Location

2014/03/09 16:11:23 61.045 -150.727 40 3.7 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  2014/03/09 16:11:23:0  61.04 -150.73  40.0 3.7 Alaska
 
 Stations used:
   AK.CRQ AK.DHY AK.GLB AK.GLI AK.KNK AK.MCK AK.RC01 AK.SAW 
   AK.SCM AK.SKN AK.SSN AK.TGL AT.MENT AT.PMR AT.SVW2 
 
 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 = 1.02e+22 dyne-cm
  Mw = 3.94 
  Z  = 58 km
  Plane   Strike  Dip  Rake
   NP1      190    75   -80
   NP2      336    18   -123
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.02e+22     29     272
    N   0.00e+00     10       7
    P  -1.02e+22     59     114

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.35e+20
       Mxy     7.51e+20
       Mxz     1.97e+21
       Myy     5.47e+21
       Myz    -8.51e+21
       Mzz    -5.04e+21
                                                     
                                                     
                                                     
                                                     
                     -#####----####                  
                 #############----#####              
              ###############--------#####           
             ###############-----------####          
           ################--------------####        
          #################---------------####       
         #################-----------------####      
        #################-------------------####     
        #################--------------------###     
       #####   ##########--------------------####    
       ##### T #########---------------------####    
       #####   #########----------   ---------###    
       #################---------- P ---------###    
        ###############-----------   --------###     
        ###############----------------------###     
         ##############----------------------##      
          #############---------------------##       
           ############--------------------##        
             ##########-------------------#          
              #########-----------------##           
                 #######--------------#              
                     ###-----------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.04e+21   1.97e+21   8.51e+21 
  1.97e+21  -4.35e+20  -7.51e+20 
  8.51e+21  -7.51e+20   5.47e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140309161123/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 = 190
      DIP = 75
     RAKE = -80
       MW = 3.94
       HS = 58.0

The NDK file is 20140309161123.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  2014/03/09 16:11:23:0  61.04 -150.73  40.0 3.7 Alaska
 
 Stations used:
   AK.CRQ AK.DHY AK.GLB AK.GLI AK.KNK AK.MCK AK.RC01 AK.SAW 
   AK.SCM AK.SKN AK.SSN AK.TGL AT.MENT AT.PMR AT.SVW2 
 
 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 = 1.02e+22 dyne-cm
  Mw = 3.94 
  Z  = 58 km
  Plane   Strike  Dip  Rake
   NP1      190    75   -80
   NP2      336    18   -123
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.02e+22     29     272
    N   0.00e+00     10       7
    P  -1.02e+22     59     114

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.35e+20
       Mxy     7.51e+20
       Mxz     1.97e+21
       Myy     5.47e+21
       Myz    -8.51e+21
       Mzz    -5.04e+21
                                                     
                                                     
                                                     
                                                     
                     -#####----####                  
                 #############----#####              
              ###############--------#####           
             ###############-----------####          
           ################--------------####        
          #################---------------####       
         #################-----------------####      
        #################-------------------####     
        #################--------------------###     
       #####   ##########--------------------####    
       ##### T #########---------------------####    
       #####   #########----------   ---------###    
       #################---------- P ---------###    
        ###############-----------   --------###     
        ###############----------------------###     
         ##############----------------------##      
          #############---------------------##       
           ############--------------------##        
             ##########-------------------#          
              #########-----------------##           
                 #######--------------#              
                     ###-----------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.04e+21   1.97e+21   8.51e+21 
  1.97e+21  -4.35e+20  -7.51e+20 
  8.51e+21  -7.51e+20   5.47e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140309161123/index.html
	
Moment
    1.06e+15 N-m
Magnitude
    4.0
Percent DC
    71%
Depth
    58.0 km
Updated
    2014-03-09 17:31:46 UTC
Author
    us
Catalog
    ak
Contributor
    us
Code
    us_c000n5yj_mwr

Principal Axes
Axis	Value	Plunge	Azimuth
T	0.987	33°	277°
N	0.139	7°	12°
P	-1.126	56°	113°
Nodal Planes
Plane	Strike	Dip	Rake
NP1	194°	78°	-82°
NP2	341°	14°	-122°

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   200    80   -10   3.10 0.1446
WVFGRD96    1.0   200    80   -10   3.14 0.1586
WVFGRD96    2.0   200    80   -15   3.25 0.2018
WVFGRD96    3.0   195    65   -20   3.34 0.2339
WVFGRD96    4.0   200    75   -15   3.37 0.2537
WVFGRD96    5.0   200    75    -5   3.41 0.2663
WVFGRD96    6.0   200    80     0   3.44 0.2745
WVFGRD96    7.0   200    80     0   3.46 0.2808
WVFGRD96    8.0   200    75    10   3.50 0.2899
WVFGRD96    9.0   200    75    10   3.51 0.2952
WVFGRD96   10.0   200    75    10   3.53 0.2960
WVFGRD96   11.0   200    80    10   3.54 0.2943
WVFGRD96   12.0   200    80    10   3.55 0.2925
WVFGRD96   13.0   200    80    20   3.56 0.2931
WVFGRD96   14.0   200    80    20   3.57 0.2970
WVFGRD96   15.0    20    85    35   3.55 0.3023
WVFGRD96   16.0    20    85    35   3.55 0.3098
WVFGRD96   17.0    20    90    35   3.56 0.3171
WVFGRD96   18.0    20    90    35   3.57 0.3244
WVFGRD96   19.0    20    90    35   3.57 0.3316
WVFGRD96   20.0   195    85   -35   3.59 0.3404
WVFGRD96   21.0   195    85   -35   3.60 0.3462
WVFGRD96   22.0    20    90    40   3.60 0.3518
WVFGRD96   23.0    20    90    40   3.60 0.3589
WVFGRD96   24.0   195    85   -40   3.61 0.3667
WVFGRD96   25.0    20    90    40   3.62 0.3716
WVFGRD96   26.0   195    85   -45   3.63 0.3803
WVFGRD96   27.0   195    85   -45   3.63 0.3873
WVFGRD96   28.0   195    85   -45   3.64 0.3941
WVFGRD96   29.0   195    85   -50   3.65 0.4012
WVFGRD96   30.0    20    90    50   3.66 0.4049
WVFGRD96   31.0    20    90    50   3.66 0.4116
WVFGRD96   32.0   195    85   -50   3.67 0.4210
WVFGRD96   33.0   195    85   -55   3.68 0.4271
WVFGRD96   34.0   195    85   -55   3.68 0.4328
WVFGRD96   35.0   195    85   -55   3.69 0.4380
WVFGRD96   36.0   195    80   -55   3.69 0.4426
WVFGRD96   37.0   195    80   -55   3.70 0.4480
WVFGRD96   38.0   195    80   -60   3.70 0.4519
WVFGRD96   39.0   195    80   -55   3.71 0.4558
WVFGRD96   40.0   195    80   -65   3.84 0.4557
WVFGRD96   41.0   195    80   -65   3.84 0.4600
WVFGRD96   42.0   195    80   -65   3.85 0.4635
WVFGRD96   43.0   195    80   -70   3.86 0.4672
WVFGRD96   44.0   195    80   -70   3.86 0.4702
WVFGRD96   45.0   195    80   -70   3.87 0.4728
WVFGRD96   46.0   195    80   -70   3.87 0.4760
WVFGRD96   47.0   195    80   -70   3.88 0.4778
WVFGRD96   48.0   190    75   -70   3.88 0.4805
WVFGRD96   49.0   190    75   -70   3.89 0.4828
WVFGRD96   50.0   190    75   -70   3.89 0.4849
WVFGRD96   51.0   190    75   -75   3.90 0.4872
WVFGRD96   52.0   190    75   -75   3.91 0.4888
WVFGRD96   53.0   190    75   -75   3.91 0.4907
WVFGRD96   54.0   190    75   -75   3.92 0.4916
WVFGRD96   55.0   190    75   -75   3.92 0.4925
WVFGRD96   56.0   190    75   -80   3.93 0.4930
WVFGRD96   57.0   190    75   -80   3.93 0.4935
WVFGRD96   58.0   190    75   -80   3.94 0.4937
WVFGRD96   59.0   190    75   -80   3.94 0.4929
WVFGRD96   60.0   185    75   -80   3.94 0.4926
WVFGRD96   61.0   190    75   -85   3.95 0.4914
WVFGRD96   62.0   190    75   -85   3.96 0.4907
WVFGRD96   63.0    10    15   -90   3.97 0.4888
WVFGRD96   64.0    10    15   -90   3.97 0.4874
WVFGRD96   65.0    10    15   -90   3.97 0.4860
WVFGRD96   66.0    45    15   -60   3.99 0.4841
WVFGRD96   67.0    45    15   -60   3.99 0.4829
WVFGRD96   68.0    45    15   -60   3.99 0.4817
WVFGRD96   69.0    60    15   -50   4.00 0.4794
WVFGRD96   70.0    50    15   -55   4.00 0.4784
WVFGRD96   71.0    65    15   -45   4.01 0.4767
WVFGRD96   72.0    65    15   -45   4.01 0.4743
WVFGRD96   73.0    65    15   -45   4.01 0.4727
WVFGRD96   74.0    75    20   -35   4.03 0.4700
WVFGRD96   75.0    75    20   -35   4.03 0.4680
WVFGRD96   76.0    75    20   -35   4.03 0.4662
WVFGRD96   77.0    75    20   -35   4.03 0.4634
WVFGRD96   78.0    85    20   -30   4.04 0.4611
WVFGRD96   79.0    85    20   -30   4.04 0.4591
WVFGRD96   80.0    90    25   -25   4.06 0.4564
WVFGRD96   81.0    90    25   -25   4.06 0.4545
WVFGRD96   82.0    90    25   -25   4.06 0.4527
WVFGRD96   83.0    90    25   -25   4.07 0.4502
WVFGRD96   84.0    90    25   -25   4.07 0.4472
WVFGRD96   85.0    90    25   -25   4.07 0.4450
WVFGRD96   86.0    90    25   -25   4.07 0.4422
WVFGRD96   87.0    95    30   -20   4.09 0.4387
WVFGRD96   88.0    95    30   -20   4.09 0.4370
WVFGRD96   89.0    95    30   -20   4.09 0.4345
WVFGRD96   90.0    95    30   -20   4.09 0.4320
WVFGRD96   91.0    95    30   -20   4.09 0.4291
WVFGRD96   92.0    95    30   -20   4.10 0.4268
WVFGRD96   93.0    95    30   -20   4.10 0.4238
WVFGRD96   94.0    95    30   -20   4.10 0.4206
WVFGRD96   95.0   100    30   -20   4.11 0.4177
WVFGRD96   96.0   100    35   -20   4.12 0.4151
WVFGRD96   97.0   100    35   -20   4.12 0.4126
WVFGRD96   98.0   105    35   -15   4.13 0.4099
WVFGRD96   99.0   105    35   -15   4.13 0.4079

The best solution is

WVFGRD96   58.0   190    75   -80   3.94 0.4937

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 00:10:10 CST 2015