Location

Location ANSS

2019/01/22 04:43:19 58.321 -155.356 127.8 5.2 Alaska

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2019/01/22 04:43:19:0  58.32 -155.36 127.8 5.2 Alaska
 
 Stations used:
   AK.BRLK AK.CNP AK.HOM AK.SII AT.CHGN AT.OHAK AV.ACH AV.ILSW 
   II.KDAK TA.M17K TA.N15K TA.N17K TA.N18K TA.N19K TA.O14K 
   TA.O16K TA.O18K TA.O19K TA.P18K TA.P19K TA.Q19K TA.Q20K 
   TA.R18K 
 
 Filtering commands used:
   cut o DIST/3.4 -50 o DIST/3.4 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 4.73e+23 dyne-cm
  Mw = 5.05 
  Z  = 130 km
  Plane   Strike  Dip  Rake
   NP1      343    71   137
   NP2       90    50    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.73e+23     43     299
    N   0.00e+00     44     144
    P  -4.73e+23     13      41

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.97e+23
       Mxy    -3.28e+23
       Mxz     3.47e+22
       Myy    -2.87e+16
       Myz    -2.76e+23
       Mzz     1.97e+23
                                                     
                                                     
                                                     
                                                     
                     ##------------                  
                 #######---------------              
              ############------------   -           
             ##############----------- P --          
           #################----------   ----        
          ###################-----------------       
         #####################-----------------      
        ########   ############-----------------     
        ######## T #############----------------     
       #########   #############-----------------    
       ##########################----------------    
       -#########################---------------#    
       --#########################-------------##    
        ---#######################-----------###     
        ------####################--------######     
         ---------#################---#########      
          -------------------------###########       
           ------------------------##########        
             ----------------------########          
              ---------------------#######           
                 ------------------####              
                     -------------#                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.97e+23   3.47e+22   2.76e+23 
  3.47e+22  -1.97e+23   3.28e+23 
  2.76e+23   3.28e+23  -2.87e+16 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190122044319/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 = 50
     RAKE = 25
       MW = 5.05
       HS = 130.0

The NDK file is 20190122044319.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2019/01/22 04:43:19:0  58.32 -155.36 127.8 5.2 Alaska
 
 Stations used:
   AK.BRLK AK.CNP AK.HOM AK.SII AT.CHGN AT.OHAK AV.ACH AV.ILSW 
   II.KDAK TA.M17K TA.N15K TA.N17K TA.N18K TA.N19K TA.O14K 
   TA.O16K TA.O18K TA.O19K TA.P18K TA.P19K TA.Q19K TA.Q20K 
   TA.R18K 
 
 Filtering commands used:
   cut o DIST/3.4 -50 o DIST/3.4 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 4.73e+23 dyne-cm
  Mw = 5.05 
  Z  = 130 km
  Plane   Strike  Dip  Rake
   NP1      343    71   137
   NP2       90    50    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.73e+23     43     299
    N   0.00e+00     44     144
    P  -4.73e+23     13      41

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.97e+23
       Mxy    -3.28e+23
       Mxz     3.47e+22
       Myy    -2.87e+16
       Myz    -2.76e+23
       Mzz     1.97e+23
                                                     
                                                     
                                                     
                                                     
                     ##------------                  
                 #######---------------              
              ############------------   -           
             ##############----------- P --          
           #################----------   ----        
          ###################-----------------       
         #####################-----------------      
        ########   ############-----------------     
        ######## T #############----------------     
       #########   #############-----------------    
       ##########################----------------    
       -#########################---------------#    
       --#########################-------------##    
        ---#######################-----------###     
        ------####################--------######     
         ---------#################---#########      
          -------------------------###########       
           ------------------------##########        
             ----------------------########          
              ---------------------#######           
                 ------------------####              
                     -------------#                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.97e+23   3.47e+22   2.76e+23 
  3.47e+22  -1.97e+23   3.28e+23 
  2.76e+23   3.28e+23  -2.87e+16 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20190122044319/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 using wvfgrd96

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/3.4 -50 o DIST/3.4 +50
rtr
taper w 0.1
hp c 0.03 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    2.0   350    50    70   4.11 0.1485
WVFGRD96    4.0   335    70    40   4.12 0.1920
WVFGRD96    6.0   335    75    35   4.19 0.2340
WVFGRD96    8.0   335    80    40   4.29 0.2702
WVFGRD96   10.0   335    75    35   4.34 0.3000
WVFGRD96   12.0   335    75    35   4.39 0.3183
WVFGRD96   14.0   335    75    35   4.42 0.3263
WVFGRD96   16.0   335    75    35   4.45 0.3250
WVFGRD96   18.0   335    75    35   4.48 0.3165
WVFGRD96   20.0   335    70    35   4.50 0.3016
WVFGRD96   22.0   250    60    15   4.52 0.3040
WVFGRD96   24.0   250    60    15   4.54 0.3089
WVFGRD96   26.0   250    60    10   4.57 0.3143
WVFGRD96   28.0   250    60    10   4.59 0.3187
WVFGRD96   30.0   250    65    10   4.60 0.3224
WVFGRD96   32.0   250    65    10   4.62 0.3224
WVFGRD96   34.0   250    65     5   4.64 0.3253
WVFGRD96   36.0   250    65     5   4.66 0.3367
WVFGRD96   38.0   250    75     0   4.70 0.3534
WVFGRD96   40.0   245    65    -5   4.77 0.3854
WVFGRD96   42.0   245    70    -5   4.80 0.4021
WVFGRD96   44.0   245    70    -5   4.82 0.4147
WVFGRD96   46.0   245    70    -5   4.84 0.4224
WVFGRD96   48.0   245    70    -5   4.86 0.4270
WVFGRD96   50.0   250    75    -5   4.89 0.4289
WVFGRD96   52.0   250    75    -5   4.90 0.4299
WVFGRD96   54.0   250    75    -5   4.91 0.4296
WVFGRD96   56.0   250    75    -5   4.92 0.4312
WVFGRD96   58.0   245    75   -10   4.91 0.4316
WVFGRD96   60.0    70    80     5   4.90 0.4336
WVFGRD96   62.0    70    75     0   4.90 0.4415
WVFGRD96   64.0    70    75     0   4.90 0.4499
WVFGRD96   66.0    70    70     5   4.90 0.4558
WVFGRD96   68.0    75    70    10   4.92 0.4654
WVFGRD96   70.0    75    70    10   4.93 0.4733
WVFGRD96   72.0    75    65    10   4.92 0.4815
WVFGRD96   74.0    75    65    10   4.93 0.4894
WVFGRD96   76.0    75    65    10   4.93 0.4969
WVFGRD96   78.0    75    65    15   4.93 0.5072
WVFGRD96   80.0    80    60    20   4.95 0.5322
WVFGRD96   82.0    80    60    20   4.96 0.5571
WVFGRD96   84.0    80    60    20   4.97 0.5802
WVFGRD96   86.0    80    60    20   4.97 0.6004
WVFGRD96   88.0    85    55    25   4.98 0.6160
WVFGRD96   90.0    85    55    25   4.99 0.6266
WVFGRD96   92.0    85    55    25   4.99 0.6332
WVFGRD96   94.0    85    55    25   4.99 0.6391
WVFGRD96   96.0    85    55    25   5.00 0.6447
WVFGRD96   98.0    85    55    25   5.00 0.6495
WVFGRD96  100.0    85    55    25   5.00 0.6547
WVFGRD96  102.0    85    55    25   5.00 0.6591
WVFGRD96  104.0    85    55    25   5.01 0.6624
WVFGRD96  106.0    85    55    25   5.01 0.6655
WVFGRD96  108.0    85    55    25   5.01 0.6687
WVFGRD96  110.0    85    55    25   5.01 0.6718
WVFGRD96  112.0    90    50    25   5.03 0.6749
WVFGRD96  114.0    90    50    25   5.03 0.6786
WVFGRD96  116.0    90    50    25   5.03 0.6816
WVFGRD96  118.0    90    50    25   5.03 0.6834
WVFGRD96  120.0    90    50    25   5.04 0.6869
WVFGRD96  122.0    90    50    25   5.04 0.6890
WVFGRD96  124.0    90    50    25   5.04 0.6898
WVFGRD96  126.0    90    50    25   5.04 0.6898
WVFGRD96  128.0    90    50    25   5.05 0.6909
WVFGRD96  130.0    90    50    25   5.05 0.6917
WVFGRD96  132.0    90    50    30   5.04 0.6909
WVFGRD96  134.0    95    50    30   5.06 0.6913
WVFGRD96  136.0    95    45    25   5.07 0.6908
WVFGRD96  138.0    95    50    30   5.06 0.6889
WVFGRD96  140.0    95    50    30   5.07 0.6892
WVFGRD96  142.0    95    45    30   5.06 0.6882
WVFGRD96  144.0    95    45    25   5.07 0.6858
WVFGRD96  146.0    95    45    25   5.08 0.6849
WVFGRD96  148.0    95    45    25   5.08 0.6837
WVFGRD96  150.0    95    45    25   5.08 0.6822
WVFGRD96  152.0    95    45    25   5.08 0.6800
WVFGRD96  154.0    95    45    25   5.08 0.6772
WVFGRD96  156.0    95    50    25   5.09 0.6762
WVFGRD96  158.0    95    50    25   5.09 0.6735

The best solution is

WVFGRD96  130.0    90    50    25   5.05 0.6917

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/3.4 -50 o DIST/3.4 +50
rtr
taper w 0.1
hp c 0.03 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.
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 Tue Jan 22 06:38:48 CST 2019