Location

2015/06/15 21:13:40 63.248 -150.626 128.7.0 4.0 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  2015/06/15 21:13:40:0  63.25 -150.63 128.7 0.0 Alaska
 
 Stations used:
   AK.CCB AK.CUT AK.DOT AK.FIRE AK.GHO AK.GLI AK.HDA AK.HIN 
   AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA2 AK.PAX 
   AK.PWL AK.RC01 AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.TRF 
   AK.WAT3 AK.WAT4 AK.WRH AT.PMR AT.TTA IM.IL31 IU.COLA 
   TA.I23K TA.POKR TA.TCOL 
 
 Filtering commands used:
   cut a -20 a 100
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.30e+22 dyne-cm
  Mw = 4.01 
  Z  = 110 km
  Plane   Strike  Dip  Rake
   NP1       40    75    60
   NP2      286    33   152
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.30e+22     51     276
    N   0.00e+00     29      49
    P  -1.30e+22     24     153

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -8.53e+21
       Mxy     3.87e+21
       Mxz     4.99e+21
       Myy     2.89e+21
       Myz    -8.57e+21
       Mzz     5.64e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ---------------------------#           
             --------#########-----------##          
           ----#####################----#####        
          --##################################       
         -############################---######      
        -############################------#####     
        ############################--------####     
       ##########   ###############-----------###    
       ########## T ##############------------###    
       ##########   ############---------------##    
       ########################-----------------#    
        #####################-------------------     
        ###################---------------------     
         ################----------------------      
          #############-----------------------       
           ##########-------------   --------        
             ######--------------- P ------          
              #-------------------   -----           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.64e+21   4.99e+21   8.57e+21 
  4.99e+21  -8.53e+21  -3.87e+21 
  8.57e+21  -3.87e+21   2.89e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150615211340/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 = 40
      DIP = 75
     RAKE = 60
       MW = 4.01
       HS = 110.0

The NDK file is 20150615211340.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2015/06/15 21:13:40:0  63.25 -150.63 128.7 0.0 Alaska
 
 Stations used:
   AK.CCB AK.CUT AK.DOT AK.FIRE AK.GHO AK.GLI AK.HDA AK.HIN 
   AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA2 AK.PAX 
   AK.PWL AK.RC01 AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.TRF 
   AK.WAT3 AK.WAT4 AK.WRH AT.PMR AT.TTA IM.IL31 IU.COLA 
   TA.I23K TA.POKR TA.TCOL 
 
 Filtering commands used:
   cut a -20 a 100
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.30e+22 dyne-cm
  Mw = 4.01 
  Z  = 110 km
  Plane   Strike  Dip  Rake
   NP1       40    75    60
   NP2      286    33   152
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.30e+22     51     276
    N   0.00e+00     29      49
    P  -1.30e+22     24     153

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -8.53e+21
       Mxy     3.87e+21
       Mxz     4.99e+21
       Myy     2.89e+21
       Myz    -8.57e+21
       Mzz     5.64e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ---------------------------#           
             --------#########-----------##          
           ----#####################----#####        
          --##################################       
         -############################---######      
        -############################------#####     
        ############################--------####     
       ##########   ###############-----------###    
       ########## T ##############------------###    
       ##########   ############---------------##    
       ########################-----------------#    
        #####################-------------------     
        ###################---------------------     
         ################----------------------      
          #############-----------------------       
           ##########-------------   --------        
             ######--------------- P ------          
              #-------------------   -----           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.64e+21   4.99e+21   8.57e+21 
  4.99e+21  -8.53e+21  -3.87e+21 
  8.57e+21  -3.87e+21   2.89e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150615211340/index.html
	

Magnitudes

mLg Magnitude


(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

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 -20 a 100
rtr
taper w 0.1
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   50.0   215    75   -40   3.83 0.3119
WVFGRD96   52.0   210    75   -30   3.85 0.3263
WVFGRD96   54.0   210    75   -30   3.87 0.3441
WVFGRD96   56.0   210    80   -30   3.88 0.3600
WVFGRD96   58.0   210    80   -30   3.90 0.3757
WVFGRD96   60.0   205    80   -25   3.93 0.3903
WVFGRD96   62.0   210    90   -30   3.92 0.4044
WVFGRD96   64.0    35    85    35   3.92 0.4191
WVFGRD96   66.0    35    80    35   3.93 0.4306
WVFGRD96   68.0    35    80    35   3.94 0.4418
WVFGRD96   70.0    35    80    35   3.94 0.4517
WVFGRD96   72.0    35    80    35   3.95 0.4587
WVFGRD96   74.0    35    80    40   3.95 0.4661
WVFGRD96   76.0    35    80    40   3.95 0.4719
WVFGRD96   78.0    35    80    40   3.96 0.4802
WVFGRD96   80.0    35    80    40   3.96 0.4885
WVFGRD96   82.0    35    80    45   3.97 0.4968
WVFGRD96   84.0    35    80    45   3.97 0.5044
WVFGRD96   86.0    35    80    45   3.98 0.5103
WVFGRD96   88.0    35    80    50   3.98 0.5176
WVFGRD96   90.0    35    80    50   3.98 0.5224
WVFGRD96   92.0    35    80    50   3.99 0.5284
WVFGRD96   94.0    40    75    55   3.98 0.5334
WVFGRD96   96.0    40    75    55   3.99 0.5372
WVFGRD96   98.0    40    75    55   3.99 0.5428
WVFGRD96  100.0    40    75    55   3.99 0.5463
WVFGRD96  102.0    40    75    55   4.00 0.5471
WVFGRD96  104.0    40    75    60   4.00 0.5505
WVFGRD96  106.0    40    75    60   4.00 0.5513
WVFGRD96  108.0    40    75    60   4.01 0.5528
WVFGRD96  110.0    40    75    60   4.01 0.5543
WVFGRD96  112.0    40    75    60   4.01 0.5537
WVFGRD96  114.0    40    75    60   4.01 0.5536
WVFGRD96  116.0    40    75    65   4.02 0.5533
WVFGRD96  118.0    40    75    65   4.02 0.5538
WVFGRD96  120.0    40    75    65   4.02 0.5535
WVFGRD96  122.0    40    75    65   4.02 0.5530
WVFGRD96  124.0    40    75    65   4.02 0.5509
WVFGRD96  126.0    40    75    65   4.03 0.5504
WVFGRD96  128.0    40    75    65   4.03 0.5502
WVFGRD96  130.0    40    75    65   4.03 0.5477
WVFGRD96  132.0    40    75    65   4.03 0.5464
WVFGRD96  134.0    40    75    70   4.04 0.5463
WVFGRD96  136.0    40    75    70   4.04 0.5436
WVFGRD96  138.0    40    75    70   4.04 0.5417

The best solution is

WVFGRD96  110.0    40    75    60   4.01 0.5543

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 -20 a 100
rtr
taper w 0.1
hp c 0.02 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 Mon Dec 7 00:04:21 CST 2015