Location

2010/01/18 08:41:07 36.8500 -104.8700 5.0 4.00 New Mexico

Arrival Times (from USGS)

Arrival time list

SLU Location

After an initial inversion run, large time shifts were required. We picked arrivals form the permanent and the TA network for use with the elocate programs and the CUS model. The SLU location isabout 0.1 degree west of the initial NEIC location. I prefer the SLU location because the waveform time shifts are no longer as large as -4 seconds at short distances. Output of elocate

Felt Map

USGS Felt map for this earthquake

USGS Felt reports main page

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2010/01/18 08:41:07:0  36.85 -104.87   5.0 4.0 New Mexico
 
 Stations used:
   IU.ANMO TA.KSCO TA.MSTX TA.P27A TA.P28A TA.Q23A TA.Q26A 
   TA.Q28A TA.Q29A TA.R24A TA.R25A TA.R26A TA.R27A TA.S22A 
   TA.S23A TA.S24A TA.S25A TA.S26A TA.S27A TA.T23A TA.T24B 
   TA.T25A TA.T26A TA.U23A TA.U24A TA.U25A TA.U26A TA.U27A 
   TA.U28A TA.V22A TA.V23A TA.V24A TA.V25A TA.V26A TA.V27A 
   TA.V28A TA.V29A TA.W23A TA.W24A TA.W26A TA.W27A TA.W28A 
   TA.W29A TA.W30A TA.X23A TA.X24A TA.X26A TA.X27A TA.X28A 
   TA.X29A TA.Y24A TA.Z24A US.MVCO US.SDCO 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 7.24e+21 dyne-cm
  Mw = 3.84 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1       20    65   -45
   NP2      133    50   -147
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.24e+21      9      80
    N   0.00e+00     40     177
    P  -7.24e+21     49     339

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.53e+21
       Mxy     2.30e+21
       Mxz    -3.16e+21
       Myy     6.45e+21
       Myz     2.35e+21
       Mzz    -3.92e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 -------------------###              
              ----------------------######           
             -----------------------#######          
           #-----------   -----------########        
          ##----------- P -----------#########       
         ####----------   ----------###########      
        #####-----------------------#########        
        #####-----------------------######### T      
       #######---------------------##########   #    
       ########--------------------##############    
       #########------------------###############    
       ##########-----------------###############    
        ###########--------------###############     
        ############------------################     
         #############---------################      
          ###############-----################       
           #################-################        
             ###############----###########          
              ############----------------           
                 #######---------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.92e+21  -3.16e+21  -2.35e+21 
 -3.16e+21  -2.53e+21  -2.30e+21 
 -2.35e+21  -2.30e+21   6.45e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100118084107/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 = 20
      DIP = 65
     RAKE = -45
       MW = 3.84
       HS = 5.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2010/01/18 08:41:07:0  36.85 -104.87   5.0 4.0 New Mexico
 
 Stations used:
   IU.ANMO TA.KSCO TA.MSTX TA.P27A TA.P28A TA.Q23A TA.Q26A 
   TA.Q28A TA.Q29A TA.R24A TA.R25A TA.R26A TA.R27A TA.S22A 
   TA.S23A TA.S24A TA.S25A TA.S26A TA.S27A TA.T23A TA.T24B 
   TA.T25A TA.T26A TA.U23A TA.U24A TA.U25A TA.U26A TA.U27A 
   TA.U28A TA.V22A TA.V23A TA.V24A TA.V25A TA.V26A TA.V27A 
   TA.V28A TA.V29A TA.W23A TA.W24A TA.W26A TA.W27A TA.W28A 
   TA.W29A TA.W30A TA.X23A TA.X24A TA.X26A TA.X27A TA.X28A 
   TA.X29A TA.Y24A TA.Z24A US.MVCO US.SDCO 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 7.24e+21 dyne-cm
  Mw = 3.84 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1       20    65   -45
   NP2      133    50   -147
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.24e+21      9      80
    N   0.00e+00     40     177
    P  -7.24e+21     49     339

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.53e+21
       Mxy     2.30e+21
       Mxz    -3.16e+21
       Myy     6.45e+21
       Myz     2.35e+21
       Mzz    -3.92e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 -------------------###              
              ----------------------######           
             -----------------------#######          
           #-----------   -----------########        
          ##----------- P -----------#########       
         ####----------   ----------###########      
        #####-----------------------#########        
        #####-----------------------######### T      
       #######---------------------##########   #    
       ########--------------------##############    
       #########------------------###############    
       ##########-----------------###############    
        ###########--------------###############     
        ############------------################     
         #############---------################      
          ###############-----################       
           #################-################        
             ###############----###########          
              ############----------------           
                 #######---------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.92e+21  -3.16e+21  -2.35e+21 
 -3.16e+21  -2.53e+21  -2.30e+21 
 -2.35e+21  -2.30e+21   6.45e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100118084107/index.html
	

First motion plot using elocate take-off angles and azimuths

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    30    85   -55   3.84 0.3379
WVFGRD96    1.0   215    90    60   3.89 0.3453
WVFGRD96    2.0    30    80   -50   3.83 0.3752
WVFGRD96    3.0    25    70   -45   3.83 0.4005
WVFGRD96    4.0    20    65   -45   3.84 0.4191
WVFGRD96    5.0    20    65   -45   3.84 0.4248
WVFGRD96    6.0    25    70   -40   3.83 0.4246
WVFGRD96    7.0    25    70   -35   3.84 0.4223
WVFGRD96    8.0    30    75   -30   3.84 0.4168
WVFGRD96    9.0    30    80   -30   3.84 0.4123
WVFGRD96   10.0    30    80   -30   3.86 0.4060
WVFGRD96   11.0    30    80   -30   3.87 0.3983
WVFGRD96   12.0    30    80   -30   3.88 0.3906
WVFGRD96   13.0    30    80   -30   3.88 0.3822
WVFGRD96   14.0    30    85   -30   3.89 0.3729
WVFGRD96   15.0    30    80   -30   3.89 0.3641
WVFGRD96   16.0    30    80   -25   3.90 0.3552
WVFGRD96   17.0   215    80    25   3.91 0.3479
WVFGRD96   18.0    30    90   -25   3.91 0.3357
WVFGRD96   19.0    30    85   -25   3.92 0.3266
WVFGRD96   20.0   215    80    30   3.93 0.3204
WVFGRD96   21.0   215    80    30   3.94 0.3124
WVFGRD96   22.0   215    80    30   3.94 0.3046
WVFGRD96   23.0    30    90   -30   3.95 0.2951
WVFGRD96   24.0    30    90   -25   3.95 0.2885
WVFGRD96   25.0    30    85   -25   3.96 0.2831
WVFGRD96   26.0   215    80    25   3.96 0.2807
WVFGRD96   27.0   215    80    25   3.97 0.2762
WVFGRD96   28.0   215    80    25   3.97 0.2721
WVFGRD96   29.0   215    80    25   3.97 0.2687

The best solution is

WVFGRD96    5.0    20    65   -45   3.84 0.4248

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 0.02 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.

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 CUS 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:

DATE=Wed Jan 20 05:45:45 CST 2010

Last Changed 2010/01/18