Location

2010/08/07 11:19:04 43.609 -110.448 5.0 3.30 Wyoming

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  2010/08/07 11:19:04:0  43.61 -110.45   5.0 3.3 Wyoming
 
 Stations used:
   IU.RSSD IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.LOHW IW.MFID 
   IW.MOOW IW.PLID IW.REDW IW.SNOW IW.TPAW US.AHID US.BW06 
   US.HLID UU.BGU UU.CTU UU.HVU UU.SPU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 4.17e+21 dyne-cm
  Mw = 3.68 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1       25    75   -45
   NP2      130    47   -159
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.17e+21     17      83
    N   0.00e+00     43     190
    P  -4.17e+21     42     337

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.92e+21
       Mxy     1.27e+21
       Mxz    -1.77e+21
       Myy     3.39e+21
       Myz     1.99e+21
       Mzz    -1.47e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 --------------------##              
              -----------------------#####           
             -----------------------#######          
           #----------   -----------#########        
          ##---------- P -----------##########       
         ###----------   ----------############      
        ####-----------------------#############     
        ####----------------------##########   #     
       ######--------------------########### T ##    
       #######-------------------###########   ##    
       ########-----------------#################    
       #########---------------##################    
        #########-------------##################     
        ###########----------###################     
         ############-------###################      
          ##############---###################       
           ##############--##################        
             ###########--------##########-          
              #########-------------------           
                 ####------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.47e+21  -1.77e+21  -1.99e+21 
 -1.77e+21  -1.92e+21  -1.27e+21 
 -1.99e+21  -1.27e+21   3.39e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100807111904/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 = 25
      DIP = 75
     RAKE = -45
       MW = 3.68
       HS = 8.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2010/08/07 11:19:04:0  43.61 -110.45   5.0 3.3 Wyoming
 
 Stations used:
   IU.RSSD IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.LOHW IW.MFID 
   IW.MOOW IW.PLID IW.REDW IW.SNOW IW.TPAW US.AHID US.BW06 
   US.HLID UU.BGU UU.CTU UU.HVU UU.SPU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 4.17e+21 dyne-cm
  Mw = 3.68 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1       25    75   -45
   NP2      130    47   -159
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.17e+21     17      83
    N   0.00e+00     43     190
    P  -4.17e+21     42     337

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.92e+21
       Mxy     1.27e+21
       Mxz    -1.77e+21
       Myy     3.39e+21
       Myz     1.99e+21
       Mzz    -1.47e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 --------------------##              
              -----------------------#####           
             -----------------------#######          
           #----------   -----------#########        
          ##---------- P -----------##########       
         ###----------   ----------############      
        ####-----------------------#############     
        ####----------------------##########   #     
       ######--------------------########### T ##    
       #######-------------------###########   ##    
       ########-----------------#################    
       #########---------------##################    
        #########-------------##################     
        ###########----------###################     
         ############-------###################      
          ##############---###################       
           ##############--##################        
             ###########--------##########-          
              #########-------------------           
                 ####------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.47e+21  -1.77e+21  -1.99e+21 
 -1.77e+21  -1.92e+21  -1.27e+21 
 -1.99e+21  -1.27e+21   3.39e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100807111904/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
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    10    55   -90   3.31 0.3673
WVFGRD96    1.0    25    65   -60   3.30 0.3353
WVFGRD96    2.0    20    65   -65   3.48 0.4545
WVFGRD96    3.0    25    80   -60   3.54 0.5491
WVFGRD96    4.0    25    75   -55   3.55 0.6297
WVFGRD96    5.0    25    75   -50   3.57 0.6856
WVFGRD96    6.0    25    75   -45   3.60 0.7181
WVFGRD96    7.0    25    75   -40   3.62 0.7354
WVFGRD96    8.0    25    75   -45   3.68 0.7507
WVFGRD96    9.0    25    75   -40   3.70 0.7437
WVFGRD96   10.0    30    80   -35   3.71 0.7320
WVFGRD96   11.0    30    80   -35   3.73 0.7130
WVFGRD96   12.0   215    85    30   3.72 0.6957
WVFGRD96   13.0   220    75    30   3.73 0.6768
WVFGRD96   14.0   220    75    30   3.74 0.6596
WVFGRD96   15.0   220    75    30   3.75 0.6399
WVFGRD96   16.0   220    75    35   3.75 0.6199
WVFGRD96   17.0   225    70    35   3.76 0.6012
WVFGRD96   18.0   225    70    35   3.76 0.5834
WVFGRD96   19.0   225    65    35   3.77 0.5661
WVFGRD96   20.0   225    65    40   3.78 0.5514
WVFGRD96   21.0   225    65    40   3.79 0.5385
WVFGRD96   22.0   225    65    45   3.80 0.5260
WVFGRD96   23.0   225    65    45   3.80 0.5159
WVFGRD96   24.0   225    65    45   3.81 0.5044
WVFGRD96   25.0   230    60    50   3.82 0.4947
WVFGRD96   26.0   230    60    50   3.82 0.4850
WVFGRD96   27.0   230    60    50   3.82 0.4752
WVFGRD96   28.0   230    60    50   3.83 0.4657
WVFGRD96   29.0    25    85   -45   3.86 0.4575

The best solution is

WVFGRD96    8.0    25    75   -45   3.68 0.7507

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
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=Sat Aug 7 06:14:15 MDT 2010

Last Changed 2010/08/07