Location

2011/06/16 19:06:05 60.765 -151.048 57 5.20 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  2011/06/16 19:06:05:0  60.76 -151.05  57.0 5.2 Alaska
 
 Stations used:
   AK.BPAW AK.BRLK AK.BWN AK.CNP AK.DIV AK.HOM AK.KLU AK.KTH 
   AK.MCK AK.PPLA AK.RC01 AK.RND AK.SAW AK.SCM AK.SSN AK.SWD 
   AT.MENT AT.PMR II.KDAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.05 n 3
 
 Best Fitting Double Couple
  Mo = 3.85e+23 dyne-cm
  Mw = 4.99 
  Z  = 74 km
  Plane   Strike  Dip  Rake
   NP1       45    75    20
   NP2      310    71   164
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.85e+23     25     268
    N   0.00e+00     65      80
    P  -3.85e+23      3     177

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.82e+23
       Mxy     3.29e+22
       Mxz     1.44e+22
       Myy     3.16e+23
       Myz    -1.47e+23
       Mzz     6.58e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             -----------------------------#          
           ######-------------------------###        
          ############-------------------#####       
         ################---------------#######      
        ####################----------##########     
        ######################-------###########     
       #########################----#############    
       ####   ###################################    
       #### T ##################----#############    
       ####   #################-------###########    
        #####################----------#########     
        ###################--------------#######     
         ###############------------------#####      
          ############---------------------###       
           ########-------------------------#        
             ###---------------------------          
              ----------------------------           
                 -----------   --------              
                     ------- P ----                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  6.58e+22   1.44e+22   1.47e+23 
  1.44e+22  -3.82e+23  -3.29e+22 
  1.47e+23  -3.29e+22   3.16e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110616190605/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 = 45
      DIP = 75
     RAKE = 20
       MW = 4.99
       HS = 74.0

The NDK file is 20110616190605.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  2011/06/16 19:06:05:0  60.76 -151.05  57.0 5.2 Alaska
 
 Stations used:
   AK.BPAW AK.BRLK AK.BWN AK.CNP AK.DIV AK.HOM AK.KLU AK.KTH 
   AK.MCK AK.PPLA AK.RC01 AK.RND AK.SAW AK.SCM AK.SSN AK.SWD 
   AT.MENT AT.PMR II.KDAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.05 n 3
 
 Best Fitting Double Couple
  Mo = 3.85e+23 dyne-cm
  Mw = 4.99 
  Z  = 74 km
  Plane   Strike  Dip  Rake
   NP1       45    75    20
   NP2      310    71   164
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.85e+23     25     268
    N   0.00e+00     65      80
    P  -3.85e+23      3     177

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.82e+23
       Mxy     3.29e+22
       Mxz     1.44e+22
       Myy     3.16e+23
       Myz    -1.47e+23
       Mzz     6.58e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             -----------------------------#          
           ######-------------------------###        
          ############-------------------#####       
         ################---------------#######      
        ####################----------##########     
        ######################-------###########     
       #########################----#############    
       ####   ###################################    
       #### T ##################----#############    
       ####   #################-------###########    
        #####################----------#########     
        ###################--------------#######     
         ###############------------------#####      
          ############---------------------###       
           ########-------------------------#        
             ###---------------------------          
              ----------------------------           
                 -----------   --------              
                     ------- P ----                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  6.58e+22   1.44e+22   1.47e+23 
  1.44e+22  -3.82e+23  -3.29e+22 
  1.47e+23  -3.29e+22   3.16e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110616190605/index.html
	
USGS/SLU Regional Moment Solution

11/06/16 19:06:05.42

Epicenter:  60.807 -151.216
MW 5.0

USGS/SLU REGIONAL MOMENT TENSOR
Depth  66         No. of sta: 58
Moment Tensor;   Scale 10**16 Nm
  Mrr= 0.17       Mtt=-3.62
  Mpp= 3.45       Mrt= 0.40
  Mrp= 1.31       Mtp=-0.15
 Principal axes:
  T  Val=  3.91  Plg=19  Azm=270
  N       -0.23      69       69
  P       -3.68       7      177

Best Double Couple:Mo=3.8*10**16
 NP1:Strike= 45 Dip=81 Slip=  19
 NP2:       312     71       171


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 0.05 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   315    70    15   4.16 0.2134
WVFGRD96    1.0   130    90     0   4.17 0.2321
WVFGRD96    2.0   315    75    15   4.28 0.2934
WVFGRD96    3.0   130    90     0   4.31 0.3228
WVFGRD96    4.0   310    85     0   4.34 0.3423
WVFGRD96    5.0   220    80    15   4.38 0.3570
WVFGRD96    6.0   220    80    15   4.41 0.3814
WVFGRD96    7.0   215    90     5   4.44 0.4071
WVFGRD96    8.0   220    85    15   4.47 0.4348
WVFGRD96    9.0   220    85    15   4.49 0.4543
WVFGRD96   10.0    40    90   -10   4.51 0.4660
WVFGRD96   11.0   220    85    15   4.53 0.4798
WVFGRD96   12.0    35    90   -15   4.54 0.4834
WVFGRD96   13.0    35    90   -15   4.55 0.4884
WVFGRD96   14.0    35    90   -10   4.56 0.4929
WVFGRD96   15.0   220    85    15   4.57 0.4991
WVFGRD96   16.0    35    90   -15   4.58 0.4999
WVFGRD96   17.0   220    85    15   4.59 0.5038
WVFGRD96   18.0    35    90   -10   4.59 0.5057
WVFGRD96   19.0    35    90   -10   4.60 0.5084
WVFGRD96   20.0    35    90   -10   4.61 0.5117
WVFGRD96   21.0   220    85    10   4.62 0.5164
WVFGRD96   22.0    35    90   -10   4.62 0.5188
WVFGRD96   23.0    35    90   -10   4.63 0.5215
WVFGRD96   24.0   215    90    10   4.64 0.5238
WVFGRD96   25.0    35    90   -10   4.64 0.5263
WVFGRD96   26.0    40    90    10   4.64 0.5287
WVFGRD96   27.0    40    90    10   4.65 0.5323
WVFGRD96   28.0    40    90    10   4.66 0.5366
WVFGRD96   29.0   215    85   -15   4.67 0.5429
WVFGRD96   30.0   215    85   -15   4.67 0.5481
WVFGRD96   31.0    40    85    10   4.69 0.5524
WVFGRD96   32.0    40    85    10   4.70 0.5592
WVFGRD96   33.0    40    85    10   4.71 0.5665
WVFGRD96   34.0    40    85    10   4.72 0.5743
WVFGRD96   35.0   220    90   -10   4.73 0.5775
WVFGRD96   36.0   220    90   -10   4.75 0.5850
WVFGRD96   37.0    40    85    10   4.76 0.5995
WVFGRD96   38.0    40    85    10   4.77 0.6087
WVFGRD96   39.0   220    90   -10   4.79 0.6082
WVFGRD96   40.0    40    80    20   4.82 0.6257
WVFGRD96   41.0    40    80    15   4.83 0.6297
WVFGRD96   42.0    40    80    15   4.83 0.6338
WVFGRD96   43.0    40    80    15   4.84 0.6377
WVFGRD96   44.0    40    80    15   4.85 0.6417
WVFGRD96   45.0    40    80    15   4.86 0.6455
WVFGRD96   46.0    40    80    15   4.86 0.6492
WVFGRD96   47.0    40    80    15   4.87 0.6531
WVFGRD96   48.0    40    80    15   4.88 0.6571
WVFGRD96   49.0    40    80    15   4.88 0.6613
WVFGRD96   50.0    40    80    15   4.89 0.6651
WVFGRD96   51.0    40    80    15   4.90 0.6685
WVFGRD96   52.0    40    80    15   4.90 0.6724
WVFGRD96   53.0    40    80    15   4.91 0.6766
WVFGRD96   54.0    40    80    15   4.91 0.6798
WVFGRD96   55.0    40    80    15   4.92 0.6825
WVFGRD96   56.0    40    80    15   4.93 0.6863
WVFGRD96   57.0    40    80    15   4.93 0.6895
WVFGRD96   58.0    40    80    15   4.93 0.6915
WVFGRD96   59.0    40    80    15   4.94 0.6948
WVFGRD96   60.0    40    80    20   4.94 0.6973
WVFGRD96   61.0    45    75    20   4.95 0.6989
WVFGRD96   62.0    45    75    20   4.95 0.7020
WVFGRD96   63.0    45    75    20   4.95 0.7038
WVFGRD96   64.0    45    75    20   4.96 0.7058
WVFGRD96   65.0    45    75    20   4.96 0.7079
WVFGRD96   66.0    45    75    20   4.96 0.7086
WVFGRD96   67.0    45    75    20   4.97 0.7107
WVFGRD96   68.0    45    75    20   4.97 0.7112
WVFGRD96   69.0    45    75    20   4.97 0.7126
WVFGRD96   70.0    45    75    20   4.98 0.7134
WVFGRD96   71.0    45    75    20   4.98 0.7137
WVFGRD96   72.0    45    75    20   4.98 0.7145
WVFGRD96   73.0    45    75    20   4.98 0.7139
WVFGRD96   74.0    45    75    20   4.99 0.7146
WVFGRD96   75.0    45    75    20   4.99 0.7139
WVFGRD96   76.0    45    75    20   4.99 0.7145
WVFGRD96   77.0    45    75    20   4.99 0.7132
WVFGRD96   78.0    45    75    20   5.00 0.7133
WVFGRD96   79.0    45    75    20   5.00 0.7122
WVFGRD96   80.0    45    75    20   5.00 0.7123
WVFGRD96   81.0    45    75    20   5.00 0.7105
WVFGRD96   82.0    45    75    20   5.00 0.7101
WVFGRD96   83.0    45    75    20   5.01 0.7088
WVFGRD96   84.0    45    75    20   5.01 0.7078
WVFGRD96   85.0    45    75    20   5.01 0.7062
WVFGRD96   86.0    45    75    20   5.01 0.7050
WVFGRD96   87.0    45    75    20   5.01 0.7037
WVFGRD96   88.0    45    75    20   5.01 0.7012
WVFGRD96   89.0    45    75    20   5.02 0.7006
WVFGRD96   90.0    40    80    20   5.02 0.6981
WVFGRD96   91.0    40    80    20   5.02 0.6973
WVFGRD96   92.0    40    80    20   5.02 0.6958
WVFGRD96   93.0    40    80    20   5.02 0.6939
WVFGRD96   94.0    40    80    25   5.02 0.6927
WVFGRD96   95.0    40    80    25   5.02 0.6906
WVFGRD96   96.0    40    80    25   5.02 0.6895
WVFGRD96   97.0    40    80    25   5.02 0.6878
WVFGRD96   98.0    40    80    25   5.02 0.6861
WVFGRD96   99.0    40    80    25   5.02 0.6842

The best solution is

WVFGRD96   74.0    45    75    20   4.99 0.7146

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 0.05 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 Sun Dec 6 20:45:07 CST 2015