Location

2014/03/30 01:32:54 62.219 -151.228 83.2 4.7 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  2014/03/30 01:32:54:0  62.22 -151.23  83.2 4.7 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ 
   AK.CTG AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN 
   AK.KNK AK.KTH AK.MCAR AK.MCK AK.MDM AK.MLY AK.NEA AK.PPLA 
   AK.RAG AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCRK AK.SKN AK.SSN 
   AK.SWD AK.TGL AK.TRF AK.VRDI AK.WRH AT.MENT AT.PMR AT.SVW2 
   IM.IL31 IU.COLA 
 
 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 = 3.35e+23 dyne-cm
  Mw = 4.95 
  Z  = 88 km
  Plane   Strike  Dip  Rake
   NP1      351    85   120
   NP2       90    30    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.35e+23     42     290
    N   0.00e+00     29     168
    P  -3.35e+23     33      57

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -5.04e+22
       Mxy    -1.65e+23
       Mxz    -2.91e+22
       Myy    -1.44e+16
       Myz    -2.86e+23
       Mzz     5.04e+22
                                                     
                                                     
                                                     
                                                     
                     ####----------                  
                 #########-------------              
              ############----------------           
             ##############----------------          
           ################------------------        
          #################-----------   -----       
         ###################---------- P ------      
        #######   ##########----------   -------     
        ####### T ###########-------------------     
       ########   ###########--------------------    
       ######################--------------------    
       -#####################-------------------#    
       -######################------------------#    
        -#####################-----------------#     
        ---###################---------------###     
         ---##################--------------###      
          ----#################-----------####       
           ------##############--------######        
             ---------#########---#########          
              -----------------###########           
                 --------------########              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.04e+22  -2.91e+22   2.86e+23 
 -2.91e+22  -5.04e+22   1.65e+23 
  2.86e+23   1.65e+23  -1.44e+16 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140330013254/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 = 90
      DIP = 30
     RAKE = 10
       MW = 4.95
       HS = 88.0

The NDK file is 20140330013254.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2014/03/30 01:32:54:0  62.22 -151.23  83.2 4.7 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ 
   AK.CTG AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN 
   AK.KNK AK.KTH AK.MCAR AK.MCK AK.MDM AK.MLY AK.NEA AK.PPLA 
   AK.RAG AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCRK AK.SKN AK.SSN 
   AK.SWD AK.TGL AK.TRF AK.VRDI AK.WRH AT.MENT AT.PMR AT.SVW2 
   IM.IL31 IU.COLA 
 
 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 = 3.35e+23 dyne-cm
  Mw = 4.95 
  Z  = 88 km
  Plane   Strike  Dip  Rake
   NP1      351    85   120
   NP2       90    30    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.35e+23     42     290
    N   0.00e+00     29     168
    P  -3.35e+23     33      57

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -5.04e+22
       Mxy    -1.65e+23
       Mxz    -2.91e+22
       Myy    -1.44e+16
       Myz    -2.86e+23
       Mzz     5.04e+22
                                                     
                                                     
                                                     
                                                     
                     ####----------                  
                 #########-------------              
              ############----------------           
             ##############----------------          
           ################------------------        
          #################-----------   -----       
         ###################---------- P ------      
        #######   ##########----------   -------     
        ####### T ###########-------------------     
       ########   ###########--------------------    
       ######################--------------------    
       -#####################-------------------#    
       -######################------------------#    
        -#####################-----------------#     
        ---###################---------------###     
         ---##################--------------###      
          ----#################-----------####       
           ------##############--------######        
             ---------#########---#########          
              -----------------###########           
                 --------------########              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.04e+22  -2.91e+22   2.86e+23 
 -2.91e+22  -5.04e+22   1.65e+23 
  2.86e+23   1.65e+23  -1.44e+16 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140330013254/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 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    2.0    70    65   -20   4.12 0.2554
WVFGRD96    4.0    75    85     5   4.19 0.2986
WVFGRD96    6.0   255    90   -10   4.25 0.3223
WVFGRD96    8.0   255    90   -15   4.30 0.3421
WVFGRD96   10.0    75    80    15   4.33 0.3572
WVFGRD96   12.0    75    80    15   4.35 0.3646
WVFGRD96   14.0    75    80    15   4.38 0.3709
WVFGRD96   16.0    75    80    15   4.40 0.3774
WVFGRD96   18.0    75    80    15   4.42 0.3846
WVFGRD96   20.0    75    80    15   4.44 0.3927
WVFGRD96   22.0    75    80    10   4.46 0.4019
WVFGRD96   24.0    75    80    10   4.48 0.4127
WVFGRD96   26.0    75    80    10   4.50 0.4238
WVFGRD96   28.0    75    75    10   4.52 0.4344
WVFGRD96   30.0    75    75    10   4.54 0.4449
WVFGRD96   32.0    75    75    10   4.57 0.4562
WVFGRD96   34.0    75    75    10   4.59 0.4689
WVFGRD96   36.0    75    80    10   4.62 0.4849
WVFGRD96   38.0    75    80    10   4.66 0.5045
WVFGRD96   40.0    75    80    15   4.71 0.5246
WVFGRD96   42.0    75    75    10   4.73 0.5338
WVFGRD96   44.0    75    75    10   4.75 0.5436
WVFGRD96   46.0    75    70    10   4.76 0.5518
WVFGRD96   48.0    80    60     5   4.77 0.5621
WVFGRD96   50.0    75    55     0   4.79 0.5801
WVFGRD96   52.0    80    55     5   4.80 0.5996
WVFGRD96   54.0    80    50     5   4.82 0.6193
WVFGRD96   56.0    80    50     5   4.83 0.6390
WVFGRD96   58.0    80    45     5   4.84 0.6560
WVFGRD96   60.0    80    45     5   4.86 0.6738
WVFGRD96   62.0    80    45     5   4.86 0.6884
WVFGRD96   64.0    80    45     5   4.87 0.7029
WVFGRD96   66.0    80    40     5   4.89 0.7153
WVFGRD96   68.0    80    40     5   4.89 0.7258
WVFGRD96   70.0    80    40     5   4.90 0.7342
WVFGRD96   72.0    85    40    10   4.90 0.7437
WVFGRD96   74.0    85    35    10   4.91 0.7521
WVFGRD96   76.0    85    35     5   4.92 0.7588
WVFGRD96   78.0    85    35     5   4.93 0.7642
WVFGRD96   80.0    90    35    10   4.93 0.7681
WVFGRD96   82.0    90    30    10   4.94 0.7717
WVFGRD96   84.0    90    30    10   4.95 0.7745
WVFGRD96   86.0    90    30    10   4.95 0.7753
WVFGRD96   88.0    90    30    10   4.95 0.7754
WVFGRD96   90.0    90    30    10   4.96 0.7738
WVFGRD96   92.0    95    30    10   4.97 0.7722
WVFGRD96   94.0    95    30    10   4.97 0.7704
WVFGRD96   96.0    95    30    10   4.98 0.7673
WVFGRD96   98.0    95    30    10   4.98 0.7633
WVFGRD96  100.0    95    30    10   4.98 0.7597
WVFGRD96  102.0    95    30    10   4.98 0.7550
WVFGRD96  104.0    95    30    10   4.99 0.7494
WVFGRD96  106.0   100    25    15   4.99 0.7421
WVFGRD96  108.0   100    25    15   4.99 0.7357
WVFGRD96  110.0   100    25    15   4.99 0.7305
WVFGRD96  112.0   100    25    10   5.01 0.7243
WVFGRD96  114.0   100    25    10   5.01 0.7168
WVFGRD96  116.0   100    25    10   5.01 0.7088
WVFGRD96  118.0   105    25    15   5.01 0.7024
WVFGRD96  120.0   105    25    15   5.01 0.6954
WVFGRD96  122.0   105    25    15   5.01 0.6865
WVFGRD96  124.0   105    25    15   5.02 0.6803
WVFGRD96  126.0   105    25    15   5.02 0.6725
WVFGRD96  128.0   105    25    15   5.02 0.6630

The best solution is

WVFGRD96   88.0    90    30    10   4.95 0.7754

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 00:10:31 CST 2015