -4.23e+14 2.42e+21 4.19e+21 2.42e+21 -2.38e+22 -1.37e+22 4.19e+21 -1.37e+22 2.38e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160216232730/index.html |
TMTS Moment 3.577e+15 N-m Magnitude 4.30 Depth 18.0 km Percent DC 90% Half Duration – Catalog NC (nc72592705) Data Source NC1 Contributor NC1 Nodal Planes Plane Strike Dip Rake NP1 298 77 -178 NP2 208 88 -13 Principal Axes Axis Value Plunge Azimuth T 3.482 8 254 N 0.184 77 19 P -3.665 11 162 |
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 1.0 210 90 -5 3.76 0.2914 WVFGRD96 2.0 210 80 -15 3.89 0.3844 WVFGRD96 3.0 210 85 -15 3.93 0.4278 WVFGRD96 4.0 210 90 -20 3.98 0.4605 WVFGRD96 5.0 30 90 20 4.01 0.4898 WVFGRD96 6.0 210 85 -20 4.04 0.5184 WVFGRD96 7.0 30 90 20 4.06 0.5473 WVFGRD96 8.0 30 90 20 4.10 0.5781 WVFGRD96 9.0 210 85 -20 4.12 0.6033 WVFGRD96 10.0 210 85 -20 4.14 0.6242 WVFGRD96 11.0 210 85 -15 4.15 0.6423 WVFGRD96 12.0 30 90 15 4.17 0.6588 WVFGRD96 13.0 30 90 15 4.18 0.6718 WVFGRD96 14.0 30 90 15 4.19 0.6822 WVFGRD96 15.0 30 90 10 4.20 0.6895 WVFGRD96 16.0 210 90 -10 4.21 0.6952 WVFGRD96 17.0 210 90 -10 4.22 0.6983 WVFGRD96 18.0 30 90 10 4.23 0.6991 WVFGRD96 19.0 210 90 -10 4.24 0.6979 WVFGRD96 20.0 30 90 10 4.24 0.6952 WVFGRD96 21.0 30 90 10 4.25 0.6911 WVFGRD96 22.0 210 90 -10 4.26 0.6860 WVFGRD96 23.0 30 90 10 4.27 0.6798 WVFGRD96 24.0 210 90 -10 4.27 0.6728 WVFGRD96 25.0 210 90 -10 4.28 0.6654 WVFGRD96 26.0 210 90 -10 4.28 0.6576 WVFGRD96 27.0 210 90 -10 4.29 0.6491 WVFGRD96 28.0 30 90 10 4.30 0.6403 WVFGRD96 29.0 30 90 10 4.30 0.6311
The best solution is
WVFGRD96 18.0 30 90 10 4.23 0.6991
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