Location

2010/01/24 07:14:51 35.567 -97.284 5.0 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  2010/01/24 07:14:51:0  35.57  -97.28   5.0 3.7 Oklahoma
 
 Stations used:
   TA.TUL1 TA.U31A TA.U34A TA.V33A TA.V34A TA.W34A TA.X34A 
   TA.Y33A 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 3.27e+21 dyne-cm
  Mw = 3.61 
  Z  = 6 km
  Plane   Strike  Dip  Rake
   NP1      115    85    25
   NP2       23    65   174
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.27e+21     21     342
    N   0.00e+00     65     126
    P  -3.27e+21     14     246

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.07e+21
       Mxy    -1.99e+21
       Mxz     1.34e+21
       Myy    -2.31e+21
       Myz     3.41e+20
       Mzz     2.40e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ####   ############---              
              ####### T #############-----           
             ########   #############------          
           ##########################--------        
          ###########################---------       
         -###########################----------      
        -----########################-----------     
        --------####################------------     
       ------------#################-------------    
       ----------------############--------------    
       --------------------#######---------------    
       ------------------------###---------------    
        --   --------------------##-------------     
        -- P -------------------########--------     
         -   ------------------##############--      
          --------------------################       
           -----------------#################        
             --------------################          
              -----------#################           
                 ------################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.40e+20   1.34e+21  -3.41e+20 
  1.34e+21   2.07e+21   1.99e+21 
 -3.41e+20   1.99e+21  -2.31e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100124071451/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 = 115
      DIP = 85
     RAKE = 25
       MW = 3.61
       HS = 6.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2010/01/24 07:14:51:0  35.57  -97.28   5.0 3.7 Oklahoma
 
 Stations used:
   TA.TUL1 TA.U31A TA.U34A TA.V33A TA.V34A TA.W34A TA.X34A 
   TA.Y33A 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 3.27e+21 dyne-cm
  Mw = 3.61 
  Z  = 6 km
  Plane   Strike  Dip  Rake
   NP1      115    85    25
   NP2       23    65   174
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.27e+21     21     342
    N   0.00e+00     65     126
    P  -3.27e+21     14     246

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.07e+21
       Mxy    -1.99e+21
       Mxz     1.34e+21
       Myy    -2.31e+21
       Myz     3.41e+20
       Mzz     2.40e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ####   ############---              
              ####### T #############-----           
             ########   #############------          
           ##########################--------        
          ###########################---------       
         -###########################----------      
        -----########################-----------     
        --------####################------------     
       ------------#################-------------    
       ----------------############--------------    
       --------------------#######---------------    
       ------------------------###---------------    
        --   --------------------##-------------     
        -- P -------------------########--------     
         -   ------------------##############--      
          --------------------################       
           -----------------#################        
             --------------################          
              -----------#################           
                 ------################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.40e+20   1.34e+21  -3.41e+20 
  1.34e+21   2.07e+21   1.99e+21 
 -3.41e+20   1.99e+21  -2.31e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100124071451/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:

hp c 0.02 n 3
lp c 0.10 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   110    90     0   3.18 0.2129
WVFGRD96    1.0   110    90     0   3.23 0.2405
WVFGRD96    2.0   290    80    -5   3.43 0.4094
WVFGRD96    3.0   295    90   -20   3.50 0.4717
WVFGRD96    4.0   115    85    30   3.56 0.5185
WVFGRD96    5.0   115    85    30   3.59 0.5418
WVFGRD96    6.0   115    85    25   3.61 0.5493
WVFGRD96    7.0   115    85    25   3.63 0.5482
WVFGRD96    8.0   115    85    30   3.66 0.5424
WVFGRD96    9.0   115    85    25   3.66 0.5336
WVFGRD96   10.0   115    85    25   3.67 0.5246
WVFGRD96   11.0   120    80    25   3.68 0.5163
WVFGRD96   12.0   120    80    25   3.69 0.5085
WVFGRD96   13.0   120    80    25   3.70 0.5000
WVFGRD96   14.0   120    80    25   3.71 0.4910
WVFGRD96   15.0   120    80    20   3.71 0.4839
WVFGRD96   16.0   120    80    20   3.72 0.4771
WVFGRD96   17.0   120    80    20   3.73 0.4703
WVFGRD96   18.0   120    80    20   3.74 0.4635
WVFGRD96   19.0   115    85    20   3.75 0.4582
WVFGRD96   20.0   115    85    20   3.76 0.4535
WVFGRD96   21.0   115    85    20   3.76 0.4480
WVFGRD96   22.0   115    85    20   3.77 0.4429
WVFGRD96   23.0   115    85    20   3.78 0.4380
WVFGRD96   24.0   115    85    20   3.79 0.4328
WVFGRD96   25.0   295    90   -20   3.79 0.4278
WVFGRD96   26.0   115    90    20   3.79 0.4243
WVFGRD96   27.0   115    85    15   3.80 0.4212
WVFGRD96   28.0   295    90   -20   3.81 0.4186
WVFGRD96   29.0   295    90   -15   3.81 0.4162

The best solution is

WVFGRD96    6.0   115    85    25   3.61 0.5493

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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was

hp c 0.02 n 3
lp c 0.10 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.

Discussion

The Future

Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.

Acknowledgements

Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The WUS 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:

DATE=Sun Jan 24 11:17:44 CST 2010

Last Changed 2010/01/24