Location

Location ANSS

2016/03/07 00:43:36 36.456 -98.701 3.2 4.0 Oklahoma

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2016/03/07 00:43:36:0  36.46  -98.70   3.2 4.0 Oklahoma
 
 Stations used:
   GS.KAN08 GS.KAN14 GS.OK029 GS.OK032 GS.OK035 GS.OK041 
   N4.T35B OK.BCOK OK.CROK OK.GORE OK.U32A OK.W35A US.CBKS 
   US.KSU1 
 
 Filtering commands used:
   cut o DIST/3.3 -20 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 2.66e+21 dyne-cm
  Mw = 3.55 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      310    75   -20
   NP2       45    71   -164
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.66e+21      3     358
    N   0.00e+00     65      95
    P  -2.66e+21     25     267

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.65e+21
       Mxy    -1.95e+20
       Mxz     1.88e+20
       Myy    -2.19e+21
       Myz     1.00e+21
       Mzz    -4.55e+20
                                                     
                                                     
                                                     
                                                     
                     ##### T ######                  
                 #########   ##########              
              ############################           
             ##############################          
           -----##########################---        
          ----------#####################-----       
         --------------#################-------      
        ------------------#############---------     
        --------------------##########----------     
       ------------------------######------------    
       ----   -------------------###-------------    
       ---- P --------------------#--------------    
       ----   ------------------#####------------    
        ----------------------########----------     
        --------------------############--------     
         -----------------###############------      
          -------------###################----       
           ---------#######################--        
             ---###########################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.55e+20   1.88e+20  -1.00e+21 
  1.88e+20   2.65e+21   1.95e+20 
 -1.00e+21   1.95e+20  -2.19e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160307004336/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 = 310
      DIP = 75
     RAKE = -20
       MW = 3.55
       HS = 5.0

The NDK file is 20160307004336.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
MTGRDDC
MTGRDDEV
MTGRD
USGSMT
 USGS/SLU Moment Tensor Solution
 ENS  2016/03/07 00:43:36:0  36.46  -98.70   3.2 4.0 Oklahoma
 
 Stations used:
   GS.KAN08 GS.KAN14 GS.OK029 GS.OK032 GS.OK035 GS.OK041 
   N4.T35B OK.BCOK OK.CROK OK.GORE OK.U32A OK.W35A US.CBKS 
   US.KSU1 
 
 Filtering commands used:
   cut o DIST/3.3 -20 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 2.66e+21 dyne-cm
  Mw = 3.55 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      310    75   -20
   NP2       45    71   -164
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.66e+21      3     358
    N   0.00e+00     65      95
    P  -2.66e+21     25     267

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.65e+21
       Mxy    -1.95e+20
       Mxz     1.88e+20
       Myy    -2.19e+21
       Myz     1.00e+21
       Mzz    -4.55e+20
                                                     
                                                     
                                                     
                                                     
                     ##### T ######                  
                 #########   ##########              
              ############################           
             ##############################          
           -----##########################---        
          ----------#####################-----       
         --------------#################-------      
        ------------------#############---------     
        --------------------##########----------     
       ------------------------######------------    
       ----   -------------------###-------------    
       ---- P --------------------#--------------    
       ----   ------------------#####------------    
        ----------------------########----------     
        --------------------############--------     
         -----------------###############------      
          -------------###################----       
           ---------#######################--        
             ---###########################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.55e+20   1.88e+20  -1.00e+21 
  1.88e+20   2.65e+21   1.95e+20 
 -1.00e+21   1.95e+20  -2.19e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160307004336/index.html
	
 Moment (dyne-cm)   2.66E+21   dyne-cm
 Magnitude (Mw)    3.55
  
 Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.66E+21      3.    358.
    N  -8.77E+17     65.     95.
    P  -2.66E+21     25.    267.
 Moment Tensor: (dyne-cm) Aki-Richards
    Component   Value
       Mxx    2.64E+21
       Mxy    2.64E+21
       Mxz    1.88E+20
       Myy   -1.95E+20
       Myz    1.00E+21
       Mzz   -4.54E+20
                                                     
                                                     
                                                     
                    ##### T ######                   
                #########   ##########               
             ############################            
            ##############################           
          -----##########################---         
         ----------#####################-----        
        --------------#################-------       
       ------------------#############---------      
       --------------------##########----------      
      ------------------------######------------     
      ----   -------------------##--------------     
      ---- P --------------------#--------------     
      ----   ------------------#####------------     
       ----------------------########----------      
       --------------------############--------      
        -----------------###############------       
         -------------###################----        
          ---------#######################--         
            ---###########################           
             ############################            
                ######################               
                    ##############                   
                                                     
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor: (dyne-cm)
         R         T         F
  R -4.54E+20  1.88E+20 -1.00E+21
  T  1.88E+20  2.64E+21  1.95E+20
  F -1.00E+21  1.95E+20 -2.19E+21
        
 Moment (dyne-cm)   2.68E+21   dyne-cm
 Magnitude (Mw)    3.55
  
 Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.87E+21      3.    358.
    N  -4.33E+20     65.     95.
    P  -2.43E+21     25.    267.
 Moment Tensor: (dyne-cm) Aki-Richards
    Component   Value
       Mxx    2.85E+21
       Mxy    2.85E+21
       Mxz    2.07E+20
       Myy   -1.85E+20
       Myz    7.51E+20
       Mzz   -7.71E+20
                                                     
                                                     
                                                     
                    ##### T ######                   
                #########   ##########               
             ############################            
            ##############################           
          ---############################---         
         ---------######################-----        
        --------------#################-------       
       -------------------###########----------      
       ----------------------------------------      
      ------------------------------------------     
      ----   -----------------------------------     
      ---- P -----------------------------------     
      ----   -----------------------------------     
       ----------------------------------------      
       -----------------------######-----------      
        ------------------#############-------       
         -------------###################----        
          --------#########################-         
            -#############################           
             ############################            
                ######################               
                    ##############                   
                                                     
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor: (dyne-cm)
         R         T         F
  R -7.71E+20  2.07E+20 -7.51E+20
  T  2.07E+20  2.85E+21  1.85E+20
  F -7.51E+20  1.85E+20 -2.08E+21
        
 Moment (dyne-cm)   2.70E+21   dyne-cm
 Magnitude (Mw)    3.55
  
 Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.45E+21      3.    358.
    N  -8.23E+20     65.     95.
    P  -2.81E+21     25.    267.
 Moment Tensor: (dyne-cm) Aki-Richards
    Component   Value
       Mxx    2.43E+21
       Mxy    2.43E+21
       Mxz    2.05E+20
       Myy   -1.84E+20
       Myz    7.47E+20
       Mzz   -1.16E+21
                                                     
                                                     
                                                     
                    ##### T ######                   
                #########   ##########               
             ############################            
            #############################-           
          -------#######################----         
         ------------#################-------        
        ------------------##########----------       
       ----------------------------------------      
       ----------------------------------------      
      ------------------------------------------     
      ----   -----------------------------------     
      ---- P -----------------------------------     
      ----   -----------------------------------     
       ----------------------------------------      
       ----------------------------------------      
        ------------------------##------------       
         ----------------##############------        
          -----------####################---         
            -----#########################           
             ############################            
                ######################               
                    ##############                   
                                                     
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor: (dyne-cm)
         R         T         F
  R -1.16E+21  2.05E+20 -7.47E+20
  T  2.05E+20  2.43E+21  1.84E+20
  F -7.47E+20  1.84E+20 -2.46E+21
        
Regional Moment Tensor (Mwr)
Moment	3.305e+14 N-m
Magnitude	3.61
Depth	6.0 km
Percent DC	58%
Half Duration	–
Catalog	US (us10004vsc)
Data Source	US1
Contributor	US1
Nodal Planes
Plane	Strike	Dip	Rake
NP1	138	76	11
NP2	46	79	166
Principal Axes
Axis	Value	Plunge	Azimuth
T	3.620	18	2
N	-0.764	72	189
P	-2.856	2	92

        

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

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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 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   310    85   -15   3.25 0.4395
WVFGRD96    2.0   310    80   -25   3.41 0.5690
WVFGRD96    3.0   310    80   -25   3.47 0.6318
WVFGRD96    4.0   310    75   -20   3.52 0.6612
WVFGRD96    5.0   310    75   -20   3.55 0.6695
WVFGRD96    6.0   310    75   -15   3.58 0.6609
WVFGRD96    7.0   315    80   -15   3.59 0.6463
WVFGRD96    8.0   310    75   -15   3.64 0.6288
WVFGRD96    9.0   315    80   -15   3.64 0.6015
WVFGRD96   10.0   135    90    15   3.65 0.5709
WVFGRD96   11.0   135    90    15   3.66 0.5446
WVFGRD96   12.0   135    90    15   3.67 0.5193
WVFGRD96   13.0   315    90   -10   3.68 0.4958
WVFGRD96   14.0   140    85    10   3.69 0.4746
WVFGRD96   15.0   140    80    15   3.70 0.4544
WVFGRD96   16.0   140    75    15   3.71 0.4375
WVFGRD96   17.0   140    75    15   3.72 0.4216
WVFGRD96   18.0   140    75    15   3.73 0.4055
WVFGRD96   19.0   140    70    15   3.74 0.3924
WVFGRD96   20.0   140    70    15   3.74 0.3807
WVFGRD96   21.0   140    70    15   3.75 0.3693
WVFGRD96   22.0   140    60    15   3.77 0.3615
WVFGRD96   23.0   140    60    15   3.78 0.3554
WVFGRD96   24.0   140    60    15   3.79 0.3518
WVFGRD96   25.0   140    60    10   3.79 0.3489
WVFGRD96   26.0   200    70   -15   3.85 0.3580
WVFGRD96   27.0   200    70   -15   3.86 0.3647
WVFGRD96   28.0   200    70   -15   3.86 0.3687
WVFGRD96   29.0   200    70   -15   3.87 0.3717

The best solution is

WVFGRD96    5.0   310    75   -20   3.55 0.6695

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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 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.


Grid Search Full Moment Tensor Inversion using wvfmtgrd96

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 wvfmtgrd96 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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 n 3 
The results of this grid search over depth are as follow:

MT Program  H(km) Mxx(dyne-cm)   Myy        Mxy        Mxz        Myz        Mzz       Mw      Fit
WVFMTGRD96    1.0  0.964E+21 -0.853E+21 -0.152E+21  0.330E+21 -0.923E+20 -0.281E+21  3.2679  0.4425
WVFMTGRD96    2.0  0.149E+22 -0.142E+22 -0.135E+21  0.822E+21  0.190E+21 -0.356E+21  3.4212  0.5703
WVFMTGRD96    3.0  0.175E+22 -0.190E+22 -0.146E+21  0.456E+21  0.624E+21 -0.756E+21  3.4757  0.6346
WVFMTGRD96    4.0  0.206E+22 -0.227E+22 -0.225E+21  0.364E+21  0.633E+21 -0.832E+21  3.5168  0.6657
WVFMTGRD96    5.0  0.243E+22 -0.246E+22 -0.184E+21  0.205E+21  0.747E+21 -0.116E+22  3.5546  0.6757
WVFMTGRD96    6.0  0.309E+22 -0.242E+22 -0.200E+21  0.238E+21  0.710E+21 -0.118E+22  3.5844  0.6712
WVFMTGRD96    7.0  0.357E+22 -0.253E+22 -0.218E+21  0.270E+21  0.691E+21 -0.132E+22  3.6147  0.6578
WVFMTGRD96    8.0  0.392E+22 -0.296E+22 -0.245E+21  0.304E+21  0.779E+21 -0.160E+22  3.6500  0.6406
WVFMTGRD96    9.0  0.464E+22 -0.271E+22 -0.262E+21  0.325E+21  0.831E+21 -0.125E+22  3.6687  0.6139

The best solution is

WVFMTGRD96    5.0  0.243E+22 -0.246E+22 -0.184E+21  0.205E+21  0.747E+21 -0.116E+22  3.5546  0.6757

The complete moment tensor decomposition using the program mtinfo is given in the text file MTGRDinfo.txt. (Jost, M. L., and R. B. Herrmann (1989). A student's guide to and review of moment tensors, Seism. Res. Letters 60, 37-57. SRL_60_2_37-57.pdf.

The P-wave first motion mechanism corresponding 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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 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.

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.


Grid Search Double Couple Inversion using wvfmtgrd96

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 wvfmtgrd96 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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 n 3 
The results of this grid search over depth are as follow:

MT Program  H(km) Mxx(dyne-cm)   Myy        Mxy        Mxz        Myz        Mzz       Mw      Fit
WVFMTGRD96    1.0  0.932E+21 -0.889E+21 -0.139E+21  0.135E+21  0.218E+21 -0.430E+20  3.2538  0.4395
WVFMTGRD96    2.0  0.159E+22 -0.136E+22 -0.139E+21  0.336E+21  0.622E+21 -0.239E+21  3.4124  0.5690
WVFMTGRD96    3.0  0.198E+22 -0.168E+22 -0.172E+21  0.417E+21  0.771E+21 -0.297E+21  3.4748  0.6318
WVFMTGRD96    4.0  0.235E+22 -0.194E+22 -0.173E+21  0.167E+21  0.889E+21 -0.404E+21  3.5154  0.6612
WVFMTGRD96    5.0  0.264E+22 -0.219E+22 -0.195E+21  0.188E+21  0.100E+22 -0.454E+21  3.5496  0.6695
WVFMTGRD96    6.0  0.291E+22 -0.253E+22 -0.287E+21  0.322E+20  0.981E+21 -0.378E+21  3.5772  0.6609
WVFMTGRD96    7.0  0.307E+22 -0.280E+22  0.137E+21  0.165E+21  0.897E+21 -0.273E+21  3.5929  0.6463
WVFMTGRD96    8.0  0.361E+22 -0.314E+22 -0.357E+21  0.399E+20  0.122E+22 -0.469E+21  3.6398  0.6288
WVFMTGRD96    9.0  0.366E+22 -0.334E+22  0.163E+21  0.196E+21  0.107E+22 -0.326E+21  3.6439  0.6015
WVFMTGRD96   10.0  0.378E+22 -0.361E+22 -0.837E+20  0.495E+21  0.905E+21 -0.167E+21  3.6562  0.5726
WVFMTGRD96   11.0  0.393E+22 -0.375E+22 -0.869E+20  0.515E+21  0.940E+21 -0.174E+21  3.6673  0.5450
WVFMTGRD96   12.0  0.395E+22 -0.395E+22  0.000E+00  0.749E+21  0.749E+21  0.183E+15  3.6747  0.5193
WVFMTGRD96   13.0  0.396E+22 -0.415E+22  0.918E+20  0.993E+21  0.543E+21  0.184E+21  3.6830  0.4961
WVFMTGRD96   14.0  0.410E+22 -0.423E+22  0.669E+21  0.756E+21  0.326E+21  0.130E+21  3.6890  0.4746
WVFMTGRD96   15.0  0.401E+22 -0.440E+22  0.541E+21  0.127E+22  0.349E+21  0.394E+21  3.6989  0.4544
WVFMTGRD96   16.0  0.401E+22 -0.461E+22  0.455E+21  0.155E+22  0.510E+20  0.599E+21  3.7105  0.4375
WVFMTGRD96   17.0  0.412E+22 -0.473E+22  0.468E+21  0.160E+22  0.524E+20  0.616E+21  3.7184  0.4216
WVFMTGRD96   18.0  0.422E+22 -0.485E+22  0.479E+21  0.164E+22  0.537E+20  0.631E+21  3.7254  0.4055
WVFMTGRD96   19.0  0.420E+22 -0.504E+22  0.385E+21  0.194E+22 -0.308E+21  0.846E+21  3.7377  0.3924
WVFMTGRD96   20.0  0.430E+22 -0.517E+22  0.395E+21  0.198E+22 -0.315E+21  0.868E+21  3.7448  0.3807
WVFMTGRD96   21.0  0.441E+22 -0.530E+22  0.405E+21  0.203E+22 -0.323E+21  0.890E+21  3.7521  0.3693
WVFMTGRD96   22.0  0.420E+22 -0.549E+22  0.200E+21  0.260E+22 -0.121E+22  0.129E+22  3.7727  0.3615
WVFMTGRD96   23.0  0.430E+22 -0.562E+22  0.205E+21  0.267E+22 -0.124E+22  0.132E+22  3.7797  0.3554
WVFMTGRD96   24.0  0.441E+22 -0.576E+22  0.211E+21  0.273E+22 -0.127E+22  0.135E+22  3.7871  0.3518
WVFMTGRD96   25.0  0.472E+22 -0.564E+22  0.450E+21  0.263E+22 -0.152E+22  0.913E+21  3.7889  0.3489
WVFMTGRD96   26.0 -0.422E+22  0.546E+22  0.480E+22  0.283E+22 -0.548E+21 -0.124E+22  3.8491  0.3580
WVFMTGRD96   27.0 -0.434E+22  0.562E+22  0.494E+22  0.291E+22 -0.564E+21 -0.128E+22  3.8575  0.3647
WVFMTGRD96   28.0 -0.444E+22  0.575E+22  0.506E+22  0.298E+22 -0.578E+21 -0.131E+22  3.8642  0.3687
WVFMTGRD96   29.0 -0.453E+22  0.587E+22  0.516E+22  0.304E+22 -0.589E+21 -0.134E+22  3.8702  0.3717

The best solution is

WVFMTGRD96    5.0  0.264E+22 -0.219E+22 -0.195E+21  0.188E+21  0.100E+22 -0.454E+21  3.5496  0.6695

The complete moment tensor decomposition using the program mtinfo is given in the text file MTGRDDCinfo.txt. (Jost, M. L., and R. B. Herrmann (1989). A student's guide to and review of moment tensors, Seism. Res. Letters 60, 37-57. SRL_60_2_37-57.pdf.

The P-wave first motion mechanism corresponding 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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 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.

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.


Grid Search Deviatoric Moment Tensor Inversion using wvfmtdgrd96

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 wvfmtgrd96 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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 n 3 
The results of this grid search over depth are as follow:

MT Program  H(km) Mxx(dyne-cm)   Myy        Mxy        Mxz        Myz        Mzz       Mw      Fit
WVFMTGRD96    1.0  0.101E+22 -0.812E+21 -0.152E+21  0.323E+21 -0.963E+20 -0.203E+21  3.2669  0.4417
WVFMTGRD96    2.0  0.156E+22 -0.136E+22 -0.146E+21  0.787E+21  0.220E+21 -0.200E+21  3.4186  0.5694
WVFMTGRD96    3.0  0.201E+22 -0.165E+22 -0.162E+21  0.434E+21  0.715E+21 -0.361E+21  3.4739  0.6320
WVFMTGRD96    4.0  0.237E+22 -0.197E+22 -0.233E+21  0.352E+21  0.693E+21 -0.401E+21  3.5132  0.6621
WVFMTGRD96    5.0  0.285E+22 -0.208E+22 -0.185E+21  0.207E+21  0.751E+21 -0.771E+21  3.5515  0.6737
WVFMTGRD96    6.0  0.326E+22 -0.225E+22 -0.201E+21  0.239E+21  0.711E+21 -0.101E+22  3.5842  0.6702
WVFMTGRD96    7.0  0.368E+22 -0.244E+22 -0.218E+21  0.270E+21  0.692E+21 -0.123E+22  3.6151  0.6578
WVFMTGRD96    8.0  0.415E+22 -0.276E+22 -0.246E+21  0.305E+21  0.781E+21 -0.139E+22  3.6499  0.6403
WVFMTGRD96    9.0  0.440E+22 -0.293E+22 -0.261E+21  0.324E+21  0.830E+21 -0.148E+22  3.6674  0.6139
WVFMTGRD96   10.0  0.466E+22 -0.304E+22 -0.271E+21  0.344E+21  0.809E+21 -0.162E+22  3.6820  0.5846
WVFMTGRD96   11.0  0.449E+22 -0.337E+22  0.138E+21  0.676E+21  0.601E+21 -0.112E+22  3.6784  0.5555
WVFMTGRD96   12.0  0.473E+22 -0.339E+22  0.152E+21  0.736E+21  0.547E+21 -0.134E+22  3.6908  0.5292
WVFMTGRD96   13.0  0.461E+22 -0.370E+22  0.509E+20  0.106E+22  0.518E+21 -0.912E+21  3.6950  0.5035
WVFMTGRD96   14.0  0.485E+22 -0.386E+22  0.236E+20  0.732E+21  0.354E+21 -0.995E+21  3.7029  0.4797
WVFMTGRD96   15.0  0.482E+22 -0.405E+22 -0.521E+20  0.108E+22  0.186E+21 -0.769E+21  3.7095  0.4578
WVFMTGRD96   16.0  0.458E+22 -0.417E+22  0.634E+21  0.135E+22  0.904E+20 -0.410E+21  3.7109  0.4391
WVFMTGRD96   17.0  0.424E+22 -0.459E+22  0.465E+21  0.177E+22  0.643E+20  0.351E+21  3.7202  0.4222
WVFMTGRD96   18.0  0.420E+22 -0.478E+22  0.359E+21  0.209E+22 -0.261E+21  0.575E+21  3.7326  0.4063
WVFMTGRD96   19.0  0.431E+22 -0.490E+22  0.368E+21  0.215E+22 -0.267E+21  0.590E+21  3.7398  0.3928
WVFMTGRD96   20.0  0.442E+22 -0.502E+22  0.377E+21  0.220E+22 -0.274E+21  0.604E+21  3.7469  0.3811
WVFMTGRD96   21.0  0.436E+22 -0.486E+22  0.121E+21  0.332E+22 -0.148E+22  0.498E+21  3.7801  0.3703
WVFMTGRD96   22.0  0.448E+22 -0.499E+22  0.124E+21  0.340E+22 -0.152E+22  0.511E+21  3.7875  0.3637
WVFMTGRD96   23.0  0.457E+22 -0.531E+22 -0.486E+21  0.352E+22 -0.170E+22  0.745E+21  3.8019  0.3576
WVFMTGRD96   24.0 -0.451E+22  0.434E+22  0.408E+22  0.434E+22 -0.163E+22  0.169E+21  3.8539  0.3595
WVFMTGRD96   25.0 -0.434E+22  0.446E+22  0.361E+22  0.505E+22 -0.151E+22 -0.121E+21  3.8597  0.3689
WVFMTGRD96   26.0 -0.445E+22  0.458E+22  0.371E+22  0.518E+22 -0.155E+22 -0.124E+21  3.8674  0.3779
WVFMTGRD96   27.0 -0.455E+22  0.467E+22  0.378E+22  0.529E+22 -0.159E+22 -0.127E+21  3.8735  0.3841
WVFMTGRD96   28.0 -0.464E+22  0.477E+22  0.386E+22  0.540E+22 -0.162E+22 -0.129E+21  3.8792  0.3905
WVFMTGRD96   29.0 -0.506E+22  0.487E+22  0.457E+22  0.487E+22 -0.183E+22  0.190E+21  3.8872  0.3946

The best solution is

WVFMTGRD96    5.0  0.285E+22 -0.208E+22 -0.185E+21  0.207E+21  0.751E+21 -0.771E+21  3.5515  0.6737

The complete moment tensor decomposition using the program mtinfo is given in the text file MTGRDDEVinfo.txt. (Jost, M. L., and R. B. Herrmann (1989). A student's guide to and review of moment tensors, Seism. Res. Letters 60, 37-57. SRL_60_2_37-57.pdf.

The P-wave first motion mechanism corresponding 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 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 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.

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 Sat May 7 22:10:45 CDT 2016