Location

2013/03/10 21:05:18 61.510 -150.478 4.2 61.2 Alaska

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  2013/03/10 21:05:18:0  61.51 -150.48   4.2 61.2 Alaska
 
 Stations used:
   AK.CAST AK.DIV AK.HIN AK.KNK AK.PPLA AK.RC01 AK.RIDG AK.SAW 
   AK.SCM AK.SSN AK.SWD AT.MENT AT.PMR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.69e+22 dyne-cm
  Mw = 4.22 
  Z  = 71 km
  Plane   Strike  Dip  Rake
   NP1      145    90   -155
   NP2       55    65     0
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.69e+22     17     277
    N   0.00e+00     65     145
    P  -2.69e+22     17      13

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.29e+22
       Mxy    -8.34e+21
       Mxz    -6.52e+21
       Myy     2.29e+22
       Myz    -9.32e+21
       Mzz     0.00e+00
                                                     
                                                     
                                                     
                                                     
                     ---------   --                  
                 ------------- P ------              
              ###-------------   ---------           
             #####-------------------------          
           #########-------------------------        
          ###########------------------------#       
         #############----------------------###      
        ###############--------------------#####     
        #   #############-----------------######     
       ## T ##############--------------#########    
       ##   ###############------------##########    
       ######################--------############    
       #######################-----##############    
        #######################-################     
        ######################---###############     
         ##################-------#############      
          ############-------------###########       
           -##----------------------#########        
             -------------------------#####          
              -------------------------###           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  0.00e+00  -6.52e+21   9.32e+21 
 -6.52e+21  -2.29e+22   8.34e+21 
  9.32e+21   8.34e+21   2.29e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130310210518/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 = 55
      DIP = 65
     RAKE = 0
       MW = 4.22
       HS = 71.0

The NDK file is 20130310210518.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2013/03/10 21:05:18:0  61.51 -150.48   4.2 61.2 Alaska
 
 Stations used:
   AK.CAST AK.DIV AK.HIN AK.KNK AK.PPLA AK.RC01 AK.RIDG AK.SAW 
   AK.SCM AK.SSN AK.SWD AT.MENT AT.PMR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.69e+22 dyne-cm
  Mw = 4.22 
  Z  = 71 km
  Plane   Strike  Dip  Rake
   NP1      145    90   -155
   NP2       55    65     0
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.69e+22     17     277
    N   0.00e+00     65     145
    P  -2.69e+22     17      13

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.29e+22
       Mxy    -8.34e+21
       Mxz    -6.52e+21
       Myy     2.29e+22
       Myz    -9.32e+21
       Mzz     0.00e+00
                                                     
                                                     
                                                     
                                                     
                     ---------   --                  
                 ------------- P ------              
              ###-------------   ---------           
             #####-------------------------          
           #########-------------------------        
          ###########------------------------#       
         #############----------------------###      
        ###############--------------------#####     
        #   #############-----------------######     
       ## T ##############--------------#########    
       ##   ###############------------##########    
       ######################--------############    
       #######################-----##############    
        #######################-################     
        ######################---###############     
         ##################-------#############      
          ############-------------###########       
           -##----------------------#########        
             -------------------------#####          
              -------------------------###           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  0.00e+00  -6.52e+21   9.32e+21 
 -6.52e+21  -2.29e+22   8.34e+21 
  9.32e+21   8.34e+21   2.29e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130310210518/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 0.06 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    50    55   -15   3.24 0.1165
WVFGRD96    1.0    50    60   -10   3.28 0.1303
WVFGRD96    2.0    55    55     0   3.42 0.1849
WVFGRD96    3.0    55    55     5   3.49 0.2140
WVFGRD96    4.0    55    60    20   3.55 0.2415
WVFGRD96    5.0    55    65    20   3.57 0.2678
WVFGRD96    6.0    55    65    20   3.60 0.2877
WVFGRD96    7.0    50    70    15   3.63 0.3107
WVFGRD96    8.0    50    65    15   3.68 0.3340
WVFGRD96    9.0    50    65    15   3.70 0.3533
WVFGRD96   10.0    50    70    15   3.72 0.3702
WVFGRD96   11.0    50    70    15   3.73 0.3818
WVFGRD96   12.0    50    70    10   3.74 0.3943
WVFGRD96   13.0    50    70    10   3.76 0.4044
WVFGRD96   14.0    50    75    10   3.77 0.4130
WVFGRD96   15.0    50    75    10   3.78 0.4226
WVFGRD96   16.0    50    75    10   3.79 0.4308
WVFGRD96   17.0    50    75     5   3.80 0.4364
WVFGRD96   18.0    50    80    10   3.81 0.4439
WVFGRD96   19.0    50    80    10   3.82 0.4495
WVFGRD96   20.0    50    80     5   3.83 0.4568
WVFGRD96   21.0    55    80    10   3.83 0.4620
WVFGRD96   22.0    55    80    10   3.84 0.4684
WVFGRD96   23.0    55    80    10   3.85 0.4731
WVFGRD96   24.0    55    80    10   3.86 0.4790
WVFGRD96   25.0    55    80     5   3.87 0.4842
WVFGRD96   26.0    55    80     5   3.88 0.4902
WVFGRD96   27.0    55    80     5   3.89 0.4951
WVFGRD96   28.0    55    80     5   3.90 0.5005
WVFGRD96   29.0    55    80     5   3.90 0.5063
WVFGRD96   30.0    55    80     5   3.91 0.5119
WVFGRD96   31.0    50    85     5   3.93 0.5179
WVFGRD96   32.0    50    85     5   3.94 0.5232
WVFGRD96   33.0    50    85     5   3.96 0.5289
WVFGRD96   34.0    50    85     5   3.97 0.5346
WVFGRD96   35.0    50    85     5   3.98 0.5392
WVFGRD96   36.0    50    85     0   3.99 0.5431
WVFGRD96   37.0    50    85     0   4.01 0.5487
WVFGRD96   38.0    50    85     0   4.02 0.5544
WVFGRD96   39.0    50    85     0   4.04 0.5597
WVFGRD96   40.0    50    80     0   4.06 0.5662
WVFGRD96   41.0    50    80     0   4.07 0.5696
WVFGRD96   42.0    50    80     0   4.08 0.5717
WVFGRD96   43.0    50    80     0   4.09 0.5733
WVFGRD96   44.0    50    80     0   4.10 0.5763
WVFGRD96   45.0    50    80     0   4.10 0.5785
WVFGRD96   46.0    50    80     0   4.11 0.5796
WVFGRD96   47.0    50    80     0   4.12 0.5824
WVFGRD96   48.0    50    80     0   4.13 0.5843
WVFGRD96   49.0    50    80     0   4.13 0.5850
WVFGRD96   50.0    50    80     0   4.14 0.5875
WVFGRD96   51.0    50    80     0   4.15 0.5886
WVFGRD96   52.0    50    80     0   4.15 0.5894
WVFGRD96   53.0    50    80     0   4.16 0.5911
WVFGRD96   54.0    50    80     0   4.16 0.5912
WVFGRD96   55.0    50    80     0   4.17 0.5927
WVFGRD96   56.0    50    75     0   4.17 0.5931
WVFGRD96   57.0    50    75     0   4.17 0.5941
WVFGRD96   58.0    50    75     0   4.18 0.5948
WVFGRD96   59.0    50    75     5   4.18 0.5957
WVFGRD96   60.0    50    75     5   4.19 0.5969
WVFGRD96   61.0    50    75     5   4.19 0.5975
WVFGRD96   62.0    50    75     5   4.20 0.5985
WVFGRD96   63.0    50    75     5   4.20 0.5986
WVFGRD96   64.0    50    75     5   4.21 0.5993
WVFGRD96   65.0    50    75     5   4.21 0.5989
WVFGRD96   66.0    55    65     0   4.20 0.5996
WVFGRD96   67.0    55    65     0   4.20 0.6000
WVFGRD96   68.0    55    65     0   4.21 0.6002
WVFGRD96   69.0    55    65     0   4.21 0.6003
WVFGRD96   70.0    55    65     0   4.21 0.5999
WVFGRD96   71.0    55    65     0   4.22 0.6004
WVFGRD96   72.0    55    65     0   4.22 0.5988
WVFGRD96   73.0    55    65     0   4.22 0.5991
WVFGRD96   74.0    55    65     0   4.23 0.5981
WVFGRD96   75.0    55    65     5   4.23 0.5974
WVFGRD96   76.0    55    65     5   4.23 0.5965
WVFGRD96   77.0    55    65     5   4.24 0.5953
WVFGRD96   78.0    55    65     5   4.24 0.5953
WVFGRD96   79.0    55    65     5   4.24 0.5935
WVFGRD96   80.0    55    65     5   4.25 0.5927
WVFGRD96   81.0    55    65     5   4.25 0.5915
WVFGRD96   82.0    55    65     5   4.25 0.5888
WVFGRD96   83.0    55    65     5   4.25 0.5885
WVFGRD96   84.0    55    65    10   4.26 0.5865
WVFGRD96   85.0    55    65    10   4.26 0.5845
WVFGRD96   86.0    55    65    10   4.26 0.5838
WVFGRD96   87.0    55    65    10   4.26 0.5815
WVFGRD96   88.0    55    65    10   4.27 0.5797
WVFGRD96   89.0    55    65    10   4.27 0.5783
WVFGRD96   90.0    55    65    10   4.27 0.5757
WVFGRD96   91.0    55    65    10   4.27 0.5739
WVFGRD96   92.0    55    65    10   4.28 0.5720
WVFGRD96   93.0    55    65    10   4.28 0.5692
WVFGRD96   94.0    55    65    15   4.28 0.5669
WVFGRD96   95.0    55    65    15   4.28 0.5654
WVFGRD96   96.0    55    65    15   4.28 0.5627
WVFGRD96   97.0    55    65    15   4.29 0.5606
WVFGRD96   98.0    55    65    15   4.29 0.5587
WVFGRD96   99.0    55    65    15   4.29 0.5563

The best solution is

WVFGRD96   71.0    55    65     0   4.22 0.6004

The mechanism corresponding 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 0.06 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 00:20:48 CST 2015