Location

2009/06/07 23:24:39 58.9670 -136.7190 37.0 5.00 Alaska

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports main page

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2009/06/07 23:24:39:0  58.97 -136.72  37.0 5.0 Alaska
 
 Stations used:
   AK.BESE AK.DIV AK.EYAK AK.PNL AT.CRAG AT.MID AT.SKAG 
   CN.DAWY CN.DLBC CN.FNBB CN.MOBC CN.RUBB CN.WHY US.WRAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.05 n 3
 
 Best Fitting Double Couple
  Mo = 1.68e+23 dyne-cm
  Mw = 4.75 
  Z  = 15 km
  Plane   Strike  Dip  Rake
   NP1       32    57   130
   NP2      155    50    45
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.68e+23     57     359
    N   0.00e+00     33     188
    P  -1.68e+23      4      95

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     4.88e+22
       Mxy     1.37e+22
       Mxz     7.79e+22
       Myy    -1.66e+23
       Myz    -1.36e+22
       Mzz     1.17e+23
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 -#####################              
              ----######################--           
             ----#######################---          
           -----########################-----        
          ------##########   ###########------       
         -------########## T ###########-------      
        --------##########   ###########--------     
        --------#######################---------     
       ----------######################----------    
       ----------#####################-----------    
       -----------###################---------       
       -----------##################---------- P     
        -----------################-----------       
        ------------##############--------------     
         ------------###########---------------      
          -------------########---------------       
           -------------#####----------------        
             ------------------------------          
              ---------#####--------------           
                 ###############-------              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.17e+23   7.79e+22   1.36e+22 
  7.79e+22   4.88e+22  -1.37e+22 
  1.36e+22  -1.37e+22  -1.66e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090607232439/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 = 155
      DIP = 50
     RAKE = 45
       MW = 4.75
       HS = 15.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2009/06/07 23:24:39:0  58.97 -136.72  37.0 5.0 Alaska
 
 Stations used:
   AK.BESE AK.DIV AK.EYAK AK.PNL AT.CRAG AT.MID AT.SKAG 
   CN.DAWY CN.DLBC CN.FNBB CN.MOBC CN.RUBB CN.WHY US.WRAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.05 n 3
 
 Best Fitting Double Couple
  Mo = 1.68e+23 dyne-cm
  Mw = 4.75 
  Z  = 15 km
  Plane   Strike  Dip  Rake
   NP1       32    57   130
   NP2      155    50    45
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.68e+23     57     359
    N   0.00e+00     33     188
    P  -1.68e+23      4      95

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     4.88e+22
       Mxy     1.37e+22
       Mxz     7.79e+22
       Myy    -1.66e+23
       Myz    -1.36e+22
       Mzz     1.17e+23
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 -#####################              
              ----######################--           
             ----#######################---          
           -----########################-----        
          ------##########   ###########------       
         -------########## T ###########-------      
        --------##########   ###########--------     
        --------#######################---------     
       ----------######################----------    
       ----------#####################-----------    
       -----------###################---------       
       -----------##################---------- P     
        -----------################-----------       
        ------------##############--------------     
         ------------###########---------------      
          -------------########---------------       
           -------------#####----------------        
             ------------------------------          
              ---------#####--------------           
                 ###############-------              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.17e+23   7.79e+22   1.36e+22 
  7.79e+22   4.88e+22  -1.37e+22 
  1.36e+22  -1.37e+22  -1.66e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090607232439/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   270    45   -85   4.45 0.3224
WVFGRD96    1.0   170    90     5   4.38 0.3136
WVFGRD96    2.0   330    70   -30   4.48 0.3710
WVFGRD96    3.0   155    90    45   4.55 0.3942
WVFGRD96    4.0   320    80   -50   4.59 0.4340
WVFGRD96    5.0   320    80   -50   4.60 0.4676
WVFGRD96    6.0   320    80   -45   4.60 0.4917
WVFGRD96    7.0   320    80   -40   4.61 0.5108
WVFGRD96    8.0   320    80   -45   4.65 0.5250
WVFGRD96    9.0   315    75   -45   4.66 0.5342
WVFGRD96   10.0   160    45    50   4.73 0.5619
WVFGRD96   11.0   165    45    55   4.74 0.6043
WVFGRD96   12.0   165    45    55   4.75 0.6334
WVFGRD96   13.0   165    45    55   4.76 0.6493
WVFGRD96   14.0   165    45    55   4.76 0.6577
WVFGRD96   15.0   155    50    45   4.75 0.6593
WVFGRD96   16.0   155    50    45   4.75 0.6585
WVFGRD96   17.0   155    50    45   4.75 0.6529
WVFGRD96   18.0   155    50    40   4.76 0.6467
WVFGRD96   19.0   150    55    35   4.76 0.6403
WVFGRD96   20.0   150    55    35   4.76 0.6321
WVFGRD96   21.0   150    55    35   4.77 0.6256
WVFGRD96   22.0   150    55    30   4.77 0.6166
WVFGRD96   23.0   150    55    30   4.78 0.6062
WVFGRD96   24.0   150    55    30   4.78 0.5961
WVFGRD96   25.0   145    60    25   4.78 0.5851
WVFGRD96   26.0   320    75    25   4.79 0.5733
WVFGRD96   27.0   320    75    25   4.79 0.5667
WVFGRD96   28.0   320    75    25   4.80 0.5599
WVFGRD96   29.0   320    75    25   4.81 0.5525
WVFGRD96   30.0   320    75    25   4.81 0.5445
WVFGRD96   31.0   320    75    25   4.82 0.5363
WVFGRD96   32.0   150    75   -15   4.82 0.5271
WVFGRD96   33.0   150    75   -15   4.83 0.5197
WVFGRD96   34.0   150    75   -15   4.84 0.5128
WVFGRD96   35.0   150    75   -15   4.84 0.5056
WVFGRD96   36.0   150    80   -15   4.85 0.4980
WVFGRD96   37.0   150    80   -15   4.86 0.4908
WVFGRD96   38.0   150    80   -15   4.87 0.4834
WVFGRD96   39.0   150    80   -15   4.88 0.4752
WVFGRD96   40.0   115    50   -50   4.98 0.4886
WVFGRD96   41.0   115    55   -50   4.98 0.4832
WVFGRD96   42.0   115    55   -50   4.98 0.4777
WVFGRD96   43.0   115    55   -50   4.99 0.4724
WVFGRD96   44.0   115    55   -50   4.99 0.4669
WVFGRD96   45.0   115    55   -50   5.00 0.4613
WVFGRD96   46.0   115    55   -50   5.01 0.4557
WVFGRD96   47.0   155    70    25   4.98 0.4519
WVFGRD96   48.0   155    70    25   4.99 0.4491
WVFGRD96   49.0   155    70    25   4.99 0.4458

The best solution is

WVFGRD96   15.0   155    50    45   4.75 0.6593

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=Sun Jun 7 21:10:29 CDT 2009

Last Changed 2009/06/07