Location

Location ANSS

2017/06/13 07:39:36 63.868 -148.255 100.6 3.8 Alaska

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2017/06/13 07:39:36:0  63.87 -148.26 100.6 3.8 Alaska
 
 Stations used:
   AK.BPAW AK.BWN AK.CAST AK.CCB AK.DHY AK.HDA AK.KNK AK.KTH 
   AK.MDM AK.MLY AK.NEA2 AK.PPD AK.PPLA AK.RC01 AK.RIDG AK.RND 
   AK.SAW AK.SCM AK.SCRK AK.TRF AT.PMR IM.IL31 IU.COLA TA.H23K 
   TA.H24K TA.I21K TA.I23K TA.J20K TA.J25K TA.J26L TA.K20K 
   TA.L26K TA.L27K TA.M26K 
 
 Filtering commands used:
   cut o DIST/3.5 -40 o DIST/3.5 +40
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.10e+22 dyne-cm
  Mw = 3.96 
  Z  = 120 km
  Plane   Strike  Dip  Rake
   NP1      352    86   150
   NP2       85    60     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.10e+22     24     305
    N   0.00e+00     60     165
    P  -1.10e+22     17      43

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.46e+21
       Mxy    -9.24e+21
       Mxz    -3.27e+14
       Myy     1.64e+21
       Myz    -5.48e+21
       Mzz     8.28e+20
                                                     
                                                     
                                                     
                                                     
                     #####---------                  
                 #########-------------              
              ############----------------           
             ##############------------   -          
           ################------------ P ---        
          ###   ############-----------   ----       
         #### T ############-------------------      
        #####   ############--------------------     
        ####################--------------------     
       ######################--------------------    
       ######################-------------------#    
       ######################-----------------###    
       -#####################---------------#####    
        ---###################----------########     
        --------##############-----#############     
         ---------------------#################      
          --------------------################       
           -------------------###############        
             ------------------############          
              -----------------###########           
                 --------------########              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  8.28e+20  -3.27e+14   5.48e+21 
 -3.27e+14  -2.46e+21   9.24e+21 
  5.48e+21   9.24e+21   1.64e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170613073936/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 = 85
      DIP = 60
     RAKE = 5
       MW = 3.96
       HS = 120.0

The NDK file is 20170613073936.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2017/06/13 07:39:36:0  63.87 -148.26 100.6 3.8 Alaska
 
 Stations used:
   AK.BPAW AK.BWN AK.CAST AK.CCB AK.DHY AK.HDA AK.KNK AK.KTH 
   AK.MDM AK.MLY AK.NEA2 AK.PPD AK.PPLA AK.RC01 AK.RIDG AK.RND 
   AK.SAW AK.SCM AK.SCRK AK.TRF AT.PMR IM.IL31 IU.COLA TA.H23K 
   TA.H24K TA.I21K TA.I23K TA.J20K TA.J25K TA.J26L TA.K20K 
   TA.L26K TA.L27K TA.M26K 
 
 Filtering commands used:
   cut o DIST/3.5 -40 o DIST/3.5 +40
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.10e+22 dyne-cm
  Mw = 3.96 
  Z  = 120 km
  Plane   Strike  Dip  Rake
   NP1      352    86   150
   NP2       85    60     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.10e+22     24     305
    N   0.00e+00     60     165
    P  -1.10e+22     17      43

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.46e+21
       Mxy    -9.24e+21
       Mxz    -3.27e+14
       Myy     1.64e+21
       Myz    -5.48e+21
       Mzz     8.28e+20
                                                     
                                                     
                                                     
                                                     
                     #####---------                  
                 #########-------------              
              ############----------------           
             ##############------------   -          
           ################------------ P ---        
          ###   ############-----------   ----       
         #### T ############-------------------      
        #####   ############--------------------     
        ####################--------------------     
       ######################--------------------    
       ######################-------------------#    
       ######################-----------------###    
       -#####################---------------#####    
        ---###################----------########     
        --------##############-----#############     
         ---------------------#################      
          --------------------################       
           -------------------###############        
             ------------------############          
              -----------------###########           
                 --------------########              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  8.28e+20  -3.27e+14   5.48e+21 
 -3.27e+14  -2.46e+21   9.24e+21 
  5.48e+21   9.24e+21   1.64e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170613073936/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 using wvfgrd96

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 o DIST/3.5 -40 o DIST/3.5 +40
rtr
taper w 0.1
hp c 0.03 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    2.0   310    45   -65   3.02 0.2250
WVFGRD96    4.0   330    80   -35   3.04 0.2411
WVFGRD96    6.0   155    80    30   3.10 0.2715
WVFGRD96    8.0   155    80    30   3.18 0.2956
WVFGRD96   10.0   335    75    30   3.23 0.3080
WVFGRD96   12.0   335    75    30   3.27 0.3132
WVFGRD96   14.0   335    75    30   3.30 0.3108
WVFGRD96   16.0   310    85    25   3.34 0.3029
WVFGRD96   18.0   100    70    25   3.37 0.3046
WVFGRD96   20.0   100    70    25   3.40 0.3239
WVFGRD96   22.0    95    70    20   3.43 0.3405
WVFGRD96   24.0    95    70    20   3.45 0.3578
WVFGRD96   26.0    85    70     5   3.47 0.3753
WVFGRD96   28.0    85    70     5   3.48 0.3864
WVFGRD96   30.0    85    90    15   3.49 0.3934
WVFGRD96   32.0    90    75    20   3.51 0.4006
WVFGRD96   34.0    90    75    20   3.53 0.4038
WVFGRD96   36.0    90    70    20   3.55 0.4064
WVFGRD96   38.0    90    75    15   3.58 0.4103
WVFGRD96   40.0    85    50     0   3.67 0.4210
WVFGRD96   42.0    80    60   -15   3.68 0.4307
WVFGRD96   44.0    85    55     0   3.71 0.4410
WVFGRD96   46.0    85    55     0   3.73 0.4516
WVFGRD96   48.0    80    55   -10   3.75 0.4634
WVFGRD96   50.0    80    50   -10   3.77 0.4775
WVFGRD96   52.0    80    50   -10   3.79 0.4923
WVFGRD96   54.0    80    50   -10   3.80 0.5065
WVFGRD96   56.0    80    50   -10   3.81 0.5201
WVFGRD96   58.0    80    50    -5   3.81 0.5335
WVFGRD96   60.0    80    50    -5   3.82 0.5475
WVFGRD96   62.0    80    50    -5   3.83 0.5625
WVFGRD96   64.0    80    50    -5   3.84 0.5769
WVFGRD96   66.0    80    50    -5   3.84 0.5889
WVFGRD96   68.0    80    50    -5   3.85 0.6031
WVFGRD96   70.0    80    50    -5   3.86 0.6145
WVFGRD96   72.0    80    50    -5   3.86 0.6255
WVFGRD96   74.0    80    50    -5   3.87 0.6351
WVFGRD96   76.0    80    50    -5   3.87 0.6447
WVFGRD96   78.0    85    55     0   3.87 0.6519
WVFGRD96   80.0    85    55     0   3.88 0.6601
WVFGRD96   82.0    85    55     0   3.88 0.6682
WVFGRD96   84.0    85    55     0   3.89 0.6741
WVFGRD96   86.0    85    55     5   3.89 0.6801
WVFGRD96   88.0    85    55     5   3.89 0.6859
WVFGRD96   90.0    85    55     5   3.90 0.6918
WVFGRD96   92.0    85    60     5   3.90 0.6981
WVFGRD96   94.0    85    60     5   3.90 0.7038
WVFGRD96   96.0    85    60     5   3.91 0.7107
WVFGRD96   98.0    85    60     5   3.91 0.7166
WVFGRD96  100.0    85    60     5   3.92 0.7218
WVFGRD96  102.0    85    60     5   3.92 0.7259
WVFGRD96  104.0    85    60     5   3.92 0.7297
WVFGRD96  106.0    85    60     5   3.93 0.7351
WVFGRD96  108.0    85    60     5   3.93 0.7389
WVFGRD96  110.0    85    60     5   3.94 0.7418
WVFGRD96  112.0    85    60     5   3.94 0.7438
WVFGRD96  114.0    85    60     5   3.94 0.7462
WVFGRD96  116.0    85    60     5   3.95 0.7479
WVFGRD96  118.0    85    60     5   3.95 0.7499
WVFGRD96  120.0    85    60     5   3.96 0.7500
WVFGRD96  122.0    85    60     5   3.96 0.7490
WVFGRD96  124.0    85    60     5   3.96 0.7491
WVFGRD96  126.0    85    60     5   3.97 0.7494
WVFGRD96  128.0    85    65     5   3.97 0.7481

The best solution is

WVFGRD96  120.0    85    60     5   3.96 0.7500

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 o DIST/3.5 -40 o DIST/3.5 +40
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 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 Wed Jun 14 12:01:16 CDT 2017