Location

2013/05/06 03:20:56 42.620 -111.955 4.9 3.6 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 03:20:56:0  42.62 -111.96   4.9 3.6 Idaho
 
 Stations used:
   IW.FLWY IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW 
   IW.TPAW LB.BMN TA.H17A TA.R11A US.AHID US.BW06 US.DUG 
   US.HLID US.HWUT US.RLMT UU.BGU UU.HVU UU.JLU UU.MPU UU.SPU 
   UU.SZCU WY.YFT WY.YHB 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 = 2.40e+21 dyne-cm
  Mw = 3.52 
  Z  = 13 km
  Plane   Strike  Dip  Rake
   NP1      339    77   -98
   NP2      190    15   -60
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.40e+21     32      75
    N   0.00e+00      7     341
    P  -2.40e+21     57     239

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -7.49e+19
       Mxy     1.14e+20
       Mxz     8.29e+20
       Myy     1.11e+21
       Myz     1.97e+21
       Mzz    -1.04e+21
                                                     
                                                     
                                                     
                                                     
                     ---###########                  
                 ###--#################              
              ####------##################           
             ###---------##################          
           ###------------###################        
          ###--------------###################       
         ###----------------###################      
        ###------------------###########   #####     
        ###-------------------########## T #####     
       ###--------------------##########   ######    
       ###---------------------##################    
       ###----------------------#################    
       ###---------   ----------#################    
        ##--------- P -----------###############     
        ###--------   ------------##############     
         ###----------------------#############      
          ##-----------------------###########       
           ##----------------------##########        
             ##--------------------########          
              ##-------------------#######           
                 ##----------------####              
                     #-------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.04e+21   8.29e+20  -1.97e+21 
  8.29e+20  -7.49e+19  -1.14e+20 
 -1.97e+21  -1.14e+20   1.11e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130506032056/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 = 15
     RAKE = -60
       MW = 3.52
       HS = 13.0

The NDK file is 20130506032056.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2013/05/06 03:20:56:0  42.62 -111.96   4.9 3.6 Idaho
 
 Stations used:
   IW.FLWY IW.FXWY IW.IMW IW.LOHW IW.MOOW IW.REDW IW.SNOW 
   IW.TPAW LB.BMN TA.H17A TA.R11A US.AHID US.BW06 US.DUG 
   US.HLID US.HWUT US.RLMT UU.BGU UU.HVU UU.JLU UU.MPU UU.SPU 
   UU.SZCU WY.YFT WY.YHB 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 = 2.40e+21 dyne-cm
  Mw = 3.52 
  Z  = 13 km
  Plane   Strike  Dip  Rake
   NP1      339    77   -98
   NP2      190    15   -60
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.40e+21     32      75
    N   0.00e+00      7     341
    P  -2.40e+21     57     239

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -7.49e+19
       Mxy     1.14e+20
       Mxz     8.29e+20
       Myy     1.11e+21
       Myz     1.97e+21
       Mzz    -1.04e+21
                                                     
                                                     
                                                     
                                                     
                     ---###########                  
                 ###--#################              
              ####------##################           
             ###---------##################          
           ###------------###################        
          ###--------------###################       
         ###----------------###################      
        ###------------------###########   #####     
        ###-------------------########## T #####     
       ###--------------------##########   ######    
       ###---------------------##################    
       ###----------------------#################    
       ###---------   ----------#################    
        ##--------- P -----------###############     
        ###--------   ------------##############     
         ###----------------------#############      
          ##-----------------------###########       
           ##----------------------##########        
             ##--------------------########          
              ##-------------------#######           
                 ##----------------####              
                     #-------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.04e+21   8.29e+20  -1.97e+21 
  8.29e+20  -7.49e+19  -1.14e+20 
 -1.97e+21  -1.14e+20   1.11e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130506032056/index.html
	

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   145    45    90   3.13 0.3580
WVFGRD96    1.0   295    50    65   3.17 0.3097
WVFGRD96    2.0   140    45    85   3.30 0.3542
WVFGRD96    3.0    90    30    35   3.32 0.2530
WVFGRD96    4.0   245    20     5   3.32 0.3022
WVFGRD96    5.0   235    20    -5   3.33 0.3685
WVFGRD96    6.0   230    20   -15   3.35 0.4221
WVFGRD96    7.0   225    20   -25   3.36 0.4621
WVFGRD96    8.0   215    15   -30   3.44 0.4856
WVFGRD96    9.0   210    15   -40   3.46 0.5152
WVFGRD96   10.0   200    15   -50   3.48 0.5367
WVFGRD96   11.0   195    15   -55   3.49 0.5517
WVFGRD96   12.0   190    15   -60   3.51 0.5603
WVFGRD96   13.0   190    15   -60   3.52 0.5635
WVFGRD96   14.0   180    15   -70   3.53 0.5619
WVFGRD96   15.0   345    80   -90   3.55 0.5572
WVFGRD96   16.0   165    10   -90   3.57 0.5494
WVFGRD96   17.0   160    10   -95   3.58 0.5384
WVFGRD96   18.0   155    10   -95   3.58 0.5255
WVFGRD96   19.0   185    10   -65   3.59 0.5108
WVFGRD96   20.0   190    10   -60   3.60 0.4951
WVFGRD96   21.0   190    10   -60   3.61 0.4786
WVFGRD96   22.0   170     5   -80   3.62 0.4608
WVFGRD96   23.0   145    90    70   3.61 0.4418
WVFGRD96   24.0   145    90    70   3.62 0.4258
WVFGRD96   25.0   145    90    70   3.63 0.4094
WVFGRD96   26.0   145    90    70   3.64 0.3923
WVFGRD96   27.0   140    90    70   3.64 0.3745
WVFGRD96   28.0   140    90    70   3.65 0.3566
WVFGRD96   29.0   145    85    70   3.66 0.3384

The best solution is

WVFGRD96   13.0   190    15   -60   3.52 0.5635

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
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 00:21:01 CST 2015