Location

2014/07/29 02:46:36 36.732 -97.987 7.6 4.3 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  2014/07/29 02:46:36:0  36.73  -97.99   7.6 4.3 Oklahoma
 
 Stations used:
   AG.FCAR AG.HHAR AG.WHAR AG.WLAR GS.KAN10 GS.KAN12 GS.KAN13 
   GS.OK025 GS.OK026 GS.OK027 GS.OK028 GS.OK029 N4.237B 
   N4.L34B N4.N33B N4.N35B N4.P38B N4.R32B N4.R40B N4.S39B 
   N4.U38B N4.Z35B N4.Z38B NM.MGMO NM.UALR OK.BCOK OK.CROK 
   OK.FNO OK.U32A OK.X37A TA.ABTX TA.BGNE TA.KSCO TA.MSTX 
   TA.T25A TA.TUL1 TA.U40A TA.W39A TA.W41B TA.WHTX US.AMTX 
   US.CBKS US.KSU1 US.MIAR US.WMOK 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +60
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 3.09e+22 dyne-cm
  Mw = 4.26 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      305    65   -40
   NP2       55    54   -149
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.09e+22      6       2
    N   0.00e+00     44      98
    P  -3.09e+22     45     265

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.04e+22
       Mxy    -1.89e+20
       Mxz     4.72e+21
       Myy    -1.52e+22
       Myz     1.55e+22
       Mzz    -1.52e+22
                                                     
                                                     
                                                     
                                                     
                     ###### T #####                  
                 ##########   #########              
              ############################           
             ##############################          
           #--###############################        
          ------------#######################-       
         ------------------##################--      
        ----------------------##############----     
        ------------------------###########-----     
       ----------------------------#######-------    
       --------   -------------------####--------    
       -------- P ---------------------#---------    
       --------   --------------------##---------    
        -----------------------------#####------     
        --------------------------#########-----     
         -----------------------############---      
          ------------------#################-       
           -------------#####################        
             ##############################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.52e+22   4.72e+21  -1.55e+22 
  4.72e+21   3.04e+22   1.89e+20 
 -1.55e+22   1.89e+20  -1.52e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140729024636/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 = 305
      DIP = 65
     RAKE = -40
       MW = 4.26
       HS = 3.0

The NDK file is 20140729024636.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  2014/07/29 02:46:36:0  36.73  -97.99   7.6 4.3 Oklahoma
 
 Stations used:
   AG.FCAR AG.HHAR AG.WHAR AG.WLAR GS.KAN10 GS.KAN12 GS.KAN13 
   GS.OK025 GS.OK026 GS.OK027 GS.OK028 GS.OK029 N4.237B 
   N4.L34B N4.N33B N4.N35B N4.P38B N4.R32B N4.R40B N4.S39B 
   N4.U38B N4.Z35B N4.Z38B NM.MGMO NM.UALR OK.BCOK OK.CROK 
   OK.FNO OK.U32A OK.X37A TA.ABTX TA.BGNE TA.KSCO TA.MSTX 
   TA.T25A TA.TUL1 TA.U40A TA.W39A TA.W41B TA.WHTX US.AMTX 
   US.CBKS US.KSU1 US.MIAR US.WMOK 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +60
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 3.09e+22 dyne-cm
  Mw = 4.26 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      305    65   -40
   NP2       55    54   -149
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.09e+22      6       2
    N   0.00e+00     44      98
    P  -3.09e+22     45     265

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.04e+22
       Mxy    -1.89e+20
       Mxz     4.72e+21
       Myy    -1.52e+22
       Myz     1.55e+22
       Mzz    -1.52e+22
                                                     
                                                     
                                                     
                                                     
                     ###### T #####                  
                 ##########   #########              
              ############################           
             ##############################          
           #--###############################        
          ------------#######################-       
         ------------------##################--      
        ----------------------##############----     
        ------------------------###########-----     
       ----------------------------#######-------    
       --------   -------------------####--------    
       -------- P ---------------------#---------    
       --------   --------------------##---------    
        -----------------------------#####------     
        --------------------------#########-----     
         -----------------------############---      
          ------------------#################-       
           -------------#####################        
             ##############################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.52e+22   4.72e+21  -1.55e+22 
  4.72e+21   3.04e+22   1.89e+20 
 -1.55e+22   1.89e+20  -1.52e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140729024636/index.html
	
Regional Moment Tensor (Mwr)

Moment magnitude derived from a moment tensor 
inversion of complete waveforms at regional distances 
(less than ~8 degrees), generally used for the 
analysis of small to moderate size earthquakes 
(typically Mw 3.5-6.0) crust or upper mantle earthquakes.

Moment
    3.28e+15 N-m
Magnitude
    4.3
Percent DC
    81%
Depth
    3.0 km
Updated
    2014-07-29 03:40:31 UTC
Author
    us
Catalog
    us
Contributor
    us
Code
    us_b000ry6y_mwr

Principal Axes
Axis	Value	Plunge	Azimuth
T	3.425	3 	356 
N	-0.313	52 	263 
P	-3.112	38 	88 
Nodal Planes
Plane	Strike	Dip	Rake
NP1	229 	66 	-149 
NP2	125 	62 	-27 

        

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 -40 o DIST/3.3 +60
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.06 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   130    70   -25   4.10 0.5185
WVFGRD96    2.0   310    65   -35   4.19 0.5939
WVFGRD96    3.0   305    65   -40   4.26 0.6245
WVFGRD96    4.0   125    70   -30   4.28 0.6037
WVFGRD96    5.0   130    85   -10   4.28 0.5678
WVFGRD96    6.0   130    90   -15   4.30 0.5349
WVFGRD96    7.0   130    90   -20   4.31 0.5127
WVFGRD96    8.0   130    90   -30   4.34 0.4985
WVFGRD96    9.0   315    75    25   4.35 0.4878
WVFGRD96   10.0   315    75    25   4.35 0.4769
WVFGRD96   11.0   140    70    30   4.36 0.4689
WVFGRD96   12.0   140    70    30   4.36 0.4699
WVFGRD96   13.0   140    70    30   4.37 0.4690
WVFGRD96   14.0   140    70    25   4.37 0.4666
WVFGRD96   15.0   145    65    25   4.37 0.4629
WVFGRD96   16.0   145    65    25   4.37 0.4584
WVFGRD96   17.0   145    65    25   4.38 0.4527
WVFGRD96   18.0   140    60    15   4.38 0.4463
WVFGRD96   19.0   145    60    25   4.38 0.4403
WVFGRD96   20.0   145    60    25   4.39 0.4337
WVFGRD96   21.0   145    60    25   4.40 0.4258
WVFGRD96   22.0   145    55    20   4.39 0.4185
WVFGRD96   23.0   145    55    20   4.40 0.4108
WVFGRD96   24.0   145    55    20   4.40 0.4031
WVFGRD96   25.0   140    55    15   4.41 0.3951
WVFGRD96   26.0   140    55    15   4.41 0.3874
WVFGRD96   27.0   140    55    10   4.41 0.3798
WVFGRD96   28.0   140    55    10   4.42 0.3725
WVFGRD96   29.0   140    55    10   4.42 0.3655

The best solution is

WVFGRD96    3.0   305    65   -40   4.26 0.6245

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 +60
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.06 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 Mon Dec 7 00:14:11 CST 2015