Location

2012/08/20 13:43:08 35.46 124.68 10.0 4.2 Korea

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  2012/08/20 13:43:08:0   0.00   35.46 124.7 10.0 Korea
 
 Stations used:
   KS.BUS KS.BUS2 KS.CHC KS.CHJ KS.DAG2 KS.DGY2 KS.GAHB 
   KS.HWCB KS.JEO KS.JJU KS.KOHB KS.KWJ KS.SEO KS.SES KS.YNCB 
 
 Filtering commands used:
   hp c 0.03 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.40e+21 dyne-cm
  Mw = 3.52 
  Z  = 11 km
  Plane   Strike  Dip  Rake
   NP1      192    74   -143
   NP2       90    55   -20
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.40e+21     12     317
    N   0.00e+00     50     212
    P  -2.40e+21     37      56

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     7.71e+20
       Mxy    -1.85e+21
       Mxz    -2.81e+20
       Myy    -1.61e+14
       Myz    -1.29e+21
       Mzz    -7.71e+20
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 #############---------              
                 ############-------------           
             # T ###########---------------          
           ###   ##########------------------        
          #################-------------------       
         #################------------   ------      
        #################------------- P -------     
        #################-------------   -------     
       #################-------------------------    
       #################-------------------------    
       -################------------------------#    
       ---#############-----------------------###    
        ----###########---------------------####     
        --------#######-----------------########     
         -------------#-----------#############      
          -------------#######################       
           ------------######################        
             ----------####################          
              ---------###################           
                 ------################              
                     --############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -7.71e+20  -2.81e+20   1.29e+21 
 -2.81e+20   7.71e+20   1.85e+21 
  1.29e+21   1.85e+21  -1.61e+14 


Details of the solution is found at

http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20120820134308/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 = 90
      DIP = 55
     RAKE = -20
       MW = 3.52
       HS = 11.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2012/08/20 13:43:08:0   0.00   35.46 124.7 10.0 Korea
 
 Stations used:
   KS.BUS KS.BUS2 KS.CHC KS.CHJ KS.DAG2 KS.DGY2 KS.GAHB 
   KS.HWCB KS.JEO KS.JJU KS.KOHB KS.KWJ KS.SEO KS.SES KS.YNCB 
 
 Filtering commands used:
   hp c 0.03 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 2.40e+21 dyne-cm
  Mw = 3.52 
  Z  = 11 km
  Plane   Strike  Dip  Rake
   NP1      192    74   -143
   NP2       90    55   -20
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.40e+21     12     317
    N   0.00e+00     50     212
    P  -2.40e+21     37      56

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     7.71e+20
       Mxy    -1.85e+21
       Mxz    -2.81e+20
       Myy    -1.61e+14
       Myz    -1.29e+21
       Mzz    -7.71e+20
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 #############---------              
                 ############-------------           
             # T ###########---------------          
           ###   ##########------------------        
          #################-------------------       
         #################------------   ------      
        #################------------- P -------     
        #################-------------   -------     
       #################-------------------------    
       #################-------------------------    
       -################------------------------#    
       ---#############-----------------------###    
        ----###########---------------------####     
        --------#######-----------------########     
         -------------#-----------#############      
          -------------#######################       
           ------------######################        
             ----------####################          
              ---------###################           
                 ------################              
                     --############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -7.71e+20  -2.81e+20   1.29e+21 
 -2.81e+20   7.71e+20   1.85e+21 
  1.29e+21   1.85e+21  -1.61e+14 


Details of the solution is found at

http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20120820134308/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 0.03 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   290    55    20   3.40 0.5926
WVFGRD96    1.0   290    55    25   3.42 0.6045
WVFGRD96    2.0   290    50    30   3.47 0.6127
WVFGRD96    3.0   100    40    10   3.51 0.6231
WVFGRD96    4.0   100    40    10   3.51 0.6347
WVFGRD96    5.0    95    45     0   3.50 0.6484
WVFGRD96    6.0    95    50    -5   3.49 0.6588
WVFGRD96    7.0    90    50   -15   3.50 0.6691
WVFGRD96    8.0    90    50   -15   3.50 0.6765
WVFGRD96    9.0    90    55   -20   3.51 0.6833
WVFGRD96   10.0    90    55   -20   3.51 0.6860
WVFGRD96   11.0    90    55   -20   3.52 0.6864
WVFGRD96   12.0    85    55   -30   3.53 0.6846
WVFGRD96   13.0    85    55   -30   3.54 0.6814
WVFGRD96   14.0    90    60   -25   3.54 0.6758
WVFGRD96   15.0    90    60   -20   3.54 0.6702
WVFGRD96   16.0    90    60   -20   3.55 0.6636
WVFGRD96   17.0    90    60   -20   3.56 0.6553
WVFGRD96   18.0    90    60   -20   3.57 0.6467
WVFGRD96   19.0    90    60   -20   3.58 0.6371
WVFGRD96   20.0    90    60   -20   3.58 0.6267
WVFGRD96   21.0    90    60   -20   3.59 0.6165
WVFGRD96   22.0    90    65   -15   3.60 0.6060
WVFGRD96   23.0    90    65   -15   3.61 0.5967
WVFGRD96   24.0    95    65   -10   3.62 0.5870
WVFGRD96   25.0    95    65   -10   3.63 0.5773
WVFGRD96    0.0     0     0******   0.00-2.0000
WVFGRD96    0.0     0     0******   0.00-2.0000
WVFGRD96    0.0     0     0******   0.00-2.0000
WVFGRD96    0.0     0     0******   0.00-2.0000

The best solution is

WVFGRD96   11.0    90    55   -20   3.52 0.6864

The mechanism corresponding 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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).

The bandpass filter used in the processing and for the display was

hp c 0.03 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.

A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:

Assuming only a mislocation, the time shifts are fit to a functional form:

 Time_shift = A + B cos Azimuth + C Sin Azimuth

The time shifts for this inversion lead to the next figure:

The derived shift in origin time and epicentral coordinates are given at the bottom of the figure.

Discussion

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 Louis University, University of Memphis, Lamont Doherty Earth Observatory, the IRIS stations and the Transportable Array of EarthScope.

Velocity Model

The t6.invSNU.CUVEL model was used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
Model after    30 iterations
ISOTROPIC
KGS
SPHERICAL 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     5.3800     3.0009     2.5772  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     1.0000     5.8057     3.2383     2.6606  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     1.0000     6.1732     3.4433     2.7513  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     3.0000     6.2872     3.5067     2.7862  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     6.3245     3.5281     2.7970  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     6.4165     3.5788     2.8248  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     4.0000     6.5576     3.6576     2.8653  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     6.6402     3.7038     2.8865  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     2.5000     6.6540     3.7115     2.8897  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     2.5000     7.0960     3.9579     3.0111  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     2.5000     7.9155     4.4148     3.2804  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     2.5000     7.8925     4.4019     3.2735  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.8665     4.3876     3.2643  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.5675     4.2211     3.1625  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.7550     4.3252     3.2262  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.7602     4.3280     3.2282  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.7958     4.3487     3.2398  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.7415     4.3195     3.2217  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.6497     4.2688     3.1915  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.6408     4.2653     3.1889  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.6666     4.2716     3.1976  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.6699     4.2830     3.1986  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.6780     4.2885     3.2014  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.6816     4.2896     3.2028  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
     5.0000     7.6946     4.2996     3.2072  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
    10.0000     7.7349     4.3197     3.2208  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
    10.0000     7.7791     4.3484     3.2355  0.118E-02  0.167E-02   0.00       0.00       1.00       1.00    
    10.0000     7.8331     4.3722     3.2536  0.862E-02  0.131E-01   0.00       0.00       1.00       1.00    
    10.0000     7.8824     4.3863     3.2703  0.862E-02  0.131E-01   0.00       0.00       1.00       1.00    
    10.0000     7.9360     4.4024     3.2883  0.855E-02  0.131E-01   0.00       0.00       1.00       1.00    
    10.0000     7.9967     4.4237     3.3088  0.847E-02  0.131E-01   0.00       0.00       1.00       1.00    
    10.0000     8.0529     4.4423     3.3289  0.847E-02  0.131E-01   0.00       0.00       1.00       1.00    
    10.0000     8.1110     4.4603     3.3496  0.833E-02  0.130E-01   0.00       0.00       1.00       1.00    
    10.0000     8.1762     4.4832     3.3728  0.826E-02  0.129E-01   0.00       0.00       1.00       1.00    
    10.0000     8.2410     4.5054     3.3959  0.813E-02  0.128E-01   0.00       0.00       1.00       1.00    
    10.0000     8.3022     4.5257     3.4176  0.806E-02  0.126E-01   0.00       0.00       1.00       1.00    
    10.0000     8.3635     4.5514     3.4395  0.474E-02  0.746E-02   0.00       0.00       1.00       1.00    
    10.0000     8.4257     4.5839     3.4617  0.472E-02  0.741E-02   0.00       0.00       1.00       1.00    
    10.0000     8.4845     4.6145     3.4827  0.469E-02  0.741E-02   0.00       0.00       1.00       1.00    
    10.0000     8.5403     4.6434     3.5020  0.467E-02  0.735E-02   0.00       0.00       1.00       1.00    
    10.0000     8.5934     4.6708     3.5199  0.465E-02  0.735E-02   0.00       0.00       1.00       1.00    
    10.0000     8.6436     4.6959     3.5369  0.463E-02  0.730E-02   0.00       0.00       1.00       1.00    
    10.0000     8.6912     4.7194     3.5530  0.461E-02  0.730E-02   0.00       0.00       1.00       1.00    
    10.0000     8.7365     4.7413     3.5684  0.459E-02  0.725E-02   0.00       0.00       1.00       1.00    
    10.0000     8.7797     4.7622     3.5831  0.455E-02  0.725E-02   0.00       0.00       1.00       1.00    
    10.0000     8.8199     4.7819     3.5967  0.452E-02  0.719E-02   0.00       0.00       1.00       1.00    
    10.0000     8.8587     4.8001     3.6099  0.450E-02  0.714E-02   0.00       0.00       1.00       1.00    
    10.0000     8.8958     4.8177     3.6226  0.448E-02  0.714E-02   0.00       0.00       1.00       1.00    
    10.0000     8.9314     4.8346     3.6347  0.446E-02  0.709E-02   0.00       0.00       1.00       1.00    
    10.0000     8.9647     4.8500     3.6461  0.442E-02  0.704E-02   0.00       0.00       1.00       1.00    
    10.0000     8.9962     4.8651     3.6569  0.441E-02  0.704E-02   0.00       0.00       1.00       1.00    
    10.0000     9.0263     4.8783     3.6685  0.439E-02  0.699E-02   0.00       0.00       1.00       1.00    
    10.0000     9.0547     4.8915     3.6800  0.435E-02  0.694E-02   0.00       0.00       1.00       1.00    
    10.0000     9.0822     4.9041     3.6911  0.433E-02  0.690E-02   0.00       0.00       1.00       1.00    
    10.0000     9.1091     4.9164     3.7020  0.431E-02  0.690E-02   0.00       0.00       1.00       1.00    
    10.0000     9.1346     4.9280     3.7123  0.427E-02  0.685E-02   0.00       0.00       1.00       1.00    
    10.0000     9.4876     5.1513     3.8537  0.388E-02  0.613E-02   0.00       0.00       1.00       1.00    
    10.0000     9.5095     5.1663     3.8624  0.388E-02  0.613E-02   0.00       0.00       1.00       1.00    
    10.0000     9.5299     5.1806     3.8703  0.386E-02  0.610E-02   0.00       0.00       1.00       1.00    
    10.0000     9.5507     5.1944     3.8784  0.386E-02  0.610E-02   0.00       0.00       1.00       1.00    
    10.0000     9.5706     5.2080     3.8861  0.385E-02  0.606E-02   0.00       0.00       1.00       1.00    
    10.0000     9.5900     5.2214     3.8937  0.385E-02  0.606E-02   0.00       0.00       1.00       1.00    
    10.0000     9.6090     5.2347     3.9011  0.383E-02  0.606E-02   0.00       0.00       1.00       1.00    
    10.0000     9.6272     5.2480     3.9081  0.383E-02  0.602E-02   0.00       0.00       1.00       1.00    
    10.0000     9.6458     5.2604     3.9154  0.383E-02  0.602E-02   0.00       0.00       1.00       1.00    
    10.0000     9.6794     5.2816     3.9282  0.382E-02  0.599E-02   0.00       0.00       1.00       1.00    
    10.0000     9.7130     5.3029     3.9409  0.382E-02  0.599E-02   0.00       0.00       1.00       1.00    
    10.0000     9.7466     5.3242     3.9537  0.380E-02  0.599E-02   0.00       0.00       1.00       1.00    
    10.0000     9.7799     5.3454     3.9664  0.380E-02  0.595E-02   0.00       0.00       1.00       1.00    
    10.0000     9.8137     5.3669     3.9792  0.380E-02  0.595E-02   0.00       0.00       1.00       1.00    
    10.0000     9.8473     5.3883     3.9920  0.379E-02  0.592E-02   0.00       0.00       1.00       1.00    
    10.0000     9.8808     5.4094     4.0047  0.379E-02  0.592E-02   0.00       0.00       1.00       1.00    
     0.0000     9.9144     5.4306     4.0175  0.377E-02  0.592E-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=Sun Aug 26 20:03:30 CDT 2012

Last Changed 2012/08/20