Location

2011/09/11 12:27:45 32.874 -100.804 10.0 4.40 Texas

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  2011/09/11 12:27:45:6  32.87 -100.80  10.0 4.4 Texas
 
 Stations used:
   EP.KIDD IU.ANMO TA.136A TA.137A TA.233A TA.234A TA.236A 
   TA.333A TA.334A TA.335A TA.336A TA.433A TA.434A TA.435B 
   TA.436A TA.534A TA.535A TA.536A TA.633A TA.634A TA.635A 
   TA.733A TA.ABTX TA.MSTX TA.T25A TA.TUL1 TA.U32A TA.U35A 
   TA.V36A TA.W35A TA.W36A TA.W37B TA.WHTX TA.X35A TA.X36A 
   TA.X37A TA.Y35A TA.Y36A TA.Y37A TA.Y38A TA.Z33A TA.Z36A 
   US.AMTX US.JCT US.MNTX US.WMOK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 5.19e+22 dyne-cm
  Mw = 4.41 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      207    85   -160
   NP2      115    70    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.19e+22     11     339
    N   0.00e+00     69     219
    P  -5.19e+22     17      73

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.96e+22
       Mxy    -3.01e+22
       Mxz     4.33e+21
       Myy    -3.67e+22
       Myz    -1.75e+22
       Mzz    -2.91e+21
                                                     
                                                     
                                                     
                                                     
                       ############                  
                 ### T ##############--              
              ######   ############-------           
             #####################---------          
           ######################------------        
          ######################--------------       
         ######################----------------      
        ---###################-------------   --     
        ----#################-------------- P --     
       -------##############---------------   ---    
       ----------##########----------------------    
       ------------#######-----------------------    
       ---------------###------------------------    
        ----------------##----------------------     
        ----------------######------------------     
         --------------##############----------      
          ------------########################       
           ----------########################        
             -------#######################          
              ------######################           
                 --####################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.91e+21   4.33e+21   1.75e+22 
  4.33e+21   3.96e+22   3.01e+22 
  1.75e+22   3.01e+22  -3.67e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110911122745/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 = 115
      DIP = 70
     RAKE = -5
       MW = 4.41
       HS = 5.0

The NDK file is 20110911122745.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
GCMT
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2011/09/11 12:27:45:6  32.87 -100.80  10.0 4.4 Texas
 
 Stations used:
   EP.KIDD IU.ANMO TA.136A TA.137A TA.233A TA.234A TA.236A 
   TA.333A TA.334A TA.335A TA.336A TA.433A TA.434A TA.435B 
   TA.436A TA.534A TA.535A TA.536A TA.633A TA.634A TA.635A 
   TA.733A TA.ABTX TA.MSTX TA.T25A TA.TUL1 TA.U32A TA.U35A 
   TA.V36A TA.W35A TA.W36A TA.W37B TA.WHTX TA.X35A TA.X36A 
   TA.X37A TA.Y35A TA.Y36A TA.Y37A TA.Y38A TA.Z33A TA.Z36A 
   US.AMTX US.JCT US.MNTX US.WMOK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 5.19e+22 dyne-cm
  Mw = 4.41 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      207    85   -160
   NP2      115    70    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.19e+22     11     339
    N   0.00e+00     69     219
    P  -5.19e+22     17      73

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.96e+22
       Mxy    -3.01e+22
       Mxz     4.33e+21
       Myy    -3.67e+22
       Myz    -1.75e+22
       Mzz    -2.91e+21
                                                     
                                                     
                                                     
                                                     
                       ############                  
                 ### T ##############--              
              ######   ############-------           
             #####################---------          
           ######################------------        
          ######################--------------       
         ######################----------------      
        ---###################-------------   --     
        ----#################-------------- P --     
       -------##############---------------   ---    
       ----------##########----------------------    
       ------------#######-----------------------    
       ---------------###------------------------    
        ----------------##----------------------     
        ----------------######------------------     
         --------------##############----------      
          ------------########################       
           ----------########################        
             -------#######################          
              ------######################           
                 --####################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.91e+21   4.33e+21   1.75e+22 
  4.33e+21   3.96e+22   3.01e+22 
  1.75e+22   3.01e+22  -3.67e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110911122745/index.html
	
USGS/SLU Regional Moment Solution
WESTERN TEXAS

11/09/11 12:27:45.27

Epicenter:  32.855 -100.899
MW 4.3

USGS/SLU REGIONAL MOMENT TENSOR
Depth   6         No. of sta: 17
Moment Tensor;   Scale 10**15 Nm
  Mrr=-0.55       Mtt= 3.29
  Mpp=-2.74       Mrt=-0.71
  Mrp=-0.66       Mtp= 1.78
 Principal axes:
  T  Val=  3.94  Plg=11  Azm=164
  N       -0.64      75       26
  P       -3.30      10      256

Best Double Couple:Mo=3.7*10**15
 NP1:Strike=210 Dip=89 Slip= 165
 NP2:       300     75         1


eptember 11, 2011, WESTERN TEXAS, MW=4.5

Meredith Nettles

CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     S201109111227A
DATA: IU II LD G  CU TA US BK
SURFACE WAVES:  80S, 107C, T= 50
TIMESTAMP:      Q-20110911220257
CENTROID LOCATION:
ORIGIN TIME:      12:27:45.8 0.5
LAT:32.83N 0.03;LON:100.80W 0.02
DEP: 12.0  FIX;TRIANG HDUR:  0.4
MOMENT TENSOR: SCALE 10**22 D-CM
RR=-1.600 0.242; TT= 5.360 0.252
PP=-3.760 0.237; RT= 1.570 0.873
RP= 2.710 0.786; TP= 3.420 0.214
PRINCIPAL AXES:
1.(T) VAL=  7.156;PLG=16;AZM=339
2.(N)      -1.166;    58;    223
3.(P)      -5.990;    28;     77
BEST DBLE.COUPLE:M0= 6.57*10**22
NP1: STRIKE=115;DIP=59;SLIP=  -9
NP2: STRIKE=210;DIP=82;SLIP=-148

             #########
       ### T ###########--
     #####   ##########-----
   ##################---------
  ##################-----------
 -#################-------------
 -###############----------   --
 ----############----------- P ---
 -----##########------------   ---
 -------#######-------------------
 ---------####--------------------
 -------------------------------
 ----------#####----------------
  --------#############----####
   -------####################
     ----###################
       -##################
           ###########
        


First motions and takeoff angles from an elocate run.

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 0.06 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   115    50    -5   4.39 0.5939
WVFGRD96    1.0   115    55    -5   4.39 0.6132
WVFGRD96    2.0   115    65   -10   4.39 0.6413
WVFGRD96    3.0   115    70   -10   4.40 0.6553
WVFGRD96    4.0   115    70   -10   4.41 0.6605
WVFGRD96    5.0   115    70    -5   4.41 0.6609
WVFGRD96    6.0   115    70    -5   4.42 0.6587
WVFGRD96    7.0   115    70    -5   4.43 0.6553
WVFGRD96    8.0   115    70    -5   4.43 0.6513
WVFGRD96    9.0   115    70    -5   4.44 0.6468
WVFGRD96   10.0   115    70    -5   4.45 0.6438
WVFGRD96   11.0   115    70   -10   4.46 0.6364
WVFGRD96   12.0   115    85   -30   4.48 0.6323
WVFGRD96   13.0   115    85   -30   4.49 0.6288
WVFGRD96   14.0   115    85   -25   4.49 0.6251
WVFGRD96   15.0   115    85   -25   4.50 0.6205
WVFGRD96   16.0   115    85   -25   4.50 0.6152
WVFGRD96   17.0   115    85   -25   4.51 0.6090
WVFGRD96   18.0   115    85   -25   4.51 0.6019
WVFGRD96   19.0   115    85   -25   4.52 0.5939
WVFGRD96   20.0   115    80   -25   4.53 0.5854
WVFGRD96   21.0   115    80   -25   4.54 0.5771
WVFGRD96   22.0   115    80   -25   4.54 0.5681
WVFGRD96   23.0   115    80   -25   4.55 0.5585
WVFGRD96   24.0   300    80    20   4.55 0.5437
WVFGRD96   25.0   300    80    20   4.55 0.5335
WVFGRD96   26.0   300    80    20   4.56 0.5231
WVFGRD96   27.0   300    85    30   4.57 0.5126
WVFGRD96   28.0   300    85    30   4.58 0.5030
WVFGRD96   29.0   300    85    30   4.59 0.4929

The best solution is

WVFGRD96    5.0   115    70    -5   4.41 0.6609

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

hp c 0.02 n 3
lp c 0.06 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 Sun Dec 6 22:41:34 CST 2015