Location

Location ANSS

2017/05/10 15:14:26 65.001 -134.132 22.4 4.9 Yukon, Canada

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2017/05/10 15:14:26:0  65.00 -134.13  22.4 4.9 Yukon, Canada
 
 Stations used:
   AK.BAL AK.BARN AK.BCP AK.CCB AK.CTG AK.DOT AK.FYU AK.GLB 
   AK.HDA AK.KIAG AK.LOGN AK.MCAR AK.MDM AK.PAX AK.PIN AK.PNL 
   AK.PPD AK.PTPK AK.RIDG AK.SAMH AK.SCRK AK.VRDI AK.WRH 
   AT.MENT AT.SKAG CN.DAWY CN.HYT CN.INK CN.PLBC CN.YUK2 
   CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 CN.YUK8 IM.IL31 
   IU.COLA NY.MAYO NY.MMPY NY.WGLY TA.C36M TA.E27K TA.EPYK 
   TA.F31M TA.G24K TA.G26K TA.G27K TA.G30M TA.H24K TA.H25L 
   TA.H27K TA.HARP TA.I27K TA.I29M TA.J25K TA.J26L TA.J29M 
   TA.K24K TA.K29M TA.L26K TA.L27K TA.L29M TA.M26K TA.M27K 
   TA.M29M TA.M30M TA.M31M TA.N25K TA.N30M TA.N31M TA.O28M 
   TA.O29M TA.O30N TA.P29M TA.P30M TA.P32M TA.P33M TA.POKR 
   TA.R33M US.EGAK 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +60
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 4.52e+22 dyne-cm
  Mw = 4.37 
  Z  = 12 km
  Plane   Strike  Dip  Rake
   NP1      275    65    70
   NP2      136    32   126
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.52e+22     64     151
    N   0.00e+00     18     284
    P  -4.52e+22     18      20

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.98e+22
       Mxy    -1.66e+22
       Mxz    -2.78e+22
       Myy    -2.68e+21
       Myz     4.13e+21
       Mzz     3.25e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------------   ----              
              ------------------ P -------           
             -------------------   --------          
           #---------------------------------        
          ##----------------------------------       
         ##------------------------------------      
        ###------------###----------------------     
        ###--#########################----------     
       ##--###############################-------    
       -----##################################---    
       -----####################################-    
       ------####################################    
        ------################   ###############     
        -------############### T ###############     
         -------##############   ##############      
          --------############################       
           ---------#########################        
             ----------####################          
              -------------##############-           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  3.25e+22  -2.78e+22  -4.13e+21 
 -2.78e+22  -2.98e+22   1.66e+22 
 -4.13e+21   1.66e+22  -2.68e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170510151426/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 = 275
      DIP = 65
     RAKE = 70
       MW = 4.37
       HS = 12.0

The NDK file is 20170510151426.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  2017/05/10 15:14:26:0  65.00 -134.13  22.4 4.9 Yukon, Canada
 
 Stations used:
   AK.BAL AK.BARN AK.BCP AK.CCB AK.CTG AK.DOT AK.FYU AK.GLB 
   AK.HDA AK.KIAG AK.LOGN AK.MCAR AK.MDM AK.PAX AK.PIN AK.PNL 
   AK.PPD AK.PTPK AK.RIDG AK.SAMH AK.SCRK AK.VRDI AK.WRH 
   AT.MENT AT.SKAG CN.DAWY CN.HYT CN.INK CN.PLBC CN.YUK2 
   CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 CN.YUK8 IM.IL31 
   IU.COLA NY.MAYO NY.MMPY NY.WGLY TA.C36M TA.E27K TA.EPYK 
   TA.F31M TA.G24K TA.G26K TA.G27K TA.G30M TA.H24K TA.H25L 
   TA.H27K TA.HARP TA.I27K TA.I29M TA.J25K TA.J26L TA.J29M 
   TA.K24K TA.K29M TA.L26K TA.L27K TA.L29M TA.M26K TA.M27K 
   TA.M29M TA.M30M TA.M31M TA.N25K TA.N30M TA.N31M TA.O28M 
   TA.O29M TA.O30N TA.P29M TA.P30M TA.P32M TA.P33M TA.POKR 
   TA.R33M US.EGAK 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +60
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 4.52e+22 dyne-cm
  Mw = 4.37 
  Z  = 12 km
  Plane   Strike  Dip  Rake
   NP1      275    65    70
   NP2      136    32   126
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.52e+22     64     151
    N   0.00e+00     18     284
    P  -4.52e+22     18      20

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.98e+22
       Mxy    -1.66e+22
       Mxz    -2.78e+22
       Myy    -2.68e+21
       Myz     4.13e+21
       Mzz     3.25e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------------   ----              
              ------------------ P -------           
             -------------------   --------          
           #---------------------------------        
          ##----------------------------------       
         ##------------------------------------      
        ###------------###----------------------     
        ###--#########################----------     
       ##--###############################-------    
       -----##################################---    
       -----####################################-    
       ------####################################    
        ------################   ###############     
        -------############### T ###############     
         -------##############   ##############      
          --------############################       
           ---------#########################        
             ----------####################          
              -------------##############-           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  3.25e+22  -2.78e+22  -4.13e+21 
 -2.78e+22  -2.98e+22   1.66e+22 
 -4.13e+21   1.66e+22  -2.68e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170510151426/index.html
	
Regional Moment Tensor (Mwr)
Moment	4.222e+15 N-m
Magnitude	4.4 Mwr
Depth	16.0 km
Percent DC	87 %
Half Duration	–
Catalog	AK
Data Source	US2
Contributor	US2
Nodal Planes
Plane	Strike	Dip	Rake
NP1	256	58	37
NP2	144	60	142
Principal Axes
Axis	Value	Plunge	Azimuth
T	4.074e+15 N-m	47	109
N	0.284e+15 N-m	43	291
P	-4.357e+15 N-m	1	200

        

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 -30 o DIST/3.3 +60
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    1.0   115    55    95   4.24 0.5534
WVFGRD96    2.0   110    60    90   4.34 0.5349
WVFGRD96    3.0    60    45   -20   4.28 0.5191
WVFGRD96    4.0    60    45   -20   4.28 0.5475
WVFGRD96    5.0    55    45   -25   4.29 0.5761
WVFGRD96    6.0    55    50   -30   4.30 0.6054
WVFGRD96    7.0    55    55   -35   4.32 0.6303
WVFGRD96    8.0    55    55   -35   4.32 0.6502
WVFGRD96    9.0    55    55   -35   4.33 0.6649
WVFGRD96   10.0   275    65    70   4.36 0.6654
WVFGRD96   11.0    55    55   -35   4.37 0.6709
WVFGRD96   12.0   275    65    70   4.37 0.6720
WVFGRD96   13.0   270    65    65   4.38 0.6699
WVFGRD96   14.0   270    70    60   4.38 0.6660
WVFGRD96   15.0   270    70    60   4.39 0.6588
WVFGRD96   16.0   265    70    55   4.41 0.6498
WVFGRD96   17.0   265    70    55   4.41 0.6387
WVFGRD96   18.0   265    70    55   4.42 0.6249
WVFGRD96   19.0   265    70    55   4.43 0.6098
WVFGRD96   20.0   265    70    60   4.46 0.5962
WVFGRD96   21.0   265    70    55   4.47 0.5783
WVFGRD96   22.0   265    70    55   4.47 0.5596
WVFGRD96   23.0   265    70    55   4.48 0.5401
WVFGRD96   24.0   260    75    55   4.48 0.5202
WVFGRD96   25.0   260    75    55   4.49 0.5001
WVFGRD96   26.0   260    75    55   4.50 0.4799
WVFGRD96   27.0   260    75    55   4.50 0.4600
WVFGRD96   28.0   260    75    55   4.50 0.4403
WVFGRD96   29.0   260    75    55   4.51 0.4209

The best solution is

WVFGRD96   12.0   275    65    70   4.37 0.6720

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 -30 o DIST/3.3 +60
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 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 Wed May 17 08:34:34 CDT 2017