Location

2013/09/21 14:48:23 49.797 -66.067 5.0 4.4 Quebec

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  2013/09/21 14:48:23:0  49.80  -66.07   5.0 4.4 Quebec
 
 Stations used:
   CN.A11 CN.A16 CN.A21 CN.A54 CN.A61 CN.A64 CN.BATG CN.DMCQ 
   CN.DRLN CN.ICQ CN.NATG CN.SCHQ NE.EMMW NE.PQI NE.WVL 
   PO.CHGQ PO.LATQ TA.D58A TA.D59A TA.D60A TA.D61A TA.E58A 
   TA.E59A TA.E60A TA.E61A TA.F59A TA.F60A TA.F61A TA.H65A 
 
 Filtering commands used:
   cut a -30 a 210
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 1.10e+22 dyne-cm
  Mw = 3.96 
  Z  = 27 km
  Plane   Strike  Dip  Rake
   NP1      135    50    60
   NP2      357    48   121
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.10e+22     67     338
    N   0.00e+00     23     155
    P  -1.10e+22      1     246

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.76e+20
       Mxy    -4.68e+21
       Mxz     3.66e+21
       Myy    -8.88e+21
       Myz    -1.33e+21
       Mzz     9.35e+21
                                                     
                                                     
                                                     
                                                     
                     ########------                  
                 ##############--------              
              ###################---------           
             #####################---------          
           --######################----------        
          ---#######################----------       
         ----###########   ##########----------      
        -----########### T ##########-----------     
        ------##########   ###########----------     
       -------########################-----------    
       --------#######################-----------    
       ---------######################-----------    
       ----------#####################-----------    
        -----------###################----------     
           ---------##################----------     
         P -----------################---------      
           -------------#############---------       
           ----------------#########---------        
             ------------------####--------          
              --------------------########           
                 ----------------######              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  9.35e+21   3.66e+21   1.33e+21 
  3.66e+21  -4.76e+20   4.68e+21 
  1.33e+21   4.68e+21  -8.88e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130921144823/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 = 135
      DIP = 50
     RAKE = 60
       MW = 3.96
       HS = 27.0

The NDK file is 20130921144823.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2013/09/21 14:48:23:0  49.80  -66.07   5.0 4.4 Quebec
 
 Stations used:
   CN.A11 CN.A16 CN.A21 CN.A54 CN.A61 CN.A64 CN.BATG CN.DMCQ 
   CN.DRLN CN.ICQ CN.NATG CN.SCHQ NE.EMMW NE.PQI NE.WVL 
   PO.CHGQ PO.LATQ TA.D58A TA.D59A TA.D60A TA.D61A TA.E58A 
   TA.E59A TA.E60A TA.E61A TA.F59A TA.F60A TA.F61A TA.H65A 
 
 Filtering commands used:
   cut a -30 a 210
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 1.10e+22 dyne-cm
  Mw = 3.96 
  Z  = 27 km
  Plane   Strike  Dip  Rake
   NP1      135    50    60
   NP2      357    48   121
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.10e+22     67     338
    N   0.00e+00     23     155
    P  -1.10e+22      1     246

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.76e+20
       Mxy    -4.68e+21
       Mxz     3.66e+21
       Myy    -8.88e+21
       Myz    -1.33e+21
       Mzz     9.35e+21
                                                     
                                                     
                                                     
                                                     
                     ########------                  
                 ##############--------              
              ###################---------           
             #####################---------          
           --######################----------        
          ---#######################----------       
         ----###########   ##########----------      
        -----########### T ##########-----------     
        ------##########   ###########----------     
       -------########################-----------    
       --------#######################-----------    
       ---------######################-----------    
       ----------#####################-----------    
        -----------###################----------     
           ---------##################----------     
         P -----------################---------      
           -------------#############---------       
           ----------------#########---------        
             ------------------####--------          
              --------------------########           
                 ----------------######              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  9.35e+21   3.66e+21   1.33e+21 
  3.66e+21  -4.76e+20   4.68e+21 
  1.33e+21   4.68e+21  -8.88e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130921144823/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 a -30 a 210
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 n 3 
br c 0.12 0.25 n 4 p 2
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   125    45   -85   3.65 0.5768
WVFGRD96    1.0   305    45   -90   3.68 0.5995
WVFGRD96    2.0   325    45   -90   3.75 0.6009
WVFGRD96    3.0   190    65   -30   3.83 0.5238
WVFGRD96    4.0    20    65     5   3.85 0.4751
WVFGRD96    5.0   200    30   -10   3.77 0.5010
WVFGRD96    6.0   205    30    -5   3.75 0.5296
WVFGRD96    7.0   210    30     0   3.74 0.5516
WVFGRD96    8.0   210    45    20   3.80 0.5685
WVFGRD96    9.0   210    45    20   3.79 0.5827
WVFGRD96   10.0   215    35    15   3.78 0.5913
WVFGRD96   11.0   210    45    20   3.82 0.6031
WVFGRD96   12.0   210    45    20   3.83 0.6138
WVFGRD96   13.0   215    45    30   3.84 0.6240
WVFGRD96   14.0   215    45    30   3.85 0.6332
WVFGRD96   15.0   215    45    30   3.85 0.6411
WVFGRD96   16.0   215    45    30   3.86 0.6480
WVFGRD96   17.0   220    40    25   3.84 0.6543
WVFGRD96   18.0   210    50    30   3.89 0.6597
WVFGRD96   19.0   210    50    30   3.90 0.6644
WVFGRD96   20.0   220    35    20   3.88 0.6658
WVFGRD96   21.0   225    30    20   3.87 0.6684
WVFGRD96   22.0   135    60    60   3.91 0.6764
WVFGRD96   23.0   140    55    60   3.92 0.6841
WVFGRD96   24.0   135    55    55   3.94 0.6900
WVFGRD96   25.0   135    55    55   3.95 0.6944
WVFGRD96   26.0   130    55    55   3.96 0.6962
WVFGRD96   27.0   135    50    60   3.96 0.6964
WVFGRD96   28.0   135    50    60   3.97 0.6954
WVFGRD96   29.0   135    50    60   3.98 0.6921
WVFGRD96   30.0   130    50    55   4.00 0.6882
WVFGRD96   31.0   130    50    55   4.01 0.6821
WVFGRD96   32.0   130    50    55   4.03 0.6738
WVFGRD96   33.0   135    45    60   4.03 0.6650
WVFGRD96   34.0   135    45    60   4.04 0.6543
WVFGRD96   35.0   135    45    60   4.05 0.6417
WVFGRD96   36.0   135    45    55   4.08 0.6283
WVFGRD96   37.0   130    45    55   4.09 0.6122
WVFGRD96   38.0   130    45    55   4.11 0.5947
WVFGRD96   39.0   145    40    60   4.12 0.5750
WVFGRD96   40.0   305    70   -70   4.16 0.5656
WVFGRD96   41.0   305    70   -70   4.17 0.5488
WVFGRD96   42.0   310    70   -65   4.17 0.5340
WVFGRD96   43.0   310    70   -65   4.17 0.5206
WVFGRD96   44.0   310    70   -60   4.18 0.5080
WVFGRD96   45.0   310    70   -60   4.18 0.4821
WVFGRD96   46.0   310    70   -60   4.18 0.4709
WVFGRD96   47.0   310    70   -55   4.20 0.4601
WVFGRD96   48.0   310    70   -55   4.20 0.4500
WVFGRD96   49.0   310    70   -55   4.21 0.4401
WVFGRD96   50.0   310    70   -55   4.21 0.4304

The best solution is

WVFGRD96   27.0   135    50    60   3.96 0.6964

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 a -30 a 210
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 n 3 
br c 0.12 0.25 n 4 p 2
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 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 00:23:08 CST 2015