Location

2015/07/27 18:12:15 36.006 -97.576 3.2 4.5 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  2015/07/27 18:12:15:0  36.01  -97.58   3.2 4.5 Oklahoma
 
 Stations used:
   GS.KAN05 GS.KAN08 GS.KAN09 GS.KAN10 GS.KAN11 GS.KAN12 
   GS.KAN13 GS.KAN17 GS.KS20 GS.KS21 GS.OK025 GS.OK029 
   GS.OK031 GS.OK032 N4.R32B N4.T35B N4.U38B N4.Z35B N4.Z38B 
   OK.BCOK OK.BLOK OK.CCOK OK.CHOK OK.CROK OK.FNO OK.LOOK 
   OK.QUOK OK.U32A OK.X34A OK.X37A TA.ABTX TA.U40A TA.W39A 
   TA.WHTX US.CBKS US.KSU1 US.MIAR US.WMOK 
 
 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 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 6.38e+22 dyne-cm
  Mw = 4.47 
  Z  = 4 km
  Plane   Strike  Dip  Rake
   NP1      100    80   -15
   NP2      193    75   -170
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.38e+22      3     147
    N   0.00e+00     72     247
    P  -6.38e+22     18      56

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.62e+22
       Mxy    -5.61e+22
       Mxz    -1.34e+22
       Myy    -2.06e+22
       Myz    -1.32e+22
       Mzz    -5.65e+21
                                                     
                                                     
                                                     
                                                     
                     ###########---                  
                 ##############--------              
              ################------------           
             ################--------------          
           #################-------------   -        
          #################-------------- P --       
         #################---------------   ---      
        ##################----------------------     
        #################-----------------------     
       --################------------------------    
       -------##########-------------------------    
       -------------####-------------------------    
       -----------------#####--------------------    
        ---------------#########################     
        ---------------#########################     
         --------------########################      
          -------------#######################       
           ------------######################        
             ----------####################          
              ---------##############   ##           
                 ------############## T              
                     --############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.65e+21  -1.34e+22   1.32e+22 
 -1.34e+22   2.62e+22   5.61e+22 
  1.32e+22   5.61e+22  -2.06e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150727181215/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 = 100
      DIP = 80
     RAKE = -15
       MW = 4.47
       HS = 4.0

The NDK file is 20150727181215.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
 USGS/SLU Moment Tensor Solution
 ENS  2015/07/27 18:12:15:0  36.01  -97.58   3.2 4.5 Oklahoma
 
 Stations used:
   GS.KAN05 GS.KAN08 GS.KAN09 GS.KAN10 GS.KAN11 GS.KAN12 
   GS.KAN13 GS.KAN17 GS.KS20 GS.KS21 GS.OK025 GS.OK029 
   GS.OK031 GS.OK032 N4.R32B N4.T35B N4.U38B N4.Z35B N4.Z38B 
   OK.BCOK OK.BLOK OK.CCOK OK.CHOK OK.CROK OK.FNO OK.LOOK 
   OK.QUOK OK.U32A OK.X34A OK.X37A TA.ABTX TA.U40A TA.W39A 
   TA.WHTX US.CBKS US.KSU1 US.MIAR US.WMOK 
 
 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 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 6.38e+22 dyne-cm
  Mw = 4.47 
  Z  = 4 km
  Plane   Strike  Dip  Rake
   NP1      100    80   -15
   NP2      193    75   -170
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.38e+22      3     147
    N   0.00e+00     72     247
    P  -6.38e+22     18      56

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.62e+22
       Mxy    -5.61e+22
       Mxz    -1.34e+22
       Myy    -2.06e+22
       Myz    -1.32e+22
       Mzz    -5.65e+21
                                                     
                                                     
                                                     
                                                     
                     ###########---                  
                 ##############--------              
              ################------------           
             ################--------------          
           #################-------------   -        
          #################-------------- P --       
         #################---------------   ---      
        ##################----------------------     
        #################-----------------------     
       --################------------------------    
       -------##########-------------------------    
       -------------####-------------------------    
       -----------------#####--------------------    
        ---------------#########################     
        ---------------#########################     
         --------------########################      
          -------------#######################       
           ------------######################        
             ----------####################          
              ---------##############   ##           
                 ------############## T              
                     --############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.65e+21  -1.34e+22   1.32e+22 
 -1.34e+22   2.62e+22   5.61e+22 
  1.32e+22   5.61e+22  -2.06e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150727181215/index.html
	
Regional Moment Tensor (Mwr)
Moment	8.202e+15 N-m
Magnitude	4.54
Depth	5.0 km
Percent DC	65%
Half Duration	–
Catalog	US (us200030gd)
Data Source	US1
Contributor	US1
Nodal Planes
Plane	Strike	Dip	Rake
NP1	103	84	-11
NP2	194	79	-174
Principal Axes
Axis	Value	Plunge	Azimuth
T	8.870	4	149
N	-1.560	77	255
P	-7.310	12	58

        

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; (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.

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 +70
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   280    75   -10   4.26 0.4109
WVFGRD96    2.0   100    85   -15   4.38 0.5170
WVFGRD96    3.0   100    80   -20   4.44 0.5588
WVFGRD96    4.0   100    80   -15   4.47 0.5728
WVFGRD96    5.0   280    90    15   4.49 0.5713
WVFGRD96    6.0   280    90    15   4.52 0.5680
WVFGRD96    7.0   280    90    15   4.54 0.5630
WVFGRD96    8.0   280    90    20   4.57 0.5576
WVFGRD96    9.0   100    90   -20   4.58 0.5424
WVFGRD96   10.0   280    80    15   4.59 0.5296
WVFGRD96   11.0   280    80    15   4.60 0.5172
WVFGRD96   12.0   280    75    15   4.61 0.5054
WVFGRD96   13.0   280    75    15   4.62 0.4935
WVFGRD96   14.0   280    75    15   4.63 0.4817
WVFGRD96   15.0   280    75    15   4.63 0.4703
WVFGRD96   16.0   280    75    15   4.64 0.4594
WVFGRD96   17.0   280    75    15   4.65 0.4491
WVFGRD96   18.0   280    75    15   4.65 0.4391
WVFGRD96   19.0   280    75    15   4.66 0.4292
WVFGRD96   20.0   280    75    15   4.66 0.4196
WVFGRD96   21.0   280    75    20   4.67 0.4113
WVFGRD96   22.0   280    75    20   4.67 0.4032
WVFGRD96   23.0   280    75    20   4.68 0.3964
WVFGRD96   24.0   280    75    15   4.69 0.3900
WVFGRD96   25.0   280    75    15   4.69 0.3850
WVFGRD96   26.0   280    75    15   4.70 0.3801
WVFGRD96   27.0   280    75    15   4.71 0.3755
WVFGRD96   28.0   280    75    15   4.71 0.3709
WVFGRD96   29.0   280    75    15   4.72 0.3659

The best solution is

WVFGRD96    4.0   100    80   -15   4.47 0.5728

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 +70
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 was 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 Mon Jul 27 13:51:09 CDT 2015