Location

2012/02/21 09:58:43 36.850 -89.409 5.0 4.0 Missouri

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  2012/02/21 09:58:43:0  36.85  -89.41   5.0 4.0 Missouri
 
 Stations used:
   IU.CCM IU.WCI IU.WVT NM.BLO NM.FVM NM.MGMO NM.MPH NM.OLIL 
   NM.PBMO NM.PLAL NM.PVMO NM.SIUC NM.SLM NM.UALR NM.USIN 
   NM.UTMT TA.147A TA.N40A TA.N41A TA.N42A TA.O37A TA.O38A 
   TA.O39A TA.O40A TA.O41A TA.O42A TA.O43A TA.O44A TA.O45A 
   TA.P38A TA.P39B TA.P40A TA.P41A TA.P42A TA.P43A TA.P44A 
   TA.P47A TA.Q37A TA.Q38A TA.Q39A TA.Q40A TA.Q41A TA.Q42A 
   TA.Q43A TA.Q44A TA.R38A TA.R39A TA.R40A TA.R41A TA.R42A 
   TA.R43A TA.R44A TA.S37A TA.S38A TA.S39A TA.S40A TA.S41A 
   TA.S42A TA.S43A TA.S44A TA.S45A TA.SFIN TA.T37A TA.T38A 
   TA.T39A TA.T40A TA.T41A TA.T42A TA.T43A TA.TUL1 TA.U39A 
   TA.U40A TA.U41A TA.U42A TA.U43A TA.U44A TA.U44B TA.U45A 
   TA.V39A TA.V40A TA.V41A TA.V42A TA.V43A TA.V44A TA.V45A 
   TA.W38A TA.W39A TA.W40A TA.W41B TA.W42A TA.W43A TA.W44A 
   TA.W45A TA.X39A TA.X40A TA.X41A TA.X44A TA.X45A TA.Y40A 
   TA.Y44A TA.Y45A TA.Y46A TA.Y47A TA.Z44A TA.Z47A TA.Z48A 
   US.HDIL US.LRAL US.OXF US.TZTN 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 7.76e+21 dyne-cm
  Mw = 3.86 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1       42    73   132
   NP2      150    45    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.76e+21     45     354
    N   0.00e+00     40     207
    P  -7.76e+21     17     102

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.49e+21
       Mxy     1.07e+21
       Mxz     4.31e+21
       Myy    -6.77e+21
       Myz    -2.49e+21
       Mzz     3.28e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              --##########################           
             ---#########   #############--          
           ----########## T #############----        
          -----##########   ############------       
         ------########################--------      
        -------#######################----------     
        -------######################-----------     
       --------#####################-------------    
       ---------###################--------------    
       ---------#################-----------   --    
       ----------##############------------- P --    
        ----------############--------------   -     
        -----------#########--------------------     
         -----------######---------------------      
          ------------##----------------------       
           ----------##----------------------        
             -----########-----------------          
              ###############-------------           
                 ################------              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  3.28e+21   4.31e+21   2.49e+21 
  4.31e+21   3.49e+21  -1.07e+21 
  2.49e+21  -1.07e+21  -6.77e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120221095843/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 = 150
      DIP = 45
     RAKE = 25
       MW = 3.86
       HS = 8.0

The NDK file is 20120221095843.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2012/02/21 09:58:43:0  36.85  -89.41   5.0 4.0 Missouri
 
 Stations used:
   IU.CCM IU.WCI IU.WVT NM.BLO NM.FVM NM.MGMO NM.MPH NM.OLIL 
   NM.PBMO NM.PLAL NM.PVMO NM.SIUC NM.SLM NM.UALR NM.USIN 
   NM.UTMT TA.147A TA.N40A TA.N41A TA.N42A TA.O37A TA.O38A 
   TA.O39A TA.O40A TA.O41A TA.O42A TA.O43A TA.O44A TA.O45A 
   TA.P38A TA.P39B TA.P40A TA.P41A TA.P42A TA.P43A TA.P44A 
   TA.P47A TA.Q37A TA.Q38A TA.Q39A TA.Q40A TA.Q41A TA.Q42A 
   TA.Q43A TA.Q44A TA.R38A TA.R39A TA.R40A TA.R41A TA.R42A 
   TA.R43A TA.R44A TA.S37A TA.S38A TA.S39A TA.S40A TA.S41A 
   TA.S42A TA.S43A TA.S44A TA.S45A TA.SFIN TA.T37A TA.T38A 
   TA.T39A TA.T40A TA.T41A TA.T42A TA.T43A TA.TUL1 TA.U39A 
   TA.U40A TA.U41A TA.U42A TA.U43A TA.U44A TA.U44B TA.U45A 
   TA.V39A TA.V40A TA.V41A TA.V42A TA.V43A TA.V44A TA.V45A 
   TA.W38A TA.W39A TA.W40A TA.W41B TA.W42A TA.W43A TA.W44A 
   TA.W45A TA.X39A TA.X40A TA.X41A TA.X44A TA.X45A TA.Y40A 
   TA.Y44A TA.Y45A TA.Y46A TA.Y47A TA.Z44A TA.Z47A TA.Z48A 
   US.HDIL US.LRAL US.OXF US.TZTN 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 7.76e+21 dyne-cm
  Mw = 3.86 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1       42    73   132
   NP2      150    45    25
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.76e+21     45     354
    N   0.00e+00     40     207
    P  -7.76e+21     17     102

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.49e+21
       Mxy     1.07e+21
       Mxz     4.31e+21
       Myy    -6.77e+21
       Myz    -2.49e+21
       Mzz     3.28e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              --##########################           
             ---#########   #############--          
           ----########## T #############----        
          -----##########   ############------       
         ------########################--------      
        -------#######################----------     
        -------######################-----------     
       --------#####################-------------    
       ---------###################--------------    
       ---------#################-----------   --    
       ----------##############------------- P --    
        ----------############--------------   -     
        -----------#########--------------------     
         -----------######---------------------      
          ------------##----------------------       
           ----------##----------------------        
             -----########-----------------          
              ###############-------------           
                 ################------              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  3.28e+21   4.31e+21   2.49e+21 
  4.31e+21   3.49e+21  -1.07e+21 
  2.49e+21  -1.07e+21  -6.77e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20120221095843/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:

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    20    45    90   3.74 0.3698
WVFGRD96    1.0    15    35    80   3.81 0.3733
WVFGRD96    2.0   150    30    10   3.88 0.3980
WVFGRD96    3.0   150    30    15   3.86 0.4293
WVFGRD96    4.0   150    35    20   3.85 0.4557
WVFGRD96    5.0   155    35    30   3.85 0.4773
WVFGRD96    6.0   155    40    30   3.86 0.4919
WVFGRD96    7.0   155    40    30   3.86 0.4993
WVFGRD96    8.0   150    45    25   3.86 0.5024
WVFGRD96    9.0   150    45    25   3.86 0.5012
WVFGRD96   10.0   150    45    25   3.89 0.4954
WVFGRD96   11.0   150    45    20   3.89 0.4888
WVFGRD96   12.0   150    45    20   3.90 0.4793
WVFGRD96   13.0   135    40   -20   3.90 0.4687
WVFGRD96   14.0   135    40   -20   3.90 0.4576
WVFGRD96   15.0   135    40   -20   3.91 0.4453
WVFGRD96   16.0   135    40   -20   3.92 0.4318
WVFGRD96   17.0   135    40   -20   3.92 0.4179
WVFGRD96   18.0   135    40   -20   3.93 0.4037
WVFGRD96   19.0   135    40   -20   3.93 0.3897
WVFGRD96   20.0   135    40   -20   3.96 0.3767
WVFGRD96   21.0   135    40   -25   3.97 0.3630
WVFGRD96   22.0   135    40   -25   3.97 0.3493
WVFGRD96   23.0   130    40   -30   3.98 0.3361
WVFGRD96   24.0   130    40   -30   3.98 0.3235
WVFGRD96   25.0   130    40   -25   3.99 0.3111
WVFGRD96   26.0   130    40   -25   3.99 0.2991
WVFGRD96   27.0   130    40   -25   3.99 0.2881
WVFGRD96   28.0   125    40   -30   4.00 0.2774
WVFGRD96   29.0   125    40   -30   4.00 0.2681

The best solution is

WVFGRD96    8.0   150    45    25   3.86 0.5024

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:

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 CUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
CUS Model with Q from simple gamma values
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
  1.0000  5.0000  2.8900  2.5000 0.172E-02 0.387E-02 0.00  0.00  1.00  1.00 
  9.0000  6.1000  3.5200  2.7300 0.160E-02 0.363E-02 0.00  0.00  1.00  1.00 
 10.0000  6.4000  3.7000  2.8200 0.149E-02 0.336E-02 0.00  0.00  1.00  1.00 
 20.0000  6.7000  3.8700  2.9020 0.000E-04 0.000E-04 0.00  0.00  1.00  1.00 
  0.0000  8.1500  4.7000  3.3640 0.194E-02 0.431E-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 Mon Dec 7 00:24:21 CST 2015