Location

2010/02/15 03:32:15 35.5587 -97.3002 5.5 2.80 Oklahoma

SLU Location

Error Ellipse  X=   0.2889 km  Y= 0.3782 km  Theta =   8.1622 deg

 RMS Error        :               0.031              sec
 Travel_Time_Table:          WUS
 Latitude         :             35.5621 +-    0.0026 N         0.2910 km
 Longitude        :            -97.2997 +-    0.0042 E         0.3766 km
 Depth            :                5.56 +-      0.34 km
 Epoch Time       :      1266204745.733 +-      0.05 sec
 Event Time       :  20100215033225.733 +-      0.05 sec
 Event (OCAL)     :  2010 02 15 03 32 25 733
 HYPO71 Quality   :                  BA
 Gap              :                  71              deg

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.

USGS Location

MAG     DATE      TIME      LAT     LON  H(km)   State
2.8   2010/02/15 03:32:25 35.570 -97.275  5.0   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  2010/02/15 03:32:25:7  35.56  -97.30   5.5 2.8 Oklahoma
 
 Stations used:
   GS.OK001 GS.OK003 GS.OK004 GS.OK005 GS.OK006 TA.V34A 
   TA.W34A 
 
 Filtering commands used:
   rtr
   hp c 0.5 n 3
   lp c 2.00 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 4.12e+20 dyne-cm
  Mw = 3.01 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      228    71   137
   NP2      335    50    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.12e+20     43     184
    N   0.00e+00     44      29
    P  -4.12e+20     13     286

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.89e+20
       Mxy     1.18e+20
       Mxz    -2.30e+20
       Myy    -3.60e+20
       Myz     7.41e+19
       Mzz     1.72e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 -------###############              
              --------------##############           
             -----------------#############          
           ---------------------#####--------        
          -----------------------#------------       
         ----------------------####------------      
        -   ----------------########------------     
        - P --------------###########-----------     
       --   ------------##############-----------    
       ---------------################-----------    
       -------------###################----------    
       ------------####################----------    
        ---------#######################--------     
        --------########################--------     
         ------#########################-------      
          ----############   ###########------       
           --############# T ###########-----        
             #############   ##########----          
              ########################----           
                 #####################-              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.72e+20  -2.30e+20  -7.41e+19 
 -2.30e+20   1.89e+20  -1.18e+20 
 -7.41e+19  -1.18e+20  -3.60e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100215033225/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 = 335
      DIP = 50
     RAKE = 25
       MW = 3.01
       HS = 5.0

Station OK002 was not used since there seemed to be some P on the transverse component. Distance weighting was such that a weighting factor of (dist/8) was used for dist <= 8 km and (8/dist0 dist dist >= 8 km. For larger earthquakes I normally used a reference distance of 100 km. The purpose of the reference distance is to down-weight close-in data which have large amplitudes but whose source-to-station azimuths are strongly dependent on the location. Data at larger distances are down-weighted to overcome imperfections of the velocity model on the Green functions .

Moment Tensor Comparison

The following compares this source inversion to others
SLU
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2010/02/15 00:07:00:0  36.08 -117.86   5.0 4.1 
 
 Stations used:
   GS.OK001 GS.OK002 GS.OK003 GS.OK004 GS.OK005 GS.OK006 
 
 Filtering commands used:
   hp c 0.5 n 3
   lp c 2.00 n 3
 
 Best Fitting Double Couple
  Mo = 3.85e+20 dyne-cm
  Mw = 2.99 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      235    79   139
   NP2      335    50    15
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.85e+20     36     187
    N   0.00e+00     48      42
    P  -3.85e+20     18     291

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.00e+20
       Mxy     1.45e+20
       Mxz    -2.24e+20
       Myy    -2.99e+20
       Myz     8.53e+19
       Mzz     9.80e+19
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 -------###############              
              --------------##############           
             -----------------#############          
           ---------------------#############        
          -----------------------#######------       
         -   ----------------------#-----------      
        -- P --------------------###------------     
        --   -----------------#######-----------     
       --------------------###########-----------    
       -----------------##############-----------    
       ---------------#################----------    
       -------------###################----------    
        ---------#######################--------     
        -------#########################--------     
         -----##########################-------      
          --############################------       
           ##############   ############-----        
             ############ T ###########----          
              ###########   ##########----           
                 #####################-              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  9.80e+19  -2.24e+20  -8.53e+19 
 -2.24e+20   2.00e+20  -1.45e+20 
 -8.53e+19  -1.45e+20  -2.99e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100215000700/index.html
 USGS/SLU Moment Tensor Solution
 ENS  2010/02/15 03:32:25:7  35.56  -97.30   5.5 2.8 Oklahoma
 
 Stations used:
   GS.OK001 GS.OK003 GS.OK004 GS.OK005 GS.OK006 TA.V34A 
   TA.W34A 
 
 Filtering commands used:
   rtr
   hp c 0.5 n 3
   lp c 2.00 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 4.12e+20 dyne-cm
  Mw = 3.01 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      228    71   137
   NP2      335    50    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.12e+20     43     184
    N   0.00e+00     44      29
    P  -4.12e+20     13     286

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.89e+20
       Mxy     1.18e+20
       Mxz    -2.30e+20
       Myy    -3.60e+20
       Myz     7.41e+19
       Mzz     1.72e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 -------###############              
              --------------##############           
             -----------------#############          
           ---------------------#####--------        
          -----------------------#------------       
         ----------------------####------------      
        -   ----------------########------------     
        - P --------------###########-----------     
       --   ------------##############-----------    
       ---------------################-----------    
       -------------###################----------    
       ------------####################----------    
        ---------#######################--------     
        --------########################--------     
         ------#########################-------      
          ----############   ###########------       
           --############# T ###########-----        
             #############   ##########----          
              ########################----           
                 #####################-              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.72e+20  -2.30e+20  -7.41e+19 
 -2.30e+20   1.89e+20  -1.18e+20 
 -7.41e+19  -1.18e+20  -3.60e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100215033225/index.html
	



The first motion plot is not very satisfying. I plot the observed Z components about the P-arrival pick. The takeoff angles and picks are in the elocate.txt file. At these short distances there is sensitivity of the take-off angles and azimuths to the location. The nodal planes are sensitive to the distance weighting. So this may be an apparent inconsistency in the comparison of observed and predicted first motions.

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:

rtr
hp c 0.5 n 3
lp c 2.00 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    55    75    25   2.09 0.1183
WVFGRD96    1.0    55    30   -20   2.22 0.1464
WVFGRD96    2.0    65    40     0   2.63 0.2466
WVFGRD96    3.0    45    50    75   2.73 0.2339
WVFGRD96    4.0   355    85   -30   2.96 0.3653
WVFGRD96    5.0   335    50    25   3.01 0.7015
WVFGRD96    6.0   335    50    30   3.06 0.6728
WVFGRD96    7.0   340    50    40   3.10 0.6844
WVFGRD96    8.0   340    50    45   3.15 0.5398
WVFGRD96    9.0   345    80    85   3.11 0.3674
WVFGRD96   10.0   345    80    80   3.13 0.3560
WVFGRD96   11.0   325    70   -75   3.04 0.1569
WVFGRD96   12.0   330    75   -70   3.03 0.1445
WVFGRD96   13.0   335    75   -70   2.97 0.0826
WVFGRD96   14.0    70    45    30   2.82 0.0251
WVFGRD96   15.0    70    50    25   2.84 0.0242
WVFGRD96   16.0    70    50    25   2.84 0.0214
WVFGRD96   17.0    20    80    30   2.83 0.0086
WVFGRD96   18.0   180    60   -30   2.82 0.0084
WVFGRD96   19.0   195    10    55   2.73 0.0077
WVFGRD96   20.0   190    65   -50   2.80 0.0073
WVFGRD96   21.0    20    40   -70   2.80 0.0059
WVFGRD96   22.0    30    45   -65   2.80 0.0055
WVFGRD96   23.0   295    65    45   2.80 0.0060
WVFGRD96   24.0     5    45   -30   2.84 0.0052
WVFGRD96   25.0   180    55    75   2.83 0.0054
WVFGRD96   26.0   175    55    65   2.86 0.0059
WVFGRD96   27.0   315    65   -60   2.77 0.0047
WVFGRD96   28.0   300    70   -55   2.85 0.0076
WVFGRD96   29.0   295    65   -50   2.89 0.0078

The best solution is

WVFGRD96    5.0   335    50    25   3.01 0.7015

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

rtr
hp c 0.5 n 3
lp c 2.00 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=Mon Feb 15 11:36:44 CST 2010

Last Changed 2010/02/15