Location

2012/06/28 05:58:57 62.470 -148.263 43.2 3.70 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  2012/06/28 05:58:57:0  62.47 -148.26  43.2 3.7 Alaska
 
 Stations used:
   AK.BWN AK.DHY AK.KTH AK.PPLA AK.SAW AK.TRF AT.PMR 
 
 Filtering commands used:
   hp c 0.025 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 4.47e+21 dyne-cm
  Mw = 3.70 
  Z  = 79 km
  Plane   Strike  Dip  Rake
   NP1      214    55   -93
   NP2       40    35   -85
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.47e+21     10     306
    N   0.00e+00      3     216
    P  -4.47e+21     79     110

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.51e+21
       Mxy    -2.02e+21
       Mxz     7.34e+20
       Myy     2.67e+21
       Myz    -1.37e+21
       Mzz    -4.18e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              ###################--------#           
               ###############------------#          
           # T ############----------------##        
          ##   ##########-------------------##       
         ##############---------------------###      
        ##############----------------------####     
        #############-----------------------####     
       ############-------------------------#####    
       ###########-----------   -----------######    
       ###########----------- P -----------######    
       ##########------------   ----------#######    
        ########-------------------------#######     
        ########------------------------########     
         #######-----------------------########      
          #####----------------------#########       
           ####--------------------##########        
             ###----------------###########          
              ##-------------#############           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.18e+21   7.34e+20   1.37e+21 
  7.34e+20   1.51e+21   2.02e+21 
  1.37e+21   2.02e+21   2.67e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120628055857/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 = 40
      DIP = 35
     RAKE = -85
       MW = 3.70
       HS = 79.0

The NDK file is 20120628055857.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2012/06/28 05:58:57:0  62.47 -148.26  43.2 3.7 Alaska
 
 Stations used:
   AK.BWN AK.DHY AK.KTH AK.PPLA AK.SAW AK.TRF AT.PMR 
 
 Filtering commands used:
   hp c 0.025 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 4.47e+21 dyne-cm
  Mw = 3.70 
  Z  = 79 km
  Plane   Strike  Dip  Rake
   NP1      214    55   -93
   NP2       40    35   -85
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.47e+21     10     306
    N   0.00e+00      3     216
    P  -4.47e+21     79     110

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.51e+21
       Mxy    -2.02e+21
       Mxz     7.34e+20
       Myy     2.67e+21
       Myz    -1.37e+21
       Mzz    -4.18e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              ###################--------#           
               ###############------------#          
           # T ############----------------##        
          ##   ##########-------------------##       
         ##############---------------------###      
        ##############----------------------####     
        #############-----------------------####     
       ############-------------------------#####    
       ###########-----------   -----------######    
       ###########----------- P -----------######    
       ##########------------   ----------#######    
        ########-------------------------#######     
        ########------------------------########     
         #######-----------------------########      
          #####----------------------#########       
           ####--------------------##########        
             ###----------------###########          
              ##-------------#############           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.18e+21   7.34e+20   1.37e+21 
  7.34e+20   1.51e+21   2.02e+21 
  1.37e+21   2.02e+21   2.67e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120628055857/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 0.025 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    90    45    85   2.63 0.1824
WVFGRD96    1.0    65    90     0   2.77 0.1966
WVFGRD96    2.0   245    90     0   2.90 0.2305
WVFGRD96    3.0   245    90     0   3.02 0.2405
WVFGRD96    4.0    60    70   -15   3.01 0.2080
WVFGRD96    5.0    60    70   -20   3.03 0.2234
WVFGRD96    6.0    60    70   -15   3.07 0.2462
WVFGRD96    7.0    60    70   -15   3.09 0.2643
WVFGRD96    8.0    60    65   -15   3.16 0.2813
WVFGRD96    9.0   200    35    20   2.97 0.2884
WVFGRD96   10.0   195    40    15   3.00 0.2994
WVFGRD96   11.0   190    45     5   3.02 0.3043
WVFGRD96   12.0   180    50    -5   3.05 0.3125
WVFGRD96   13.0   180    50    -5   3.06 0.3100
WVFGRD96   14.0   180    50    -5   3.08 0.3125
WVFGRD96   15.0   180    50    -5   3.09 0.3121
WVFGRD96   16.0   145    60    40   3.15 0.3012
WVFGRD96   17.0   145    60    40   3.17 0.3018
WVFGRD96   18.0   145    55    45   3.17 0.3016
WVFGRD96   19.0   140    55    45   3.18 0.3037
WVFGRD96   20.0   135    55    45   3.18 0.3047
WVFGRD96   21.0   135    55    45   3.20 0.3062
WVFGRD96   22.0   135    55    45   3.22 0.3056
WVFGRD96   23.0   120    60    40   3.22 0.3070
WVFGRD96   24.0   285    60   -50   3.20 0.3081
WVFGRD96   25.0   280    60   -50   3.21 0.3079
WVFGRD96   26.0   280    65   -50   3.22 0.3053
WVFGRD96   27.0   120    65    35   3.25 0.3102
WVFGRD96   28.0   120    65    35   3.26 0.3153
WVFGRD96   29.0   110    70    35   3.27 0.3182
WVFGRD96   30.0   140    60    45   3.30 0.3195
WVFGRD96   31.0   140    60    45   3.31 0.3241
WVFGRD96   32.0   145    65    35   3.34 0.3281
WVFGRD96   33.0   270    70   -40   3.30 0.3322
WVFGRD96   34.0   275    70   -45   3.30 0.3427
WVFGRD96   35.0   265    65   -45   3.33 0.3543
WVFGRD96   36.0   265    65   -45   3.35 0.3642
WVFGRD96   37.0   265    65   -45   3.36 0.3736
WVFGRD96   38.0   265    65   -45   3.37 0.3804
WVFGRD96   39.0   265    60   -45   3.39 0.3884
WVFGRD96   40.0   255    60   -55   3.51 0.4154
WVFGRD96   41.0   255    60   -55   3.52 0.4147
WVFGRD96   42.0   260    65   -45   3.52 0.4104
WVFGRD96   43.0   260    65   -45   3.53 0.4098
WVFGRD96   44.0   260    65   -45   3.54 0.4080
WVFGRD96   45.0   260    65   -45   3.55 0.4065
WVFGRD96   46.0   135    35   -10   3.57 0.4133
WVFGRD96   47.0   120    25   -30   3.57 0.4273
WVFGRD96   48.0   100    20   -50   3.57 0.4409
WVFGRD96   49.0   100    20   -50   3.57 0.4530
WVFGRD96   50.0   245    70   -85   3.57 0.4638
WVFGRD96   51.0   260    75   -55   3.57 0.4745
WVFGRD96   52.0   260    75   -55   3.58 0.4852
WVFGRD96   53.0   260    75   -55   3.58 0.4949
WVFGRD96   54.0   260    75   -50   3.60 0.5020
WVFGRD96   55.0   260    75   -50   3.60 0.5083
WVFGRD96   56.0   225    55   -90   3.66 0.5226
WVFGRD96   57.0   225    55   -90   3.66 0.5315
WVFGRD96   58.0   225    55   -90   3.66 0.5392
WVFGRD96   59.0   225    55   -90   3.66 0.5458
WVFGRD96   60.0   225    55   -90   3.66 0.5501
WVFGRD96   61.0   225    55   -90   3.66 0.5555
WVFGRD96   62.0   225    55   -90   3.66 0.5594
WVFGRD96   63.0   225    55   -90   3.66 0.5639
WVFGRD96   64.0   225    55   -90   3.65 0.5663
WVFGRD96   65.0   225    55   -90   3.65 0.5692
WVFGRD96   66.0   220    55   -90   3.67 0.5714
WVFGRD96   67.0   220    55   -90   3.67 0.5740
WVFGRD96   68.0   220    55   -90   3.67 0.5778
WVFGRD96   69.0   220    55   -90   3.67 0.5800
WVFGRD96   70.0   220    55   -90   3.67 0.5816
WVFGRD96   71.0   220    55   -90   3.67 0.5836
WVFGRD96   72.0   220    55   -90   3.67 0.5841
WVFGRD96   73.0   220    55   -90   3.68 0.5867
WVFGRD96   74.0   220    55   -90   3.68 0.5880
WVFGRD96   75.0   220    55   -90   3.68 0.5884
WVFGRD96   76.0   220    55   -90   3.68 0.5888
WVFGRD96   77.0   220    55   -90   3.68 0.5903
WVFGRD96   78.0   225    50   -85   3.69 0.5888
WVFGRD96   79.0    40    35   -85   3.70 0.5905
WVFGRD96   80.0    40    35   -85   3.70 0.5883
WVFGRD96   81.0    35    40  -100   3.69 0.5904
WVFGRD96   82.0    35    40  -100   3.70 0.5879
WVFGRD96   83.0    35    40  -100   3.70 0.5876
WVFGRD96   84.0    35    40  -100   3.70 0.5855
WVFGRD96   85.0    40    40   -90   3.71 0.5849
WVFGRD96   86.0    35    40  -100   3.70 0.5834
WVFGRD96   87.0    40    40   -90   3.71 0.5819
WVFGRD96   88.0    40    40   -90   3.71 0.5805
WVFGRD96   89.0   220    50   -90   3.71 0.5800

The best solution is

WVFGRD96   79.0    40    35   -85   3.70 0.5905

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 0.025 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 00:25:03 CST 2015