Discussion of velocity model and metadata

Discussion of QC and tests

Location

2010/02/13 05:30:55 35.5331 -97.2982 5.5 3.20 Oklahoma

SLU Location

Error Ellipse  X=   0.3202 km  Y= 0.3824 km  Theta =   6.2905 deg

 RMS Error        :               0.051              sec
 Travel_Time_Table:          WUS     
 Latitude         :             35.5331 +-    0.0029 N         0.3210 km
 Longitude        :            -97.2982 +-    0.0042 E         0.3817 km
 Depth            :                5.52 +-      0.42 km
 Epoch Time       :      1266039055.968 +-      0.06 sec
 Event Time       :  20100213053055.968 +-      0.06 sec
 Event (OCAL)     :  2010 02 13 05 30 55 968
 HYPO71 Quality   :                  BA
 Gap              :                  84              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. Station GSOK002 is not used since there seems to be a significant timing error. We got nearby TA stations but were not able to get the "35" stations.

USGS Location


MAG    DATE    TIME(UT)   LAT     LON    H   State
3.2 2010/02/13 05:30:56  35.566 -97.215 5.0 OKLAHOMA

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2010/02/13 05:30:55:9  35.53  -97.30   5.5 3.2 Oklahoma
 
 Stations used:
   GS.OK001 GS.OK002 GS.OK003 GS.OK004 GS.OK005 GS.OK006 
 
 Filtering commands used:
   hp c 0.50 n 2
   lp c 1.00 n 2
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 7.16e+20 dyne-cm
  Mw = 3.17 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1       57    80   -170
   NP2      325    80   -10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.16e+20      0     191
    N   0.00e+00     76     100
    P  -7.16e+20     14     281

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     6.67e+20
       Mxy     2.58e+20
       Mxz    -3.33e+19
       Myy    -6.24e+20
       Myz     1.66e+20
       Mzz    -4.25e+19
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              ----########################           
             -------#######################          
           -----------#######################        
          -------------#####################--       
         ----------------##################----      
        ------------------###############-------     
        -   ----------------###########---------     
       -- P -----------------#######-------------    
       --   ------------------####---------------    
       ------------------------#-----------------    
       ---------------------#####----------------    
        -----------------#########--------------     
        --------------#############-------------     
         ----------#################-----------      
          ----#######################---------       
           ###########################-------        
             ##########################----          
              ##########################--           
                 ######   #############              
                     ## T #########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.25e+19  -3.33e+19  -1.66e+20 
 -3.33e+19   6.67e+20  -2.58e+20 
 -1.66e+20  -2.58e+20  -6.24e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100213053055/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 = 80
     RAKE = -10
       MW = 3.17
       HS = 5.0

A check on particle motion indicate that the trace with name HNZ was Z and HNE was E but the CMPINC and CMPAZ headers in the SAC file was not correctly set. The absolute time of GSOK002 was adjusted when the clock correction was determined. Green functions for the WUS model were recomputed with DT=0.05 sec. Finally to have a good S/N ratio the signal was filtered between 0.5 and 1.0 Hz, P-wave first arrivals hand picked, the time shift of the grid search severely restricted. The filtering was selected to have good S/N for the low frequency corner and still a simple waveform for the high frequency corner, Since high frequency fit is sensitive to the velocity model, or more precisely the ratio of distance to wavelength.

Finally the mechanism and depth are very similar to those of the 3 larger earthquakes in January in this source region.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2010/02/13 05:30:55:9  35.53  -97.30   5.5 3.2 Oklahoma
 
 Stations used:
   GS.OK001 GS.OK002 GS.OK003 GS.OK004 GS.OK005 GS.OK006 
 
 Filtering commands used:
   hp c 0.50 n 2
   lp c 1.00 n 2
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 7.16e+20 dyne-cm
  Mw = 3.17 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1       57    80   -170
   NP2      325    80   -10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.16e+20      0     191
    N   0.00e+00     76     100
    P  -7.16e+20     14     281

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     6.67e+20
       Mxy     2.58e+20
       Mxz    -3.33e+19
       Myy    -6.24e+20
       Myz     1.66e+20
       Mzz    -4.25e+19
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              ----########################           
             -------#######################          
           -----------#######################        
          -------------#####################--       
         ----------------##################----      
        ------------------###############-------     
        -   ----------------###########---------     
       -- P -----------------#######-------------    
       --   ------------------####---------------    
       ------------------------#-----------------    
       ---------------------#####----------------    
        -----------------#########--------------     
        --------------#############-------------     
         ----------#################-----------      
          ----#######################---------       
           ###########################-------        
             ##########################----          
              ##########################--           
                 ######   #############              
                     ## T #########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.25e+19  -3.33e+19  -1.66e+20 
 -3.33e+19   6.67e+20  -2.58e+20 
 -1.66e+20  -2.58e+20  -6.24e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100213053055/index.html
	
First motions plotted with waveform inversion 
nodal planes. Take-off angles are from WUS model and
elocate run.

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 0.50 n 2
lp c 1.00 n 2
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   150    90     0   2.42 0.2947
WVFGRD96    1.0    20    80     0   2.47 0.3078
WVFGRD96    2.0   290    55   -25   2.73 0.1387
WVFGRD96    3.0   325    80   -20   3.03 0.2812
WVFGRD96    4.0   325    80   -15   3.13 0.4226
WVFGRD96    5.0   325    80   -10   3.17 0.4562
WVFGRD96    6.0   325    75    -5   3.18 0.4549
WVFGRD96    7.0   325    65     0   3.19 0.4430
WVFGRD96    8.0   330    60     0   3.23 0.4255
WVFGRD96    9.0   330    65     0   3.29 0.4370
WVFGRD96   10.0   330    65     0   3.32 0.4253
WVFGRD96   11.0   330    65     0   3.34 0.4072
WVFGRD96   12.0   330    70     5   3.36 0.3641
WVFGRD96   13.0   335    70     5   3.36 0.3139
WVFGRD96   14.0   320    90    30   3.38 0.2995
WVFGRD96   15.0   340    55    15   3.23 0.1142
WVFGRD96   16.0   340    25    20   3.12 0.0631
WVFGRD96   17.0   345    25    25   3.12 0.0608
WVFGRD96   18.0   335    30     5   3.10 0.0457
WVFGRD96   19.0   110    75     0   3.22 0.0370

The best solution is

WVFGRD96    5.0   325    80   -10   3.17 0.4562

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 0.50 n 2
lp c 1.00 n 2
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:

Other Earthquakes

Update time = Sat Feb 13 15:00:33 CST 2010
Here are the earthquakes appearing on this map, most recent at top ...

 MAG    DATE    LOCAL-TIME  LAT     LON    DEPTH    LOCATION
        y/m/d     h:m:s     deg     deg     km

 3.2  2010/02/12 23:30:55 35.566N 97.215W  5.0   17 km (10 mi) SE  of Arcadia, OK 
 2.5  2010/02/01 17:43:04 35.547N 97.236W  5.0   16 km (10 mi) SSE of Arcadia, OK 
 3.7  2010/01/24 01:14:51 35.517N 97.245W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 3.8  2010/01/15 09:27:01 35.569N 97.277W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 4.0  2010/01/15 09:18:25 35.574N 97.249W  5.0   10 km ( 6 mi) SE  of Arcadia, OK 
 3.3  2010/01/14 04:05:34 35.539N 97.238W  5.0    8 km ( 5 mi) NNE of Arcadia, OK 
 2.8  2010/01/10 23:16:00 35.566N 97.287W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.8  2010/01/01 12:45:51 35.634N 97.184W  5.0   13 km ( 8 mi) ESE of Arcadia, OK 
 3.0  2009/12/19 23:05:20 35.541N 97.298W  5.0   13 km ( 8 mi) E   of Lake Aluma, OK 
 2.8  2009/12/17 20:25:39 35.542N 97.271W  5.0   15 km ( 9 mi) SSE of Arcadia, OK 
 2.2  2009/12/17 17:52:01 35.566N 97.287W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.4  2009/12/15 09:39:15 35.576N 97.289W  5.0   11 km ( 7 mi) SSE of Arcadia, OK 
 3.4  2009/12/13 02:38:25 35.586N 97.277W  5.0    8 km ( 5 mi) SSE of Arcadia, OK 
 3.1  2009/12/12 05:34:05 35.556N 97.315W  5.0    9 km ( 6 mi) E   of Lake Aluma, OK 
 2.8  2009/12/11 08:00:17 35.587N 97.324W  5.0    1 km ( 1 mi) NNE of Arcadia, OK 
 3.5  2009/12/07 11:44:25 35.559N 97.259W  5.0   13 km ( 8 mi) SSE of Arcadia, OK 
 3.0  2009/11/28 19:36:58 35.566N 97.274W  5.0    8 km ( 5 mi) SSE of Arcadia, OK 
 2.1  2009/11/25 10:51:39 35.529N 97.273W  5.0   14 km ( 9 mi) NE  of Midwest City, OK 
 2.6  2009/11/22 23:47:12 35.493N 97.230W  5.0   16 km (10 mi) ENE of Midwest City, OK 
 2.5  2009/11/16 05:12:37 35.493N 97.230W  5.0   16 km (10 mi) ENE of Midwest City, OK 
 3.0  2009/11/14 05:13:01 35.524N 97.219W  5.0   18 km (11 mi) ENE of Midwest City, OK 
 2.7  2009/11/02 12:27:05 35.432N 96.550W  5.0   17 km (11 mi) WNW of Bearden, OK 
 3.0  2009/10/22 22:56:29 35.794N 97.017W  5.0   10 km ( 6 mi) ESE of Fallis, OK 
 2.3  2009/09/08 09:03:12 35.633N 97.205W  5.0   12 km ( 7 mi) ESE of Arcadia, OK 
 2.3  2009/08/27 23:15:50 35.566N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.4  2009/08/27 22:30:55 35.566N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 3.5  2009/08/27 21:09:06 35.565N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.7  2009/08/27 13:32:06 35.566N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.6  2009/08/27 12:13:52 35.566N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.5  2009/08/27 10:31:24 35.566N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.7  2009/08/27 10:17:52 35.566N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
 2.5  2009/08/27 07:58:25 35.566N 97.290W  5.0   12 km ( 7 mi) SSE of Arcadia, OK 
DATE=Sun Feb 14 11:46:48 CST 2010
Last Changed 2010/02/13