Location

2008/11/03 13:14:13 42.7820 -105.1210 5.0 4.10 Wyoming

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for

Focal Mechanism

 SLU Moment Tensor Solution
 2008/11/03 13:14:13  42.7820  -105.1210  5.0  4.10 Wyoming
 
 Best Fitting Double Couple
    Mo = 2.57e+21 dyne-cm
    Mw = 3.54 
    Z  = 18 km
     Plane   Strike  Dip  Rake
      NP1       60    73   -121
      NP2      305    35   -30
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   2.57e+21     22     174
     N   0.00e+00     30      70
     P  -2.57e+21     51     294



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     2.01e+21
       Mxy     1.31e+20
       Mxz    -1.41e+21
       Myy    -8.02e+20
       Myz     1.24e+21
       Mzz    -1.21e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              ############################           
             #-----------------############          
           -----------------------###########        
          ---------------------------#########       
         ------------------------------######--      
        ----------   --------------------##-----     
        ---------- P --------------------#------     
       -----------   ------------------####------    
       ------------------------------#######-----    
       ----------------------------##########----    
       -------------------------#############----    
        --------------------##################--     
        -----------------#####################--     
         -----------##########################-      
          --#################################-       
           ##################################        
             ###############   ############          
              ############## T ###########           
                 ###########   ########              
                     ##############                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -1.21e+21  -1.41e+21  -1.24e+21 
 -1.41e+21   2.01e+21  -1.31e+20 
 -1.24e+21  -1.31e+20  -8.02e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081103131413/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 = 305
      DIP = 35
     RAKE = -30
       MW = 3.54
       HS = 18.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 SLU Moment Tensor Solution
 2008/11/03 13:14:13  42.7820  -105.1210  5.0  4.10 Wyoming
 
 Best Fitting Double Couple
    Mo = 2.57e+21 dyne-cm
    Mw = 3.54 
    Z  = 18 km
     Plane   Strike  Dip  Rake
      NP1       60    73   -121
      NP2      305    35   -30
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   2.57e+21     22     174
     N   0.00e+00     30      70
     P  -2.57e+21     51     294



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     2.01e+21
       Mxy     1.31e+20
       Mxz    -1.41e+21
       Myy    -8.02e+20
       Myz     1.24e+21
       Mzz    -1.21e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              ############################           
             #-----------------############          
           -----------------------###########        
          ---------------------------#########       
         ------------------------------######--      
        ----------   --------------------##-----     
        ---------- P --------------------#------     
       -----------   ------------------####------    
       ------------------------------#######-----    
       ----------------------------##########----    
       -------------------------#############----    
        --------------------##################--     
        -----------------#####################--     
         -----------##########################-      
          --#################################-       
           ##################################        
             ###############   ############          
              ############## T ###########           
                 ###########   ########              
                     ##############                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -1.21e+21  -1.41e+21  -1.24e+21 
 -1.41e+21   2.01e+21  -1.31e+20 
 -1.24e+21  -1.31e+20  -8.02e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081103131413/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   225    45    90   3.35 0.3452
WVFGRD96    1.0   225    45    90   3.40 0.3571
WVFGRD96    2.0   250    45    90   3.45 0.3381
WVFGRD96    3.0   335    30    25   3.48 0.3091
WVFGRD96    4.0   335    30    25   3.48 0.3438
WVFGRD96    5.0   330    30    15   3.47 0.3708
WVFGRD96    6.0   330    30    15   3.46 0.3904
WVFGRD96    7.0   325    35     5   3.46 0.4047
WVFGRD96    8.0   315    35   -20   3.46 0.4177
WVFGRD96    9.0   315    35   -20   3.46 0.4292
WVFGRD96   10.0   315    35   -20   3.49 0.4372
WVFGRD96   11.0   310    35   -25   3.50 0.4459
WVFGRD96   12.0   310    35   -30   3.50 0.4522
WVFGRD96   13.0   310    35   -30   3.51 0.4577
WVFGRD96   14.0   310    35   -25   3.51 0.4619
WVFGRD96   15.0   310    35   -25   3.52 0.4650
WVFGRD96   16.0   305    35   -30   3.53 0.4673
WVFGRD96   17.0   310    35   -25   3.53 0.4688
WVFGRD96   18.0   305    35   -30   3.54 0.4693
WVFGRD96   19.0   305    35   -30   3.55 0.4690
WVFGRD96   20.0   305    35   -30   3.58 0.4677
WVFGRD96   21.0   310    35   -25   3.59 0.4656
WVFGRD96   22.0   310    35   -25   3.60 0.4626
WVFGRD96   23.0   310    35   -25   3.60 0.4583
WVFGRD96   24.0   310    35   -25   3.61 0.4533
WVFGRD96   25.0   310    35   -25   3.62 0.4479
WVFGRD96   26.0   310    30   -25   3.63 0.4418
WVFGRD96   27.0   310    30   -20   3.64 0.4350
WVFGRD96   28.0   310    30   -20   3.64 0.4273
WVFGRD96   29.0   310    30   -20   3.65 0.4186
WVFGRD96   30.0   310    30   -20   3.66 0.4092
WVFGRD96   31.0   310    30   -20   3.67 0.3996
WVFGRD96   32.0   310    30   -20   3.67 0.3891
WVFGRD96   33.0   310    35   -20   3.68 0.3785
WVFGRD96   34.0   310    35   -20   3.69 0.3675
WVFGRD96   35.0   310    35   -25   3.69 0.3564
WVFGRD96   36.0   310    35   -20   3.69 0.3452
WVFGRD96   37.0   310    35   -20   3.70 0.3346
WVFGRD96   38.0   340    30    25   3.70 0.3262
WVFGRD96   39.0   340    30    25   3.70 0.3199
WVFGRD96   40.0   340    20    20   3.82 0.3121
WVFGRD96   41.0   340    25    25   3.83 0.3016
WVFGRD96   42.0   250    75    65   3.80 0.2933
WVFGRD96   43.0   250    75    65   3.81 0.2866
WVFGRD96   44.0   250    75    60   3.81 0.2800
WVFGRD96   45.0   250    75    60   3.81 0.2734
WVFGRD96   46.0   215    65   -65   3.86 0.2689
WVFGRD96   47.0   215    65   -65   3.87 0.2669
WVFGRD96   48.0   215    65   -60   3.87 0.2647
WVFGRD96   49.0   215    65   -60   3.88 0.2631
WVFGRD96   50.0   215    65   -60   3.88 0.2612

The best solution is

WVFGRD96   18.0   305    35   -30   3.54 0.4693

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 CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
CUS Model with Q from simple gamma values
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
  1.0000  5.0000  2.8900  2.5000 0.172E-02 0.387E-02 0.00  0.00  1.00  1.00 
  9.0000  6.1000  3.5200  2.7300 0.160E-02 0.363E-02 0.00  0.00  1.00  1.00 
 10.0000  6.4000  3.7000  2.8200 0.149E-02 0.336E-02 0.00  0.00  1.00  1.00 
 20.0000  6.7000  3.8700  2.9020 0.000E-04 0.000E-04 0.00  0.00  1.00  1.00 
  0.0000  8.1500  4.7000  3.3640 0.194E-02 0.431E-02 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 Nov 3 11:12:53 CST 2008

Last Changed 2008/11/03