Location

2011/11/06 17:52:34 35.548 -96.819 5 3.70 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 17:52:34:7  35.55  -96.82   5.0 3.7 Oklahoma
 
 Stations used:
   TA.136A TA.Q35A TA.R35A TA.R36A TA.R37A TA.S35A TA.S36A 
   TA.T34A TA.T35A TA.T36A TA.T37A TA.T38A TA.TUL1 TA.U32A 
   TA.U35A TA.U36A TA.U38A TA.U39A TA.V35A TA.V36A TA.V37A 
   TA.V38A TA.V40A TA.W35A TA.W36A TA.W37B TA.W38A TA.W39A 
   TA.W40A TA.X35A TA.X36A TA.X37A TA.X39A TA.Y35A TA.Y36A 
   TA.Y37A US.KSU1 US.MIAR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 1.76e+21 dyne-cm
  Mw = 3.43 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1       54    85   165
   NP2      145    75     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.76e+21     14       8
    N   0.00e+00     74     216
    P  -1.76e+21      7     100

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.56e+21
       Mxy     5.43e+20
       Mxz     4.47e+20
       Myy    -1.64e+21
       Myz    -1.51e+20
       Mzz     7.66e+19
                                                     
                                                     
                                                     
                                                     
                     ########   ###                  
                 ############ T #######              
              --#############   ##########           
             ----##########################          
           ------###########################-        
          --------#########################---       
         ----------#####################-------      
        ------------##################----------     
        -------------###############------------     
       ---------------############---------------    
       ----------------########------------------    
       -----------------#####-----------------       
       ------------------#-------------------- P     
        ----------------###-------------------       
        -------------#######--------------------     
         ---------############-----------------      
          -----################---------------       
           -#####################------------        
             ######################--------          
              ########################----           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  7.66e+19   4.47e+20   1.51e+20 
  4.47e+20   1.56e+21  -5.43e+20 
  1.51e+20  -5.43e+20  -1.64e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111106175234/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 = 145
      DIP = 75
     RAKE = 5
       MW = 3.43
       HS = 3.0

The NDK file is 20111106175234.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 17:52:34:7  35.55  -96.82   5.0 3.7 Oklahoma
 
 Stations used:
   TA.136A TA.Q35A TA.R35A TA.R36A TA.R37A TA.S35A TA.S36A 
   TA.T34A TA.T35A TA.T36A TA.T37A TA.T38A TA.TUL1 TA.U32A 
   TA.U35A TA.U36A TA.U38A TA.U39A TA.V35A TA.V36A TA.V37A 
   TA.V38A TA.V40A TA.W35A TA.W36A TA.W37B TA.W38A TA.W39A 
   TA.W40A TA.X35A TA.X36A TA.X37A TA.X39A TA.Y35A TA.Y36A 
   TA.Y37A US.KSU1 US.MIAR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 1.76e+21 dyne-cm
  Mw = 3.43 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1       54    85   165
   NP2      145    75     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.76e+21     14       8
    N   0.00e+00     74     216
    P  -1.76e+21      7     100

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.56e+21
       Mxy     5.43e+20
       Mxz     4.47e+20
       Myy    -1.64e+21
       Myz    -1.51e+20
       Mzz     7.66e+19
                                                     
                                                     
                                                     
                                                     
                     ########   ###                  
                 ############ T #######              
              --#############   ##########           
             ----##########################          
           ------###########################-        
          --------#########################---       
         ----------#####################-------      
        ------------##################----------     
        -------------###############------------     
       ---------------############---------------    
       ----------------########------------------    
       -----------------#####-----------------       
       ------------------#-------------------- P     
        ----------------###-------------------       
        -------------#######--------------------     
         ---------############-----------------      
          -----################---------------       
           -#####################------------        
             ######################--------          
              ########################----           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  7.66e+19   4.47e+20   1.51e+20 
  4.47e+20   1.56e+21  -5.43e+20 
  1.51e+20  -5.43e+20  -1.64e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111106175234/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
br c 0.12 0.25 n 4 p 2
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   145    85   -10   3.29 0.4586
WVFGRD96    1.0   145    90     0   3.32 0.4840
WVFGRD96    2.0   145    85     5   3.39 0.5494
WVFGRD96    3.0   145    75     5   3.43 0.5519
WVFGRD96    4.0   145    65     5   3.47 0.5454
WVFGRD96    5.0   140    55    -5   3.52 0.5396
WVFGRD96    6.0   140    55     0   3.53 0.5335
WVFGRD96    7.0   140    60     0   3.54 0.5285
WVFGRD96    8.0   140    55     0   3.57 0.5221
WVFGRD96    9.0   140    55     5   3.59 0.5140
WVFGRD96   10.0   140    55     5   3.59 0.5076
WVFGRD96   11.0   145    60    25   3.61 0.5026
WVFGRD96   12.0   145    60    25   3.61 0.5001
WVFGRD96   13.0   145    60    25   3.62 0.4969
WVFGRD96   14.0   150    55    25   3.62 0.4934
WVFGRD96   15.0   150    55    25   3.62 0.4890
WVFGRD96   16.0   140    80   -30   3.59 0.4848
WVFGRD96   17.0   140    80   -30   3.60 0.4852
WVFGRD96   18.0   140    80   -30   3.61 0.4843
WVFGRD96   19.0   140    80   -30   3.61 0.4826
WVFGRD96   20.0   140    80   -30   3.62 0.4797
WVFGRD96   21.0   145    85   -30   3.63 0.4766
WVFGRD96   22.0   145    90   -30   3.63 0.4737
WVFGRD96   23.0   325    90    30   3.64 0.4704
WVFGRD96   24.0   325    90    30   3.65 0.4667
WVFGRD96   25.0   325    90    30   3.65 0.4623
WVFGRD96   26.0   325    85    25   3.66 0.4577
WVFGRD96   27.0   325    85    25   3.66 0.4534
WVFGRD96   28.0   325    85    25   3.67 0.4484
WVFGRD96   29.0   330    80    25   3.68 0.4434

The best solution is

WVFGRD96    3.0   145    75     5   3.43 0.5519

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
br c 0.12 0.25 n 4 p 2
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 01:16:41 CST 2015