Location

2013/05/06 03:13:42 42.608 -111.947 11.3 4.2 Idaho

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  2013/05/06 03:13:42:0  42.61 -111.95  11.3 4.2 Idaho
 
 Stations used:
   IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.PHWY 
   IW.REDW IW.SMCO IW.SNOW IW.TPAW UU.BGU UU.BRPU UU.CCUT 
   UU.CTU UU.CVRU UU.HVU UU.JLU UU.MPU UU.MTPU UU.NLU UU.PKCU 
   UU.PSUT UU.SPU UU.SRU UU.SZCU UU.TCRU UU.TCU UU.TMU WY.YFT 
   WY.YHB WY.YMR WY.YNR WY.YPP WY.YUF 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 1.10e+22 dyne-cm
  Mw = 3.96 
  Z  = 13 km
  Plane   Strike  Dip  Rake
   NP1      340    81   -95
   NP2      190    10   -60
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.10e+22     36      74
    N   0.00e+00      5     340
    P  -1.10e+22     53     244

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.28e+20
       Mxy     3.39e+20
       Mxz     3.77e+21
       Myy     3.48e+21
       Myz     9.73e+21
       Mzz    -3.25e+21
                                                     
                                                     
                                                     
                                                     
                     --############                  
                 ##---#################              
              ###------###################           
             ##---------###################          
           ##------------####################        
          ##--------------####################       
         ##----------------####################      
        ##------------------###########   ######     
        ##-------------------########## T ######     
       ##--------------------##########   #######    
       ##---------------------###################    
       ##----------------------##################    
       ##---------   ----------##################    
        ##-------- P -----------################     
        ##--------   ------------###############     
         ##----------------------##############      
          ##----------------------############       
           ##---------------------###########        
             #--------------------#########          
              ##-------------------#######           
                 #-----------------####              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.25e+21   3.77e+21  -9.73e+21 
  3.77e+21  -2.28e+20  -3.39e+20 
 -9.73e+21  -3.39e+20   3.48e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130506031342/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 = 190
      DIP = 10
     RAKE = -60
       MW = 3.96
       HS = 13.0

The NDK file is 20130506031342.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
 USGS/SLU Moment Tensor Solution
 ENS  2013/05/06 03:13:42:0  42.61 -111.95  11.3 4.2 Idaho
 
 Stations used:
   IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.PHWY 
   IW.REDW IW.SMCO IW.SNOW IW.TPAW UU.BGU UU.BRPU UU.CCUT 
   UU.CTU UU.CVRU UU.HVU UU.JLU UU.MPU UU.MTPU UU.NLU UU.PKCU 
   UU.PSUT UU.SPU UU.SRU UU.SZCU UU.TCRU UU.TCU UU.TMU WY.YFT 
   WY.YHB WY.YMR WY.YNR WY.YPP WY.YUF 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 1.10e+22 dyne-cm
  Mw = 3.96 
  Z  = 13 km
  Plane   Strike  Dip  Rake
   NP1      340    81   -95
   NP2      190    10   -60
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.10e+22     36      74
    N   0.00e+00      5     340
    P  -1.10e+22     53     244

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.28e+20
       Mxy     3.39e+20
       Mxz     3.77e+21
       Myy     3.48e+21
       Myz     9.73e+21
       Mzz    -3.25e+21
                                                     
                                                     
                                                     
                                                     
                     --############                  
                 ##---#################              
              ###------###################           
             ##---------###################          
           ##------------####################        
          ##--------------####################       
         ##----------------####################      
        ##------------------###########   ######     
        ##-------------------########## T ######     
       ##--------------------##########   #######    
       ##---------------------###################    
       ##----------------------##################    
       ##---------   ----------##################    
        ##-------- P -----------################     
        ##--------   ------------###############     
         ##----------------------##############      
          ##----------------------############       
           ##---------------------###########        
             #--------------------#########          
              ##-------------------#######           
                 #-----------------####              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.25e+21   3.77e+21  -9.73e+21 
  3.77e+21  -2.28e+20  -3.39e+20 
 -9.73e+21  -3.39e+20   3.48e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130506031342/index.html
	

USGS/SLU Regional Moment Solution
SOUTHERN IDAHO

13/05/06 03:13:43.06

Epicenter:  42.613 -111.944
MW 3.9

USGS/SLU REGIONAL MOMENT TENSOR
Depth  13         No. of sta: 85
Moment Tensor;   Scale 10**14 Nm
  Mrr=-5.08       Mtt= 0.97
  Mpp= 4.11       Mrt= 4.71
  Mrp=-6.82       Mtp=-0.54
 Principal axes:
  T  Val=  8.78  Plg=31  Azm= 65
  N        1.35       7      331
  P       -10.13      58      229

Best Double Couple:Mo=9.5*10**14
 NP1:Strike=329 Dip=76 Slip= -97
 NP2:       177     16       -63


        

Magnitudes

ML Magnitude


(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.


(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.

Context

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).

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   320    45    90   3.56 0.4530
WVFGRD96    1.0   295    50    70   3.61 0.4176
WVFGRD96    2.0   300    50    75   3.73 0.4644
WVFGRD96    3.0    95    30    40   3.76 0.3215
WVFGRD96    4.0   255    10    10   3.78 0.3925
WVFGRD96    5.0   240    10    -5   3.78 0.4792
WVFGRD96    6.0   240    10    -5   3.79 0.5472
WVFGRD96    7.0   235    10   -10   3.79 0.5974
WVFGRD96    8.0   230     5   -15   3.88 0.6275
WVFGRD96    9.0   215    10   -30   3.89 0.6633
WVFGRD96   10.0   210    10   -35   3.91 0.6890
WVFGRD96   11.0   200    10   -50   3.93 0.7065
WVFGRD96   12.0   195    10   -55   3.95 0.7165
WVFGRD96   13.0   190    10   -60   3.96 0.7203
WVFGRD96   14.0   185    10   -65   3.97 0.7188
WVFGRD96   15.0   185    10   -65   3.99 0.7127
WVFGRD96   16.0   185    10   -65   4.00 0.7027
WVFGRD96   17.0   165     5   -85   4.01 0.6897
WVFGRD96   18.0   170     5   -80   4.02 0.6747
WVFGRD96   19.0   170     5   -75   4.02 0.6581
WVFGRD96   20.0   170     5   -75   4.03 0.6402
WVFGRD96   21.0   180     5   -65   4.05 0.6214
WVFGRD96   22.0   175     5   -70   4.06 0.6009
WVFGRD96   23.0   175     5   -70   4.07 0.5796
WVFGRD96   24.0   335    85   -90   4.08 0.5579
WVFGRD96   25.0   155    90    85   4.09 0.5326
WVFGRD96   26.0   155    90    85   4.09 0.5094
WVFGRD96   27.0   155    90    85   4.10 0.4853
WVFGRD96   28.0   155    90    85   4.11 0.4600
WVFGRD96   29.0   335    85   -90   4.11 0.4346

The best solution is

WVFGRD96   13.0   190    10   -60   3.96 0.7203

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

hp c 0.02 n 3
lp c 0.10 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

Acknowledgements

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, 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, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The WUS model 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:

Last Changed Mon Dec 7 00:20:58 CST 2015