Location

2011/11/06 09:39:57 35.506 -96.865 5 4.90 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  2011/11/06 09:39:57:4  35.51  -96.86   5.0 4.9 Oklahoma
 
 Stations used:
   TA.Q35A TA.Q36A TA.R34A TA.R37A TA.R38A TA.S34A TA.S35A 
   TA.S36A TA.S37A TA.S39A TA.T34A TA.T35A TA.T36A TA.T39A 
   TA.TUL1 TA.U35A TA.U36A TA.U39A TA.U40A TA.V35A TA.V36A 
   TA.V37A TA.V38A TA.V39A TA.V40A TA.W35A TA.W36A TA.W37B 
   TA.W39A TA.X35A TA.X36A TA.X38A TA.Y36A TA.Y38A TA.Y39A 
   US.KSU1 US.MIAR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 3.76e+21 dyne-cm
  Mw = 3.65 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      320    90   -10
   NP2       50    80   -180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.76e+21      7       5
    N   0.00e+00     80     140
    P  -3.76e+21      7     275

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.65e+21
       Mxy     6.43e+20
       Mxz     4.20e+20
       Myy    -3.65e+21
       Myz     5.00e+20
       Mzz     5.71e+13
                                                     
                                                     
                                                     
                                                     
                     ####### T ####                  
                 ###########   ########              
              -###########################           
             ---###########################          
           -------#########################--        
          ---------#######################----       
         ------------###################-------      
        ---------------################---------     
        ----------------#############-----------     
          ----------------#########--------------    
        P -----------------######----------------    
          -------------------##------------------    
       ----------------------#-------------------    
        ------------------######----------------     
        ----------------#########---------------     
         ------------##############------------      
          --------###################---------       
           ----#######################-------        
             ###########################---          
              ###########################-           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.71e+13   4.20e+20  -5.00e+20 
  4.20e+20   3.65e+21  -6.43e+20 
 -5.00e+20  -6.43e+20  -3.65e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111106093957/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 = 320
      DIP = 90
     RAKE = -10
       MW = 3.65
       HS = 3.0

The NDK file is 20111106093957.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2011/11/06 09:39:57:4  35.51  -96.86   5.0 4.9 Oklahoma
 
 Stations used:
   TA.Q35A TA.Q36A TA.R34A TA.R37A TA.R38A TA.S34A TA.S35A 
   TA.S36A TA.S37A TA.S39A TA.T34A TA.T35A TA.T36A TA.T39A 
   TA.TUL1 TA.U35A TA.U36A TA.U39A TA.U40A TA.V35A TA.V36A 
   TA.V37A TA.V38A TA.V39A TA.V40A TA.W35A TA.W36A TA.W37B 
   TA.W39A TA.X35A TA.X36A TA.X38A TA.Y36A TA.Y38A TA.Y39A 
   US.KSU1 US.MIAR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 3.76e+21 dyne-cm
  Mw = 3.65 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1      320    90   -10
   NP2       50    80   -180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.76e+21      7       5
    N   0.00e+00     80     140
    P  -3.76e+21      7     275

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.65e+21
       Mxy     6.43e+20
       Mxz     4.20e+20
       Myy    -3.65e+21
       Myz     5.00e+20
       Mzz     5.71e+13
                                                     
                                                     
                                                     
                                                     
                     ####### T ####                  
                 ###########   ########              
              -###########################           
             ---###########################          
           -------#########################--        
          ---------#######################----       
         ------------###################-------      
        ---------------################---------     
        ----------------#############-----------     
          ----------------#########--------------    
        P -----------------######----------------    
          -------------------##------------------    
       ----------------------#-------------------    
        ------------------######----------------     
        ----------------#########---------------     
         ------------##############------------      
          --------###################---------       
           ----#######################-------        
             ###########################---          
              ###########################-           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.71e+13   4.20e+20  -5.00e+20 
  4.20e+20   3.65e+21  -6.43e+20 
 -5.00e+20  -6.43e+20  -3.65e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111106093957/index.html
	

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:

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    0.5   315    80   -30   3.52 0.3899
WVFGRD96    1.0   140    90    10   3.52 0.4134
WVFGRD96    2.0   135    70   -15   3.62 0.4824
WVFGRD96    3.0   320    90   -10   3.65 0.4945
WVFGRD96    4.0   140    90    15   3.68 0.4851
WVFGRD96    5.0   140    85    20   3.70 0.4716
WVFGRD96    6.0   140    85    25   3.72 0.4636
WVFGRD96    7.0   140    85    25   3.74 0.4590
WVFGRD96    8.0   140    55     0   3.78 0.4568
WVFGRD96    9.0   140    55     0   3.78 0.4511
WVFGRD96   10.0   140    55     0   3.79 0.4445
WVFGRD96   11.0   140    60     5   3.79 0.4373
WVFGRD96   12.0   140    60     5   3.80 0.4305
WVFGRD96   13.0   140    60     0   3.81 0.4275
WVFGRD96   14.0   140    60    -5   3.81 0.4242
WVFGRD96   15.0   140    60    -5   3.82 0.4201
WVFGRD96   16.0   140    65    -5   3.83 0.4156
WVFGRD96   17.0   140    65   -10   3.83 0.4111
WVFGRD96   18.0   140    65   -10   3.84 0.4069
WVFGRD96   19.0   135    65   -15   3.85 0.4024
WVFGRD96   20.0   135    65   -15   3.86 0.3982
WVFGRD96   21.0   135    65   -15   3.87 0.3938
WVFGRD96   22.0   135    65   -15   3.88 0.3888
WVFGRD96   23.0   135    65   -15   3.88 0.3837
WVFGRD96   24.0   135    70   -15   3.89 0.3789
WVFGRD96   25.0   135    70   -15   3.90 0.3745
WVFGRD96   26.0   135    70   -15   3.90 0.3701
WVFGRD96   27.0   135    70   -15   3.91 0.3658
WVFGRD96   28.0   135    70   -15   3.92 0.3616
WVFGRD96   29.0   135    70   -15   3.93 0.3570

The best solution is

WVFGRD96    3.0   320    90   -10   3.65 0.4945

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

hp c 0.02 n 3
lp c 0.06 n 3
Figure 3. Waveform comparison for selected depth
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 02:22:25 CST 2015