Location

2009/01/02 14:17:13 58.5260 -152.2540 60.0 5.20 Alaska

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2009/01/02 14:17:13:0  58.53 -152.25  60.0 5.2 Alaska
 
 Stations used:
   AK.CAST AK.PPLA AK.RAG AK.SWD AT.OHAK AT.PMR II.KDAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.05 n 3
 
 Best Fitting Double Couple
  Mo = 7.41e+23 dyne-cm
  Mw = 5.18 
  Z  = 62 km
  Plane   Strike  Dip  Rake
   NP1      235    80    35
   NP2      138    56   168
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.41e+23     31     102
    N   0.00e+00     54     249
    P  -7.41e+23     16       2

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -6.60e+23
       Mxy    -1.36e+23
       Mxz    -2.67e+23
       Myy     5.14e+23
       Myz     3.16e+23
       Mzz     1.45e+23
                                                     
                                                     
                                                     
                                                     
                     ------   -----                  
                 ---------- P ---------              
              -------------   ------------           
             #-----------------------------          
           ###-------------------------------        
          ####--------------------------######       
         #####-----------------------##########      
        #######------------------###############     
        #######---------------##################     
       #########------------#####################    
       ##########--------########################    
       ###########----##################   ######    
       ############-#################### T ######    
        ##########---###################   #####     
        ########------##########################     
         #####----------#######################      
          ##--------------####################       
           ------------------################        
             --------------------##########          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          F
  1.45e+23  -2.67e+23  -3.16e+23 
 -2.67e+23  -6.60e+23   1.36e+23 
 -3.16e+23   1.36e+23   5.14e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090102141713/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 = 235
      DIP = 80
     RAKE = 35
       MW = 5.18
       HS = 62.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2009/01/02 14:17:13:0  58.53 -152.25  60.0 5.2 Alaska
 
 Stations used:
   AK.CAST AK.PPLA AK.RAG AK.SWD AT.OHAK AT.PMR II.KDAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.05 n 3
 
 Best Fitting Double Couple
  Mo = 7.41e+23 dyne-cm
  Mw = 5.18 
  Z  = 62 km
  Plane   Strike  Dip  Rake
   NP1      235    80    35
   NP2      138    56   168
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.41e+23     31     102
    N   0.00e+00     54     249
    P  -7.41e+23     16       2

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -6.60e+23
       Mxy    -1.36e+23
       Mxz    -2.67e+23
       Myy     5.14e+23
       Myz     3.16e+23
       Mzz     1.45e+23
                                                     
                                                     
                                                     
                                                     
                     ------   -----                  
                 ---------- P ---------              
              -------------   ------------           
             #-----------------------------          
           ###-------------------------------        
          ####--------------------------######       
         #####-----------------------##########      
        #######------------------###############     
        #######---------------##################     
       #########------------#####################    
       ##########--------########################    
       ###########----##################   ######    
       ############-#################### T ######    
        ##########---###################   #####     
        ########------##########################     
         #####----------#######################      
          ##--------------####################       
           ------------------################        
             --------------------##########          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          F
  1.45e+23  -2.67e+23  -3.16e+23 
 -2.67e+23  -6.60e+23   1.36e+23 
 -3.16e+23   1.36e+23   5.14e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090102141713/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 0.05 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    40    50   -70   4.64 0.2158
WVFGRD96    1.0    35    45   -85   4.58 0.2043
WVFGRD96    2.0    35    45   -80   4.74 0.3029
WVFGRD96    3.0   205    45   -95   4.76 0.2949
WVFGRD96    4.0   255    90    20   4.57 0.2925
WVFGRD96    5.0   255    90    20   4.60 0.3138
WVFGRD96    6.0    75    90   -15   4.63 0.3313
WVFGRD96    7.0    75    90   -15   4.65 0.3485
WVFGRD96    8.0    75    90   -20   4.69 0.3698
WVFGRD96    9.0    75    90   -15   4.71 0.3874
WVFGRD96   10.0    75    90   -15   4.72 0.4008
WVFGRD96   11.0    75    90   -15   4.73 0.4110
WVFGRD96   12.0    75    85   -10   4.74 0.4192
WVFGRD96   13.0    75    85   -10   4.75 0.4253
WVFGRD96   14.0    75    85   -15   4.74 0.4306
WVFGRD96   15.0    75    80   -10   4.75 0.4345
WVFGRD96   16.0    75    80   -10   4.76 0.4384
WVFGRD96   17.0    75    70   -35   4.71 0.4379
WVFGRD96   18.0    75    70   -35   4.72 0.4507
WVFGRD96   19.0    75    70   -35   4.73 0.4630
WVFGRD96   20.0    75    70   -35   4.74 0.4738
WVFGRD96   21.0    30    70   -50   4.81 0.4847
WVFGRD96   22.0    30    70   -50   4.82 0.5012
WVFGRD96   23.0    30    70   -50   4.83 0.5171
WVFGRD96   24.0    30    75   -55   4.87 0.5325
WVFGRD96   25.0    30    75   -55   4.88 0.5472
WVFGRD96   26.0    30    70   -50   4.86 0.5610
WVFGRD96   27.0    30    75   -55   4.89 0.5744
WVFGRD96   28.0    30    75   -55   4.90 0.5867
WVFGRD96   29.0    35    75   -50   4.89 0.5988
WVFGRD96   30.0    35    75   -50   4.90 0.6107
WVFGRD96   31.0    35    75   -50   4.90 0.6219
WVFGRD96   32.0    35    75   -50   4.91 0.6325
WVFGRD96   33.0    35    75   -50   4.92 0.6422
WVFGRD96   34.0    35    75   -50   4.93 0.6516
WVFGRD96   35.0    35    75   -45   4.92 0.6604
WVFGRD96   36.0    35    75   -45   4.93 0.6687
WVFGRD96   37.0    35    75   -45   4.94 0.6763
WVFGRD96   38.0    35    75   -45   4.94 0.6832
WVFGRD96   39.0    35    75   -45   4.95 0.6888
WVFGRD96   40.0    35    75   -60   5.08 0.6919
WVFGRD96   41.0    35    75   -55   5.07 0.6984
WVFGRD96   42.0    35    75   -55   5.08 0.7053
WVFGRD96   43.0    35    75   -55   5.09 0.7117
WVFGRD96   44.0   235    70    40   5.07 0.7172
WVFGRD96   45.0   235    70    40   5.07 0.7294
WVFGRD96   46.0   235    70    40   5.08 0.7408
WVFGRD96   47.0   235    75    35   5.09 0.7518
WVFGRD96   48.0   235    75    35   5.10 0.7626
WVFGRD96   49.0   235    75    35   5.11 0.7727
WVFGRD96   50.0   235    75    35   5.12 0.7814
WVFGRD96   51.0   235    75    35   5.12 0.7889
WVFGRD96   52.0   235    75    35   5.13 0.7963
WVFGRD96   53.0   235    75    40   5.13 0.8026
WVFGRD96   54.0   235    75    40   5.14 0.8075
WVFGRD96   55.0   235    75    40   5.14 0.8124
WVFGRD96   56.0   235    75    40   5.15 0.8158
WVFGRD96   57.0   235    75    40   5.15 0.8184
WVFGRD96   58.0   235    80    35   5.16 0.8220
WVFGRD96   59.0   235    80    35   5.17 0.8251
WVFGRD96   60.0   235    80    35   5.17 0.8280
WVFGRD96   61.0   235    80    35   5.18 0.8293
WVFGRD96   62.0   235    80    35   5.18 0.8303
WVFGRD96   63.0   235    80    35   5.19 0.8302
WVFGRD96   64.0   235    80    40   5.18 0.8301
WVFGRD96   65.0   235    80    40   5.19 0.8288
WVFGRD96   66.0   235    80    40   5.19 0.8274
WVFGRD96   67.0   235    85    35   5.20 0.8260
WVFGRD96   68.0   235    85    35   5.20 0.8250
WVFGRD96   69.0   235    85    35   5.21 0.8249

The best solution is

WVFGRD96   62.0   235    80    35   5.18 0.8303

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 0.05 n 3
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 WUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
Model after     8 iterations
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
     1.9000     3.4065     2.0089     2.2150  0.302E-02  0.679E-02   0.00       0.00       1.00       1.00    
     6.1000     5.5445     3.2953     2.6089  0.349E-02  0.784E-02   0.00       0.00       1.00       1.00    
    13.0000     6.2708     3.7396     2.7812  0.212E-02  0.476E-02   0.00       0.00       1.00       1.00    
    19.0000     6.4075     3.7680     2.8223  0.111E-02  0.249E-02   0.00       0.00       1.00       1.00    
     0.0000     7.9000     4.6200     3.2760  0.164E-10  0.370E-10   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=Tue Jan 6 10:50:48 MST 2009

Last Changed 2009/01/02