Location

2010/06/25 04:56:53 61.894 -147.703 26.4 4.70 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  2010/06/25 04:56:53:0  61.89 -147.70  26.4 4.7 Alaska
 
 Stations used:
   AK.BMR AK.BPAW AK.BRLK AK.BWN AK.CCB AK.DIV AK.EYAK AK.FYU 
   AK.HDA AK.MCK AK.MDM AK.MLY AK.PAX AK.RAG AK.RC01 AK.RIDG 
   AK.RND AK.SCM AK.SKN AK.SSN AK.SWD AK.TRF AK.WRH CN.DAWY 
   IU.COLA US.EGAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 7.08e+22 dyne-cm
  Mw = 4.50 
  Z  = 40 km
  Plane   Strike  Dip  Rake
   NP1      245    85   -75
   NP2      353    16   -161
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.08e+22     38     322
    N   0.00e+00     15      64
    P  -7.08e+22     48     171

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.23e+21
       Mxy    -1.63e+22
       Mxz     6.17e+22
       Myy     1.61e+22
       Myz    -2.70e+22
       Mzz    -1.19e+22
                                                     
                                                     
                                                     
                                                     
                     ###########---                  
                 ###################---              
              ########################----           
             ###########################---          
           ########   ####################---        
          ######### T #####################---       
         ##########   ######################-##      
        ################################-----###     
        ###########################----------###     
       ########################--------------####    
       ####################-------------------###    
       ################-----------------------###    
       ############---------------------------###    
        ########-----------------------------###     
        #####--------------------------------###     
         #------------------   -------------###      
          ------------------ P ------------###       
           -----------------   -----------###        
             ----------------------------##          
              -------------------------###           
                 --------------------##              
                     -------------#                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.19e+22   6.17e+22   2.70e+22 
  6.17e+22  -4.23e+21   1.63e+22 
  2.70e+22   1.63e+22   1.61e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100625045653/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 = 245
      DIP = 85
     RAKE = -75
       MW = 4.50
       HS = 40.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2010/06/25 04:56:53:0  61.89 -147.70  26.4 4.7 Alaska
 
 Stations used:
   AK.BMR AK.BPAW AK.BRLK AK.BWN AK.CCB AK.DIV AK.EYAK AK.FYU 
   AK.HDA AK.MCK AK.MDM AK.MLY AK.PAX AK.RAG AK.RC01 AK.RIDG 
   AK.RND AK.SCM AK.SKN AK.SSN AK.SWD AK.TRF AK.WRH CN.DAWY 
   IU.COLA US.EGAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 7.08e+22 dyne-cm
  Mw = 4.50 
  Z  = 40 km
  Plane   Strike  Dip  Rake
   NP1      245    85   -75
   NP2      353    16   -161
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.08e+22     38     322
    N   0.00e+00     15      64
    P  -7.08e+22     48     171

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.23e+21
       Mxy    -1.63e+22
       Mxz     6.17e+22
       Myy     1.61e+22
       Myz    -2.70e+22
       Mzz    -1.19e+22
                                                     
                                                     
                                                     
                                                     
                     ###########---                  
                 ###################---              
              ########################----           
             ###########################---          
           ########   ####################---        
          ######### T #####################---       
         ##########   ######################-##      
        ################################-----###     
        ###########################----------###     
       ########################--------------####    
       ####################-------------------###    
       ################-----------------------###    
       ############---------------------------###    
        ########-----------------------------###     
        #####--------------------------------###     
         #------------------   -------------###      
          ------------------ P ------------###       
           -----------------   -----------###        
             ----------------------------##          
              -------------------------###           
                 --------------------##              
                     -------------#                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.19e+22   6.17e+22   2.70e+22 
  6.17e+22  -4.23e+21   1.63e+22 
  2.70e+22   1.63e+22   1.61e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100625045653/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    45    85   3.82 0.2824
WVFGRD96    1.0    55    45    85   3.88 0.2907
WVFGRD96    2.0    55    45    85   3.98 0.3575
WVFGRD96    3.0   240    45    95   4.05 0.3635
WVFGRD96    4.0    50    45    80   4.08 0.3113
WVFGRD96    5.0    20    50    40   4.05 0.2446
WVFGRD96    6.0    10    60    20   4.03 0.2143
WVFGRD96    7.0   170    25    15   3.97 0.2310
WVFGRD96    8.0   240    90   -75   4.05 0.2547
WVFGRD96    9.0    65    90    70   4.06 0.2917
WVFGRD96   10.0    65    90    70   4.07 0.3252
WVFGRD96   11.0    65    90    70   4.07 0.3557
WVFGRD96   12.0    65    90    70   4.08 0.3828
WVFGRD96   13.0    65    90    70   4.09 0.4075
WVFGRD96   14.0    65    90    65   4.10 0.4308
WVFGRD96   15.0    65    90    65   4.11 0.4517
WVFGRD96   16.0   245    85   -65   4.13 0.4726
WVFGRD96   17.0   245    85   -65   4.14 0.4911
WVFGRD96   18.0   245    85   -65   4.15 0.5083
WVFGRD96   19.0   245    85   -65   4.16 0.5249
WVFGRD96   20.0   245    85   -65   4.17 0.5399
WVFGRD96   21.0   245    85   -70   4.19 0.5538
WVFGRD96   22.0   245    85   -70   4.20 0.5684
WVFGRD96   23.0   245    85   -70   4.21 0.5817
WVFGRD96   24.0   245    85   -70   4.22 0.5951
WVFGRD96   25.0   245    85   -70   4.23 0.6073
WVFGRD96   26.0   245    85   -70   4.24 0.6189
WVFGRD96   27.0   245    85   -70   4.26 0.6305
WVFGRD96   28.0   245    85   -70   4.27 0.6409
WVFGRD96   29.0   245    85   -70   4.28 0.6503
WVFGRD96   30.0   245    85   -70   4.29 0.6594
WVFGRD96   31.0   245    85   -70   4.30 0.6669
WVFGRD96   32.0   245    85   -70   4.31 0.6735
WVFGRD96   33.0   245    85   -70   4.32 0.6793
WVFGRD96   34.0   245    85   -70   4.32 0.6838
WVFGRD96   35.0   245    85   -70   4.33 0.6873
WVFGRD96   36.0   245    85   -70   4.34 0.6898
WVFGRD96   37.0   245    85   -65   4.35 0.6913
WVFGRD96   38.0   245    85   -65   4.35 0.6924
WVFGRD96   39.0   245    85   -65   4.35 0.6920
WVFGRD96   40.0   245    85   -75   4.50 0.6931
WVFGRD96   41.0   245    85   -75   4.51 0.6912
WVFGRD96   42.0   245    85   -75   4.51 0.6885
WVFGRD96   43.0   245    85   -75   4.52 0.6848
WVFGRD96   44.0   245    85   -70   4.53 0.6816
WVFGRD96   45.0   245    85   -70   4.53 0.6773
WVFGRD96   46.0   245    85   -70   4.54 0.6726
WVFGRD96   47.0   245    85   -70   4.55 0.6673
WVFGRD96   48.0   245    85   -70   4.55 0.6615
WVFGRD96   49.0   245    85   -70   4.56 0.6552

The best solution is

WVFGRD96   40.0   245    85   -75   4.50 0.6931

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 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=Fri Jun 25 01:51:01 MDT 2010

Last Changed 2010/06/25