Location

2013/02/05 12:25:36 35.77 127.97 10.0 3.50 Korea

Arrival Times (from USGS)

Felt Map

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2013/02/05 12:25:36:0 0.77 127.97 10.0 3.5 Korea Stations used: KS.BAR KS.BUS KS.BUS2 KS.CHC2 KS.CHJ KS.CHJ2 KS.DAG2 KS.DGY2 KS.HWCB KS.JJU KS.KOHB KS.KWJ KS.OKEB KS.SEO2 KS.SHHB KS.SMKB KS.ULJ2 Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.17e+21 dyne-cm Mw = 3.68 Z = 7 km Plane Strike Dip Rake NP1 130 70 35 NP2 27 57 156 Principal Axes: Axis Value Plunge Azimuth T 4.17e+21 39 352 N 0.00e+00 50 156 P -4.17e+21 8 256 Moment Tensor: (dyne-cm) Component Value Mxx 2.26e+21 Mxy -1.31e+21 Mxz 2.15e+21 Myy -3.80e+21 Myz 2.83e+20 Mzz 1.54e+21 ############## #####################- ########################---- ############ ###########---- -############# T ###########------ ---############ ###########------- -----#########################-------- -------########################--------- ---------#####################---------- -----------####################----------- -------------#################------------ --------------################------------ - ------------#############------------- P ---------------#########------------- -----------------######-------------- ----------------------##-------------- ---------------------###------------ -------------------########------- ---------------############### -----------################# -----################# ############## Global CMT Convention Moment Tensor: R T P 1.54e+21 2.15e+21 -2.83e+20 2.15e+21 2.26e+21 1.31e+21 -2.83e+20 1.31e+21 -3.80e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130205122536/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 = 130
      DIP = 70
     RAKE = 35
       MW = 3.68
       HS = 7.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGS/SLU Moment Tensor Solution ENS 2013/02/05 12:25:36:0 0.77 127.97 10.0 3.5 Korea Stations used: KS.BAR KS.BUS KS.BUS2 KS.CHC2 KS.CHJ KS.CHJ2 KS.DAG2 KS.DGY2 KS.HWCB KS.JJU KS.KOHB KS.KWJ KS.OKEB KS.SEO2 KS.SHHB KS.SMKB KS.ULJ2 Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 4.17e+21 dyne-cm Mw = 3.68 Z = 7 km Plane Strike Dip Rake NP1 130 70 35 NP2 27 57 156 Principal Axes: Axis Value Plunge Azimuth T 4.17e+21 39 352 N 0.00e+00 50 156 P -4.17e+21 8 256 Moment Tensor: (dyne-cm) Component Value Mxx 2.26e+21 Mxy -1.31e+21 Mxz 2.15e+21 Myy -3.80e+21 Myz 2.83e+20 Mzz 1.54e+21 ############## #####################- ########################---- ############ ###########---- -############# T ###########------ ---############ ###########------- -----#########################-------- -------########################--------- ---------#####################---------- -----------####################----------- -------------#################------------ --------------################------------ - ------------#############------------- P ---------------#########------------- -----------------######-------------- ----------------------##-------------- ---------------------###------------ -------------------########------- ---------------############### -----------################# -----################# ############## Global CMT Convention Moment Tensor: R T P 1.54e+21 2.15e+21 -2.83e+20 2.15e+21 2.26e+21 1.31e+21 -2.83e+20 1.31e+21 -3.80e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130205122536/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 0.10 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   295    70   -30   3.55 0.3568
WVFGRD96    1.0   295    55   -25   3.59 0.3595
WVFGRD96    2.0   295    80   -50   3.63 0.3612
WVFGRD96    3.0   120    90    45   3.63 0.3723
WVFGRD96    4.0   130    75    40   3.65 0.3871
WVFGRD96    5.0   130    70    40   3.66 0.4031
WVFGRD96    6.0   130    70    35   3.67 0.4132
WVFGRD96    7.0   130    70    35   3.68 0.4176
WVFGRD96    8.0   130    70    35   3.68 0.4173
WVFGRD96    9.0   130    65    30   3.70 0.4140
WVFGRD96   10.0   130    65    30   3.71 0.4096
WVFGRD96   11.0   125    75    30   3.70 0.4038
WVFGRD96   12.0   125    75    30   3.71 0.3958
WVFGRD96   13.0   125    80    30   3.72 0.3879
WVFGRD96   14.0   125    75    30   3.73 0.3804
WVFGRD96   15.0   125    75    30   3.74 0.3726
WVFGRD96   16.0   125    75    30   3.75 0.3644
WVFGRD96   17.0   300    90   -30   3.76 0.3531
WVFGRD96   18.0   300    90   -30   3.77 0.3445
WVFGRD96   19.0   300    90   -30   3.77 0.3356
WVFGRD96   20.0   125    80    30   3.79 0.3273
WVFGRD96   21.0   300    90   -30   3.80 0.3187
WVFGRD96   22.0   120    90    30   3.80 0.3098
WVFGRD96   23.0   300    90   -30   3.81 0.3012
WVFGRD96   24.0   120    90    30   3.82 0.2938
WVFGRD96   25.0   120    90    30   3.83 0.2865
WVFGRD96    0.0****** 32767     1   0.00-2.0000
WVFGRD96    0.0****** 32767     1   0.00-2.0000
WVFGRD96    0.0****** 32767     1   0.00-2.0000
WVFGRD96    0.0****** 32767     1   0.00-2.0000

The best solution is

WVFGRD96    7.0   130    70    35   3.68 0.4176

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 0.02 n 3
lp c 0.10 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:

The origin time and epicentral distance are incorrect
The velocity model used for the inversion is incorrect
The velocity model used to define the P-arrival time is not the same as the velocity model used for the waveform inversion (assuming that the initial trace alignment is based on the P arrival time)

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

Acknowledgements

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, 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 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:

Last Changed Tue Feb 5 14:54:08 CST 2013