Location

2013/11/19 14:44:21 59.484 -139.026 10.0 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  2013/11/19 14:44:21:0  59.48 -139.03  10.0 4.0 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BCP AK.CTG AK.DCPH AK.DOT AK.GLB AK.GRNC 
   AK.JIS AK.KIAG AK.MCAR AK.PTPK AK.RIDG AK.SAMH AK.YAH 
   CN.BVCY CN.DAWY CN.DLBC CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 
   US.EGAK US.WRAK 
 
 Filtering commands used:
   CUTL=`echo $DIST | awk '{print $1/5.0 - 10.0}' `
   CUTH=`echo $CUTL | awk '{print $1 + 120 }' `
   cut o ${CUTL} o ${CUTH}
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.50e+22 dyne-cm
  Mw = 4.05 
  Z  = 16 km
  Plane   Strike  Dip  Rake
   NP1      298    61   -99
   NP2      135    30   -75
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.50e+22     16      34
    N   0.00e+00      7     302
    P  -1.50e+22     73     187

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     8.19e+21
       Mxy     6.26e+21
       Mxz     7.48e+21
       Myy     4.32e+21
       Myz     2.74e+21
       Mzz    -1.25e+22
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              #######################   ##           
             ######################## T ###          
           -#########################   #####        
          -#---------#########################       
         ##----------------####################      
        ###--------------------#################     
        ###------------------------#############     
       ####--------------------------############    
       ####----------------------------##########    
       #####-----------------------------########    
       ######-------------   --------------######    
        #####------------- P ---------------####     
        ######------------   ----------------###     
         #######------------------------------#      
          #######-----------------------------       
           ########--------------------------        
             #########---------------------          
              ############--------------##           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.25e+22   7.48e+21  -2.74e+21 
  7.48e+21   8.19e+21  -6.26e+21 
 -2.74e+21  -6.26e+21   4.32e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131119144421/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 = 135
      DIP = 30
     RAKE = -75
       MW = 4.05
       HS = 16.0

The NDK file is 20131119144421.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2013/11/19 14:44:21:0  59.48 -139.03  10.0 4.0 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BCP AK.CTG AK.DCPH AK.DOT AK.GLB AK.GRNC 
   AK.JIS AK.KIAG AK.MCAR AK.PTPK AK.RIDG AK.SAMH AK.YAH 
   CN.BVCY CN.DAWY CN.DLBC CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 
   US.EGAK US.WRAK 
 
 Filtering commands used:
   CUTL=`echo $DIST | awk '{print $1/5.0 - 10.0}' `
   CUTH=`echo $CUTL | awk '{print $1 + 120 }' `
   cut o ${CUTL} o ${CUTH}
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.50e+22 dyne-cm
  Mw = 4.05 
  Z  = 16 km
  Plane   Strike  Dip  Rake
   NP1      298    61   -99
   NP2      135    30   -75
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.50e+22     16      34
    N   0.00e+00      7     302
    P  -1.50e+22     73     187

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     8.19e+21
       Mxy     6.26e+21
       Mxz     7.48e+21
       Myy     4.32e+21
       Myz     2.74e+21
       Mzz    -1.25e+22
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              #######################   ##           
             ######################## T ###          
           -#########################   #####        
          -#---------#########################       
         ##----------------####################      
        ###--------------------#################     
        ###------------------------#############     
       ####--------------------------############    
       ####----------------------------##########    
       #####-----------------------------########    
       ######-------------   --------------######    
        #####------------- P ---------------####     
        ######------------   ----------------###     
         #######------------------------------#      
          #######-----------------------------       
           ########--------------------------        
             #########---------------------          
              ############--------------##           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.25e+22   7.48e+21  -2.74e+21 
  7.48e+21   8.19e+21  -6.26e+21 
 -2.74e+21  -6.26e+21   4.32e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131119144421/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:

CUTL=`echo $DIST | awk '{print $1/5.0 - 10.0}' `
CUTH=`echo $CUTL | awk '{print $1 + 120 }' `

cut o ${CUTL} o ${CUTH}
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    1.0     0    85     0   3.52 0.2205
WVFGRD96    2.0    10    60    30   3.64 0.2600
WVFGRD96    3.0     0    80     5   3.74 0.2628
WVFGRD96    4.0     0    75    -5   3.77 0.2220
WVFGRD96    5.0   100    65    40   3.75 0.2181
WVFGRD96    6.0   280    45    20   3.76 0.2444
WVFGRD96    7.0   285    40    20   3.75 0.2712
WVFGRD96    8.0   285    40    20   3.84 0.2895
WVFGRD96    9.0   285    40    20   3.86 0.3119
WVFGRD96   10.0   150    30   -65   3.96 0.3354
WVFGRD96   11.0   145    30   -70   3.98 0.3589
WVFGRD96   12.0   135    30   -75   3.99 0.3778
WVFGRD96   13.0   130    25   -80   4.02 0.3921
WVFGRD96   14.0   130    25   -80   4.03 0.4017
WVFGRD96   15.0   130    30   -80   4.04 0.4073
WVFGRD96   16.0   135    30   -75   4.05 0.4096
WVFGRD96   17.0   135    30   -75   4.06 0.4082
WVFGRD96   18.0   135    30   -75   4.07 0.4034
WVFGRD96   19.0   130    30   -80   4.08 0.3958
WVFGRD96   20.0   265    70   -45   4.03 0.3904
WVFGRD96   21.0   265    70   -45   4.04 0.3795
WVFGRD96   22.0   280    45     5   4.05 0.3702
WVFGRD96   23.0   280    40     0   4.04 0.3655
WVFGRD96   24.0   280    40     0   4.05 0.3596
WVFGRD96   25.0   280    40     0   4.06 0.3526
WVFGRD96   26.0   280    40     0   4.07 0.3447
WVFGRD96   27.0   280    35    -5   4.06 0.3366
WVFGRD96   28.0   280    35    -5   4.07 0.3271
WVFGRD96   29.0   285    35     0   4.07 0.3164

The best solution is

WVFGRD96   16.0   135    30   -75   4.05 0.4096

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

CUTL=-10
CUTH=90
cut o ${CUTL} o ${CUTH}
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. The traces begins at Distance/5.0 - 10 seconds after the origin time and is 120 seconds long.
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 00:23:45 CST 2015