Location

Location ANSS

The ANSS event ID is us7000ga56 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us7000ga56/executive.

2022/01/08 08:16:42 60.390 -140.533 37.8 5.2 Yukon, Canada

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2022/01/08 08:16:42:0  60.39 -140.53  37.8 5.2 Yukon, Canada
 
 Stations used:
   AK.BARN AK.BMR AK.CRQ AK.CYK AK.DIV AK.EYAK AK.FID AK.GLB 
   AK.GLI AK.GRNC AK.HARP AK.HIN AK.KAI AK.KIAG AK.KLU AK.L26K 
   AK.LOGN AK.M26K AK.M27K AK.MCAR AK.PIN AK.PNL AK.PS12 
   AK.PTPK AK.RAG AK.SAMH AK.TGL AK.VMT AK.VRDI AT.SKAG 
   AV.N25K CN.BRWY CN.BVCY CN.PLBC CN.WHY CN.YUK3 
 
 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 = 5.82e+23 dyne-cm
  Mw = 5.11 
  Z  = 44 km
  Plane   Strike  Dip  Rake
   NP1      205    79   -139
   NP2      105    50   -15
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.82e+23     18     329
    N   0.00e+00     48     218
    P  -5.82e+23     36      73

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.54e+23
       Mxy    -3.36e+23
       Mxz     6.83e+22
       Myy    -2.05e+23
       Myz    -3.56e+23
       Mzz    -1.48e+23
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ##################----              
              ####   #############--------           
             ##### T ###########-----------          
           #######   ##########--------------        
          ####################----------------       
         ####################------------------      
        ####################-----------   ------     
        ###################------------ P ------     
       --#################-------------   -------    
       ---###############------------------------    
       ----#############-------------------------    
       ------###########-------------------------    
        -------########-------------------------     
        ----------####-------------------------#     
         ------------#----------------------###      
          -----------######------------#######       
           ---------#########################        
             -------#######################          
              ------######################           
                 --####################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.48e+23   6.83e+22   3.56e+23 
  6.83e+22   3.54e+23   3.36e+23 
  3.56e+23   3.36e+23  -2.05e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220108081642/index.html
        

Preferred Solution

The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is

      STK = 105
      DIP = 50
     RAKE = -15
       MW = 5.11
       HS = 44.0

The NDK file is 20220108081642.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
SLU
USGSW
 USGS/SLU Moment Tensor Solution
 ENS  2022/01/08 08:16:42:0  60.39 -140.53  37.8 5.2 Yukon, Canada
 
 Stations used:
   AK.BARN AK.BMR AK.CRQ AK.CYK AK.DIV AK.EYAK AK.FID AK.GLB 
   AK.GLI AK.GRNC AK.HARP AK.HIN AK.KAI AK.KIAG AK.KLU AK.L26K 
   AK.LOGN AK.M26K AK.M27K AK.MCAR AK.PIN AK.PNL AK.PS12 
   AK.PTPK AK.RAG AK.SAMH AK.TGL AK.VMT AK.VRDI AT.SKAG 
   AV.N25K CN.BRWY CN.BVCY CN.PLBC CN.WHY CN.YUK3 
 
 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 = 5.82e+23 dyne-cm
  Mw = 5.11 
  Z  = 44 km
  Plane   Strike  Dip  Rake
   NP1      205    79   -139
   NP2      105    50   -15
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.82e+23     18     329
    N   0.00e+00     48     218
    P  -5.82e+23     36      73

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.54e+23
       Mxy    -3.36e+23
       Mxz     6.83e+22
       Myy    -2.05e+23
       Myz    -3.56e+23
       Mzz    -1.48e+23
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ##################----              
              ####   #############--------           
             ##### T ###########-----------          
           #######   ##########--------------        
          ####################----------------       
         ####################------------------      
        ####################-----------   ------     
        ###################------------ P ------     
       --#################-------------   -------    
       ---###############------------------------    
       ----#############-------------------------    
       ------###########-------------------------    
        -------########-------------------------     
        ----------####-------------------------#     
         ------------#----------------------###      
          -----------######------------#######       
           ---------#########################        
             -------#######################          
              ------######################           
                 --####################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.48e+23   6.83e+22   3.56e+23 
  6.83e+22   3.54e+23   3.36e+23 
  3.56e+23   3.36e+23  -2.05e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220108081642/index.html
	
W-phase Moment Tensor (Mww)
Moment 6.922e+16 N-m
Magnitude 5.16 Mww
Depth 30.5 km
Percent DC 77%
Half Duration 1.08 s
Catalog US
Data Source US 3
Contributor US 3

Nodal Planes
Plane Strike Dip Rake
NP1 208° 73° -131°
NP2 99° 44° -25°

Principal Axes
Axis Value Plunge Azimuth
T 6.456e+16 N-m 17° 327°
N 0.853e+16 N-m 39° 222°
P -7.309e+16 N-m 46° 76°

        

Magnitudes

Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.

ML Magnitude


Left: ML computed using the IASPEI formula for Horizontal components. Center: 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. Right: Residuals from new relation as a function of distance and azimuth.


Left: ML computed using the IASPEI formula for Vertical components (research). Center: 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. Right: Residuals from new relation as a function of distance and azimuth.

Context

The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. 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). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.

Waveform Inversion using wvfgrd96

The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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   200    70    25   4.29 0.2218
WVFGRD96    2.0   215    55    45   4.45 0.2870
WVFGRD96    3.0   205    60    30   4.48 0.3011
WVFGRD96    4.0   200    80    25   4.49 0.3040
WVFGRD96    5.0    15    60   -20   4.53 0.3115
WVFGRD96    6.0    15    60   -15   4.55 0.3212
WVFGRD96    7.0    15    60   -20   4.57 0.3305
WVFGRD96    8.0    10    70   -30   4.62 0.3370
WVFGRD96    9.0   295    65    35   4.65 0.3479
WVFGRD96   10.0   295    65    35   4.67 0.3622
WVFGRD96   11.0   295    70    25   4.67 0.3749
WVFGRD96   12.0   295    70    25   4.69 0.3864
WVFGRD96   13.0   295    70    20   4.71 0.3968
WVFGRD96   14.0   110    70    20   4.72 0.4078
WVFGRD96   15.0   110    70    20   4.74 0.4211
WVFGRD96   16.0   110    70    20   4.75 0.4336
WVFGRD96   17.0   110    65    15   4.76 0.4464
WVFGRD96   18.0   110    65    15   4.78 0.4595
WVFGRD96   19.0   110    65    15   4.79 0.4719
WVFGRD96   20.0   110    65    15   4.81 0.4834
WVFGRD96   21.0   110    65    15   4.82 0.4950
WVFGRD96   22.0   105    65    10   4.84 0.5071
WVFGRD96   23.0   105    60     0   4.84 0.5192
WVFGRD96   24.0   105    60    -5   4.85 0.5324
WVFGRD96   25.0   105    60    -5   4.87 0.5463
WVFGRD96   26.0   105    60    -5   4.88 0.5608
WVFGRD96   27.0   105    60    -5   4.89 0.5741
WVFGRD96   28.0   105    60   -10   4.90 0.5886
WVFGRD96   29.0   105    60   -10   4.91 0.6012
WVFGRD96   30.0   105    60   -10   4.92 0.6133
WVFGRD96   31.0   105    55   -10   4.93 0.6236
WVFGRD96   32.0   105    55   -10   4.94 0.6356
WVFGRD96   33.0   105    55   -10   4.95 0.6452
WVFGRD96   34.0   105    55   -10   4.96 0.6535
WVFGRD96   35.0   105    55   -10   4.96 0.6598
WVFGRD96   36.0   105    55   -15   4.97 0.6653
WVFGRD96   37.0   105    55   -15   4.98 0.6688
WVFGRD96   38.0   105    55   -15   4.99 0.6725
WVFGRD96   39.0   105    55   -15   5.00 0.6736
WVFGRD96   40.0   105    45   -15   5.08 0.6747
WVFGRD96   41.0   105    50   -15   5.08 0.6781
WVFGRD96   42.0   105    50   -15   5.09 0.6826
WVFGRD96   43.0   105    50   -15   5.10 0.6837
WVFGRD96   44.0   105    50   -15   5.11 0.6846
WVFGRD96   45.0   105    50   -15   5.11 0.6839
WVFGRD96   46.0   105    50   -15   5.12 0.6824
WVFGRD96   47.0   105    50   -15   5.12 0.6805
WVFGRD96   48.0   105    50   -15   5.13 0.6767
WVFGRD96   49.0   105    50   -15   5.13 0.6738
WVFGRD96   50.0   105    50   -15   5.14 0.6693
WVFGRD96   51.0   105    50   -15   5.14 0.6657
WVFGRD96   52.0   105    50   -15   5.15 0.6604
WVFGRD96   53.0   105    50   -15   5.15 0.6554
WVFGRD96   54.0   105    50   -15   5.15 0.6504
WVFGRD96   55.0   105    50   -15   5.15 0.6445
WVFGRD96   56.0   105    50   -15   5.16 0.6393
WVFGRD96   57.0   110    50   -15   5.16 0.6339
WVFGRD96   58.0   110    50   -15   5.16 0.6296
WVFGRD96   59.0   110    50   -15   5.17 0.6242

The best solution is

WVFGRD96   44.0   105    50   -15   5.11 0.6846

The mechanism corresponding 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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. The time scale is relative to the first trace sample.

Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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.

Velocity Model

The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).

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    
Last Changed Wed Apr 24 08:59:48 PM CDT 2024