Location

2011/07/04 03:57:55 60.255 -152.721 114 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  2011/07/04 03:57:55:0  60.26 -152.72 114.0 4.4 Alaska
 
 Stations used:
   AK.BPAW AK.CAST AK.CNP AK.KTH AK.PPLA AK.RC01 AK.SSN AK.TRF 
   AT.OHAK AT.PMR AT.SVW2 II.KDAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.43e+22 dyne-cm
  Mw = 4.19 
  Z  = 124 km
  Plane   Strike  Dip  Rake
   NP1      259    71   114
   NP2       25    30    40
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.43e+22     57     201
    N   0.00e+00     23      71
    P  -2.43e+22     23     331

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -9.53e+21
       Mxy     1.11e+22
       Mxz    -1.79e+22
       Myy    -3.98e+21
       Myz     2.65e+20
       Mzz     1.35e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------------------#              
              ----   -------------------##           
             ----- P --------------------##          
           -------   ---------------------###        
          --------------------------------####       
         ----------------------------------####      
        -----------------------------------#####     
        -------------------################----#     
       -------------#######################------    
       --------############################------    
       -----###############################------    
       --##################################------    
        ##################################------     
        ###############   ###############-------     
         ############## T ##############-------      
          #############   #############-------       
           ##########################--------        
             #######################-------          
              ###################---------           
                 #############---------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.35e+22  -1.79e+22  -2.65e+20 
 -1.79e+22  -9.53e+21  -1.11e+22 
 -2.65e+20  -1.11e+22  -3.98e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110704035755/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 = 25
      DIP = 30
     RAKE = 40
       MW = 4.19
       HS = 124.0

The NDK file is 20110704035755.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2011/07/04 03:57:55:0  60.26 -152.72 114.0 4.4 Alaska
 
 Stations used:
   AK.BPAW AK.CAST AK.CNP AK.KTH AK.PPLA AK.RC01 AK.SSN AK.TRF 
   AT.OHAK AT.PMR AT.SVW2 II.KDAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.43e+22 dyne-cm
  Mw = 4.19 
  Z  = 124 km
  Plane   Strike  Dip  Rake
   NP1      259    71   114
   NP2       25    30    40
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.43e+22     57     201
    N   0.00e+00     23      71
    P  -2.43e+22     23     331

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -9.53e+21
       Mxy     1.11e+22
       Mxz    -1.79e+22
       Myy    -3.98e+21
       Myz     2.65e+20
       Mzz     1.35e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------------------#              
              ----   -------------------##           
             ----- P --------------------##          
           -------   ---------------------###        
          --------------------------------####       
         ----------------------------------####      
        -----------------------------------#####     
        -------------------################----#     
       -------------#######################------    
       --------############################------    
       -----###############################------    
       --##################################------    
        ##################################------     
        ###############   ###############-------     
         ############## T ##############-------      
          #############   #############-------       
           ##########################--------        
             #######################-------          
              ###################---------           
                 #############---------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.35e+22  -1.79e+22  -2.65e+20 
 -1.79e+22  -9.53e+21  -1.11e+22 
 -2.65e+20  -1.11e+22  -3.98e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110704035755/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    85    50   -70   3.27 0.1747
WVFGRD96    1.0    75    50   -85   3.31 0.1879
WVFGRD96    2.0   190    45   -90   3.39 0.2344
WVFGRD96    3.0   355    45   -80   3.44 0.2553
WVFGRD96    4.0     5    50   -60   3.46 0.2597
WVFGRD96    5.0    20    80     5   3.43 0.2734
WVFGRD96    6.0    20    80     5   3.46 0.2872
WVFGRD96    7.0    20    80     5   3.48 0.3006
WVFGRD96    8.0    20    80     5   3.52 0.3139
WVFGRD96    9.0    20    80    10   3.54 0.3217
WVFGRD96   10.0    20    70   -20   3.54 0.3300
WVFGRD96   11.0   210    70    25   3.54 0.3414
WVFGRD96   12.0   210    70    25   3.56 0.3531
WVFGRD96   13.0   210    70    25   3.57 0.3637
WVFGRD96   14.0   210    70    25   3.58 0.3733
WVFGRD96   15.0   210    70    25   3.60 0.3823
WVFGRD96   16.0   210    70    25   3.61 0.3916
WVFGRD96   17.0   210    70    25   3.62 0.3999
WVFGRD96   18.0   210    70    25   3.63 0.4073
WVFGRD96   19.0   210    70    25   3.64 0.4141
WVFGRD96   20.0   210    70    25   3.65 0.4218
WVFGRD96   21.0   210    70    25   3.66 0.4281
WVFGRD96   22.0   210    75    30   3.68 0.4339
WVFGRD96   23.0   205    70    25   3.71 0.4405
WVFGRD96   24.0   210    75    35   3.71 0.4473
WVFGRD96   25.0   210    75    35   3.72 0.4531
WVFGRD96   26.0   205    75    30   3.74 0.4583
WVFGRD96   27.0   205    75    30   3.75 0.4642
WVFGRD96   28.0   205    75    30   3.76 0.4685
WVFGRD96   29.0   205    75    30   3.77 0.4713
WVFGRD96   30.0   205    75    30   3.78 0.4745
WVFGRD96   31.0   205    75    30   3.79 0.4776
WVFGRD96   32.0   205    75    30   3.80 0.4791
WVFGRD96   33.0   210    75    35   3.80 0.4793
WVFGRD96   34.0   205    75    30   3.82 0.4804
WVFGRD96   35.0   205    75    30   3.83 0.4818
WVFGRD96   36.0   210    75    30   3.82 0.4827
WVFGRD96   37.0   210    75    30   3.83 0.4837
WVFGRD96   38.0   210    80    35   3.85 0.4837
WVFGRD96   39.0   210    75    30   3.86 0.4854
WVFGRD96   40.0   210    75    45   3.95 0.4821
WVFGRD96   41.0   210    75    45   3.96 0.4810
WVFGRD96   42.0   210    75    45   3.97 0.4792
WVFGRD96   43.0   210    75    45   3.98 0.4769
WVFGRD96   44.0   210    75    45   3.99 0.4743
WVFGRD96   45.0   210    75    45   4.00 0.4713
WVFGRD96   46.0   210    75    45   4.00 0.4678
WVFGRD96   47.0   210    75    45   4.01 0.4641
WVFGRD96   48.0   210    75    45   4.02 0.4599
WVFGRD96   49.0   215    70    45   4.01 0.4556
WVFGRD96   50.0   215    70    45   4.01 0.4515
WVFGRD96   51.0   215    70    45   4.02 0.4473
WVFGRD96   52.0   215    70    45   4.02 0.4433
WVFGRD96   53.0   215    70    45   4.03 0.4390
WVFGRD96   54.0   215    70    45   4.03 0.4344
WVFGRD96   55.0   215    70    40   4.02 0.4300
WVFGRD96   56.0   215    70    40   4.02 0.4255
WVFGRD96   57.0    20    70    25   4.03 0.4284
WVFGRD96   58.0    20    70    25   4.04 0.4342
WVFGRD96   59.0    25    65    30   4.03 0.4398
WVFGRD96   60.0    25    65    30   4.03 0.4456
WVFGRD96   61.0    25    65    30   4.03 0.4508
WVFGRD96   62.0    25    65    30   4.04 0.4558
WVFGRD96   63.0    25    65    35   4.06 0.4605
WVFGRD96   64.0    25    65    35   4.06 0.4654
WVFGRD96   65.0    25    65    35   4.06 0.4710
WVFGRD96   66.0    25    65    35   4.07 0.4759
WVFGRD96   67.0    20    65    30   4.09 0.4800
WVFGRD96   68.0    20    65    30   4.09 0.4834
WVFGRD96   69.0    20    65    30   4.09 0.4880
WVFGRD96   70.0    20    65    35   4.11 0.4921
WVFGRD96   71.0    20    65    35   4.11 0.4956
WVFGRD96   72.0    20    65    35   4.11 0.4982
WVFGRD96   73.0    20    65    35   4.12 0.5024
WVFGRD96   74.0    20    65    35   4.12 0.5053
WVFGRD96   75.0    20    65    35   4.12 0.5070
WVFGRD96   76.0    20    65    35   4.12 0.5114
WVFGRD96   77.0    20    65    35   4.12 0.5144
WVFGRD96   78.0    20    65    35   4.12 0.5156
WVFGRD96   79.0    15    45    10   4.10 0.5198
WVFGRD96   80.0    20    40    20   4.09 0.5262
WVFGRD96   81.0    15    40    15   4.12 0.5324
WVFGRD96   82.0    15    40    15   4.12 0.5401
WVFGRD96   83.0    15    40    15   4.12 0.5460
WVFGRD96   84.0    15    40    15   4.12 0.5525
WVFGRD96   85.0    20    35    25   4.12 0.5585
WVFGRD96   86.0    15    40    20   4.14 0.5635
WVFGRD96   87.0    15    40    20   4.15 0.5706
WVFGRD96   88.0    15    35    20   4.15 0.5757
WVFGRD96   89.0    15    35    20   4.15 0.5820
WVFGRD96   90.0    15    35    20   4.15 0.5871
WVFGRD96   91.0    15    35    20   4.15 0.5920
WVFGRD96   92.0    15    35    20   4.15 0.5973
WVFGRD96   93.0    15    35    20   4.16 0.6010
WVFGRD96   94.0    20    35    30   4.16 0.6062
WVFGRD96   95.0    20    35    30   4.16 0.6092
WVFGRD96   96.0    20    30    30   4.16 0.6145
WVFGRD96   97.0    20    30    30   4.17 0.6168
WVFGRD96   98.0    15    35    25   4.18 0.6220
WVFGRD96   99.0    20    30    30   4.17 0.6242
WVFGRD96  100.0    20    30    30   4.17 0.6287
WVFGRD96  101.0    15    35    25   4.18 0.6303
WVFGRD96  102.0    15    35    25   4.18 0.6344
WVFGRD96  103.0    15    35    25   4.18 0.6357
WVFGRD96  104.0    15    35    25   4.19 0.6393
WVFGRD96  105.0    15    35    25   4.19 0.6399
WVFGRD96  106.0    20    30    30   4.17 0.6436
WVFGRD96  107.0    25    30    40   4.18 0.6442
WVFGRD96  108.0    25    30    40   4.19 0.6474
WVFGRD96  109.0    25    30    40   4.19 0.6480
WVFGRD96  110.0    25    30    40   4.19 0.6509
WVFGRD96  111.0    25    30    40   4.19 0.6517
WVFGRD96  112.0    25    30    40   4.19 0.6532
WVFGRD96  113.0    25    30    40   4.19 0.6544
WVFGRD96  114.0    25    30    40   4.19 0.6554
WVFGRD96  115.0    25    30    40   4.19 0.6567
WVFGRD96  116.0    25    30    40   4.19 0.6565
WVFGRD96  117.0    25    30    40   4.19 0.6584
WVFGRD96  118.0    25    30    40   4.19 0.6577
WVFGRD96  119.0    25    30    40   4.19 0.6595
WVFGRD96  120.0    25    30    40   4.19 0.6593
WVFGRD96  121.0    25    30    40   4.19 0.6597
WVFGRD96  122.0    25    30    40   4.19 0.6603
WVFGRD96  123.0    25    30    40   4.19 0.6592
WVFGRD96  124.0    25    30    40   4.19 0.6607
WVFGRD96  125.0    25    30    40   4.19 0.6595
WVFGRD96  126.0    25    30    40   4.19 0.6602
WVFGRD96  127.0    25    30    40   4.20 0.6601
WVFGRD96  128.0    25    30    40   4.20 0.6589
WVFGRD96  129.0    25    30    40   4.20 0.6597
WVFGRD96  130.0    25    30    40   4.20 0.6582
WVFGRD96  131.0    25    30    40   4.20 0.6587
WVFGRD96  132.0    25    30    40   4.20 0.6582
WVFGRD96  133.0    25    30    40   4.20 0.6563
WVFGRD96  134.0    25    30    40   4.20 0.6574
WVFGRD96  135.0    25    30    40   4.20 0.6557
WVFGRD96  136.0    25    30    40   4.20 0.6552
WVFGRD96  137.0    25    30    40   4.20 0.6552
WVFGRD96  138.0    25    30    40   4.20 0.6528
WVFGRD96  139.0    25    30    40   4.20 0.6533

The best solution is

WVFGRD96  124.0    25    30    40   4.19 0.6607

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 20:49:00 CST 2015