Location

2008/12/03 02:47:30 60.91 -138.11 5.0 4.30 Yukon, Canada

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for

Focal Mechanism

 SLU Moment Tensor Solution
 2008/12/03 02:47:30  60.91  -138.11  5.0  4.30 Yukon, Canada
 
 Best Fitting Double Couple
    Mo = 2.11e+22 dyne-cm
    Mw = 4.15 
    Z  = 6 km
     Plane   Strike  Dip  Rake
      NP1      125    60   109
      NP2      270    35    60
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   2.11e+22     69      75
     N   0.00e+00     17     295
     P  -2.11e+22     13     201



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx    -1.72e+22
       Mxy    -6.06e+21
       Mxz     6.26e+21
       Myy     4.43e+14
       Myz     8.66e+21
       Mzz     1.72e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             ------------------------------          
           --------##################--------        
          #-----########################------       
         ###-##############################----      
        ###--################################---     
        ##----################################--     
       #-------#################   #############-    
       #--------################ T #############-    
       -----------##############   ##############    
       ------------##############################    
        --------------##########################     
        ----------------########################     
         ------------------####################      
          ---------------------###############       
           --------------------------########        
             ------------------------------          
              ------   -------------------           
                 --- P ----------------              
                       ------------                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
  1.72e+22   6.26e+21  -8.66e+21 
  6.26e+21  -1.72e+22   6.06e+21 
 -8.66e+21   6.06e+21   4.43e+14 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081203024730/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 = 270
      DIP = 35
     RAKE = 60
       MW = 4.15
       HS = 6.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 SLU Moment Tensor Solution
 2008/12/03 02:47:30  60.91  -138.11  5.0  4.30 Yukon, Canada
 
 Best Fitting Double Couple
    Mo = 2.11e+22 dyne-cm
    Mw = 4.15 
    Z  = 6 km
     Plane   Strike  Dip  Rake
      NP1      125    60   109
      NP2      270    35    60
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   2.11e+22     69      75
     N   0.00e+00     17     295
     P  -2.11e+22     13     201



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx    -1.72e+22
       Mxy    -6.06e+21
       Mxz     6.26e+21
       Myy     4.43e+14
       Myz     8.66e+21
       Mzz     1.72e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             ------------------------------          
           --------##################--------        
          #-----########################------       
         ###-##############################----      
        ###--################################---     
        ##----################################--     
       #-------#################   #############-    
       #--------################ T #############-    
       -----------##############   ##############    
       ------------##############################    
        --------------##########################     
        ----------------########################     
         ------------------####################      
          ---------------------###############       
           --------------------------########        
             ------------------------------          
              ------   -------------------           
                 --- P ----------------              
                       ------------                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
  1.72e+22   6.26e+21  -8.66e+21 
  6.26e+21  -1.72e+22   6.06e+21 
 -8.66e+21   6.06e+21   4.43e+14 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081203024730/index.html
	

Waveform Inversion

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:

hp c 0.02 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    0.5   250    65    30   3.99 0.5117
WVFGRD96    1.0   245    70    30   3.98 0.5143
WVFGRD96    2.0   260    35    30   4.12 0.5355
WVFGRD96    3.0   260    45    35   4.08 0.5534
WVFGRD96    4.0   265    40    45   4.11 0.5663
WVFGRD96    5.0   270    35    55   4.15 0.5854
WVFGRD96    6.0   270    35    60   4.15 0.5960
WVFGRD96    7.0   260    40    50   4.11 0.5957
WVFGRD96    8.0   255    40    45   4.10 0.5914
WVFGRD96    9.0   245    45    35   4.08 0.5840
WVFGRD96   10.0   245    45    35   4.10 0.5844
WVFGRD96   11.0   245    45    30   4.09 0.5776
WVFGRD96   12.0   240    50    25   4.09 0.5708
WVFGRD96   13.0   240    50    20   4.09 0.5640
WVFGRD96   14.0   240    50    20   4.10 0.5586
WVFGRD96   15.0   240    50    20   4.10 0.5517
WVFGRD96   16.0   240    50    20   4.11 0.5434
WVFGRD96   17.0   235    55    15   4.12 0.5358
WVFGRD96   18.0   235    55    15   4.12 0.5266
WVFGRD96   19.0   235    55    15   4.13 0.5178
WVFGRD96   20.0   240    50    15   4.15 0.5081
WVFGRD96   21.0   240    50    15   4.16 0.4966
WVFGRD96   22.0   240    50    15   4.17 0.4855
WVFGRD96   23.0   240    50    15   4.18 0.4733
WVFGRD96   24.0   240    45    15   4.19 0.4607
WVFGRD96   25.0   240    45    15   4.20 0.4476
WVFGRD96   26.0   240    40    10   4.21 0.4355
WVFGRD96   27.0   240    35    10   4.22 0.4234
WVFGRD96   28.0   240    35    10   4.22 0.4122
WVFGRD96   29.0   240    30    10   4.23 0.4008
WVFGRD96   30.0   235    30     5   4.24 0.3898
WVFGRD96   31.0   235    30     5   4.25 0.3785
WVFGRD96   32.0   235    30     5   4.25 0.3670
WVFGRD96   33.0   235    30     5   4.26 0.3552
WVFGRD96   34.0   235    30     5   4.26 0.3440
WVFGRD96   35.0   235    30     5   4.27 0.3324
WVFGRD96   36.0   245    40     0   4.25 0.3220
WVFGRD96   37.0   245    40     0   4.25 0.3131
WVFGRD96   38.0   245    40     0   4.26 0.3057
WVFGRD96   39.0   245    45    -5   4.27 0.3000

The best solution is

WVFGRD96    6.0   270    35    60   4.15 0.5960

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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was

hp c 0.02 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
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.

Discussion

The Future

Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.

Acknowledgements

Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The CUS 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:

DATE=Wed Dec 3 06:07:52 CST 2008

Last Changed 2008/12/03