Location

SLU Location

Arrival times were read and the WUS model, listed below, was used with the program elocate to determine the location. The location information is givenin the file elocate.txt. The difference in locations are not significant, but do make a difference in the use of the clostest stations for source inversion.

Initial NEIC Location

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 2010/08/14 14:39:11:1 43.62 -110.46 7.0 2.9 Wyoming Stations used: IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW IW.TPAW Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.73e+20 dyne-cm Mw = 3.05 Z = 5 km Plane Strike Dip Rake NP1 305 76 -159 NP2 210 70 -15 Principal Axes: Axis Value Plunge Azimuth T 4.73e+20 4 77 N 0.00e+00 65 338 P -4.73e+20 24 169 Moment Tensor: (dyne-cm) Component Value Mxx -3.52e+20 Mxy 1.81e+20 Mxz 1.82e+20 Myy 4.31e+20 Myz -3.09e+18 Mzz -7.87e+19 -------------- ---------------------# ---------------------####### -------------------########### --------------------############## #######------------################# ############------#################### #################-#################### #################---################## T #################------################ ################----------################ ###############-------------############## ##############----------------############ ############-------------------######### ###########----------------------####### ##########------------------------#### ########--------------------------## #######--------------------------- #####------------ ---------- ####------------ P --------- #------------ ------ -------------- Global CMT Convention Moment Tensor: R T P -7.87e+19 1.82e+20 3.09e+18 1.82e+20 -3.52e+20 -1.81e+20 3.09e+18 -1.81e+20 4.31e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100814143911/index.html

Preferred Solution

      STK = 210
      DIP = 70
     RAKE = -15
       MW = 3.05
       HS = 5.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

SLUFM

USGS/SLU Moment Tensor Solution ENS 2010/08/14 14:39:11:1 43.62 -110.46 7.0 2.9 Wyoming Stations used: IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW IW.TPAW Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.73e+20 dyne-cm Mw = 3.05 Z = 5 km Plane Strike Dip Rake NP1 305 76 -159 NP2 210 70 -15 Principal Axes: Axis Value Plunge Azimuth T 4.73e+20 4 77 N 0.00e+00 65 338 P -4.73e+20 24 169 Moment Tensor: (dyne-cm) Component Value Mxx -3.52e+20 Mxy 1.81e+20 Mxz 1.82e+20 Myy 4.31e+20 Myz -3.09e+18 Mzz -7.87e+19 -------------- ---------------------# ---------------------####### -------------------########### --------------------############## #######------------################# ############------#################### #################-#################### #################---################## T #################------################ ################----------################ ###############-------------############## ##############----------------############ ############-------------------######### ###########----------------------####### ##########------------------------#### ########--------------------------## #######--------------------------- #####------------ ---------- ####------------ P --------- #------------ ------ -------------- Global CMT Convention Moment Tensor: R T P -7.87e+19 1.82e+20 3.09e+18 1.82e+20 -3.52e+20 -1.81e+20 3.09e+18 -1.81e+20 4.31e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100814143911/index.html USGS/SLU Moment Tensor Solution ENS 2010/08/14 14:39:12:4 43.62 -110.46 7.0 2.9 Wyoming Stations used: IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW IW.TPAW Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.73e+20 dyne-cm Mw = 3.05 Z = 5 km Plane Strike Dip Rake NP1 305 76 -159 NP2 210 70 -15 Principal Axes: Axis Value Plunge Azimuth T 4.73e+20 4 77 N 0.00e+00 65 338 P -4.73e+20 24 169 Moment Tensor: (dyne-cm) Component Value Mxx -3.52e+20 Mxy 1.81e+20 Mxz 1.82e+20 Myy 4.31e+20 Myz -3.09e+18 Mzz -7.87e+19 -------------- ---------------------# ---------------------####### -------------------########### --------------------############## #######------------################# ############------#################### #################-#################### #################---################## T #################------################ ################----------################ ###############-------------############## ##############----------------############ ############-------------------######### ###########----------------------####### ##########------------------------#### ########--------------------------## #######--------------------------- #####------------ ---------- ####------------ P --------- #------------ ------ -------------- Global CMT Convention Moment Tensor: R T P -7.87e+19 1.82e+20 3.09e+18 1.82e+20 -3.52e+20 -1.81e+20 3.09e+18 -1.81e+20 4.31e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100814143912/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

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    0.5    20    70   -55   2.83 0.4114
WVFGRD96    1.0    20    75   -50   2.83 0.4300
WVFGRD96    2.0    20    75   -50   2.98 0.5317
WVFGRD96    3.0    25    80   -40   3.01 0.5746
WVFGRD96    4.0   205    60   -25   3.04 0.6066
WVFGRD96    5.0   210    70   -15   3.05 0.6160
WVFGRD96    6.0   210    70   -15   3.08 0.6153
WVFGRD96    7.0   210    75   -10   3.11 0.6083
WVFGRD96    8.0   210    70   -10   3.15 0.5945
WVFGRD96    9.0   210    75    -5   3.17 0.5734
WVFGRD96   10.0   210    75    -5   3.19 0.5481
WVFGRD96   11.0   210    75    -5   3.20 0.5219
WVFGRD96   12.0   210    80     5   3.21 0.4965
WVFGRD96   13.0   210    75     5   3.21 0.4735
WVFGRD96   14.0   215    70    10   3.20 0.4559
WVFGRD96   15.0   215    70    10   3.21 0.4404
WVFGRD96   16.0   215    70    10   3.22 0.4257
WVFGRD96   17.0   215    70    15   3.22 0.4120
WVFGRD96   18.0   215    70    15   3.23 0.3990
WVFGRD96   19.0   255    50    85   3.32 0.3872
WVFGRD96   20.0   260    50    90   3.34 0.3868
WVFGRD96   21.0   265    50    90   3.35 0.3851
WVFGRD96   22.0    85    40    85   3.36 0.3842
WVFGRD96   23.0    75    40    80   3.38 0.3842
WVFGRD96   24.0    80    40    80   3.38 0.3825
WVFGRD96   25.0    70    40    75   3.40 0.3818
WVFGRD96   26.0   130    65    50   3.36 0.3829
WVFGRD96   27.0    45    40    45   3.47 0.3841
WVFGRD96   28.0    45    40    45   3.47 0.3853
WVFGRD96   29.0    40    45    40   3.49 0.3866

The best solution is

WVFGRD96    5.0   210    70   -15   3.05 0.6160

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 14 17:54:34 CDT 2010