Location

2013/10/13 08:26:18 65.056 -138.987 9.4 3.9 Canada

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  2013/10/13 08:26:18:0  65.06 -138.99   9.4 3.9 Canada
 
 Stations used:
   AK.BAL AK.CCB AK.DOT AK.PPD AK.RIDG AK.SAMH AK.SAW AK.SCM 
   AK.VRDI AK.WAT6 AK.WAT7 AT.MENT AT.PMR CN.BVCY CN.HYT 
   CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 IM.IL31 IU.COLA TA.EPYK 
   TA.POKR TA.TCOL TA.TOLK US.EGAK YE.PIC1 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 = 7.76e+21 dyne-cm
  Mw = 3.86 
  Z  = 20 km
  Plane   Strike  Dip  Rake
   NP1       65    90   -10
   NP2      155    80   -180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.76e+21      7     110
    N   0.00e+00     80     245
    P  -7.76e+21      7      20

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -5.86e+21
       Mxy    -4.91e+21
       Mxz    -1.22e+21
       Myy     5.86e+21
       Myz     5.70e+20
       Mzz     1.18e+14
                                                     
                                                     
                                                     
                                                     
                     ------------                    
                 ##-------------- P ---              
              ######-------------   ------           
             #######-----------------------          
           ##########------------------------        
          ###########-------------------------       
         #############------------------------#      
        ##############--------------------######     
        ###############---------------##########     
       #################----------###############    
       ##################-----###################    
       ##########################################    
       ###############----#######################    
        ##########---------##################        
        ######--------------################# T      
         #-------------------################        
          --------------------################       
           ---------------------#############        
             --------------------##########          
              --------------------########           
                 -------------------###              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.18e+14  -1.22e+21  -5.70e+20 
 -1.22e+21  -5.86e+21   4.91e+21 
 -5.70e+20   4.91e+21   5.86e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131013082618/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 = 65
      DIP = 90
     RAKE = -10
       MW = 3.86
       HS = 20.0

The NDK file is 20131013082618.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  2013/10/13 08:26:18:0  65.06 -138.99   9.4 3.9 Canada
 
 Stations used:
   AK.BAL AK.CCB AK.DOT AK.PPD AK.RIDG AK.SAMH AK.SAW AK.SCM 
   AK.VRDI AK.WAT6 AK.WAT7 AT.MENT AT.PMR CN.BVCY CN.HYT 
   CN.WHY CN.YUK1 CN.YUK2 CN.YUK3 IM.IL31 IU.COLA TA.EPYK 
   TA.POKR TA.TCOL TA.TOLK US.EGAK YE.PIC1 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 = 7.76e+21 dyne-cm
  Mw = 3.86 
  Z  = 20 km
  Plane   Strike  Dip  Rake
   NP1       65    90   -10
   NP2      155    80   -180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.76e+21      7     110
    N   0.00e+00     80     245
    P  -7.76e+21      7      20

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -5.86e+21
       Mxy    -4.91e+21
       Mxz    -1.22e+21
       Myy     5.86e+21
       Myz     5.70e+20
       Mzz     1.18e+14
                                                     
                                                     
                                                     
                                                     
                     ------------                    
                 ##-------------- P ---              
              ######-------------   ------           
             #######-----------------------          
           ##########------------------------        
          ###########-------------------------       
         #############------------------------#      
        ##############--------------------######     
        ###############---------------##########     
       #################----------###############    
       ##################-----###################    
       ##########################################    
       ###############----#######################    
        ##########---------##################        
        ######--------------################# T      
         #-------------------################        
          --------------------################       
           ---------------------#############        
             --------------------##########          
              --------------------########           
                 -------------------###              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.18e+14  -1.22e+21  -5.70e+20 
 -1.22e+21  -5.86e+21   4.91e+21 
 -5.70e+20   4.91e+21   5.86e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20131013082618/index.html
	
egional Moment Tensor (Mwr)

Moment magnitude derived from a moment tensor inversion of complete waveforms at
regional distances (less than ~8 degrees), generally used for the analysis of 
small to moderate size earthquakes (typically Mw 3.5-6.0) crust or upper mantle 
earthquakes.

Moment      8.18e+14 N-m
Magnitude   3.9
Percent DC  82%
Depth       20.0 km
Updated     2013-10-13 12:31:59 UTC
Author      us
Catalog     us
Contributor us
Code        us_b000kc6t_mwr

Principal Axes

Axis   Value   Plunge Azimuth
T      8.524    10      289
N     -0.729    80      102
P     -7.795     1      199
Nodal Planes

Plane   Strike  Dip  Rake
NP1       64    84      8
NP2      334    82    174

        

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    0.5    65    70   -10   3.37 0.1938
WVFGRD96    1.0    65    85     0   3.39 0.2117
WVFGRD96    2.0    65    75   -10   3.50 0.2802
WVFGRD96    3.0    65    75   -10   3.55 0.3104
WVFGRD96    4.0    65    75   -10   3.58 0.3347
WVFGRD96    5.0    65    75   -10   3.61 0.3561
WVFGRD96    6.0   245    85    15   3.64 0.3738
WVFGRD96    7.0   245    85    20   3.68 0.3940
WVFGRD96    8.0   245    90    30   3.72 0.4145
WVFGRD96    9.0   245    90    30   3.74 0.4312
WVFGRD96   10.0   245    90    30   3.76 0.4456
WVFGRD96   11.0   245    90    30   3.78 0.4580
WVFGRD96   12.0   245    90    25   3.79 0.4697
WVFGRD96   13.0   245    90    25   3.80 0.4806
WVFGRD96   14.0   245    90    25   3.82 0.4890
WVFGRD96   15.0   245    90    20   3.82 0.4964
WVFGRD96   16.0    65    90   -20   3.83 0.5022
WVFGRD96   17.0    65    90   -15   3.84 0.5063
WVFGRD96   18.0    65    90   -15   3.85 0.5091
WVFGRD96   19.0    65    90   -15   3.86 0.5105
WVFGRD96   20.0    65    90   -10   3.86 0.5115
WVFGRD96   21.0    65    90   -10   3.87 0.5113
WVFGRD96   22.0    65    90   -10   3.88 0.5101
WVFGRD96   23.0    65    80   -10   3.89 0.5077
WVFGRD96   24.0    65    85    -5   3.89 0.5046
WVFGRD96   25.0    65    85    -5   3.90 0.5013
WVFGRD96   26.0    65    85    -5   3.91 0.4970
WVFGRD96   27.0    65    85    -5   3.91 0.4917
WVFGRD96   28.0    65    85    -5   3.92 0.4857
WVFGRD96   29.0    65    85    -5   3.93 0.4789

The best solution is

WVFGRD96   20.0    65    90   -10   3.86 0.5115

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 00:23:23 CST 2015