Location

2010/03/02 19:37:35 36.788 -89.357 8.2 3.70 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  2010/03/02 19:37:35:0  36.79  -89.36   8.2 3.7 Missouri
 
 Stations used:
   NM.HENM NM.HICK NM.PARM 
 
 Filtering commands used:
   hp c 0.10 n 3
   lp c 0.40 n 3
 
 Best Fitting Double Couple
  Mo = 1.43e+21 dyne-cm
  Mw = 3.37 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      211    86   135
   NP2      305    45     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.43e+21     33     158
    N   0.00e+00     45      28
    P  -1.43e+21     27     267

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     8.62e+20
       Mxy    -4.03e+20
       Mxz    -5.77e+20
       Myy    -9.87e+20
       Myz     8.25e+20
       Mzz     1.25e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              #######################-----           
             ####------#############-------          
           ------------------######----------        
          ------------------------------------       
         -----------------------####-----------      
        -----------------------#######----------     
        ----------------------##########--------     
       ----------------------############--------    
       ----   --------------##############-------    
       ---- P ------------#################------    
       ----   -----------###################-----    
        ----------------#####################---     
        ---------------######################---     
         -------------#######################--      
          -----------########################-       
           ---------############   ##########        
             ------############# T ########          
              ----##############   #######           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.25e+20  -5.77e+20  -8.25e+20 
 -5.77e+20   8.62e+20   4.03e+20 
 -8.25e+20   4.03e+20  -9.87e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100302193735/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 = 305
      DIP = 45
     RAKE = 5
       MW = 3.37
       HS = 5.0

This solution is very dependent on the velocity model, filter band and width of the time window. The original PANDA model had 0.65 km of sediments, but this was reduced to 0.35 km because this event was north of the USGS well south of Noranda where the 0.65 km depth was determined. The solution is not unexpected in that the orientation of the P-axis agrees with previous mechanisms and the NNE striking nodal plane lines up with seismicity, e.g., for previous mechanisms and the seismicity .

Moment Tensor Comparison

The following compares this source inversion to others
SLU
CERIFM
 USGS/SLU Moment Tensor Solution
 ENS  2010/03/02 19:37:35:0  36.79  -89.36   8.2 3.7 Missouri
 
 Stations used:
   NM.HENM NM.HICK NM.PARM 
 
 Filtering commands used:
   hp c 0.10 n 3
   lp c 0.40 n 3
 
 Best Fitting Double Couple
  Mo = 1.43e+21 dyne-cm
  Mw = 3.37 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      211    86   135
   NP2      305    45     5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.43e+21     33     158
    N   0.00e+00     45      28
    P  -1.43e+21     27     267

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     8.62e+20
       Mxy    -4.03e+20
       Mxz    -5.77e+20
       Myy    -9.87e+20
       Myz     8.25e+20
       Mzz     1.25e+20
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ######################              
              #######################-----           
             ####------#############-------          
           ------------------######----------        
          ------------------------------------       
         -----------------------####-----------      
        -----------------------#######----------     
        ----------------------##########--------     
       ----------------------############--------    
       ----   --------------##############-------    
       ---- P ------------#################------    
       ----   -----------###################-----    
        ----------------#####################---     
        ---------------######################---     
         -------------#######################--      
          -----------########################-       
           ---------############   ##########        
             ------############# T ########          
              ----##############   #######           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.25e+20  -5.77e+20  -8.25e+20 
 -5.77e+20   8.62e+20   4.03e+20 
 -8.25e+20   4.03e+20  -9.87e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100302193735/index.html
	
First motion

Circles represent dilatations and +'s compression Note: An upper hemisphere projection is used.

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 0.10 n 3
lp c 0.40 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    1.0   300    55    15   2.94 0.3241
WVFGRD96    2.0   310    40    10   3.06 0.4482
WVFGRD96    3.0   305    50     5   3.15 0.5626
WVFGRD96    4.0   305    60     5   3.22 0.6358
WVFGRD96    5.0   305    45     5   3.37 0.6501
WVFGRD96    6.0   305    50     0   3.41 0.6433
WVFGRD96    7.0   310    50     5   3.45 0.6177
WVFGRD96    8.0   310    55     5   3.46 0.5996
WVFGRD96    9.0   305    70     0   3.43 0.5766
WVFGRD96   10.0   305    70     0   3.46 0.5681
WVFGRD96   11.0   305    75     0   3.46 0.5661
WVFGRD96   12.0   305    80     5   3.47 0.5669
WVFGRD96   13.0   305    80    10   3.51 0.5644
WVFGRD96   14.0   120    90     0   3.48 0.5487
WVFGRD96   15.0   120    85     5   3.46 0.5362
WVFGRD96   16.0   120    85     5   3.48 0.5310

The best solution is

WVFGRD96    5.0   305    45     5   3.37 0.6501

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 0.10 n 3
lp c 0.40 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 PANDA1 model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
Panda model for New Madrid
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
  0.3500  1.8000  0.6000  2.0000 200.  100.  0.00  0.00  1.00  1.00 
  1.8500  6.0200  3.0100  2.0000 200.  100.  0.00  0.00 1.00 1.00
  2.5     4.83    2.63    2.0    200.  100.  0.00  0.00  1.00  1.00
 12.0     6.17    3.38    2.2    600.  300.  0.00  0.00  1.00  1.00
 10.0     6.60    3.68    2.2    600.  300.  0.00  0.00  1.00  1.00
 10.0     7.20    3.68    2.2    600.  300.  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=Thu Mar 4 10:55:20 CST 2010

Last Changed 2010/03/02