Location

Location ANSS

2021/10/21 03:23:21 52.545 -115.294 10.0 4.3 Alberta, Canada

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2021/10/21 03:23:21:0  52.54 -115.29  10.0 4.3 Alberta, Canada
 
 Stations used:
   1E.MONT1 1E.MONT9 CN.EDM CN.FSJB CN.HOPB CN.LLLB CN.PNT 
   CN.VDEB CN.WPB CN.WSLR MB.GBMT MB.JTMT MB.LDM RE.GRCO2 
   RV.BDMTA RV.BELVA RV.BRLDA RV.FOXCA RV.HSPGA RV.PKSKA 
   RV.STPRA RV.SWHSA RV.TONYA RV.WTMTA RV.YELLA TD.TD002 
   TD.TD008 TD.TD009 TD.TD022 US.EGMT US.MSO US.NEW UW.CBS 
   UW.DAVN UW.DY2 UW.EPH2 UW.ETW UW.HOPR UW.NEL UW.OMAK 
   UW.PASS UW.RPW2 UW.RVSD UW.SAW UW.SHUK UW.SLF UW.TWISP 
   UW.WOLL XL.MG01 XL.MG10 
 
 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 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 1.02e+22 dyne-cm
  Mw = 3.94 
  Z  = 14 km
  Plane   Strike  Dip  Rake
   NP1      320    50    85
   NP2      148    40    96
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.02e+22     84     195
    N   0.00e+00      4     323
    P  -1.02e+22      5      54

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.48e+21
       Mxy    -4.82e+21
       Mxz    -1.58e+21
       Myy    -6.56e+21
       Myz    -9.88e+20
       Mzz     1.00e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              --#####---------------------           
             --###########----------------           
           ---################------------ P         
          ----##################----------   -       
         -----####################-------------      
        ------######################------------     
        ------#######################-----------     
       -------########################-----------    
       -------#########################----------    
       --------###########   ###########---------    
       ---------########## T ############--------    
        --------##########   #############------     
        ---------#########################------     
         ----------#######################-----      
          ----------######################----       
           -----------####################---        
             -----------##################-          
              --------------#############-           
                 ----------------######              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.00e+22  -1.58e+21   9.88e+20 
 -1.58e+21  -3.48e+21   4.82e+21 
  9.88e+20   4.82e+21  -6.56e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20211021032321/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 = 320
      DIP = 50
     RAKE = 85
       MW = 3.94
       HS = 14.0

The NDK file is 20211021032321.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2021/10/21 03:23:21:0  52.54 -115.29  10.0 4.3 Alberta, Canada
 
 Stations used:
   1E.MONT1 1E.MONT9 CN.EDM CN.FSJB CN.HOPB CN.LLLB CN.PNT 
   CN.VDEB CN.WPB CN.WSLR MB.GBMT MB.JTMT MB.LDM RE.GRCO2 
   RV.BDMTA RV.BELVA RV.BRLDA RV.FOXCA RV.HSPGA RV.PKSKA 
   RV.STPRA RV.SWHSA RV.TONYA RV.WTMTA RV.YELLA TD.TD002 
   TD.TD008 TD.TD009 TD.TD022 US.EGMT US.MSO US.NEW UW.CBS 
   UW.DAVN UW.DY2 UW.EPH2 UW.ETW UW.HOPR UW.NEL UW.OMAK 
   UW.PASS UW.RPW2 UW.RVSD UW.SAW UW.SHUK UW.SLF UW.TWISP 
   UW.WOLL XL.MG01 XL.MG10 
 
 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 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 1.02e+22 dyne-cm
  Mw = 3.94 
  Z  = 14 km
  Plane   Strike  Dip  Rake
   NP1      320    50    85
   NP2      148    40    96
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.02e+22     84     195
    N   0.00e+00      4     323
    P  -1.02e+22      5      54

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.48e+21
       Mxy    -4.82e+21
       Mxz    -1.58e+21
       Myy    -6.56e+21
       Myz    -9.88e+20
       Mzz     1.00e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              --#####---------------------           
             --###########----------------           
           ---################------------ P         
          ----##################----------   -       
         -----####################-------------      
        ------######################------------     
        ------#######################-----------     
       -------########################-----------    
       -------#########################----------    
       --------###########   ###########---------    
       ---------########## T ############--------    
        --------##########   #############------     
        ---------#########################------     
         ----------#######################-----      
          ----------######################----       
           -----------####################---        
             -----------##################-          
              --------------#############-           
                 ----------------######              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.00e+22  -1.58e+21   9.88e+20 
 -1.58e+21  -3.48e+21   4.82e+21 
  9.88e+20   4.82e+21  -6.56e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20211021032321/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/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.08 n 3 
br c 0.12 0.25 n 4 p 2
The results of this grid search from 0.5 to 19 km depth are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0   285    35   -90   3.77 0.4899
WVFGRD96    2.0   285    45   -85   3.80 0.4353
WVFGRD96    3.0   125    80   -75   3.91 0.4605
WVFGRD96    4.0   130    85   -75   3.89 0.4955
WVFGRD96    5.0   125    80   -75   3.87 0.5196
WVFGRD96    6.0   335    20   -60   3.89 0.5361
WVFGRD96    7.0   340    25   -55   3.89 0.5550
WVFGRD96    8.0   320    60    85   3.92 0.5800
WVFGRD96    9.0   320    55    85   3.94 0.6201
WVFGRD96   10.0   320    55    85   3.95 0.6380
WVFGRD96   11.0   320    50    85   3.96 0.6637
WVFGRD96   12.0   320    50    85   3.95 0.6775
WVFGRD96   13.0   320    50    85   3.94 0.6840
WVFGRD96   14.0   320    50    85   3.94 0.6852
WVFGRD96   15.0   320    50    85   3.93 0.6831
WVFGRD96   16.0   320    50    85   3.93 0.6786
WVFGRD96   17.0   145    40    90   3.94 0.6713
WVFGRD96   18.0   145    40    90   3.94 0.6633
WVFGRD96   19.0   145    40    90   3.94 0.6540
WVFGRD96   20.0   320    50    85   3.96 0.6468
WVFGRD96   21.0   145    40    90   3.96 0.6371
WVFGRD96   22.0   145    40    90   3.96 0.6265
WVFGRD96   23.0   325    50    95   3.97 0.6148
WVFGRD96   24.0   325    50    95   3.97 0.6032
WVFGRD96   25.0   325    50    95   3.97 0.5904
WVFGRD96   26.0   325    50    95   3.98 0.5765
WVFGRD96   27.0   135    40    80   3.98 0.5622
WVFGRD96   28.0   130    40    75   3.99 0.5470
WVFGRD96   29.0   130    40    75   3.99 0.5313

The best solution is

WVFGRD96   14.0   320    50    85   3.94 0.6852

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 
br c 0.12 0.25 n 4 p 2
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 CUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
CUS Model with Q from simple gamma values
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
  1.0000  5.0000  2.8900  2.5000 0.172E-02 0.387E-02 0.00  0.00  1.00  1.00 
  9.0000  6.1000  3.5200  2.7300 0.160E-02 0.363E-02 0.00  0.00  1.00  1.00 
 10.0000  6.4000  3.7000  2.8200 0.149E-02 0.336E-02 0.00  0.00  1.00  1.00 
 20.0000  6.7000  3.8700  2.9020 0.000E-04 0.000E-04 0.00  0.00  1.00  1.00 
  0.0000  8.1500  4.7000  3.3640 0.194E-02 0.431E-02 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 Thu Oct 21 18:05:49 CDT 2021