Location

2015/10/18 05:15:30 62.783 -149.269 65.8 4.1 Kansas

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  2015/10/18 05:15:30:0  62.78 -149.27  65.8 4.1 Kansas
 
 Stations used:
   AK.BPAW AK.BWN AK.CCB AK.DHY AK.DOT AK.GHO AK.GLI AK.HDA 
   AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA2 AK.RC01 
   AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.TRF AK.WRH 
   AT.PMR IU.COLA TA.K20K TA.N25K TA.TCOL 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.78e+22 dyne-cm
  Mw = 4.10 
  Z  = 76 km
  Plane   Strike  Dip  Rake
   NP1      140    80    45
   NP2       40    46   166
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.78e+22     38      11
    N   0.00e+00     44     150
    P  -1.78e+22     22     263

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.04e+22
       Mxy     3.27e+19
       Mxz     9.27e+21
       Myy    -1.47e+22
       Myz     7.65e+21
       Mzz     4.30e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              -##########################-           
             ---#############   ##########-          
           -----############# T ##########---        
          -------############   ###########---       
         ----------########################----      
        ------------#######################-----     
        -------------#####################------     
       ----------------###################-------    
       -----------------#################--------    
       ---   ------------###############---------    
       --- P --------------############----------    
        --   ----------------#########----------     
        ----------------------#######-----------     
         -----------------------###------------      
          -----------------------#------------       
           --------------------#####---------        
             ---------------##########-----          
              ---------##################-           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.30e+21   9.27e+21  -7.65e+21 
  9.27e+21   1.04e+22  -3.27e+19 
 -7.65e+21  -3.27e+19  -1.47e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20151018051530/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 = 140
      DIP = 80
     RAKE = 45
       MW = 4.10
       HS = 76.0

The NDK file is 20151018051530.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2015/10/18 05:15:30:0  62.78 -149.27  65.8 4.1 Kansas
 
 Stations used:
   AK.BPAW AK.BWN AK.CCB AK.DHY AK.DOT AK.GHO AK.GLI AK.HDA 
   AK.KLU AK.KNK AK.KTH AK.MCK AK.MDM AK.MLY AK.NEA2 AK.RC01 
   AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.TRF AK.WRH 
   AT.PMR IU.COLA TA.K20K TA.N25K TA.TCOL 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 1.78e+22 dyne-cm
  Mw = 4.10 
  Z  = 76 km
  Plane   Strike  Dip  Rake
   NP1      140    80    45
   NP2       40    46   166
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.78e+22     38      11
    N   0.00e+00     44     150
    P  -1.78e+22     22     263

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.04e+22
       Mxy     3.27e+19
       Mxz     9.27e+21
       Myy    -1.47e+22
       Myz     7.65e+21
       Mzz     4.30e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              -##########################-           
             ---#############   ##########-          
           -----############# T ##########---        
          -------############   ###########---       
         ----------########################----      
        ------------#######################-----     
        -------------#####################------     
       ----------------###################-------    
       -----------------#################--------    
       ---   ------------###############---------    
       --- P --------------############----------    
        --   ----------------#########----------     
        ----------------------#######-----------     
         -----------------------###------------      
          -----------------------#------------       
           --------------------#####---------        
             ---------------##########-----          
              ---------##################-           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.30e+21   9.27e+21  -7.65e+21 
  9.27e+21   1.04e+22  -3.27e+19 
 -7.65e+21  -3.27e+19  -1.47e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20151018051530/index.html
	

Magnitudes

mLg Magnitude


(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

ML Magnitude


(a) ML computed using the IASPEI formula for Horizontal components; (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.


(a) ML computed using the IASPEI formula for Vertical components (research); (b) ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.

Context

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors).

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:

cut o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
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    2.0   260    50    60   3.16 0.1735
WVFGRD96    4.0   240    60    30   3.22 0.1960
WVFGRD96    6.0    50    70   -35   3.28 0.2267
WVFGRD96    8.0   225    60   -30   3.37 0.2512
WVFGRD96   10.0   245    70    40   3.42 0.2710
WVFGRD96   12.0   240    60    35   3.47 0.2876
WVFGRD96   14.0   240    60    35   3.50 0.2910
WVFGRD96   16.0   340    55    40   3.53 0.2836
WVFGRD96   18.0   340    55    40   3.57 0.2910
WVFGRD96   20.0   335    60    40   3.60 0.3006
WVFGRD96   22.0   335    60    40   3.64 0.3132
WVFGRD96   24.0   335    60    40   3.66 0.3259
WVFGRD96   26.0   335    60    40   3.68 0.3347
WVFGRD96   28.0   335    60    40   3.70 0.3390
WVFGRD96   30.0   335    60    40   3.71 0.3374
WVFGRD96   32.0   335    60    40   3.72 0.3292
WVFGRD96   34.0   135    70   -25   3.70 0.3298
WVFGRD96   36.0   135    65   -15   3.73 0.3358
WVFGRD96   38.0   135    60   -10   3.76 0.3471
WVFGRD96   40.0   135    50   -15   3.84 0.3640
WVFGRD96   42.0   315    75   -50   3.88 0.3668
WVFGRD96   44.0   140    90    50   3.93 0.3759
WVFGRD96   46.0   140    90    50   3.95 0.3945
WVFGRD96   48.0   140    90    50   3.97 0.4126
WVFGRD96   50.0   320    90   -50   3.98 0.4313
WVFGRD96   52.0   320    90   -50   4.00 0.4519
WVFGRD96   54.0   320    90   -55   4.02 0.4717
WVFGRD96   56.0   140    90    55   4.03 0.4891
WVFGRD96   58.0   140    85    50   4.04 0.5064
WVFGRD96   60.0   140    85    50   4.05 0.5213
WVFGRD96   62.0   140    85    50   4.06 0.5360
WVFGRD96   64.0   140    80    45   4.07 0.5473
WVFGRD96   66.0   140    80    50   4.09 0.5580
WVFGRD96   68.0   140    80    50   4.09 0.5657
WVFGRD96   70.0   140    80    50   4.10 0.5725
WVFGRD96   72.0   140    80    45   4.09 0.5749
WVFGRD96   74.0   140    80    45   4.10 0.5793
WVFGRD96   76.0   140    80    45   4.10 0.5802
WVFGRD96   78.0   140    80    45   4.10 0.5795
WVFGRD96   80.0   140    80    45   4.11 0.5791
WVFGRD96   82.0   145    70    40   4.12 0.5779
WVFGRD96   84.0   145    70    40   4.12 0.5764
WVFGRD96   86.0   145    70    40   4.12 0.5731
WVFGRD96   88.0   145    70    40   4.12 0.5704
WVFGRD96   90.0   145    65    40   4.14 0.5688
WVFGRD96   92.0   145    65    40   4.14 0.5673
WVFGRD96   94.0   145    65    40   4.14 0.5660
WVFGRD96   96.0   145    65    40   4.15 0.5643
WVFGRD96   98.0   145    65    40   4.15 0.5615
WVFGRD96  100.0   145    65    40   4.15 0.5581
WVFGRD96  102.0   145    65    40   4.15 0.5546
WVFGRD96  104.0   145    65    40   4.15 0.5503
WVFGRD96  106.0   145    65    40   4.15 0.5453
WVFGRD96  108.0   145    65    40   4.15 0.5404
WVFGRD96  110.0   145    65    40   4.16 0.5357
WVFGRD96  112.0   145    65    40   4.16 0.5307
WVFGRD96  114.0   145    65    35   4.15 0.5255
WVFGRD96  116.0   145    65    35   4.15 0.5194
WVFGRD96  118.0   310    85   -30   4.10 0.5142
WVFGRD96    2.0   260    50    60   3.16 0.1799
WVFGRD96    4.0   240    60    30   3.22 0.2024
WVFGRD96    6.0    50    70   -35   3.28 0.2339
WVFGRD96    8.0   225    60   -30   3.37 0.2592
WVFGRD96   10.0   245    70    40   3.42 0.2798
WVFGRD96   12.0   240    60    35   3.47 0.2971
WVFGRD96   14.0   240    60    35   3.50 0.3006
WVFGRD96   16.0   340    55    40   3.53 0.2929
WVFGRD96   18.0   340    55    40   3.57 0.3005
WVFGRD96   20.0   335    60    40   3.60 0.3104
WVFGRD96   22.0   335    60    40   3.64 0.3236
WVFGRD96   24.0   335    60    40   3.66 0.3367
WVFGRD96   26.0   335    60    40   3.68 0.3459
WVFGRD96   28.0   335    60    40   3.70 0.3503
WVFGRD96   30.0   335    60    40   3.71 0.3487
WVFGRD96   32.0   335    60    40   3.72 0.3402
WVFGRD96   34.0   135    70   -25   3.70 0.3401
WVFGRD96   36.0   135    65   -15   3.73 0.3462
WVFGRD96   38.0   135    60   -10   3.76 0.3578
WVFGRD96   40.0   135    50   -15   3.84 0.3753
WVFGRD96   42.0   315    75   -50   3.88 0.3781
WVFGRD96   44.0   140    90    50   3.92 0.3875
WVFGRD96   46.0   140    90    50   3.95 0.4067
WVFGRD96   48.0   140    90    50   3.97 0.4253
WVFGRD96   50.0   140    90    50   3.98 0.4446
WVFGRD96   52.0   320    90   -50   4.00 0.4659
WVFGRD96   54.0   140    90    55   4.02 0.4863
WVFGRD96   56.0   140    90    55   4.03 0.5043
WVFGRD96   58.0   140    85    50   4.04 0.5222
WVFGRD96   60.0   140    85    50   4.05 0.5377
WVFGRD96   62.0   140    85    50   4.06 0.5528
WVFGRD96   64.0   140    80    45   4.07 0.5646
WVFGRD96   66.0   140    80    50   4.09 0.5756
WVFGRD96   68.0   140    80    50   4.09 0.5836
WVFGRD96   70.0   140    80    50   4.10 0.5906
WVFGRD96   72.0   140    80    45   4.09 0.5931
WVFGRD96   74.0   140    80    45   4.10 0.5977
WVFGRD96   76.0   140    80    45   4.10 0.5984
WVFGRD96   78.0   140    80    45   4.10 0.5977
WVFGRD96   80.0   140    80    45   4.11 0.5974
WVFGRD96   82.0   145    70    40   4.12 0.5961
WVFGRD96   84.0   145    70    40   4.12 0.5947
WVFGRD96   86.0   145    70    40   4.12 0.5912
WVFGRD96   88.0   145    70    40   4.12 0.5885
WVFGRD96   90.0   145    65    40   4.14 0.5868
WVFGRD96   92.0   145    65    40   4.14 0.5853
WVFGRD96   94.0   145    65    40   4.14 0.5840
WVFGRD96   96.0   145    65    40   4.15 0.5822
WVFGRD96   98.0   145    65    40   4.15 0.5794
WVFGRD96  100.0   145    65    40   4.15 0.5759
WVFGRD96  102.0   145    65    40   4.15 0.5723
WVFGRD96  104.0   145    65    40   4.15 0.5679
WVFGRD96  106.0   145    65    40   4.15 0.5627
WVFGRD96  108.0   145    65    40   4.15 0.5577
WVFGRD96  110.0   145    65    40   4.16 0.5528
WVFGRD96  112.0   145    65    40   4.16 0.5477
WVFGRD96  114.0   145    65    35   4.15 0.5422
WVFGRD96  116.0   145    65    35   4.15 0.5360
WVFGRD96  118.0   310    85   -30   4.10 0.5306

The best solution is

WVFGRD96   76.0   140    80    45   4.10 0.5984

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 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

cut o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 n 3 
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated.
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

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 WUS model 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:

Last Changed Mon Dec 7 00:08:27 CST 2015