Location

2012/07/10 04:06:54 63.437 -149.407 104.0 4.30 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  2012/07/10 04:06:54:0  63.44 -149.41 104.0 4.3 Alaska
 
 Stations used:
   AK.BPAW AK.BWN AK.CCB AK.GHO AK.GLM AK.KNK AK.KTH AK.MDM 
   AK.MLY AK.NEA AK.PAX AK.PPLA AK.SAW AK.SCM AK.TRF AK.WRH 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 3.31e+22 dyne-cm
  Mw = 4.28 
  Z  = 122 km
  Plane   Strike  Dip  Rake
   NP1      324    58   138
   NP2       80    55    40
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.31e+22     51     290
    N   0.00e+00     39     114
    P  -3.31e+22      2      23

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.65e+22
       Mxy    -1.61e+22
       Mxz     4.64e+21
       Myy     6.50e+21
       Myz    -1.56e+22
       Mzz     2.00e+22
                                                     
                                                     
                                                     
                                                     
                     ------------ P                  
                 ----------------   ---              
              #######---------------------           
             ############------------------          
           #################-----------------        
          ####################----------------       
         #######################---------------      
        #########################---------------     
        #########   ###############-------------     
       ########## T ################------------#    
       ##########   #################----------##    
       ###############################-------####    
       ################################----######    
        -##############################--#######     
        ----#########################---########     
         -------###############---------#######      
          -------------------------------#####       
           ------------------------------####        
             ----------------------------##          
              --------------------------##           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.00e+22   4.64e+21   1.56e+22 
  4.64e+21  -2.65e+22   1.61e+22 
  1.56e+22   1.61e+22   6.50e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120710040654/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 = 80
      DIP = 55
     RAKE = 40
       MW = 4.28
       HS = 122.0

The NDK file is 20120710040654.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2012/07/10 04:06:54:0  63.44 -149.41 104.0 4.3 Alaska
 
 Stations used:
   AK.BPAW AK.BWN AK.CCB AK.GHO AK.GLM AK.KNK AK.KTH AK.MDM 
   AK.MLY AK.NEA AK.PAX AK.PPLA AK.SAW AK.SCM AK.TRF AK.WRH 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 3.31e+22 dyne-cm
  Mw = 4.28 
  Z  = 122 km
  Plane   Strike  Dip  Rake
   NP1      324    58   138
   NP2       80    55    40
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.31e+22     51     290
    N   0.00e+00     39     114
    P  -3.31e+22      2      23

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.65e+22
       Mxy    -1.61e+22
       Mxz     4.64e+21
       Myy     6.50e+21
       Myz    -1.56e+22
       Mzz     2.00e+22
                                                     
                                                     
                                                     
                                                     
                     ------------ P                  
                 ----------------   ---              
              #######---------------------           
             ############------------------          
           #################-----------------        
          ####################----------------       
         #######################---------------      
        #########################---------------     
        #########   ###############-------------     
       ########## T ################------------#    
       ##########   #################----------##    
       ###############################-------####    
       ################################----######    
        -##############################--#######     
        ----#########################---########     
         -------###############---------#######      
          -------------------------------#####       
           ------------------------------####        
             ----------------------------##          
              --------------------------##           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.00e+22   4.64e+21   1.56e+22 
  4.64e+21  -2.65e+22   1.61e+22 
  1.56e+22   1.61e+22   6.50e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120710040654/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   110    50   -90   3.15 0.2028
WVFGRD96    1.0   310    45   -55   3.17 0.1923
WVFGRD96    2.0   105    50   -95   3.35 0.2757
WVFGRD96    3.0   295    40   -75   3.41 0.2676
WVFGRD96    4.0   335    60   -20   3.37 0.2360
WVFGRD96    5.0   170    50    10   3.41 0.2509
WVFGRD96    6.0   170    55    10   3.44 0.2703
WVFGRD96    7.0   165    50     5   3.44 0.2881
WVFGRD96    8.0   165    45    10   3.50 0.3005
WVFGRD96    9.0   165    50    10   3.53 0.3100
WVFGRD96   10.0   180    60    20   3.59 0.3185
WVFGRD96   11.0   180    65    20   3.63 0.3261
WVFGRD96   12.0   180    65    20   3.65 0.3329
WVFGRD96   13.0   180    65    20   3.66 0.3338
WVFGRD96   14.0   180    65    20   3.68 0.3360
WVFGRD96   15.0   180    65    20   3.69 0.3362
WVFGRD96   16.0   180    65    20   3.71 0.3315
WVFGRD96   17.0   185    65    20   3.73 0.3303
WVFGRD96   18.0   185    65    20   3.74 0.3258
WVFGRD96   19.0   185    65    20   3.76 0.3241
WVFGRD96   20.0   185    65    20   3.77 0.3211
WVFGRD96   21.0   190    65    15   3.79 0.3083
WVFGRD96   22.0   190    65    15   3.81 0.3041
WVFGRD96   23.0   190    65    15   3.81 0.2951
WVFGRD96   24.0   190    70    15   3.83 0.2747
WVFGRD96   25.0   190    70    15   3.84 0.2659
WVFGRD96   26.0   240    45    30   3.70 0.2594
WVFGRD96   27.0   240    50    25   3.71 0.2610
WVFGRD96   28.0   240    50    25   3.72 0.2627
WVFGRD96   29.0   240    50    25   3.73 0.2601
WVFGRD96   30.0     0    60   -25   3.83 0.2657
WVFGRD96   31.0     0    60   -25   3.84 0.2746
WVFGRD96   32.0     0    60   -25   3.86 0.2818
WVFGRD96   33.0     0    60   -25   3.87 0.2872
WVFGRD96   34.0     0    60   -20   3.88 0.2929
WVFGRD96   35.0     0    65   -20   3.92 0.2991
WVFGRD96   36.0     5    70   -15   3.95 0.3068
WVFGRD96   37.0     5    70   -10   3.97 0.3166
WVFGRD96   38.0     5    75    -5   4.01 0.3277
WVFGRD96   39.0     5    75    -5   4.03 0.3411
WVFGRD96   40.0     5    70   -10   4.08 0.3573
WVFGRD96   41.0     5    70    -5   4.10 0.3643
WVFGRD96   42.0     5    70    -5   4.11 0.3702
WVFGRD96   43.0     5    65    -5   4.11 0.3761
WVFGRD96   44.0     5    65    -5   4.12 0.3827
WVFGRD96   45.0     5    65    -5   4.13 0.3882
WVFGRD96   46.0     5    65    -5   4.14 0.3933
WVFGRD96   47.0     5    65    -5   4.15 0.3970
WVFGRD96   48.0     5    65    -5   4.16 0.3995
WVFGRD96   49.0     5    60    -5   4.14 0.4017
WVFGRD96   50.0    10    65    15   4.16 0.4058
WVFGRD96   51.0    10    65    15   4.17 0.4103
WVFGRD96   52.0    15    60    25   4.15 0.4164
WVFGRD96   53.0    15    60    25   4.15 0.4216
WVFGRD96   54.0    15    60    25   4.16 0.4257
WVFGRD96   55.0    15    65    25   4.19 0.4286
WVFGRD96   56.0    80    85   -30   4.15 0.4346
WVFGRD96   57.0   260    90    30   4.14 0.4372
WVFGRD96   58.0   260    90    30   4.14 0.4439
WVFGRD96   59.0    80    85   -30   4.16 0.4541
WVFGRD96   60.0   260    90    30   4.15 0.4569
WVFGRD96   61.0   260    90    30   4.15 0.4629
WVFGRD96   62.0    80    45    45   4.13 0.4786
WVFGRD96   63.0    80    45    45   4.13 0.4917
WVFGRD96   64.0    80    45    45   4.13 0.5027
WVFGRD96   65.0    80    45    40   4.15 0.5142
WVFGRD96   66.0    80    50    40   4.16 0.5247
WVFGRD96   67.0    80    50    40   4.16 0.5355
WVFGRD96   68.0    80    50    40   4.17 0.5454
WVFGRD96   69.0    80    50    40   4.17 0.5545
WVFGRD96   70.0    75    50    35   4.17 0.5623
WVFGRD96   71.0    75    50    35   4.17 0.5703
WVFGRD96   72.0    80    50    40   4.18 0.5769
WVFGRD96   73.0    80    50    40   4.18 0.5855
WVFGRD96   74.0    75    50    35   4.18 0.5917
WVFGRD96   75.0    75    50    35   4.18 0.5982
WVFGRD96   76.0    75    50    35   4.18 0.6048
WVFGRD96   77.0    75    50    35   4.18 0.6104
WVFGRD96   78.0    75    50    35   4.19 0.6170
WVFGRD96   79.0    75    50    35   4.19 0.6215
WVFGRD96   80.0    75    50    35   4.19 0.6276
WVFGRD96   81.0    75    50    35   4.20 0.6323
WVFGRD96   82.0    75    50    35   4.20 0.6388
WVFGRD96   83.0    75    50    35   4.20 0.6414
WVFGRD96   84.0    75    50    35   4.20 0.6472
WVFGRD96   85.0    75    50    35   4.21 0.6516
WVFGRD96   86.0    75    50    35   4.21 0.6563
WVFGRD96   87.0    75    50    40   4.20 0.6591
WVFGRD96   88.0    75    50    40   4.20 0.6657
WVFGRD96   89.0    75    50    40   4.21 0.6697
WVFGRD96   90.0    75    50    40   4.21 0.6733
WVFGRD96   91.0    75    50    40   4.21 0.6783
WVFGRD96   92.0    75    50    40   4.21 0.6815
WVFGRD96   93.0    75    50    40   4.22 0.6854
WVFGRD96   94.0    75    50    40   4.22 0.6888
WVFGRD96   95.0    75    50    40   4.22 0.6923
WVFGRD96   96.0    75    50    40   4.22 0.6944
WVFGRD96   97.0    75    50    40   4.23 0.6996
WVFGRD96   98.0    75    50    40   4.23 0.6995
WVFGRD96   99.0    75    50    40   4.23 0.7037
WVFGRD96  100.0    75    50    40   4.23 0.7063
WVFGRD96  101.0    75    50    40   4.23 0.7071
WVFGRD96  102.0    75    50    40   4.24 0.7102
WVFGRD96  103.0    75    50    40   4.24 0.7112
WVFGRD96  104.0    75    50    40   4.24 0.7130
WVFGRD96  105.0    75    50    40   4.24 0.7134
WVFGRD96  106.0    75    50    40   4.24 0.7161
WVFGRD96  107.0    75    50    40   4.24 0.7158
WVFGRD96  108.0    80    55    40   4.26 0.7188
WVFGRD96  109.0    80    55    40   4.26 0.7196
WVFGRD96  110.0    80    55    40   4.26 0.7200
WVFGRD96  111.0    80    55    40   4.26 0.7223
WVFGRD96  112.0    80    55    40   4.26 0.7219
WVFGRD96  113.0    80    55    40   4.27 0.7227
WVFGRD96  114.0    80    55    40   4.27 0.7241
WVFGRD96  115.0    80    55    40   4.27 0.7235
WVFGRD96  116.0    80    55    40   4.27 0.7247
WVFGRD96  117.0    80    55    40   4.27 0.7259
WVFGRD96  118.0    80    55    40   4.27 0.7242
WVFGRD96  119.0    80    55    40   4.27 0.7264
WVFGRD96  120.0    80    55    40   4.27 0.7265
WVFGRD96  121.0    80    55    40   4.27 0.7256
WVFGRD96  122.0    80    55    40   4.28 0.7271
WVFGRD96  123.0    80    55    40   4.28 0.7254
WVFGRD96  124.0    80    55    40   4.28 0.7266
WVFGRD96  125.0    80    55    40   4.28 0.7263
WVFGRD96  126.0    80    55    40   4.28 0.7268
WVFGRD96  127.0    80    55    40   4.28 0.7255
WVFGRD96  128.0    80    55    40   4.28 0.7255
WVFGRD96  129.0    80    55    40   4.28 0.7258

The best solution is

WVFGRD96  122.0    80    55    40   4.28 0.7271

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 0.10 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 00:25:10 CST 2015