Location

2007/11/03 15:35:32 66.32 -135.43 20.0 4.6 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
 2007/11/03 15:35:32 66.32 -135.43 20.0 4.6 state
 
 Best Fitting Double Couple
    Mo = 9.02e+22 dyne-cm
    Mw = 4.57 
    Z  = 6 km
     Plane   Strike  Dip  Rake
      NP1      333    71   159
      NP2       70    70    20
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   9.02e+22     28     291
     N   0.00e+00     62     113
     P  -9.02e+22      1      22



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx    -6.87e+22
       Mxy    -5.46e+22
       Mxz     1.23e+22
       Myy     4.89e+22
       Myz    -3.53e+22
       Mzz     1.98e+22
                                                     
                                                     
                                                     
                                                     
                     ------------ P                  
                 ###-------------   ---              
              ########--------------------           
             ###########-------------------          
           ###############-------------------        
          #################-------------------       
         ####################------------------      
        ####   ###############-----------------#     
        #### T ################--------------###     
       #####   #################-----------######    
       ##########################--------########    
       ###########################----###########    
       ##########################################    
        ######################-----#############     
        ################------------############     
         ---------------------------###########      
          ---------------------------#########       
           --------------------------########        
             ------------------------######          
              ------------------------####           
                 ---------------------#              
                     --------------                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
  1.98e+22   1.23e+22   3.53e+22 
  1.23e+22  -6.87e+22   5.46e+22 
  3.53e+22   5.46e+22   4.89e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071103153532/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 = 70
      DIP = 70
     RAKE = 20
       MW = 4.57
       HS = 6

The depth control is poor. The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 SLU Moment Tensor Solution
 2007/11/03 15:35:32 66.32 -135.43 20.0 4.6 state
 
 Best Fitting Double Couple
    Mo = 9.02e+22 dyne-cm
    Mw = 4.57 
    Z  = 6 km
     Plane   Strike  Dip  Rake
      NP1      333    71   159
      NP2       70    70    20
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   9.02e+22     28     291
     N   0.00e+00     62     113
     P  -9.02e+22      1      22



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx    -6.87e+22
       Mxy    -5.46e+22
       Mxz     1.23e+22
       Myy     4.89e+22
       Myz    -3.53e+22
       Mzz     1.98e+22
                                                     
                                                     
                                                     
                                                     
                     ------------ P                  
                 ###-------------   ---              
              ########--------------------           
             ###########-------------------          
           ###############-------------------        
          #################-------------------       
         ####################------------------      
        ####   ###############-----------------#     
        #### T ################--------------###     
       #####   #################-----------######    
       ##########################--------########    
       ###########################----###########    
       ##########################################    
        ######################-----#############     
        ################------------############     
         ---------------------------###########      
          ---------------------------#########       
           --------------------------########        
             ------------------------######          
              ------------------------####           
                 ---------------------#              
                     --------------                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
  1.98e+22   1.23e+22   3.53e+22 
  1.23e+22  -6.87e+22   5.46e+22 
  3.53e+22   5.46e+22   4.89e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071103153532/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 0.06 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    0.5    55    60   -40   4.57 0.3619
WVFGRD96    1.0   235    65   -45   4.59 0.3694
WVFGRD96    2.0   225    60   -60   4.64 0.3760
WVFGRD96    3.0    65    75     5   4.48 0.3872
WVFGRD96    4.0    70    70    20   4.53 0.4179
WVFGRD96    5.0    70    70    20   4.55 0.4376
WVFGRD96    6.0    70    70    20   4.57 0.4456
WVFGRD96    7.0    70    70    15   4.57 0.4450
WVFGRD96    8.0    65    75    10   4.56 0.4395
WVFGRD96    9.0    65    75    10   4.57 0.4364
WVFGRD96   10.0    65    75     5   4.57 0.4324
WVFGRD96   11.0    70    75    30   4.61 0.4334
WVFGRD96   12.0    70    80    25   4.61 0.4353
WVFGRD96   13.0    70    80    25   4.61 0.4375
WVFGRD96   14.0    70    80    20   4.62 0.4401
WVFGRD96   15.0    65    85    20   4.61 0.4400
WVFGRD96   16.0    65    80    20   4.61 0.4423
WVFGRD96   17.0    65    80    20   4.62 0.4415
WVFGRD96   18.0    65    80    20   4.62 0.4400
WVFGRD96   19.0    65    80    20   4.63 0.4409
WVFGRD96   20.0    65    80    20   4.64 0.4382
WVFGRD96   21.0    65    80    20   4.65 0.4366
WVFGRD96   22.0    65    80    20   4.65 0.4329
WVFGRD96   23.0    65    85    15   4.66 0.4288
WVFGRD96   24.0    65    80    15   4.66 0.4255
WVFGRD96   25.0    65    80    15   4.66 0.4204
WVFGRD96   26.0    65    85    15   4.67 0.4157
WVFGRD96   27.0   245    90   -15   4.68 0.4069
WVFGRD96   28.0   245    90   -15   4.69 0.4016
WVFGRD96   29.0   245    90   -15   4.69 0.3964

The best solution is

WVFGRD96    6.0    70    70    20   4.57 0.4456

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 0.06 n 3
Figure 3. Waveform comparison for depth of 8 km
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.

Surface-Wave Focal Mechanism

The following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
Location of broadband stations used to obtain focal mechanism from surface-wave spectral amplitudes

The surface-wave determined focal mechanism is shown here.


  NODAL PLANES 

  
  STK=     248.26
  DIP=      85.29
 RAKE=     -20.07
  
             OR
  
  STK=     339.97
  DIP=      70.00
 RAKE=    -174.99
 
 
DEPTH = 5.0 km
 
Mw = 4.56
Best Fit 0.8067 - P-T axis plot gives solutions with FIT greater than FIT90

First motion data

The P-wave first motion data for focal mechanism studies are as follow:

Sta Az(deg)    Dist(km)   First motion
INK        19  236 -12345
DAWY      218  312 -12345
EGAK      240  315 -12345
DOT       238  504 -12345
WHY       177  632 -12345

Surface-wave analysis

Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave radiation pattern search program srfgrd96.

Data preparation

Digital data were collected, instrument response removed and traces converted to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh- and Love-wave spectral amplitudes, respectively. These were input to the search program which examined all depths between 1 and 25 km and all possible mechanisms.
Best mechanism fit as a function of depth. The preferred depth is given above. Lower hemisphere projection

Pressure-tension axis trends. Since the surface-wave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and T-axes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here.


Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled.

Love-wave radiation patterns

Rayleigh-wave radiation patterns

Broadband station distribution

The distribution of broadband stations with azimuth and distance is

Sta Az(deg)    Dist(km)   
INK	   19	  236
DAWY	  218	  312
EGAK	  240	  315
DOT	  238	  504
PAX	  237	  607
WHY	  177	  632
COLD	  286	  657
MCK	  252	  697
BPAW	  258	  767
PNL	  197	  768
TRF	  252	  771
SAW	  237	  803
ROMN	   97	  839
PPLA	  252	  885
RC01	  237	  913
DLBC	  160	  921
CTLN	   94	  923
FIB	  238	  924
SWD	  232	  984
FNBB	  137	 1041
JERN	   81	 1075
COWN	   85	 1109
WRAK	  170	 1115
BMBC	  142	 1344
BBB	  162	 1626
RES	   40	 1724
PHC	  162	 1797
YBKN	   79	 1820
STLN	   67	 1832
BULN	   70	 1858
EDB	  161	 1892
EDM	  130	 1894
CBB	  158	 1903
LLLB	  150	 1910
KUGN	   64	 1927
SLEB	  142	 1947
SHB	  155	 1977
NUNN	   73	 1993
OZB	  159	 2016
WAGN	   70	 2034
JOSN	   79	 2075
ARVN	   86	 2083
SEDN	   79	 2085
PNT	  147	 2100
QILN	   66	 2129
LAIN	   58	 2151
SRLN	   60	 2178
GIFN	   55	 2195
ILON	   57	 2207
FCC	   92	 2237
NEW	  143	 2274
WALA	  137	 2285
HAWA	  149	 2410
ULM	  109	 2850
MUMO	  100	 2883
KASO	   96	 2884
SILO	   92	 2973
PKLO	  101	 2979
EPLO	  108	 2993
ATKO	  106	 3161
LDIO	  104	 3216
NANO	   99	 3228
PNPO	  101	 3413
OTRO	   94	 3481
KAPO	   96	 3505
VLDQ	   93	 3829

Waveform comparison for this mechanism

Since the analysis of the surface-wave radiation patterns uses only spectral amplitudes and because the surfave-wave radiation patterns have a 180 degree symmetry, each surface-wave solution consists of four possible focal mechanisms corresponding to the interchange of the P- and T-axes and a roation of the mechanism by 180 degrees. To select one mechanism, P-wave first motion can be used. This was not possible in this case because all the P-wave first motions were emergent ( a feature of the P-wave wave takeoff angle, the station location and the mechanism). The other way to select among the mechanisms is to compute forward synthetics and compare the observed and predicted waveforms.

The fits to the waveforms with the given mechanism are show below:

This figure shows the fit to the three components of motion (Z - vertical, R-radial and T - transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:

hp c 0.02 n 3
lp c 0.06 n 3

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.

Appendix A


Spectra fit plots to each station

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=Sat Nov 3 14:32:23 CDT 2007

Last Changed 2007/11/03