Location

2014/03/30 12:34:39 44.778 -110.683 6.8 4.8 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  2014/03/30 12:34:39:0  44.78 -110.68   6.8 4.8 Wyoming
 
 Stations used:
   CN.WALA IM.PD31 IU.RSSD IW.DLMT IW.FLWY IW.FXWY IW.IMW 
   IW.MFID IW.PHWY IW.REDW IW.RWWY IW.SNOW IW.TPAW MB.JTMT 
   TA.H17A TA.K22A TA.N23A TA.O20A US.AHID US.BMO US.BW06 
   US.DUG US.EGMT US.ELK US.HWUT US.LAO US.MSO US.RLMT UU.BGU 
   UU.BRPU UU.CTU UU.HVU UU.JLU UU.MPU UU.NLU UU.RDMU UU.SPU 
   UU.TCU UW.BRAN WY.YHB WY.YHH WY.YHL WY.YNE WY.YPP 
 
 Filtering commands used:
   rtr
   taper w 0.05
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.45e+23 dyne-cm
  Mw = 4.86 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1      257    86   150
   NP2      350    60     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.45e+23     24     210
    N   0.00e+00     60      70
    P  -2.45e+23     17     308

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     7.19e+22
       Mxy     1.96e+23
       Mxz    -1.22e+23
       Myy    -9.04e+22
       Myz     1.07e+22
       Mzz     1.85e+22
                                                     
                                                     
                                                     
                                                     
                     -----#########                  
                 -----------###########              
              ----------------############           
             ------------------############          
           --   ----------------#############        
          --- P -----------------#############       
         ----   ------------------#############      
        --------------------------##############     
        ---------------------------#############     
       ----------------------------#-------------    
       --------------------#########-------------    
       ------------#################-------------    
       ------#######################-------------    
        ############################------------     
        ############################------------     
         ###########################-----------      
          ##########################----------       
           ########   #############----------        
             ###### T #############--------          
              #####   ############--------           
                 ################------              
                     ###########---                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.85e+22  -1.22e+23  -1.07e+22 
 -1.22e+23   7.19e+22  -1.96e+23 
 -1.07e+22  -1.96e+23  -9.04e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140330123439/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 = 350
      DIP = 60
     RAKE = 5
       MW = 4.86
       HS = 10.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2014/03/30 12:34:39:0  44.78 -110.68   6.8 4.8 Wyoming
 
 Stations used:
   CN.WALA IM.PD31 IU.RSSD IW.DLMT IW.FLWY IW.FXWY IW.IMW 
   IW.MFID IW.PHWY IW.REDW IW.RWWY IW.SNOW IW.TPAW MB.JTMT 
   TA.H17A TA.K22A TA.N23A TA.O20A US.AHID US.BMO US.BW06 
   US.DUG US.EGMT US.ELK US.HWUT US.LAO US.MSO US.RLMT UU.BGU 
   UU.BRPU UU.CTU UU.HVU UU.JLU UU.MPU UU.NLU UU.RDMU UU.SPU 
   UU.TCU UW.BRAN WY.YHB WY.YHH WY.YHL WY.YNE WY.YPP 
 
 Filtering commands used:
   rtr
   taper w 0.05
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.45e+23 dyne-cm
  Mw = 4.86 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1      257    86   150
   NP2      350    60     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.45e+23     24     210
    N   0.00e+00     60      70
    P  -2.45e+23     17     308

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     7.19e+22
       Mxy     1.96e+23
       Mxz    -1.22e+23
       Myy    -9.04e+22
       Myz     1.07e+22
       Mzz     1.85e+22
                                                     
                                                     
                                                     
                                                     
                     -----#########                  
                 -----------###########              
              ----------------############           
             ------------------############          
           --   ----------------#############        
          --- P -----------------#############       
         ----   ------------------#############      
        --------------------------##############     
        ---------------------------#############     
       ----------------------------#-------------    
       --------------------#########-------------    
       ------------#################-------------    
       ------#######################-------------    
        ############################------------     
        ############################------------     
         ###########################-----------      
          ##########################----------       
           ########   #############----------        
             ###### T #############--------          
              #####   ############--------           
                 ################------              
                     ###########---                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.85e+22  -1.22e+23  -1.07e+22 
 -1.22e+23   7.19e+22  -1.96e+23 
 -1.07e+22  -1.96e+23  -9.04e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140330123439/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:

rtr
taper w 0.05
hp c 0.02 n 3
lp c 0.06 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   160    65   -30   4.50 0.3164
WVFGRD96    1.0   160    60   -25   4.53 0.3364
WVFGRD96    2.0   160    60   -30   4.65 0.4444
WVFGRD96    3.0   345    65   -15   4.68 0.4652
WVFGRD96    4.0   345    60   -10   4.72 0.4859
WVFGRD96    5.0   350    60     0   4.74 0.5081
WVFGRD96    6.0   350    60     0   4.77 0.5276
WVFGRD96    7.0   350    65     0   4.78 0.5441
WVFGRD96    8.0   350    60     0   4.83 0.5569
WVFGRD96    9.0   350    60     0   4.84 0.5609
WVFGRD96   10.0   350    60     5   4.86 0.5630
WVFGRD96   11.0   350    65     5   4.87 0.5614
WVFGRD96   12.0   350    65     5   4.88 0.5582
WVFGRD96   13.0   350    65     5   4.89 0.5537
WVFGRD96   14.0   350    65     5   4.90 0.5481
WVFGRD96   15.0   350    65     5   4.91 0.5410
WVFGRD96   16.0   350    65     5   4.92 0.5337
WVFGRD96   17.0   350    65     0   4.92 0.5261
WVFGRD96   18.0   350    70     0   4.93 0.5194
WVFGRD96   19.0   180    70    15   4.91 0.5162
WVFGRD96   20.0   180    70    15   4.92 0.5117
WVFGRD96   21.0   180    65    15   4.93 0.5065
WVFGRD96   22.0   180    70    15   4.93 0.5021
WVFGRD96   23.0   180    65    15   4.94 0.4975
WVFGRD96   24.0   180    70    15   4.94 0.4924
WVFGRD96   25.0   180    70    15   4.95 0.4881
WVFGRD96   26.0   180    70    15   4.95 0.4838
WVFGRD96   27.0   180    70    15   4.96 0.4792
WVFGRD96   28.0   175    75    15   4.97 0.4755
WVFGRD96   29.0   175    75    15   4.97 0.4721

The best solution is

WVFGRD96   10.0   350    60     5   4.86 0.5630

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 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

rtr
taper w 0.05
hp c 0.02 n 3
lp c 0.06 n 3
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated.
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:

Assuming only a mislocation, the time shifts are fit to a functional form:

 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.

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 Louis University, University of Memphis, Lamont Doherty 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=Sun Mar 30 11:30:14 CDT 2014

Last Changed 2014/03/30