Location

2014/10/02 21:33:15 63.044 -150.809 125.3 4.2 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  2014/10/02 21:33:15:0  63.04 -150.81 125.3 4.2 Alaska
 
 Stations used:
   AK.BPAW AK.BWN AK.CRQ AK.DHY AK.DOT AK.EYAK AK.FID AK.GHO 
   AK.GLB AK.GLI AK.HDA AK.HIN AK.KLU AK.KNK AK.KTH AK.MCAR 
   AK.MDM AK.PAX AK.PPLA AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN 
   AK.SSN AK.SWD AK.TRF AK.WRH IM.IL31 IU.COLA TA.M24K TA.Q23K 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +60
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 3.43e+22 dyne-cm
  Mw = 4.29 
  Z  = 118 km
  Plane   Strike  Dip  Rake
   NP1       50    70    85
   NP2      244    21   103
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.43e+22     65     312
    N   0.00e+00      5      52
    P  -3.43e+22     25     144

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.56e+22
       Mxy     1.03e+22
       Mxz     1.94e+22
       Myy    -6.30e+21
       Myz    -1.76e+22
       Mzz     2.19e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              --------################----           
             ------#######################-          
           -----#############################        
          ----#############################---       
         ----#############################-----      
        ---###########   ################-------     
        --############ T ##############---------     
       ---############   #############-----------    
       --###########################-------------    
       --##########################--------------    
       --########################----------------    
        -#####################------------------     
        -###################--------------------     
         ################----------------------      
          ############--------------   -------       
           #######------------------ P ------        
             -----------------------   ----          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.19e+22   1.94e+22   1.76e+22 
  1.94e+22  -1.56e+22  -1.03e+22 
  1.76e+22  -1.03e+22  -6.30e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141002213315/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 = 50
      DIP = 70
     RAKE = 85
       MW = 4.29
       HS = 118.0

The NDK file is 20141002213315.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2014/10/02 21:33:15:0  63.04 -150.81 125.3 4.2 Alaska
 
 Stations used:
   AK.BPAW AK.BWN AK.CRQ AK.DHY AK.DOT AK.EYAK AK.FID AK.GHO 
   AK.GLB AK.GLI AK.HDA AK.HIN AK.KLU AK.KNK AK.KTH AK.MCAR 
   AK.MDM AK.PAX AK.PPLA AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN 
   AK.SSN AK.SWD AK.TRF AK.WRH IM.IL31 IU.COLA TA.M24K TA.Q23K 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +60
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 3.43e+22 dyne-cm
  Mw = 4.29 
  Z  = 118 km
  Plane   Strike  Dip  Rake
   NP1       50    70    85
   NP2      244    21   103
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.43e+22     65     312
    N   0.00e+00      5      52
    P  -3.43e+22     25     144

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.56e+22
       Mxy     1.03e+22
       Mxz     1.94e+22
       Myy    -6.30e+21
       Myz    -1.76e+22
       Mzz     2.19e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              --------################----           
             ------#######################-          
           -----#############################        
          ----#############################---       
         ----#############################-----      
        ---###########   ################-------     
        --############ T ##############---------     
       ---############   #############-----------    
       --###########################-------------    
       --##########################--------------    
       --########################----------------    
        -#####################------------------     
        -###################--------------------     
         ################----------------------      
          ############--------------   -------       
           #######------------------ P ------        
             -----------------------   ----          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.19e+22   1.94e+22   1.76e+22 
  1.94e+22  -1.56e+22  -1.03e+22 
  1.76e+22  -1.03e+22  -6.30e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141002213315/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:

cut o DIST/3.3 -30 o DIST/3.3 +60
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    2.0   235    50   -90   3.49 0.1947
WVFGRD96    4.0    70    35   -75   3.58 0.1821
WVFGRD96    6.0    60    30   -80   3.58 0.1551
WVFGRD96    8.0    55    30   -85   3.67 0.1758
WVFGRD96   10.0    70    30   -70   3.64 0.1632
WVFGRD96   12.0    20    35    65   3.64 0.1759
WVFGRD96   14.0    30    35    75   3.66 0.1967
WVFGRD96   16.0    30    40    75   3.68 0.2142
WVFGRD96   18.0    30    45    70   3.68 0.2281
WVFGRD96   20.0    30    45    70   3.70 0.2394
WVFGRD96   22.0    30    45    70   3.71 0.2463
WVFGRD96   24.0    30    45    70   3.72 0.2510
WVFGRD96   26.0    25    45    65   3.73 0.2533
WVFGRD96   28.0    25    45    65   3.74 0.2539
WVFGRD96   30.0    25    45    65   3.75 0.2521
WVFGRD96   32.0    25    45    65   3.76 0.2482
WVFGRD96   34.0    30    40    70   3.77 0.2426
WVFGRD96   36.0    10    40    65   3.79 0.2367
WVFGRD96   38.0    20    55    75   3.83 0.2339
WVFGRD96   40.0    20    60    80   3.97 0.2329
WVFGRD96   42.0    25    60    85   3.99 0.2337
WVFGRD96   44.0    25    60    80   3.99 0.2350
WVFGRD96   46.0    30    55    80   4.00 0.2361
WVFGRD96   48.0    25    60    75   4.01 0.2393
WVFGRD96   50.0    25    60    70   4.01 0.2435
WVFGRD96   52.0    15    60    40   4.00 0.2495
WVFGRD96   54.0    15    60    30   4.01 0.2624
WVFGRD96   56.0    15    60    25   4.04 0.2765
WVFGRD96   58.0    20    60    30   4.05 0.2933
WVFGRD96   60.0    20    60    25   4.07 0.3124
WVFGRD96   62.0    35    75    80   4.10 0.3444
WVFGRD96   64.0    35    75    80   4.12 0.3823
WVFGRD96   66.0    40    70    80   4.14 0.4212
WVFGRD96   68.0    45    70    80   4.16 0.4597
WVFGRD96   70.0    45    70    80   4.17 0.4949
WVFGRD96   72.0    45    70    80   4.18 0.5206
WVFGRD96   74.0    45    70    80   4.19 0.5375
WVFGRD96   76.0    45    70    85   4.20 0.5542
WVFGRD96   78.0    45    70    85   4.21 0.5702
WVFGRD96   80.0    50    70    85   4.21 0.5865
WVFGRD96   82.0    50    70    85   4.22 0.6007
WVFGRD96   84.0    50    70    85   4.23 0.6119
WVFGRD96   86.0    50    70    85   4.23 0.6254
WVFGRD96   88.0    50    70    85   4.24 0.6362
WVFGRD96   90.0    50    70    90   4.25 0.6473
WVFGRD96   92.0    50    70    90   4.25 0.6567
WVFGRD96   94.0    50    65    80   4.25 0.6655
WVFGRD96   96.0    50    65    80   4.25 0.6756
WVFGRD96   98.0    50    65    80   4.26 0.6835
WVFGRD96  100.0    50    65    80   4.26 0.6910
WVFGRD96  102.0    50    65    80   4.26 0.6970
WVFGRD96  104.0    50    65    80   4.27 0.7027
WVFGRD96  106.0    50    70    80   4.27 0.7076
WVFGRD96  108.0    50    70    85   4.28 0.7114
WVFGRD96  110.0    50    70    85   4.28 0.7149
WVFGRD96  112.0    50    70    85   4.28 0.7176
WVFGRD96  114.0    50    70    85   4.29 0.7198
WVFGRD96  116.0    50    70    85   4.29 0.7205
WVFGRD96  118.0    50    70    85   4.29 0.7217
WVFGRD96  120.0    50    70    85   4.29 0.7212
WVFGRD96  122.0   235    20    95   4.30 0.7212
WVFGRD96  124.0    50    70    85   4.30 0.7214
WVFGRD96  126.0    50    70    85   4.30 0.7202
WVFGRD96  128.0    50    70    85   4.30 0.7189
WVFGRD96  130.0    50    70    85   4.30 0.7163
WVFGRD96  132.0   240    20    95   4.31 0.7163
WVFGRD96  134.0    55    70    90   4.31 0.7138
WVFGRD96  136.0    55    70    90   4.32 0.7119
WVFGRD96  138.0    55    70    90   4.32 0.7091
WVFGRD96  140.0   240    20    95   4.32 0.7069
WVFGRD96  142.0   240    20    95   4.32 0.7054
WVFGRD96  144.0   240    20    95   4.32 0.7031
WVFGRD96  146.0    55    70    90   4.33 0.7026
WVFGRD96  148.0    55    70    90   4.33 0.7003

The best solution is

WVFGRD96  118.0    50    70    85   4.29 0.7217

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/3.3 -30 o DIST/3.3 +60
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 00:16:17 CST 2015