Location

2013/11/07 05:13:09 62.040 -150.503 43.6 4.3 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  2013/11/07 05:13:09:0  62.04 -150.50  43.6 4.3 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BWN AK.CCB AK.CNP AK.CRQ AK.DHY 
   AK.DOT AK.GHO AK.GLB AK.GLI AK.GOAT AK.GRNC AK.HDA AK.HIN 
   AK.KHIT AK.KIAG AK.KNK AK.MCAR AK.MESA AK.PPD AK.PWL AK.RAG 
   AK.RIDG AK.RND AK.SAMH AK.SAW AK.SCM AK.SGA AK.SKN AK.SSN 
   AK.SUCK AK.SWD AK.TGL AK.VRDI AK.WAT1 AK.WAT2 AK.WAT3 
   AK.WAT4 AK.WAT5 AK.WAT6 AK.WAT7 AK.WAX AK.YAH AT.PMR 
   AT.SVW2 IM.IL31 IU.COLA TA.POKR US.EGAK YE.PIC2 YE.PIC4 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 4.37e+22 dyne-cm
  Mw = 4.36 
  Z  = 64 km
  Plane   Strike  Dip  Rake
   NP1      160    81   -94
   NP2        5    10   -65
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.37e+22     36     253
    N   0.00e+00      4     160
    P  -4.37e+22     54      65

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.53e+20
       Mxy     1.98e+21
       Mxz    -1.49e+22
       Myy     1.40e+22
       Myz    -3.86e+22
       Mzz    -1.35e+22
                                                     
                                                     
                                                     
                                                     
                     -------------#                  
                 ####-----------------#              
              #######-------------------##           
             #########--------------------#          
           ###########---------------------##        
          ############----------------------##       
         ##############----------------------##      
        ###############------------   --------##     
        ################----------- P --------##     
       ##################----------   ---------##    
       ##################----------------------##    
       ###################---------------------##    
       #######   ##########--------------------##    
        ###### T ##########-------------------##     
        ######   ###########------------------##     
         ####################----------------##      
          ####################--------------##       
           ####################------------##        
             ###################---------##          
              ###################-------##           
                 #################---##              
                     ############--                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.35e+22  -1.49e+22   3.86e+22 
 -1.49e+22  -4.53e+20  -1.98e+21 
  3.86e+22  -1.98e+21   1.40e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131107051309/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 = 5
      DIP = 10
     RAKE = -65
       MW = 4.36
       HS = 64.0

The NDK file is 20131107051309.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2013/11/07 05:13:09:0  62.04 -150.50  43.6 4.3 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BWN AK.CCB AK.CNP AK.CRQ AK.DHY 
   AK.DOT AK.GHO AK.GLB AK.GLI AK.GOAT AK.GRNC AK.HDA AK.HIN 
   AK.KHIT AK.KIAG AK.KNK AK.MCAR AK.MESA AK.PPD AK.PWL AK.RAG 
   AK.RIDG AK.RND AK.SAMH AK.SAW AK.SCM AK.SGA AK.SKN AK.SSN 
   AK.SUCK AK.SWD AK.TGL AK.VRDI AK.WAT1 AK.WAT2 AK.WAT3 
   AK.WAT4 AK.WAT5 AK.WAT6 AK.WAT7 AK.WAX AK.YAH AT.PMR 
   AT.SVW2 IM.IL31 IU.COLA TA.POKR US.EGAK YE.PIC2 YE.PIC4 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 4.37e+22 dyne-cm
  Mw = 4.36 
  Z  = 64 km
  Plane   Strike  Dip  Rake
   NP1      160    81   -94
   NP2        5    10   -65
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.37e+22     36     253
    N   0.00e+00      4     160
    P  -4.37e+22     54      65

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.53e+20
       Mxy     1.98e+21
       Mxz    -1.49e+22
       Myy     1.40e+22
       Myz    -3.86e+22
       Mzz    -1.35e+22
                                                     
                                                     
                                                     
                                                     
                     -------------#                  
                 ####-----------------#              
              #######-------------------##           
             #########--------------------#          
           ###########---------------------##        
          ############----------------------##       
         ##############----------------------##      
        ###############------------   --------##     
        ################----------- P --------##     
       ##################----------   ---------##    
       ##################----------------------##    
       ###################---------------------##    
       #######   ##########--------------------##    
        ###### T ##########-------------------##     
        ######   ###########------------------##     
         ####################----------------##      
          ####################--------------##       
           ####################------------##        
             ###################---------##          
              ###################-------##           
                 #################---##              
                     ############--                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.35e+22  -1.49e+22   3.86e+22 
 -1.49e+22  -4.53e+20  -1.98e+21 
  3.86e+22  -1.98e+21   1.40e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131107051309/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:

cut a -30 a 180
rtr
taper w 0.1
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    2.0   165    40   -90   3.68 0.2153
WVFGRD96    4.0   165    45   -90   3.77 0.2064
WVFGRD96    6.0    15    60   -45   3.74 0.1766
WVFGRD96    8.0   155    50    85   3.85 0.1923
WVFGRD96   10.0   100    40   -35   3.83 0.2112
WVFGRD96   12.0    90    40   -35   3.84 0.2353
WVFGRD96   14.0   230    55    55   3.89 0.2644
WVFGRD96   16.0   230    50    55   3.91 0.2914
WVFGRD96   18.0   230    50    55   3.93 0.3130
WVFGRD96   20.0   130    30    60   3.91 0.3299
WVFGRD96   22.0   130    30    60   3.94 0.3491
WVFGRD96   24.0   130    30    60   3.96 0.3657
WVFGRD96   26.0   140    25    75   3.97 0.3790
WVFGRD96   28.0    55    25   -15   3.99 0.3937
WVFGRD96   30.0    50    20   -20   4.01 0.4149
WVFGRD96   32.0    45    20   -25   4.03 0.4358
WVFGRD96   34.0    45    20   -25   4.04 0.4551
WVFGRD96   36.0    45    20   -25   4.06 0.4725
WVFGRD96   38.0    40    20   -30   4.07 0.4864
WVFGRD96   40.0    30    15   -40   4.22 0.4983
WVFGRD96   42.0    30    15   -40   4.23 0.5078
WVFGRD96   44.0    30    15   -40   4.24 0.5179
WVFGRD96   46.0    30    15   -40   4.26 0.5284
WVFGRD96   48.0    30    15   -40   4.27 0.5386
WVFGRD96   50.0    30    15   -40   4.28 0.5474
WVFGRD96   52.0    30    15   -40   4.29 0.5557
WVFGRD96   54.0    30    15   -40   4.30 0.5622
WVFGRD96   56.0    30    15   -40   4.32 0.5673
WVFGRD96   58.0    10    10   -60   4.33 0.5715
WVFGRD96   60.0    10    10   -60   4.34 0.5748
WVFGRD96   62.0     5    10   -65   4.35 0.5768
WVFGRD96   64.0     5    10   -65   4.36 0.5773
WVFGRD96   66.0     0    10   -70   4.37 0.5763
WVFGRD96   68.0   355    10   -75   4.38 0.5739
WVFGRD96   70.0   160    80   -90   4.39 0.5703
WVFGRD96   72.0   160    80   -90   4.39 0.5656
WVFGRD96   74.0   165    80   -80   4.41 0.5603
WVFGRD96   76.0   165    80   -80   4.42 0.5538
WVFGRD96   78.0   165    80   -80   4.43 0.5459
WVFGRD96   80.0   165    80   -80   4.43 0.5367
WVFGRD96   82.0   160    85   -80   4.43 0.5274
WVFGRD96   84.0   160    85   -80   4.44 0.5185
WVFGRD96   86.0   165    85   -75   4.45 0.5085
WVFGRD96   88.0   335    90    75   4.44 0.4911
WVFGRD96   90.0   160    85   -70   4.46 0.4881
WVFGRD96   92.0   155    90   -70   4.46 0.4787
WVFGRD96   94.0   335    90    70   4.46 0.4718
WVFGRD96   96.0   155    90   -70   4.46 0.4646
WVFGRD96   98.0   335    90    70   4.47 0.4567

The best solution is

WVFGRD96   64.0     5    10   -65   4.36 0.5773

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

cut a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.06 n 3 
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated.
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 00:23:40 CST 2015