Location

2014/10/08 01:48:28 35.757 -97.094 5.0 3.3 Oklahoma

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports main page

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2014/10/08 01:48:28:0  35.76  -97.09   5.0 3.3 Oklahoma
 
 Stations used:
   GS.OK026 GS.OK027 GS.OK028 GS.OK029 N4.T35B OK.BCOK OK.CROK 
   OK.U32A OK.X37A TA.TUL1 TA.W39A 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 7.94e+20 dyne-cm
  Mw = 3.20 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      200    90   -175
   NP2      110    85     0
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.94e+20      4     335
    N   0.00e+00     85     200
    P  -7.94e+20      4      65

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.09e+20
       Mxy    -6.06e+20
       Mxz     2.37e+19
       Myy    -5.09e+20
       Myz    -6.51e+19
       Mzz     0.00e+00
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 # T #############-----              
              ####   #############--------           
             ####################----------          
           #####################-------------        
          ######################-------------        
         ######################-------------- P      
        --####################---------------        
        -----#################------------------     
       ----------############--------------------    
       ---------------######---------------------    
       --------------------#---------------------    
       --------------------#####-----------------    
        ------------------############----------     
        ------------------###################---     
         ----------------######################      
          --------------######################       
           -------------#####################        
             ----------####################          
              --------####################           
                 -----#################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  0.00e+00   2.37e+19   6.51e+19 
  2.37e+19   5.09e+20   6.06e+20 
  6.51e+19   6.06e+20  -5.09e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141008014828/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 = 110
      DIP = 85
     RAKE = 0
       MW = 3.20
       HS = 3.0

The NDK file is 20141008014828.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2014/10/08 01:48:28:0  35.76  -97.09   5.0 3.3 Oklahoma
 
 Stations used:
   GS.OK026 GS.OK027 GS.OK028 GS.OK029 N4.T35B OK.BCOK OK.CROK 
   OK.U32A OK.X37A TA.TUL1 TA.W39A 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 7.94e+20 dyne-cm
  Mw = 3.20 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      200    90   -175
   NP2      110    85     0
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.94e+20      4     335
    N   0.00e+00     85     200
    P  -7.94e+20      4      65

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.09e+20
       Mxy    -6.06e+20
       Mxz     2.37e+19
       Myy    -5.09e+20
       Myz    -6.51e+19
       Mzz     0.00e+00
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 # T #############-----              
              ####   #############--------           
             ####################----------          
           #####################-------------        
          ######################-------------        
         ######################-------------- P      
        --####################---------------        
        -----#################------------------     
       ----------############--------------------    
       ---------------######---------------------    
       --------------------#---------------------    
       --------------------#####-----------------    
        ------------------############----------     
        ------------------###################---     
         ----------------######################      
          --------------######################       
           -------------#####################        
             ----------####################          
              --------####################           
                 -----#################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  0.00e+00   2.37e+19   6.51e+19 
  2.37e+19   5.09e+20   6.06e+20 
  6.51e+19   6.06e+20  -5.09e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141008014828/index.html
	

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 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.07 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   115    75    15   3.07 0.4909
WVFGRD96    2.0   110    80     0   3.16 0.5938
WVFGRD96    3.0   110    85     0   3.20 0.6249
WVFGRD96    4.0   290    90     0   3.22 0.6235
WVFGRD96    5.0   290    80     5   3.26 0.6132
WVFGRD96    6.0   290    80     5   3.28 0.6003
WVFGRD96    7.0   290    80     5   3.31 0.5887
WVFGRD96    8.0   290    75     5   3.34 0.5765
WVFGRD96    9.0   105    70   -10   3.32 0.5621
WVFGRD96   10.0   105    70   -10   3.33 0.5476
WVFGRD96   11.0   105    70    -5   3.34 0.5322
WVFGRD96   12.0   105    70    -5   3.35 0.5176
WVFGRD96   13.0   105    70    -5   3.36 0.5021
WVFGRD96   14.0   105    65    -5   3.37 0.4866
WVFGRD96   15.0   105    65    -5   3.38 0.4728
WVFGRD96   16.0   105    65    -5   3.39 0.4586
WVFGRD96   17.0   105    65   -10   3.40 0.4450
WVFGRD96   18.0   105    65   -10   3.41 0.4318
WVFGRD96   19.0   105    60   -10   3.41 0.4193
WVFGRD96   20.0   105    60   -10   3.42 0.4067
WVFGRD96   21.0   105    70    -5   3.45 0.3959
WVFGRD96   22.0   110    90   -30   3.47 0.3840
WVFGRD96   23.0   110    90   -30   3.48 0.3752
WVFGRD96   24.0   295    85    30   3.50 0.3686
WVFGRD96   25.0   290    65     0   3.54 0.3616
WVFGRD96   26.0   290    65     0   3.55 0.3570
WVFGRD96   27.0   290    70     0   3.55 0.3527
WVFGRD96   28.0   290    70     0   3.56 0.3494
WVFGRD96   29.0   290    70     0   3.56 0.3465

The best solution is

WVFGRD96    3.0   110    85     0   3.20 0.6249

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 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.07 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 Tue Oct 7 21:06:59 CDT 2014