Location

2010/02/04 09:41:29 35.486 -102.647 15.0 3.80 Texas

NEIC Location

Original NEIC location


MAG    UTC DATE TIME        LAT        LON    Depth    Region
3.8 2010/02/04 09:41:30    35.396   -102.315   5.0   TEXAS PANHANDLE REGION

The waveform inversion succeeded but there were large positive time shifts required to fit the waveform. Such time shifts indicate either the use of an incorrect model for the Grene's function or a mislocation. The positive time shifts would mean that the WUS model used for the inversion was too slow.

Revised NEIC Location - Released 1650UT 2010 02 05

MAG    UTC DATE TIME        LAT        LON    Depth    Region
3.3 2010/02/04 09:41:28    35.478   -102.562   5.0   TEXAS PANHANDLE REGION

Unfortunately this was not a sufficient change!

Arrival Times (from USGS)

Arrival time list

SLU Location - Preferred

Using the Transportable Array stations, which were not used in the initial USGS location, P and sharp S arrivals were read, and the program elocate was used with the WUS model (listed below). The solution obtained was

 Travel_Time_Table:          WUS     
 Latitude         :             35.4920 +-    0.0030 N         0.3369 km
 Longitude        :           -102.6380 +-    0.0039 E         0.3549 km
 Depth            :               16.48 +-      0.66 km
 Epoch Time       :      1265276488.483 +-      0.04 sec
 Event Time       :  20100204094128.483 +-      0.04 sec
 Event (OCAL)     :  2010 02 04 09 41 28 483
 HYPO71 Quality   :                  BC
 Gap              :                  24              deg

The complete output of the elocate run with arrival time picks and station coordinates is given in the file elocate.txt.

Note that the final computation differs in location by about 1 km and in origin time less than 1 second from the location posted at the top of this page, which was the result of an initial relation earlier this morning. The differences are not enough to change the final parameters for this event.

Felt Map

USGS Felt map for this earthquake

USGS Felt reports main page

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2010/02/04 09:41:29:0  35.49 -102.65  15.0 3.8 Texas
 
 Stations used:
   IU.ANMO TA.R25A TA.S24A TA.S25A TA.T25A TA.T27A TA.T30A 
   TA.U26A TA.U27A TA.U28A TA.U29A TA.V24A TA.V26A TA.V27A 
   TA.V29A TA.V30A TA.W25A TA.W26A TA.W27A TA.W28A TA.W29A 
   TA.X24A TA.X25A TA.X26A TA.X27A TA.X28A TA.X29A TA.X30A 
   TA.Y26A TA.Y27A TA.Y29A TA.Y30A TA.Z24A TA.Z25A TA.Z29A 
   TA.Z30A US.AMTX 
 
 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 = 1.05e+21 dyne-cm
  Mw = 3.28 
  Z  = 13 km
  Plane   Strike  Dip  Rake
   NP1      315    65   -30
   NP2       59    63   -152
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.05e+21      1       7
    N   0.00e+00     52      99
    P  -1.05e+21     38     276

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.02e+21
       Mxy     2.01e+20
       Mxz    -3.30e+19
       Myy    -6.21e+20
       Myz     5.09e+20
       Mzz    -4.01e+20
                                                     
                                                     
                                                     
                                                     
                     ######## T ###                  
                 ############   #######              
              ############################           
             -----#########################          
           -----------#######################        
          ----------------####################       
         -------------------#################--      
        ----------------------##############----     
        ------------------------###########-----     
       -------   -----------------########-------    
       ------- P -------------------####---------    
       -------   --------------------#-----------    
       -----------------------------##-----------    
        -------------------------#######--------     
        ----------------------##########--------     
         ------------------##############------      
          ------------####################----       
           ###############################---        
             ##############################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.01e+20  -3.30e+19  -5.09e+20 
 -3.30e+19   1.02e+21  -2.01e+20 
 -5.09e+20  -2.01e+20  -6.21e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100204094129/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 = 315
      DIP = 65
     RAKE = -30
       MW = 3.28
       HS = 13.0

The waveform inversion is preferred. There is a good correspondence between the relocation and waveform inversion depths. The observed P-wave first motions agree very well with the moment tensor solution determined by waveform inversion.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2010/02/04 09:41:29:0  35.49 -102.65  15.0 3.8 Texas
 
 Stations used:
   IU.ANMO TA.R25A TA.S24A TA.S25A TA.T25A TA.T27A TA.T30A 
   TA.U26A TA.U27A TA.U28A TA.U29A TA.V24A TA.V26A TA.V27A 
   TA.V29A TA.V30A TA.W25A TA.W26A TA.W27A TA.W28A TA.W29A 
   TA.X24A TA.X25A TA.X26A TA.X27A TA.X28A TA.X29A TA.X30A 
   TA.Y26A TA.Y27A TA.Y29A TA.Y30A TA.Z24A TA.Z25A TA.Z29A 
   TA.Z30A US.AMTX 
 
 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 = 1.05e+21 dyne-cm
  Mw = 3.28 
  Z  = 13 km
  Plane   Strike  Dip  Rake
   NP1      315    65   -30
   NP2       59    63   -152
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.05e+21      1       7
    N   0.00e+00     52      99
    P  -1.05e+21     38     276

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.02e+21
       Mxy     2.01e+20
       Mxz    -3.30e+19
       Myy    -6.21e+20
       Myz     5.09e+20
       Mzz    -4.01e+20
                                                     
                                                     
                                                     
                                                     
                     ######## T ###                  
                 ############   #######              
              ############################           
             -----#########################          
           -----------#######################        
          ----------------####################       
         -------------------#################--      
        ----------------------##############----     
        ------------------------###########-----     
       -------   -----------------########-------    
       ------- P -------------------####---------    
       -------   --------------------#-----------    
       -----------------------------##-----------    
        -------------------------#######--------     
        ----------------------##########--------     
         ------------------##############------      
          ------------####################----       
           ###############################---        
             ##############################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.01e+20  -3.30e+19  -5.09e+20 
 -3.30e+19   1.02e+21  -2.01e+20 
 -5.09e+20  -2.01e+20  -6.21e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100204094129/index.html
	

First motion plot using elocate take-off angles and azimuths

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   185    45    90   2.85 0.1644
WVFGRD96    1.0   145    90     0   2.78 0.1479
WVFGRD96    2.0   325    90    -5   2.96 0.2425
WVFGRD96    3.0   320    85   -20   3.03 0.2761
WVFGRD96    4.0   315    75   -30   3.09 0.3087
WVFGRD96    5.0   315    75   -35   3.14 0.3424
WVFGRD96    6.0   315    70   -35   3.17 0.3701
WVFGRD96    7.0   310    60   -35   3.19 0.3944
WVFGRD96    8.0   310    55   -40   3.25 0.4053
WVFGRD96    9.0   310    55   -40   3.26 0.4218
WVFGRD96   10.0   310    60   -40   3.26 0.4296
WVFGRD96   11.0   310    60   -35   3.26 0.4337
WVFGRD96   12.0   315    65   -30   3.27 0.4358
WVFGRD96   13.0   315    65   -30   3.28 0.4365
WVFGRD96   14.0   315    65   -30   3.29 0.4356
WVFGRD96   15.0   315    65   -25   3.29 0.4343
WVFGRD96   16.0   315    65   -25   3.30 0.4323
WVFGRD96   17.0   315    65   -25   3.31 0.4296
WVFGRD96   18.0   315    65   -25   3.32 0.4260
WVFGRD96   19.0   315    65   -25   3.33 0.4216
WVFGRD96   20.0   315    70   -20   3.34 0.4175
WVFGRD96   21.0   315    65   -25   3.35 0.4127
WVFGRD96   22.0   315    65   -25   3.36 0.4066
WVFGRD96   23.0   315    70   -20   3.37 0.4000
WVFGRD96   24.0   315    65   -20   3.37 0.3932
WVFGRD96   25.0   315    65   -20   3.38 0.3860
WVFGRD96   26.0   315    65   -20   3.39 0.3779
WVFGRD96   27.0   315    65   -20   3.40 0.3696
WVFGRD96   28.0   315    65   -20   3.40 0.3607
WVFGRD96   29.0   315    65   -20   3.41 0.3517

The best solution is

WVFGRD96   13.0   315    65   -30   3.28 0.4365

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 Feb 5 19:46:35 CST 2010

Last Changed 2010/02/04