Location

2013/06/19 07:19:43 61.431 -149.834 46.5 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  2013/06/19 07:19:43:0  61.43 -149.83  46.5 4.0 Alaska
 
 Stations used:
   AK.DIV AK.GHO AK.GLI AK.HIN AK.KNK AK.RC01 AK.SAW AK.SCM 
   AT.PMR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 1.60e+22 dyne-cm
  Mw = 4.07 
  Z  = 46 km
  Plane   Strike  Dip  Rake
   NP1      215    50   -70
   NP2        5    44   -112
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.60e+22      3     291
    N   0.00e+00     15      22
    P  -1.60e+22     74     190

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     9.34e+20
       Mxy    -5.53e+21
       Mxz     4.39e+21
       Myy     1.39e+22
       Myz    -1.21e+20
       Mzz    -1.48e+22
                                                     
                                                     
                                                     
                                                     
                     ###########---                  
                 #################-----              
              ##################---#######           
             ###############--------#######          
           ###############-----------########        
           #############--------------########       
         T ###########-----------------########      
           #########-------------------#########     
        ###########--------------------#########     
       ###########----------------------#########    
       ##########-----------------------#########    
       #########----------   ----------##########    
       #########---------- P ----------##########    
        #######-----------   ----------#########     
        #######-----------------------##########     
         ######-----------------------#########      
          #####----------------------#########       
           ####---------------------#########        
             ##--------------------########          
              ##-----------------#########           
                 --------------########              
                     --------######                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.48e+22   4.39e+21   1.21e+20 
  4.39e+21   9.34e+20   5.53e+21 
  1.21e+20   5.53e+21   1.39e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130619071943/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 = 215
      DIP = 50
     RAKE = -70
       MW = 4.07
       HS = 46.0

The NDK file is 20130619071943.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

        
SLU
USGSMT
 USGS/SLU Moment Tensor Solution
 ENS  2013/06/19 07:19:43:0  61.43 -149.83  46.5 4.0 Alaska
 
 Stations used:
   AK.DIV AK.GHO AK.GLI AK.HIN AK.KNK AK.RC01 AK.SAW AK.SCM 
   AT.PMR 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 1.60e+22 dyne-cm
  Mw = 4.07 
  Z  = 46 km
  Plane   Strike  Dip  Rake
   NP1      215    50   -70
   NP2        5    44   -112
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.60e+22      3     291
    N   0.00e+00     15      22
    P  -1.60e+22     74     190

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     9.34e+20
       Mxy    -5.53e+21
       Mxz     4.39e+21
       Myy     1.39e+22
       Myz    -1.21e+20
       Mzz    -1.48e+22
                                                     
                                                     
                                                     
                                                     
                     ###########---                  
                 #################-----              
              ##################---#######           
             ###############--------#######          
           ###############-----------########        
           #############--------------########       
         T ###########-----------------########      
           #########-------------------#########     
        ###########--------------------#########     
       ###########----------------------#########    
       ##########-----------------------#########    
       #########----------   ----------##########    
       #########---------- P ----------##########    
        #######-----------   ----------#########     
        #######-----------------------##########     
         ######-----------------------#########      
          #####----------------------#########       
           ####---------------------#########        
             ##--------------------########          
              ##-----------------#########           
                 --------------########              
                     --------######                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.48e+22   4.39e+21   1.21e+20 
  4.39e+21   9.34e+20   5.53e+21 
  1.21e+20   5.53e+21   1.39e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130619071943/index.html
	
    USGS/SLU Regional Moment Tensor Solution

Moment Tensor
Moment Tensor EQXML
Contributed Solutions
Moment Tensor
Contributed Moment Tensors
 	Contributor	Code	Type	Magnitude	Depth	NP1	NP2
	us	usc000hutt-neic-mwr	Mwr	4.1	51.0 km	210, 54, -65	352, 43, -120
us usc000hutt-neic-mwr

Type
    Mwr
Moment
    1.84e+15 N-m
Magnitude
    4.1
Percent DC
    98%
Depth
    51.0 km
Author
    neic
Updated
    2013-06-19 07:58:46 UTC

Principal Axes
Axis	Value	Plunge	Azimuth
T	1.833	6	282
N	0.013	20	15
P	-1.846	69	177
Nodal Planes
Plane	Strike	Dip	Rake
NP1	210	54	-65
NP2	352	43	-120

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 0.10 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    0.5    15    40    90   3.22 0.2436
WVFGRD96    1.0   125    90     5   3.24 0.2406
WVFGRD96    2.0   130    75    25   3.39 0.3014
WVFGRD96    3.0   125    90    15   3.47 0.3179
WVFGRD96    4.0   120    65   -30   3.51 0.3245
WVFGRD96    5.0   120    65   -30   3.54 0.3405
WVFGRD96    6.0   125    70   -25   3.55 0.3472
WVFGRD96    7.0   340    70    40   3.49 0.3480
WVFGRD96    8.0   120    70   -20   3.66 0.3591
WVFGRD96    9.0   125    80   -20   3.67 0.3577
WVFGRD96   10.0   310    80    30   3.66 0.3550
WVFGRD96   11.0   310    80    30   3.68 0.3545
WVFGRD96   12.0    65    60   -35   3.63 0.3625
WVFGRD96   13.0    65    60   -30   3.64 0.3684
WVFGRD96   14.0   245    60   -30   3.66 0.3751
WVFGRD96   15.0   245    60   -30   3.68 0.3826
WVFGRD96   16.0   245    60   -30   3.69 0.3885
WVFGRD96   17.0   245    60   -30   3.71 0.3930
WVFGRD96   18.0   245    65   -30   3.72 0.3957
WVFGRD96   19.0   245    65   -30   3.74 0.3994
WVFGRD96   20.0   245    65   -30   3.75 0.4027
WVFGRD96   21.0   245    65   -30   3.76 0.4054
WVFGRD96   22.0   245    65   -30   3.77 0.4083
WVFGRD96   23.0   245    65   -25   3.77 0.4121
WVFGRD96   24.0   245    65   -30   3.79 0.4147
WVFGRD96   25.0   245    60     5   3.79 0.4248
WVFGRD96   26.0   240    60     5   3.81 0.4359
WVFGRD96   27.0   240    60     5   3.82 0.4457
WVFGRD96   28.0   240    55     0   3.82 0.4567
WVFGRD96   29.0   240    55     0   3.83 0.4645
WVFGRD96   30.0   230    55   -25   3.84 0.4750
WVFGRD96   31.0   230    55   -30   3.85 0.4891
WVFGRD96   32.0   230    55   -30   3.85 0.5041
WVFGRD96   33.0   225    50   -55   3.87 0.5178
WVFGRD96   34.0   225    50   -55   3.88 0.5379
WVFGRD96   35.0   225    50   -55   3.88 0.5521
WVFGRD96   36.0   225    50   -60   3.90 0.5669
WVFGRD96   37.0   220    50   -60   3.90 0.5747
WVFGRD96   38.0   220    50   -65   3.92 0.5826
WVFGRD96   39.0   220    50   -65   3.93 0.5897
WVFGRD96   40.0   220    50   -65   4.01 0.5993
WVFGRD96   41.0   220    50   -65   4.02 0.6056
WVFGRD96   42.0   215    50   -70   4.04 0.6128
WVFGRD96   43.0   215    50   -70   4.05 0.6170
WVFGRD96   44.0   215    50   -70   4.06 0.6215
WVFGRD96   45.0   215    50   -70   4.06 0.6222
WVFGRD96   46.0   215    50   -70   4.07 0.6244
WVFGRD96   47.0   215    50   -70   4.07 0.6219
WVFGRD96   48.0   215    50   -70   4.08 0.6219
WVFGRD96   49.0   215    55   -70   4.08 0.6199
WVFGRD96   50.0   215    55   -70   4.09 0.6176
WVFGRD96   51.0   215    55   -70   4.09 0.6162
WVFGRD96   52.0   215    55   -70   4.09 0.6138
WVFGRD96   53.0   215    55   -70   4.09 0.6117
WVFGRD96   54.0   215    55   -70   4.09 0.6083
WVFGRD96   55.0   215    55   -75   4.10 0.6057
WVFGRD96   56.0   210    55   -75   4.11 0.6022
WVFGRD96   57.0   215    55   -75   4.11 0.6006
WVFGRD96   58.0   210    55   -80   4.12 0.5980
WVFGRD96   59.0   210    55   -80   4.12 0.5943

The best solution is

WVFGRD96   46.0   215    50   -70   4.07 0.6244

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 0.10 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 Mon Dec 7 00:21:32 CST 2015