Location

Other locations

Catalog Mag     Time     Depth   Review Status     Location       Source 
CI      6.4 mw  17:33:49 10.7 km REVIEWED      35.705°N 117.506°W CI 2
NN      6.2 ml  17:33:48 11.2 km REVIEWED      35.679°N 117.516°W NN 3
US      6.5 mww 17:33:48  8.7 km REVIEWED      35.705°N 117.508°W US 5 CI 2
PT      6.5 Mi  17:33:48  2.0 km REVIEWED      35.600°N 117.400°W PT 4

Magnitudes
Mw  Mag  Err   Stations Source
    6.4  -----    6     CI 2
Ml  6.47 0.159  291     CI 2
Mlr 5.37 0.416   15     CI 2
Me  6.6  0.302   99     CI 2

Mww 6.5  0.037   70     US
Mwr 6.4  -----    6     CI 2
ML  5.8  0.416   15     CI 2

Location ANSS

2019/07/04 17:33:49 35.705 -117.508 8.7 6.4 California

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2019/07/04 17:33:49:0  35.71 -117.51   8.7 6.4 California
 
 Stations used:
   AE.113A AE.BARN AE.PRCT AE.W13A AE.X16A AE.Y14A AZ.CPE 
   BC.SFX BC.SJX BC.TJX BC.TKX BC.VTX BK.BUCR BK.MNRC BK.MTOS 
   BK.PACP BK.WELL BK.WINE CI.BLY CI.CCA CI.ELS2 CI.GLA CI.GRA 
   CI.GSC CI.ISA CI.LDF CI.PASC CI.RAG CI.YUH2 II.PFO IM.NV31 
   LB.MVU LB.TPH NC.AFD NN.DSP NN.GMN NN.GWY NN.LHV NN.MPK 
   NN.MZPB NN.PAH NN.PIO NN.PRN NN.Q09A NN.QSM NN.R11B NN.RYN 
   NN.S11A NN.SHP NN.SPR3 NN.V12A NN.WAK NN.WDEM NN.WLDB 
   SN.HEL US.ELK US.TPNV US.WUAZ UU.CCUT UU.KNB UU.LCMT 
   UU.PSUT UU.SZCU UU.VRUT 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.05 n 3 
 
 Best Fitting Double Couple
  Mo = 2.60e+25 dyne-cm
  Mw = 6.21 
  Z  = 14 km
  Plane   Strike  Dip  Rake
   NP1       40    85   -20
   NP2      132    70   -175
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.60e+25     10      88
    N   0.00e+00     69     207
    P  -2.60e+25     18     354

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.33e+25
       Mxy     3.47e+24
       Mxz    -7.26e+24
       Myy     2.49e+25
       Myz     5.34e+24
       Mzz    -1.54e+24
                                                     
                                                     
                                                     
                                                     
                     ----   -------                  
                 -------- P -----------              
              -----------   -------------#           
             ---------------------------###          
           ##--------------------------######        
          ####------------------------########       
         ######---------------------###########      
        ########-------------------#############     
        #########----------------###############     
       ###########--------------#############   #    
       #############----------############### T #    
       ###############-------################   #    
       #################---######################    
        ########################################     
        ################----####################     
         #############--------#################      
          ###########------------#############       
           ########------------------########        
             ####--------------------------          
              #---------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.54e+24  -7.26e+24  -5.34e+24 
 -7.26e+24  -2.33e+25  -3.47e+24 
 -5.34e+24  -3.47e+24   2.49e+25 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190704173349/index.html
        

Preferred Solution

The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is

      STK = 40
      DIP = 85
     RAKE = -20
       MW = 6.21
       HS = 14.0

The NDK file is 20190704173349.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
CI
USGSW
 USGS/SLU Moment Tensor Solution
 ENS  2019/07/04 17:33:49:0  35.71 -117.51   8.7 6.4 California
 
 Stations used:
   AE.113A AE.BARN AE.PRCT AE.W13A AE.X16A AE.Y14A AZ.CPE 
   BC.SFX BC.SJX BC.TJX BC.TKX BC.VTX BK.BUCR BK.MNRC BK.MTOS 
   BK.PACP BK.WELL BK.WINE CI.BLY CI.CCA CI.ELS2 CI.GLA CI.GRA 
   CI.GSC CI.ISA CI.LDF CI.PASC CI.RAG CI.YUH2 II.PFO IM.NV31 
   LB.MVU LB.TPH NC.AFD NN.DSP NN.GMN NN.GWY NN.LHV NN.MPK 
   NN.MZPB NN.PAH NN.PIO NN.PRN NN.Q09A NN.QSM NN.R11B NN.RYN 
   NN.S11A NN.SHP NN.SPR3 NN.V12A NN.WAK NN.WDEM NN.WLDB 
   SN.HEL US.ELK US.TPNV US.WUAZ UU.CCUT UU.KNB UU.LCMT 
   UU.PSUT UU.SZCU UU.VRUT 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.05 n 3 
 
 Best Fitting Double Couple
  Mo = 2.60e+25 dyne-cm
  Mw = 6.21 
  Z  = 14 km
  Plane   Strike  Dip  Rake
   NP1       40    85   -20
   NP2      132    70   -175
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.60e+25     10      88
    N   0.00e+00     69     207
    P  -2.60e+25     18     354

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.33e+25
       Mxy     3.47e+24
       Mxz    -7.26e+24
       Myy     2.49e+25
       Myz     5.34e+24
       Mzz    -1.54e+24
                                                     
                                                     
                                                     
                                                     
                     ----   -------                  
                 -------- P -----------              
              -----------   -------------#           
             ---------------------------###          
           ##--------------------------######        
          ####------------------------########       
         ######---------------------###########      
        ########-------------------#############     
        #########----------------###############     
       ###########--------------#############   #    
       #############----------############### T #    
       ###############-------################   #    
       #################---######################    
        ########################################     
        ################----####################     
         #############--------#################      
          ###########------------#############       
           ########------------------########        
             ####--------------------------          
              #---------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.54e+24  -7.26e+24  -5.34e+24 
 -7.26e+24  -2.33e+25  -3.47e+24 
 -5.34e+24  -3.47e+24   2.49e+25 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190704173349/index.html
	
Moment Tensor (TMTS)
Moment 4.918e+18 N-m
Magnitude 6.39
Depth 8.0 km
Percent DC 74%
Half Duration -
Catalog CI
Data Source CI 2
Contributor CI 2

Nodal Planes
Plane Strike Dip Rake
NP1 228Â 66Â 4Â
NP2 137Â 86Â 156Â

Principal Axes
Axis Value Plunge Azimuth
T 4.545e+18 N-m 20Â 90Â
N 0.676e+18 N-m 65Â 308Â
P -5.221e+18 N-m 14Â 185Â

        
W-phase Moment Tensor (Mw)
Moment 6.155e+18 N-m
Magnitude 6.46 Mww
Depth 11.5 km
Percent DC 95%
Half Duration 4.44 s
Catalog US
Data Source US 4
Contributor US 4

Nodal Planes
Plane Strike Dip Rake
NP1 229Â 77Â 3Â
NP2 139Â 87Â 167Â

Principal Axes
Axis Value Plunge Azimuth
T 6.235e+18 N-m 11Â 93Â
N -0.163e+18 N-m 76Â 308Â
P -6.072e+18 N-m 8Â 185Â

        

Magnitudes

mLg Magnitude


(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

ML Magnitude


(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.


(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.

Context

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).

Waveform Inversion using wvfgrd96

The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for the waveform inversion are shown in the next figure.
Location of broadband stations used for waveform inversion

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 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 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.05 n 3 
The results of this grid search from 0.5 to 19 km depth are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0   225    90     5   5.87 0.2892
WVFGRD96    2.0    45    85   -10   5.97 0.3705
WVFGRD96    3.0   225    90     5   6.01 0.4073
WVFGRD96    4.0   225    90     5   6.04 0.4320
WVFGRD96    5.0    45    90     0   6.07 0.4496
WVFGRD96    6.0    45    90    -5   6.09 0.4639
WVFGRD96    7.0   225    90     5   6.11 0.4771
WVFGRD96    8.0    45    85   -10   6.14 0.4902
WVFGRD96    9.0    45    85   -10   6.15 0.4920
WVFGRD96   10.0    45    85   -15   6.17 0.4926
WVFGRD96   11.0    45    85   -15   6.18 0.4933
WVFGRD96   12.0   225    90    20   6.19 0.4927
WVFGRD96   13.0   220    90    20   6.20 0.4933
WVFGRD96   14.0    40    85   -20   6.21 0.4967
WVFGRD96   15.0   220    80    20   6.22 0.4943
WVFGRD96   16.0   220    80    20   6.23 0.4944
WVFGRD96   17.0   220    80    20   6.23 0.4939
WVFGRD96   18.0   220    80    20   6.24 0.4926
WVFGRD96   19.0   220    80    20   6.25 0.4907
WVFGRD96   20.0   220    80    20   6.25 0.4883
WVFGRD96   21.0   220    80    20   6.26 0.4855
WVFGRD96   22.0   220    80    20   6.27 0.4820
WVFGRD96   23.0   220    80    20   6.27 0.4781
WVFGRD96   24.0   220    80    20   6.28 0.4739
WVFGRD96   25.0   220    80    20   6.29 0.4693
WVFGRD96   26.0   220    80    20   6.29 0.4645
WVFGRD96   27.0   220    80    20   6.30 0.4595
WVFGRD96   28.0    40    85   -20   6.30 0.4550
WVFGRD96   29.0    40    85   -20   6.31 0.4508

The best solution is

WVFGRD96   14.0    40    85   -20   6.21 0.4967

The mechanism correspond to the best fit is
Figure 1. Waveform inversion focal mechanism

The best fit as a function of depth is given in the following figure:

Figure 2. Depth sensitivity for waveform mechanism

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 and because the velocity model used in the predictions may not be perfect. 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 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.05 n 3 
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.
Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. 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:

Assuming only a mislocation, the time shifts are fit to a functional form:

 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.

Discussion

Acknowledgements

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

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    

Quality Control

Here we tabulate the reasons for not using certain digital data sets

The following stations did not have a valid response files:

Last Changed Thu Jul 4 14:55:08 CDT 2019