Location

2010/01/15 15:18:26 35.592 -97.258 5.0 4.00 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  2010/01/15 15:18:26:0  35.59  -97.26   5.0 4.0 Oklahoma
 
 Stations used:
   NM.UALR TA.133A TA.134A TA.135A TA.P32A TA.P33A TA.Q30A 
   TA.Q32A TA.Q33A TA.R30A TA.R31A TA.R32A TA.R33A TA.S29A 
   TA.S30A TA.S31A TA.S33A TA.T29A TA.T30A TA.T31A TA.T32A 
   TA.T33A TA.TUL1 TA.U29A TA.U30A TA.U31A TA.U32A TA.U33A 
   TA.U34A TA.V29A TA.V31A TA.V32A TA.V33A TA.V34A TA.W29A 
   TA.W30A TA.W31A TA.W32A TA.W33A TA.W34A TA.WHTX TA.X28A 
   TA.X30A TA.X31A TA.X33A TA.X34A TA.Y30A TA.Y31A TA.Y32A 
   TA.Y33A TA.Y34A TA.Z31A TA.Z32A TA.Z33A TA.Z34A TA.Z35A 
   US.AMTX US.KSU1 US.MIAR US.WMOK 
 
 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 = 6.53e+21 dyne-cm
  Mw = 3.81 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1      145    90    25
   NP2       55    65   180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.53e+21     17      13
    N   0.00e+00     65     145
    P  -6.53e+21     17     277

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.56e+21
       Mxy     2.02e+21
       Mxz     1.58e+21
       Myy    -5.56e+21
       Myz     2.26e+21
       Mzz    -2.41e+14
                                                     
                                                     
                                                     
                                                     
                     #########   ##                  
                 ############# T ######              
              ---#############   #########           
             -----#########################          
           ---------#########################        
          -----------########################-       
         -------------######################---      
        ---------------####################-----     
        -   -------------#################------     
       -- P --------------##############---------    
       --   ---------------############----------    
       ----------------------########------------    
       -----------------------#####--------------    
        -----------------------#----------------     
        ----------------------###---------------     
         ------------------#######-------------      
          ------------#############-----------       
           #--######################---------        
             #########################-----          
              #########################---           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.41e+14   1.58e+21  -2.26e+21 
  1.58e+21   5.56e+21  -2.02e+21 
 -2.26e+21  -2.02e+21  -5.56e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100115151826/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 = 90
     RAKE = 25
       MW = 3.81
       HS = 8.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2010/01/15 15:18:26:0  35.59  -97.26   5.0 4.0 Oklahoma
 
 Stations used:
   NM.UALR TA.133A TA.134A TA.135A TA.P32A TA.P33A TA.Q30A 
   TA.Q32A TA.Q33A TA.R30A TA.R31A TA.R32A TA.R33A TA.S29A 
   TA.S30A TA.S31A TA.S33A TA.T29A TA.T30A TA.T31A TA.T32A 
   TA.T33A TA.TUL1 TA.U29A TA.U30A TA.U31A TA.U32A TA.U33A 
   TA.U34A TA.V29A TA.V31A TA.V32A TA.V33A TA.V34A TA.W29A 
   TA.W30A TA.W31A TA.W32A TA.W33A TA.W34A TA.WHTX TA.X28A 
   TA.X30A TA.X31A TA.X33A TA.X34A TA.Y30A TA.Y31A TA.Y32A 
   TA.Y33A TA.Y34A TA.Z31A TA.Z32A TA.Z33A TA.Z34A TA.Z35A 
   US.AMTX US.KSU1 US.MIAR US.WMOK 
 
 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 = 6.53e+21 dyne-cm
  Mw = 3.81 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1      145    90    25
   NP2       55    65   180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.53e+21     17      13
    N   0.00e+00     65     145
    P  -6.53e+21     17     277

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.56e+21
       Mxy     2.02e+21
       Mxz     1.58e+21
       Myy    -5.56e+21
       Myz     2.26e+21
       Mzz    -2.41e+14
                                                     
                                                     
                                                     
                                                     
                     #########   ##                  
                 ############# T ######              
              ---#############   #########           
             -----#########################          
           ---------#########################        
          -----------########################-       
         -------------######################---      
        ---------------####################-----     
        -   -------------#################------     
       -- P --------------##############---------    
       --   ---------------############----------    
       ----------------------########------------    
       -----------------------#####--------------    
        -----------------------#----------------     
        ----------------------###---------------     
         ------------------#######-------------      
          ------------#############-----------       
           #--######################---------        
             #########################-----          
              #########################---           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.41e+14   1.58e+21  -2.26e+21 
  1.58e+21   5.56e+21  -2.02e+21 
 -2.26e+21  -2.02e+21  -5.56e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100115151826/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   145    90    10   3.36 0.2558
WVFGRD96    1.0   145    85     5   3.41 0.2966
WVFGRD96    2.0   145    85     0   3.60 0.4979
WVFGRD96    3.0   145    85     0   3.66 0.5683
WVFGRD96    4.0   145    90     5   3.69 0.6006
WVFGRD96    5.0   145    90    15   3.73 0.6131
WVFGRD96    6.0   325    70     0   3.75 0.6173
WVFGRD96    7.0   325    70     0   3.77 0.6202
WVFGRD96    8.0   145    90    25   3.81 0.6211
WVFGRD96    9.0   145    90    25   3.82 0.6183
WVFGRD96   10.0   325    70     0   3.83 0.6151
WVFGRD96   11.0   330    80    25   3.85 0.6117
WVFGRD96   12.0   330    80    20   3.86 0.6100
WVFGRD96   13.0   330    80    20   3.87 0.6072
WVFGRD96   14.0   330    80    20   3.88 0.6031
WVFGRD96   15.0   325    85    15   3.89 0.5980
WVFGRD96   16.0   325    85    15   3.90 0.5924
WVFGRD96   17.0   325    85    15   3.91 0.5864
WVFGRD96   18.0   325    85    15   3.92 0.5797
WVFGRD96   19.0   325    85    15   3.93 0.5723
WVFGRD96   20.0   325    85    15   3.94 0.5650
WVFGRD96   21.0   325    85    15   3.95 0.5566
WVFGRD96   22.0   325    85    10   3.95 0.5481
WVFGRD96   23.0   325    85    10   3.96 0.5397
WVFGRD96   24.0   325    85    10   3.97 0.5303
WVFGRD96   25.0   325    85    10   3.97 0.5209
WVFGRD96   26.0   325    85    10   3.98 0.5112
WVFGRD96   27.0   325    85    10   3.98 0.5018
WVFGRD96   28.0   325    85    10   3.99 0.4915
WVFGRD96   29.0   325    75    -5   4.00 0.4823

The best solution is

WVFGRD96    8.0   145    90    25   3.81 0.6211

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=Fri Jan 15 11:13:37 CST 2010

Last Changed 2010/01/15