Location

Location ANSS

2017/12/22 08:00:12 65.495 -134.050 1.7 5.0 Yukon, Canada

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2017/12/22 08:00:12:0  65.50 -134.05   1.7 5.0 Yukon, Canada
 
 Stations used:
   AK.BARN AK.CCB AK.CTG AK.FYU AK.GLB AK.GRNC AK.HDA AK.KIAG 
   AK.LOGN AK.MCAR AK.MDM AK.PAX AK.PPD AK.PTPK AK.RIDG 
   AK.SCRK AK.TABL AK.VRDI AT.MENT AV.WAZA CN.BVCY CN.DAWY 
   CN.HYT CN.INK CN.WHY CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 
   CN.YUK6 CN.YUK7 CN.YUK8 IM.IL31 IU.COLA NY.FARO NY.MAYO 
   NY.TGTN NY.WGLY TA.C36M TA.D27M TA.D28M TA.E25K TA.E27K 
   TA.E28M TA.E29M TA.EPYK TA.F24K TA.F25K TA.F26K TA.F28M 
   TA.F30M TA.F31M TA.G26K TA.G27K TA.G29M TA.G30M TA.G31M 
   TA.H27K TA.H29M TA.H31M TA.HARP TA.I27K TA.I28M TA.I29M 
   TA.I30M TA.J25K TA.J26L TA.J30M TA.K24K TA.K27K TA.K29M 
   TA.L26K TA.L27K TA.L29M TA.M26K TA.M27K TA.M29M TA.M30M 
   TA.M31M TA.N30M TA.N31M TA.O29M TA.O30N TA.P30M TA.P32M 
   TA.P33M US.EGAK 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 4.42e+23 dyne-cm
  Mw = 5.03 
  Z  = 11 km
  Plane   Strike  Dip  Rake
   NP1      138    69   131
   NP2      250    45    30
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.42e+23     49      92
    N   0.00e+00     38     301
    P  -4.42e+23     14     199

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.69e+23
       Mxy    -1.36e+23
       Mxz     9.25e+22
       Myy     1.48e+23
       Myz     2.54e+23
       Mzz     2.21e+23
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             #-----------------------------          
           ####---------------#######--------        
          #####--------####################---       
         #######---###########################-      
        ########################################     
        #######---##############################     
       ######------##############################    
       ####---------#################   #########    
       ###------------############### T #########    
       ###-------------##############   #########    
        #----------------#######################     
        #------------------#####################     
         --------------------##################      
          ---------------------###############       
           -----------------------###########        
             ------------------------######          
              -------   ------------------           
                 ---- P ---------------              
                        -----------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.21e+23   9.25e+22  -2.54e+23 
  9.25e+22  -3.69e+23   1.36e+23 
 -2.54e+23   1.36e+23   1.48e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20171222080012/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 = 250
      DIP = 45
     RAKE = 30
       MW = 5.03
       HS = 11.0

The NDK file is 20171222080012.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSW
 USGS/SLU Moment Tensor Solution
 ENS  2017/12/22 08:00:12:0  65.50 -134.05   1.7 5.0 Yukon, Canada
 
 Stations used:
   AK.BARN AK.CCB AK.CTG AK.FYU AK.GLB AK.GRNC AK.HDA AK.KIAG 
   AK.LOGN AK.MCAR AK.MDM AK.PAX AK.PPD AK.PTPK AK.RIDG 
   AK.SCRK AK.TABL AK.VRDI AT.MENT AV.WAZA CN.BVCY CN.DAWY 
   CN.HYT CN.INK CN.WHY CN.YUK2 CN.YUK3 CN.YUK4 CN.YUK5 
   CN.YUK6 CN.YUK7 CN.YUK8 IM.IL31 IU.COLA NY.FARO NY.MAYO 
   NY.TGTN NY.WGLY TA.C36M TA.D27M TA.D28M TA.E25K TA.E27K 
   TA.E28M TA.E29M TA.EPYK TA.F24K TA.F25K TA.F26K TA.F28M 
   TA.F30M TA.F31M TA.G26K TA.G27K TA.G29M TA.G30M TA.G31M 
   TA.H27K TA.H29M TA.H31M TA.HARP TA.I27K TA.I28M TA.I29M 
   TA.I30M TA.J25K TA.J26L TA.J30M TA.K24K TA.K27K TA.K29M 
   TA.L26K TA.L27K TA.L29M TA.M26K TA.M27K TA.M29M TA.M30M 
   TA.M31M TA.N30M TA.N31M TA.O29M TA.O30N TA.P30M TA.P32M 
   TA.P33M US.EGAK 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 4.42e+23 dyne-cm
  Mw = 5.03 
  Z  = 11 km
  Plane   Strike  Dip  Rake
   NP1      138    69   131
   NP2      250    45    30
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.42e+23     49      92
    N   0.00e+00     38     301
    P  -4.42e+23     14     199

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.69e+23
       Mxy    -1.36e+23
       Mxz     9.25e+22
       Myy     1.48e+23
       Myz     2.54e+23
       Mzz     2.21e+23
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             #-----------------------------          
           ####---------------#######--------        
          #####--------####################---       
         #######---###########################-      
        ########################################     
        #######---##############################     
       ######------##############################    
       ####---------#################   #########    
       ###------------############### T #########    
       ###-------------##############   #########    
        #----------------#######################     
        #------------------#####################     
         --------------------##################      
          ---------------------###############       
           -----------------------###########        
             ------------------------######          
              -------   ------------------           
                 ---- P ---------------              
                        -----------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  2.21e+23   9.25e+22  -2.54e+23 
  9.25e+22  -3.69e+23   1.36e+23 
 -2.54e+23   1.36e+23   1.48e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20171222080012/index.html
	
W-phase Moment Tensor (Mww)
Moment	3.882e+16 N-m
Magnitude	5.0 Mww
Depth	11.5 km
Percent DC	10 %
Half Duration	0.81 s
Catalog	US
Data Source	US2
Contributor	US2
Nodal Planes
Plane	Strike	Dip	Rake
NP1	248	59	34
NP2	140	62	145
Principal Axes
Axis	Value	Plunge	Azimuth
T	2.468e+16 N-m	44	103
N	2.006e+16 N-m	46	286
P	-4.474e+16 N-m	1	194


        

Magnitudes

mLg Magnitude


(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

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 +70
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    40    35   -20   4.98 0.4181
WVFGRD96    2.0   225    30   -15   5.01 0.4438
WVFGRD96    3.0   230    35   -10   4.98 0.4716
WVFGRD96    4.0   235    35     0   4.97 0.4991
WVFGRD96    5.0   235    40     0   4.96 0.5221
WVFGRD96    6.0   235    40     0   4.97 0.5409
WVFGRD96    7.0   240    40    15   4.98 0.5545
WVFGRD96    8.0   250    45    30   4.99 0.5642
WVFGRD96    9.0   250    45    35   5.00 0.5734
WVFGRD96   10.0   250    45    35   5.03 0.5783
WVFGRD96   11.0   250    45    30   5.03 0.5792
WVFGRD96   12.0   250    45    30   5.04 0.5757
WVFGRD96   13.0   250    45    30   5.05 0.5688
WVFGRD96   14.0   245    50    25   5.05 0.5596
WVFGRD96   15.0   245    50    25   5.06 0.5492
WVFGRD96   16.0   245    50    25   5.07 0.5366
WVFGRD96   17.0   245    50    25   5.07 0.5225
WVFGRD96   18.0   245    50    25   5.08 0.5082
WVFGRD96   19.0   245    50    25   5.09 0.4936
WVFGRD96   20.0   245    45    25   5.11 0.4811
WVFGRD96   21.0   245    45    25   5.11 0.4660
WVFGRD96   22.0   245    45    25   5.12 0.4497
WVFGRD96   23.0   245    45    25   5.12 0.4338
WVFGRD96   24.0   240    45    20   5.12 0.4169
WVFGRD96   25.0   240    45    20   5.13 0.4007
WVFGRD96   26.0   230    50   -20   5.12 0.3838
WVFGRD96   27.0   230    50   -20   5.13 0.3707
WVFGRD96   28.0   230    55   -20   5.13 0.3574
WVFGRD96   29.0   230    55   -20   5.13 0.3457

The best solution is

WVFGRD96   11.0   250    45    30   5.03 0.5792

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 +70
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 Fri Dec 22 12:49:40 CST 2017