Location

SLU Location

The SLU location is made using the program elocate and arival time picks from the NetQuake instruments in the source region and adjacent TA stations. The output is given in elocate.txt. The solution is the same as the NEIC solution. However we fix the depth to the value derived from the waveform inversion, e.g., 8 km.

USGS Location

2010/03/22 02:37:18 35.542 -96.737 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  2010/03/22 02:37:18:0  35.54  -96.74   5.0 3.7 Oklahoma
 
 Stations used:
   NM.UALR TA.133A TA.135A TA.S31A TA.S33A TA.T31A TA.T33A 
   TA.TUL1 TA.U31A TA.U32A TA.U34A TA.V34A TA.W30A TA.W31A 
   TA.W32A TA.W33A TA.W34A TA.X32A TA.X33A TA.X34A TA.Y31A 
   TA.Z32A TA.Z34A 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 = 3.89e+21 dyne-cm
  Mw = 3.66 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1       57    86   -150
   NP2      325    60    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.89e+21     17     187
    N   0.00e+00     60      65
    P  -3.89e+21     24     285

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.25e+21
       Mxy     1.29e+21
       Mxz    -1.49e+21
       Myy    -2.96e+21
       Myz     1.25e+21
       Mzz    -2.94e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              -------#####################           
             ------------##################          
           ----------------##################        
          -------------------###############--       
         ----------------------###########-----      
        ---   -------------------#######--------     
        --- P --------------------###-----------     
       ----   --------------------#--------------    
       ------------------------#####-------------    
       ----------------------########------------    
       -------------------############-----------    
        ---------------################---------     
        -----------####################---------     
         -------########################-------      
          ---###########################------       
           #############################-----        
             ###########################---          
              ##########   #############--           
                 ####### T ############              
                     ###   ########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.94e+20  -1.49e+21  -1.25e+21 
 -1.49e+21   3.25e+21  -1.29e+21 
 -1.25e+21  -1.29e+21  -2.96e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100322023718/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 = 325
      DIP = 60
     RAKE = -5
       MW = 3.66
       HS = 8.0

The waveform inversion is preferred. This event has well developed short period surface waves that had to be eliminated using the band reject filter. The original data will be very valuable for surface-wave tomography.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2010/03/22 02:37:18:0  35.54  -96.74   5.0 3.7 Oklahoma
 
 Stations used:
   NM.UALR TA.133A TA.135A TA.S31A TA.S33A TA.T31A TA.T33A 
   TA.TUL1 TA.U31A TA.U32A TA.U34A TA.V34A TA.W30A TA.W31A 
   TA.W32A TA.W33A TA.W34A TA.X32A TA.X33A TA.X34A TA.Y31A 
   TA.Z32A TA.Z34A 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 = 3.89e+21 dyne-cm
  Mw = 3.66 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1       57    86   -150
   NP2      325    60    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.89e+21     17     187
    N   0.00e+00     60      65
    P  -3.89e+21     24     285

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.25e+21
       Mxy     1.29e+21
       Mxz    -1.49e+21
       Myy    -2.96e+21
       Myz     1.25e+21
       Mzz    -2.94e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              -------#####################           
             ------------##################          
           ----------------##################        
          -------------------###############--       
         ----------------------###########-----      
        ---   -------------------#######--------     
        --- P --------------------###-----------     
       ----   --------------------#--------------    
       ------------------------#####-------------    
       ----------------------########------------    
       -------------------############-----------    
        ---------------################---------     
        -----------####################---------     
         -------########################-------      
          ---###########################------       
           #############################-----        
             ###########################---          
              ##########   #############--           
                 ####### T ############              
                     ###   ########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.94e+20  -1.49e+21  -1.25e+21 
 -1.49e+21   3.25e+21  -1.29e+21 
 -1.25e+21  -1.29e+21  -2.96e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100322023718/index.html
	



The first motion plot agrees with the waveform inversion. Triangles are strong dilations, - is a weak dilatation, + a weak compression and a circle is a strong compression. The X indicates a nodal arrival. The takeoff angles and picks are in the elocate.txt file.

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    80    -5   3.21 0.2442
WVFGRD96    1.0   325    90     5   3.26 0.2831
WVFGRD96    2.0   145    85   -10   3.44 0.4731
WVFGRD96    3.0   145    90     0   3.50 0.5423
WVFGRD96    4.0   325    85     0   3.53 0.5772
WVFGRD96    5.0   325    85     5   3.56 0.5928
WVFGRD96    6.0   325    85    10   3.59 0.5981
WVFGRD96    7.0   325    65     0   3.62 0.6013
WVFGRD96    8.0   325    60    -5   3.66 0.6035
WVFGRD96    9.0   325    65    -5   3.66 0.6016
WVFGRD96   10.0   325    65    -5   3.68 0.5991
WVFGRD96   11.0   325    65    -5   3.69 0.5951
WVFGRD96   12.0   325    65     0   3.70 0.5903
WVFGRD96   13.0   325    70     0   3.71 0.5851
WVFGRD96   14.0   325    70     0   3.72 0.5795
WVFGRD96   15.0   325    70     0   3.73 0.5728
WVFGRD96   16.0   325    70     0   3.74 0.5649
WVFGRD96   17.0   325    70     0   3.75 0.5566
WVFGRD96   18.0   325    70     0   3.76 0.5482
WVFGRD96   19.0   325    65    -5   3.78 0.5394
WVFGRD96   20.0   325    65    -5   3.78 0.5306
WVFGRD96   21.0   325    65    -5   3.79 0.5219
WVFGRD96   22.0   325    60    -5   3.81 0.5132
WVFGRD96   23.0   325    60    -5   3.82 0.5043
WVFGRD96   24.0   325    60    -5   3.82 0.4954
WVFGRD96   25.0   325    60    -5   3.83 0.4862
WVFGRD96   26.0   325    60    -5   3.84 0.4774
WVFGRD96   27.0   325    55    -5   3.85 0.4694
WVFGRD96   28.0   325    55    -5   3.86 0.4613
WVFGRD96   29.0   325    55    -5   3.87 0.4538

The best solution is

WVFGRD96    8.0   325    60    -5   3.66 0.6035

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 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:

DATE=Mon Mar 22 10:14:12 CDT 2010

Last Changed 2010/03/22