Location

2009/06/22 19:28:05 61.9440 -150.5190 50.0 5.70 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  2009/06/22 19:28:05:0  61.94 -150.52  50.0 5.7 Alaska
 
 Stations used:
   AK.BRLK AK.CAST AK.CHUM AK.COLD AK.DIV AK.DOT AK.EYAK 
   AK.MCK AK.MDM AK.PAX AK.SAW AK.TRF AT.MID AT.OHAK AT.SVW2 
   US.EGAK 
 
 Filtering commands used:
   hp c 0.015 n 3
   lp c 0.04 n 3
 
 Best Fitting Double Couple
  Mo = 1.29e+24 dyne-cm
  Mw = 5.34 
  Z  = 63 km
  Plane   Strike  Dip  Rake
   NP1      141    58   -138
   NP2       25    55   -40
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.29e+24      2     262
    N   0.00e+00     39     171
    P  -1.29e+24     51     355

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.80e+23
       Mxy     2.22e+23
       Mxz    -6.33e+23
       Myy     1.26e+24
       Myz     1.75e+22
       Mzz    -7.78e+23
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 --------------------##              
              #-----------------------####           
             ##------------------------####          
           ####-----------   ----------######        
          #####----------- P ----------#######       
         ######-----------   ----------########      
        #######------------------------#########     
        ########-----------------------#########     
       ##########---------------------###########    
       ###########--------------------###########    
         ##########------------------############    
       T ###########----------------#############    
         ############---------------############     
        ###############------------#############     
         ################--------##############      
          #################-----##############       
           ##################--##############        
             ################---###########          
              ############------------####           
                 ######----------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -7.78e+23  -6.33e+23  -1.75e+22 
 -6.33e+23  -4.80e+23  -2.22e+23 
 -1.75e+22  -2.22e+23   1.26e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090622192805/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 = 25
      DIP = 55
     RAKE = -40
       MW = 5.34
       HS = 63.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
USGSCMT
AEIC
 USGS/SLU Moment Tensor Solution
 ENS  2009/06/22 19:28:05:0  61.94 -150.52  50.0 5.7 Alaska
 
 Stations used:
   AK.BRLK AK.CAST AK.CHUM AK.COLD AK.DIV AK.DOT AK.EYAK 
   AK.MCK AK.MDM AK.PAX AK.SAW AK.TRF AT.MID AT.OHAK AT.SVW2 
   US.EGAK 
 
 Filtering commands used:
   hp c 0.015 n 3
   lp c 0.04 n 3
 
 Best Fitting Double Couple
  Mo = 1.29e+24 dyne-cm
  Mw = 5.34 
  Z  = 63 km
  Plane   Strike  Dip  Rake
   NP1      141    58   -138
   NP2       25    55   -40
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.29e+24      2     262
    N   0.00e+00     39     171
    P  -1.29e+24     51     355

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.80e+23
       Mxy     2.22e+23
       Mxz    -6.33e+23
       Myy     1.26e+24
       Myz     1.75e+22
       Mzz    -7.78e+23
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 --------------------##              
              #-----------------------####           
             ##------------------------####          
           ####-----------   ----------######        
          #####----------- P ----------#######       
         ######-----------   ----------########      
        #######------------------------#########     
        ########-----------------------#########     
       ##########---------------------###########    
       ###########--------------------###########    
         ##########------------------############    
       T ###########----------------#############    
         ############---------------############     
        ###############------------#############     
         ################--------##############      
          #################-----##############       
           ##################--##############        
             ################---###########          
              ############------------####           
                 ######----------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -7.78e+23  -6.33e+23  -1.75e+22 
 -6.33e+23  -4.80e+23  -2.22e+23 
 -1.75e+22  -2.22e+23   1.26e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090622192805/index.html
	
USGS Body-Wave Moment Tensor Solution

 09/06/22 19:28:04.27
 CENTRAL ALASKA                  
 Epicenter:  62.053 -150.840
 MW 5.4

 USGS MOMENT TENSOR SOLUTION
 Depth  65         No. of sta:  8
 Moment Tensor;   Scale 10**17 Nm
   Mrr=-1.35       Mtt= 0.62
   Mpp= 0.73       Mrt=-0.95
   Mrp= 0.26       Mtp=-0.84
  Principal axes:
   T  Val=  1.76  Plg=15  Azm=222
   N       -0.02      15      127
   P       -1.73      67      355

 Best Double Couple:Mo=1.7*10**17
  NP1:Strike=120 Dip=63 Slip=-108
  NP2:       334     32       -59
                                      
               #######                
          ------###########           
        -------------########         
      -----------------########       
    ---------------------########     
   #-----------------------#######    
   ##------------   --------######    
  ####----------- P ---------######   
  ######---------   ---------######   
  ########--------------------#####   
  ##########------------------#####   
  #############---------------#####   
   ###############------------####    
   ####################-------####    
    ####   ##################----     
      ## T ##################--       
           #################-         
          ################-           
               #######                
                                      


        
USGS Centroid Moment Tensor Solution

 09/06/22 19:28:04.27
 CENTRAL ALASKA                  
 Epicenter:  62.053 -150.840
 MW 5.5

 USGS CENTROID MOMENT TENSOR
 09/06/22 19:28:18.59
 Centroid:   62.153 -151.143
 Depth  51         No. of sta:118
 Moment Tensor;   Scale 10**17 Nm
   Mrr=-0.81       Mtt=-0.59
   Mpp= 1.39       Mrt=-1.20
   Mrp= 0.20       Mtp=-0.82
  Principal axes:
   T  Val=  1.85  Plg=14  Azm=244
   N        0.10      41      140
   P       -1.95      44      349

 Best Double Couple:Mo=1.9*10**17
  NP1:Strike= 16 Dip=47 Slip= -25
  NP2:       124     72      -133
                                      
               -------                
          --------------###           
        -----------------####         
      ---------   --------#####       
    ----------- P ---------######     
   ###---------   ---------#######    
   ####--------------------#######    
  #######------------------########   
  #########----------------########   
  ###########--------------########   
  #############-----------#########   
  ##   ###########--------#########   
   # T ##############----#########    
   #   #################-#########    
    ###################---------#     
      ################---------       
        ############---------         
          #######----------           
               -------                
                                      


        

Moment tensor inversion summary for event 2009/06/22 19:28

Date: 2009/06/22
Time: 19:28 (UTC)
Region: Cook Inlet Region of Alaska
Mw=5.5

Location:

Lat.  61.9224;  Lon.  -150.6545; Depth   70 km 
(Best-fitting depth from moment tensor inversion)

Solution quality: poor
Number of stations = 6

Best Double Couple:

         strike    dip    rake 
Plane 1:  137.8   66.8  -139.3
Plane 2:   29.1   53.2   -29.5

Moment Tensor Parameters:

Mo = 1.74917e+24 dyn-cm
Mxx = -0.83; Mxy =  0.28; Mxz = -0.96
Myy =  1.64; Myz = -0.22; Mzz = -0.81


Principal Axes:

     value   azimuth   plunge
T:    1.72   260.59    8.34
N:    0.06   162.39   44.17
P:   -1.78   358.91   44.63

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 0.015 n 3
lp c 0.04 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   40.0    20    50   -35   5.17 0.4940
WVFGRD96   41.0    20    50   -35   5.18 0.5019
WVFGRD96   42.0    20    55   -40   5.20 0.5094
WVFGRD96   43.0    20    55   -40   5.21 0.5167
WVFGRD96   44.0    20    55   -40   5.21 0.5235
WVFGRD96   45.0    20    55   -40   5.22 0.5299
WVFGRD96   46.0    20    55   -40   5.23 0.5359
WVFGRD96   47.0    20    55   -40   5.23 0.5414
WVFGRD96   48.0    20    55   -40   5.24 0.5465
WVFGRD96   49.0    20    55   -40   5.25 0.5513
WVFGRD96   50.0    20    55   -40   5.26 0.5556
WVFGRD96   51.0    20    55   -40   5.26 0.5598
WVFGRD96   52.0    20    55   -40   5.27 0.5634
WVFGRD96   53.0    20    55   -40   5.27 0.5666
WVFGRD96   54.0    20    55   -40   5.28 0.5693
WVFGRD96   55.0    20    55   -45   5.29 0.5719
WVFGRD96   56.0    20    55   -45   5.30 0.5742
WVFGRD96   57.0    20    55   -45   5.31 0.5761
WVFGRD96   58.0    20    55   -45   5.31 0.5776
WVFGRD96   59.0    20    55   -45   5.32 0.5785
WVFGRD96   60.0    25    55   -40   5.32 0.5797
WVFGRD96   61.0    25    55   -40   5.33 0.5806
WVFGRD96   62.0    25    55   -40   5.33 0.5811
WVFGRD96   63.0    25    55   -40   5.34 0.5811
WVFGRD96   64.0    25    55   -40   5.34 0.5807
WVFGRD96   65.0    25    55   -40   5.35 0.5798
WVFGRD96   66.0    25    55   -40   5.35 0.5784
WVFGRD96   67.0    25    55   -40   5.36 0.5765
WVFGRD96   68.0    25    55   -40   5.36 0.5742
WVFGRD96   69.0    25    55   -40   5.36 0.5714

The best solution is

WVFGRD96   63.0    25    55   -40   5.34 0.5811

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 0.015 n 3
lp c 0.04 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=Wed Jun 24 20:35:34 CDT 2009

Last Changed 2009/06/22