Location

2011/07/02 11:45:06 63.118 -150.858 122 4.40 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  2011/07/02 11:45:06:0  63.12 -150.86 122.0 4.4 Alaska
 
 Stations used:
   AK.BPAW AK.BRLK AK.CAST AK.CCB AK.DHY AK.FIB AK.KLU AK.KTH 
   AK.MCK AK.MLY AK.PPLA AK.RC01 AK.SAW AK.SSN AK.SWD AK.TRF 
   AK.WRH AT.PMR IU.COLA 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 3.67e+22 dyne-cm
  Mw = 4.31 
  Z  = 133 km
  Plane   Strike  Dip  Rake
   NP1       55    75    85
   NP2      254    16   108
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.67e+22     60     318
    N   0.00e+00      5      56
    P  -3.67e+22     30     149

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.52e+22
       Mxy     7.54e+21
       Mxz     2.55e+22
       Myy    -3.11e+21
       Myz    -1.89e+22
       Mzz     1.83e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------#######------              
              ------##################----           
             ----########################--          
           ---##############################-        
          ---###############################-#       
         --##########   ###################----      
        --########### T #################-------     
        -############   ###############---------     
       --#############################-----------    
       -###########################--------------    
       -#########################----------------    
       -#######################------------------    
        ####################--------------------     
        #################-----------------------     
         #############-------------------------      
          #######-----------------   ---------       
           ----------------------- P --------        
             ---------------------   ------          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.83e+22   2.55e+22   1.89e+22 
  2.55e+22  -1.52e+22  -7.54e+21 
  1.89e+22  -7.54e+21  -3.11e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110702114506/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 = 75
     RAKE = 85
       MW = 4.31
       HS = 133.0

The NDK file is 20110702114506.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2011/07/02 11:45:06:0  63.12 -150.86 122.0 4.4 Alaska
 
 Stations used:
   AK.BPAW AK.BRLK AK.CAST AK.CCB AK.DHY AK.FIB AK.KLU AK.KTH 
   AK.MCK AK.MLY AK.PPLA AK.RC01 AK.SAW AK.SSN AK.SWD AK.TRF 
   AK.WRH AT.PMR IU.COLA 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 3.67e+22 dyne-cm
  Mw = 4.31 
  Z  = 133 km
  Plane   Strike  Dip  Rake
   NP1       55    75    85
   NP2      254    16   108
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.67e+22     60     318
    N   0.00e+00      5      56
    P  -3.67e+22     30     149

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.52e+22
       Mxy     7.54e+21
       Mxz     2.55e+22
       Myy    -3.11e+21
       Myz    -1.89e+22
       Mzz     1.83e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------#######------              
              ------##################----           
             ----########################--          
           ---##############################-        
          ---###############################-#       
         --##########   ###################----      
        --########### T #################-------     
        -############   ###############---------     
       --#############################-----------    
       -###########################--------------    
       -#########################----------------    
       -#######################------------------    
        ####################--------------------     
        #################-----------------------     
         #############-------------------------      
          #######-----------------   ---------       
           ----------------------- P --------        
             ---------------------   ------          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.83e+22   2.55e+22   1.89e+22 
  2.55e+22  -1.52e+22  -7.54e+21 
  1.89e+22  -7.54e+21  -3.11e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110702114506/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   110    40   -70   3.38 0.2148
WVFGRD96    1.0   105    40   -80   3.42 0.2168
WVFGRD96    2.0   115    45   -65   3.52 0.2799
WVFGRD96    3.0   135    50   -40   3.56 0.2893
WVFGRD96    4.0   145    65   -15   3.54 0.2929
WVFGRD96    5.0   335    65    20   3.57 0.3043
WVFGRD96    6.0   335    65    20   3.60 0.3204
WVFGRD96    7.0   335    65    15   3.61 0.3314
WVFGRD96    8.0   340    60    20   3.66 0.3456
WVFGRD96    9.0   340    60    20   3.68 0.3556
WVFGRD96   10.0   340    60    20   3.69 0.3645
WVFGRD96   11.0   340    55    15   3.70 0.3675
WVFGRD96   12.0   340    55    15   3.71 0.3753
WVFGRD96   13.0   340    55    20   3.72 0.3787
WVFGRD96   14.0   340    55    20   3.73 0.3835
WVFGRD96   15.0   340    55    20   3.73 0.3883
WVFGRD96   16.0   340    60    20   3.74 0.3875
WVFGRD96   17.0   340    60    20   3.75 0.3895
WVFGRD96   18.0   340    60    20   3.75 0.3876
WVFGRD96   19.0   345    60    20   3.77 0.3863
WVFGRD96   20.0   345    60    20   3.78 0.3871
WVFGRD96   21.0   230    80   -35   3.76 0.3874
WVFGRD96   22.0   230    80   -35   3.77 0.3898
WVFGRD96   23.0   230    80   -35   3.78 0.3921
WVFGRD96   24.0   230    80   -35   3.78 0.3842
WVFGRD96   25.0   215    85   -35   3.79 0.3875
WVFGRD96   26.0    35    85    30   3.82 0.3911
WVFGRD96   27.0    35    85    30   3.83 0.3945
WVFGRD96   28.0    35    85    30   3.83 0.3880
WVFGRD96   29.0    35    85    30   3.84 0.3931
WVFGRD96   30.0    35    90    30   3.84 0.3969
WVFGRD96   31.0    35    90    30   3.85 0.4020
WVFGRD96   32.0    35    90    30   3.86 0.3955
WVFGRD96   33.0    40    85    30   3.87 0.4005
WVFGRD96   34.0    40    85    30   3.88 0.4051
WVFGRD96   35.0    40    85    30   3.89 0.3992
WVFGRD96   36.0   205    25    60   3.91 0.4069
WVFGRD96   37.0   205    25    60   3.92 0.4164
WVFGRD96   38.0   225    20    85   3.92 0.4161
WVFGRD96   39.0    50    70    90   3.93 0.4265
WVFGRD96   40.0   230    20    90   4.07 0.4410
WVFGRD96   41.0   230    20    90   4.08 0.4366
WVFGRD96   42.0   230    20    90   4.09 0.4387
WVFGRD96   43.0    55    70    95   4.09 0.4401
WVFGRD96   44.0   225    20    85   4.10 0.4394
WVFGRD96   45.0   225    20    85   4.11 0.4389
WVFGRD96   46.0    55    70    95   4.11 0.4349
WVFGRD96   47.0   220    20    80   4.12 0.4324
WVFGRD96   48.0   220    20    80   4.12 0.4294
WVFGRD96   49.0   195    70   -15   4.08 0.4357
WVFGRD96   50.0   195    70   -20   4.08 0.4351
WVFGRD96   51.0   195    70   -20   4.09 0.4407
WVFGRD96   52.0   195    70   -20   4.10 0.4452
WVFGRD96   53.0   195    70   -20   4.10 0.4491
WVFGRD96   54.0   195    70   -20   4.11 0.4521
WVFGRD96   55.0   195    70   -20   4.12 0.4559
WVFGRD96   56.0   195    70   -20   4.12 0.4591
WVFGRD96   57.0   195    70   -20   4.13 0.4626
WVFGRD96   58.0   195    70   -20   4.14 0.4663
WVFGRD96   59.0   195    70   -20   4.14 0.4686
WVFGRD96   60.0   195    70   -20   4.15 0.4719
WVFGRD96   61.0   195    70   -20   4.15 0.4736
WVFGRD96   62.0    55    65    80   4.18 0.4741
WVFGRD96   63.0    55    65    80   4.19 0.4850
WVFGRD96   64.0    55    65    80   4.19 0.4956
WVFGRD96   65.0    55    65    80   4.20 0.5065
WVFGRD96   66.0    60    65    85   4.20 0.5164
WVFGRD96   67.0    60    65    85   4.21 0.5261
WVFGRD96   68.0    60    65    85   4.21 0.5358
WVFGRD96   69.0    55    65    80   4.21 0.5442
WVFGRD96   70.0    55    70    80   4.21 0.5536
WVFGRD96   71.0    55    70    80   4.22 0.5639
WVFGRD96   72.0    55    70    80   4.22 0.5733
WVFGRD96   73.0    55    70    80   4.22 0.5841
WVFGRD96   74.0    55    70    80   4.22 0.5929
WVFGRD96   75.0    55    70    80   4.23 0.6011
WVFGRD96   76.0    55    70    80   4.23 0.6109
WVFGRD96   77.0    55    70    80   4.23 0.6195
WVFGRD96   78.0    55    70    80   4.23 0.6260
WVFGRD96   79.0    55    70    80   4.24 0.6345
WVFGRD96   80.0    55    70    80   4.24 0.6429
WVFGRD96   81.0    55    70    80   4.24 0.6496
WVFGRD96   82.0    55    70    80   4.24 0.6573
WVFGRD96   83.0    55    70    80   4.25 0.6649
WVFGRD96   84.0    55    70    80   4.25 0.6720
WVFGRD96   85.0    55    70    80   4.25 0.6780
WVFGRD96   86.0    55    70    80   4.25 0.6843
WVFGRD96   87.0    55    70    80   4.25 0.6912
WVFGRD96   88.0    55    70    80   4.25 0.6960
WVFGRD96   89.0    55    70    80   4.26 0.7022
WVFGRD96   90.0    55    70    80   4.26 0.7077
WVFGRD96   91.0    55    70    80   4.26 0.7124
WVFGRD96   92.0    55    70    80   4.26 0.7174
WVFGRD96   93.0    55    70    80   4.26 0.7220
WVFGRD96   94.0    55    70    80   4.26 0.7271
WVFGRD96   95.0    55    70    80   4.27 0.7311
WVFGRD96   96.0    55    70    80   4.27 0.7349
WVFGRD96   97.0    55    70    80   4.27 0.7395
WVFGRD96   98.0    55    70    80   4.27 0.7430
WVFGRD96   99.0    55    70    80   4.27 0.7459
WVFGRD96  100.0    55    70    80   4.27 0.7500
WVFGRD96  101.0    55    70    80   4.27 0.7528
WVFGRD96  102.0    55    70    80   4.27 0.7555
WVFGRD96  103.0    55    70    80   4.28 0.7585
WVFGRD96  104.0    55    70    80   4.28 0.7609
WVFGRD96  105.0    55    70    80   4.28 0.7635
WVFGRD96  106.0    55    70    80   4.28 0.7655
WVFGRD96  107.0    55    70    80   4.28 0.7678
WVFGRD96  108.0    55    70    80   4.28 0.7696
WVFGRD96  109.0    55    70    80   4.28 0.7720
WVFGRD96  110.0    55    70    80   4.28 0.7731
WVFGRD96  111.0    55    70    80   4.29 0.7747
WVFGRD96  112.0    55    70    80   4.29 0.7765
WVFGRD96  113.0    55    70    80   4.29 0.7776
WVFGRD96  114.0    55    70    80   4.29 0.7785
WVFGRD96  115.0    55    70    80   4.29 0.7800
WVFGRD96  116.0    55    70    80   4.29 0.7809
WVFGRD96  117.0    55    70    80   4.29 0.7816
WVFGRD96  118.0    55    70    80   4.29 0.7828
WVFGRD96  119.0    55    70    80   4.29 0.7833
WVFGRD96  120.0    55    70    80   4.30 0.7841
WVFGRD96  121.0    55    70    80   4.30 0.7846
WVFGRD96  122.0    55    70    80   4.30 0.7851
WVFGRD96  123.0    55    75    80   4.30 0.7857
WVFGRD96  124.0    55    75    80   4.30 0.7856
WVFGRD96  125.0    55    75    80   4.30 0.7864
WVFGRD96  126.0    55    75    80   4.30 0.7863
WVFGRD96  127.0    55    75    80   4.30 0.7872
WVFGRD96  128.0    55    75    80   4.30 0.7872
WVFGRD96  129.0    55    75    85   4.30 0.7878
WVFGRD96  130.0    55    75    85   4.31 0.7875
WVFGRD96  131.0    55    75    85   4.31 0.7871
WVFGRD96  132.0    55    75    85   4.31 0.7881
WVFGRD96  133.0    55    75    85   4.31 0.7881
WVFGRD96  134.0   260    20   110   4.31 0.7880
WVFGRD96  135.0    55    75    85   4.31 0.7873
WVFGRD96  136.0    55    75    85   4.31 0.7870
WVFGRD96  137.0   260    20   110   4.31 0.7874
WVFGRD96  138.0   260    20   110   4.31 0.7867
WVFGRD96  139.0    55    75    85   4.31 0.7861

The best solution is

WVFGRD96  133.0    55    75    85   4.31 0.7881

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 0.06 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 Sun Dec 6 20:48:00 CST 2015