USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/09/20 00:47:22:0 43.60 110.42 5.0 3.6 Wyoming Stations used: IW.FLWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW IW.TPAW TA.H17A Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 1.76e+21 dynecm Mw = 3.43 Z = 7 km Plane Strike Dip Rake NP1 146 76 164 NP2 240 75 15 Principal Axes: Axis Value Plunge Azimuth T 1.76e+21 21 103 N 0.00e+00 69 284 P 1.76e+21 0 193 Moment Tensor: (dynecm) Component Value Mxx 1.59e+21 Mxy 7.22e+20 Mxz 1.21e+20 Myy 1.36e+21 Myz 5.78e+20 Mzz 2.27e+20   ### #### ####### ########## #################### ############################ ################################# ####################################### ######################################### ################################ ### ############################ T ### ####################### ## ######################### ################### ############### ############ ######## #####    P  Global CMT Convention Moment Tensor: R T P 2.27e+20 1.21e+20 5.78e+20 1.21e+20 1.59e+21 7.22e+20 5.78e+20 7.22e+20 1.36e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100920004722/index.html 
STK = 240 DIP = 75 RAKE = 15 MW = 3.43 HS = 7.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/09/20 00:47:22:0 43.60 110.42 5.0 3.6 Wyoming Stations used: IW.FLWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW IW.TPAW TA.H17A Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 1.76e+21 dynecm Mw = 3.43 Z = 7 km Plane Strike Dip Rake NP1 146 76 164 NP2 240 75 15 Principal Axes: Axis Value Plunge Azimuth T 1.76e+21 21 103 N 0.00e+00 69 284 P 1.76e+21 0 193 Moment Tensor: (dynecm) Component Value Mxx 1.59e+21 Mxy 7.22e+20 Mxz 1.21e+20 Myy 1.36e+21 Myz 5.78e+20 Mzz 2.27e+20   ### #### ####### ########## #################### ############################ ################################# ####################################### ######################################### ################################ ### ############################ T ### ####################### ## ######################### ################### ############### ############ ######## #####    P  Global CMT Convention Moment Tensor: R T P 2.27e+20 1.21e+20 5.78e+20 1.21e+20 1.59e+21 7.22e+20 5.78e+20 7.22e+20 1.36e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100920004722/index.html 
First motions plot using the waveform inversion nodal planes and the elcoate takeoff angles and azimuths. Symbols: o strong compression, + weak compression, Delta strong dilatation,  weak dilatation, X undetermined polarity. 
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.

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 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 220 35 45 3.17 0.3173 WVFGRD96 1.0 235 50 20 3.13 0.3219 WVFGRD96 2.0 45 70 50 3.31 0.4598 WVFGRD96 3.0 45 70 50 3.36 0.5320 WVFGRD96 4.0 240 80 25 3.35 0.5765 WVFGRD96 5.0 240 75 20 3.38 0.6085 WVFGRD96 6.0 240 75 20 3.41 0.6252 WVFGRD96 7.0 240 75 15 3.43 0.6291 WVFGRD96 8.0 240 70 20 3.48 0.6235 WVFGRD96 9.0 240 70 20 3.49 0.6139 WVFGRD96 10.0 240 70 15 3.51 0.5978 WVFGRD96 11.0 240 65 15 3.52 0.5775 WVFGRD96 12.0 240 65 15 3.53 0.5585 WVFGRD96 13.0 240 65 20 3.54 0.5353 WVFGRD96 14.0 240 65 20 3.55 0.5150 WVFGRD96 15.0 240 60 25 3.56 0.4929 WVFGRD96 16.0 240 60 25 3.57 0.4744 WVFGRD96 17.0 240 60 25 3.58 0.4542 WVFGRD96 18.0 245 55 35 3.59 0.4386 WVFGRD96 19.0 105 40 95 3.69 0.4251 WVFGRD96 20.0 100 40 90 3.71 0.4167 WVFGRD96 21.0 95 40 85 3.73 0.4062 WVFGRD96 22.0 95 45 80 3.75 0.3981 WVFGRD96 23.0 290 50 105 3.77 0.3903 WVFGRD96 24.0 90 45 75 3.77 0.3873 WVFGRD96 25.0 85 45 70 3.78 0.3833 WVFGRD96 26.0 85 50 70 3.79 0.3797 WVFGRD96 27.0 90 45 75 3.78 0.3795 WVFGRD96 28.0 85 45 70 3.80 0.3812 WVFGRD96 29.0 80 45 65 3.81 0.3820
The best solution is
WVFGRD96 7.0 240 75 15 3.43 0.6291
The mechanism correspond to the best fit is

The best fit as a function of depth is given in the following figure:

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 observedpredicted component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
hp c 0.02 n 3 lp c 0.10 n 3

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. 
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.
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 100200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
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.
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 1D 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 0.302E02 0.679E02 0.00 0.00 1.00 1.00 6.1000 5.5445 3.2953 2.6089 0.349E02 0.784E02 0.00 0.00 1.00 1.00 13.0000 6.2708 3.7396 2.7812 0.212E02 0.476E02 0.00 0.00 1.00 1.00 19.0000 6.4075 3.7680 2.8223 0.111E02 0.249E02 0.00 0.00 1.00 1.00 0.0000 7.9000 4.6200 3.2760 0.164E10 0.370E10 0.00 0.00 1.00 1.00
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Mon Sep 20 13:43:06 CDT 2010