Location

Location ANSS

2022/07/12 02:58:59 60.398 -149.012 30.1 4.3 Alaska

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2022/07/12 02:58:59:0  60.40 -149.01  30.1 4.3 Alaska
 
 Stations used:
   AK.BRLK AK.CAPN AK.FID AK.FIRE AK.GLB AK.GLI AK.K24K AK.KLU 
   AK.MCAR AK.P23K AK.RC01 AK.RIDG AK.SCM AK.SKN AK.SWD AV.ILS 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.08 n 3 
 
 Best Fitting Double Couple
  Mo = 7.59e+22 dyne-cm
  Mw = 4.52 
  Z  = 41 km
  Plane   Strike  Dip  Rake
   NP1      210    60   -65
   NP2      347    38   -126
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.59e+22     12     282
    N   0.00e+00     21      17
    P  -7.59e+22     65     166

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -9.16e+21
       Mxy    -1.19e+22
       Mxz     3.11e+22
       Myy     6.87e+22
       Myz    -2.18e+22
       Mzz    -5.95e+22
                                                     
                                                     
                                                     
                                                     
                     ######--------                  
                 #############-------##              
              ############################           
             #################-----########          
           #################--------#########        
          ################------------########       
         ###############---------------########      
           ############----------------#########     
         T ###########------------------########     
       #   ##########--------------------########    
       #############---------------------########    
       ############----------------------########    
       ###########-----------------------########    
        ##########----------   ----------#######     
        #########----------- P ----------#######     
         ########-----------   ----------######      
          #######-----------------------######       
           ######----------------------######        
             ####---------------------#####          
              ###--------------------#####           
                 -------------------###              
                     -------------#                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.95e+22   3.11e+22   2.18e+22 
  3.11e+22  -9.16e+21   1.19e+22 
  2.18e+22   1.19e+22   6.87e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220712025859/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 = 210
      DIP = 60
     RAKE = -65
       MW = 4.52
       HS = 41.0

The NDK file is 20220712025859.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMWR
 USGS/SLU Moment Tensor Solution
 ENS  2022/07/12 02:58:59:0  60.40 -149.01  30.1 4.3 Alaska
 
 Stations used:
   AK.BRLK AK.CAPN AK.FID AK.FIRE AK.GLB AK.GLI AK.K24K AK.KLU 
   AK.MCAR AK.P23K AK.RC01 AK.RIDG AK.SCM AK.SKN AK.SWD AV.ILS 
 
 Filtering commands used:
   cut o DIST/3.3 -40 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.08 n 3 
 
 Best Fitting Double Couple
  Mo = 7.59e+22 dyne-cm
  Mw = 4.52 
  Z  = 41 km
  Plane   Strike  Dip  Rake
   NP1      210    60   -65
   NP2      347    38   -126
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.59e+22     12     282
    N   0.00e+00     21      17
    P  -7.59e+22     65     166

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -9.16e+21
       Mxy    -1.19e+22
       Mxz     3.11e+22
       Myy     6.87e+22
       Myz    -2.18e+22
       Mzz    -5.95e+22
                                                     
                                                     
                                                     
                                                     
                     ######--------                  
                 #############-------##              
              ############################           
             #################-----########          
           #################--------#########        
          ################------------########       
         ###############---------------########      
           ############----------------#########     
         T ###########------------------########     
       #   ##########--------------------########    
       #############---------------------########    
       ############----------------------########    
       ###########-----------------------########    
        ##########----------   ----------#######     
        #########----------- P ----------#######     
         ########-----------   ----------######      
          #######-----------------------######       
           ######----------------------######        
             ####---------------------#####          
              ###--------------------#####           
                 -------------------###              
                     -------------#                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.95e+22   3.11e+22   2.18e+22 
  3.11e+22  -9.16e+21   1.19e+22 
  2.18e+22   1.19e+22   6.87e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220712025859/index.html
	
Regional Moment Tensor (Mwr)
Moment 4.726e+15 N-m
Magnitude 4.38 Mwr
Depth 35.0 km
Percent DC 66%
Half Duration -
Catalog US
Data Source US 2
Contributor US 2

Nodal Planes
Plane Strike Dip Rake
NP1 355 48 -118
NP2 214 49 -62

Principal Axes
Axis Value Plunge Azimuth
T 5.098e+15 N-m 0 284
N -0.861e+15 N-m 21 14
P -4.237e+15 N-m 69 193

        

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/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.08 n 3 
The results of this grid search are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0   210    50    85   3.79 0.1947
WVFGRD96    2.0    80    45    95   3.96 0.2529
WVFGRD96    3.0   180    50   -95   3.97 0.2744
WVFGRD96    4.0   185    50   -85   4.00 0.2639
WVFGRD96    5.0   225    80    50   3.98 0.3009
WVFGRD96    6.0   225    75    45   4.00 0.3304
WVFGRD96    7.0   225    75    45   4.02 0.3538
WVFGRD96    8.0   225    80    50   4.08 0.3690
WVFGRD96    9.0   225    80    45   4.09 0.3828
WVFGRD96   10.0   225    80    45   4.10 0.3926
WVFGRD96   11.0   225    80    45   4.12 0.3986
WVFGRD96   12.0    40    90   -45   4.13 0.3986
WVFGRD96   13.0   225    80    40   4.14 0.4032
WVFGRD96   14.0   225    80    40   4.16 0.4033
WVFGRD96   15.0   225    80    40   4.17 0.4022
WVFGRD96   16.0   230    80    40   4.17 0.4014
WVFGRD96   17.0   230    80    40   4.18 0.4008
WVFGRD96   18.0   230    80    40   4.19 0.3997
WVFGRD96   19.0   215    70   -45   4.21 0.4017
WVFGRD96   20.0   220    70   -45   4.21 0.4060
WVFGRD96   21.0   220    70   -45   4.23 0.4109
WVFGRD96   22.0   220    70   -45   4.24 0.4139
WVFGRD96   23.0   220    70   -45   4.25 0.4159
WVFGRD96   24.0   220    75   -45   4.26 0.4173
WVFGRD96   25.0   220    75   -45   4.27 0.4195
WVFGRD96   26.0   220    75   -45   4.28 0.4215
WVFGRD96   27.0   220    75   -45   4.29 0.4227
WVFGRD96   28.0   220    70   -45   4.30 0.4255
WVFGRD96   29.0   220    65   -45   4.31 0.4315
WVFGRD96   30.0   220    65   -45   4.32 0.4384
WVFGRD96   31.0   220    65   -45   4.33 0.4473
WVFGRD96   32.0   215    60   -50   4.35 0.4558
WVFGRD96   33.0   215    60   -55   4.36 0.4635
WVFGRD96   34.0   215    60   -55   4.37 0.4695
WVFGRD96   35.0   215    60   -55   4.38 0.4743
WVFGRD96   36.0   215    60   -55   4.39 0.4767
WVFGRD96   37.0   215    60   -55   4.40 0.4771
WVFGRD96   38.0   215    60   -55   4.41 0.4761
WVFGRD96   39.0   215    60   -55   4.42 0.4730
WVFGRD96   40.0   210    60   -65   4.50 0.4862
WVFGRD96   41.0   210    60   -65   4.52 0.4864
WVFGRD96   42.0   210    60   -65   4.52 0.4848
WVFGRD96   43.0   205    55   -65   4.54 0.4832
WVFGRD96   44.0   205    55   -65   4.54 0.4818
WVFGRD96   45.0   205    55   -65   4.55 0.4793
WVFGRD96   46.0   205    55   -65   4.56 0.4767
WVFGRD96   47.0   205    55   -65   4.56 0.4744
WVFGRD96   48.0   205    55   -65   4.57 0.4712
WVFGRD96   49.0   205    55   -65   4.57 0.4682
WVFGRD96   50.0   205    55   -65   4.58 0.4648
WVFGRD96   51.0   205    55   -65   4.58 0.4605
WVFGRD96   52.0   205    55   -65   4.59 0.4561
WVFGRD96   53.0   205    55   -65   4.59 0.4526
WVFGRD96   54.0   205    55   -65   4.59 0.4537
WVFGRD96   55.0   205    55   -60   4.60 0.4537
WVFGRD96   56.0   205    55   -60   4.60 0.4539
WVFGRD96   57.0   205    55   -60   4.60 0.4537
WVFGRD96   58.0   205    55   -60   4.61 0.4531
WVFGRD96   59.0   210    60   -55   4.60 0.4514

The best solution is

WVFGRD96   41.0   210    60   -65   4.52 0.4864

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 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.08 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 Bureau of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Oklahoma Geological Survey, TexNet, the Iris stations, the Transportable Array of EarthScope and other networks.

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 Jul 12 07:20:45 CDT 2022