Location

2014/04/10 17:49:10 -20.035 -70.963 11.8 5.0 Chile

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  2014/04/10 17:49:10:0 -20.03  -70.96  11.8 5.0 Chile
 
 Stations used:
   C.GO01 C.GO02 CX.MNMCX CX.PATCX CX.PB01 CX.PB04 CX.PB06 
   CX.PB07 CX.PB08 CX.PB09 CX.PB10 CX.PB11 CX.PB12 CX.PB14 
   CX.PB15 CX.PB16 CX.PSGCX GT.LPAZ 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 3.59e+23 dyne-cm
  Mw = 4.97 
  Z  = 18 km
  Plane   Strike  Dip  Rake
   NP1      160    60    80
   NP2      359    31   107
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.59e+23     73      45
    N   0.00e+00      9     165
    P  -3.59e+23     14     257

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.11e+21
       Mxy    -5.70e+22
       Mxz     8.97e+22
       Myy    -3.05e+23
       Myz     1.55e+23
       Mzz     3.06e+23
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 ---##############-----              
              -----#################------           
             ------###################-----          
           --------####################------        
          ---------#####################------       
         ----------######################------      
        -----------######################-------     
        -----------##########   ##########------     
       ------------########## T ##########-------    
       -------------#########   ##########-------    
       -------------######################-------    
       --   ---------#####################-------    
        - P ----------####################------     
        -   -----------##################-------     
         --------------##################------      
          ---------------###############------       
           ---------------#############------        
             --------------###########-----          
              ---------------#######------           
                 --------------###-----              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  3.06e+23   8.97e+22  -1.55e+23 
  8.97e+22  -1.11e+21   5.70e+22 
 -1.55e+23   5.70e+22  -3.05e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140410174910/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 = 160
      DIP = 60
     RAKE = 80
       MW = 4.97
       HS = 18.0

The NDK file is 20140410174910.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2014/04/10 17:49:10:0 -20.03  -70.96  11.8 5.0 Chile
 
 Stations used:
   C.GO01 C.GO02 CX.MNMCX CX.PATCX CX.PB01 CX.PB04 CX.PB06 
   CX.PB07 CX.PB08 CX.PB09 CX.PB10 CX.PB11 CX.PB12 CX.PB14 
   CX.PB15 CX.PB16 CX.PSGCX GT.LPAZ 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 3.59e+23 dyne-cm
  Mw = 4.97 
  Z  = 18 km
  Plane   Strike  Dip  Rake
   NP1      160    60    80
   NP2      359    31   107
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.59e+23     73      45
    N   0.00e+00      9     165
    P  -3.59e+23     14     257

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.11e+21
       Mxy    -5.70e+22
       Mxz     8.97e+22
       Myy    -3.05e+23
       Myz     1.55e+23
       Mzz     3.06e+23
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 ---##############-----              
              -----#################------           
             ------###################-----          
           --------####################------        
          ---------#####################------       
         ----------######################------      
        -----------######################-------     
        -----------##########   ##########------     
       ------------########## T ##########-------    
       -------------#########   ##########-------    
       -------------######################-------    
       --   ---------#####################-------    
        - P ----------####################------     
        -   -----------##################-------     
         --------------##################------      
          ---------------###############------       
           ---------------#############------        
             --------------###########-----          
              ---------------#######------           
                 --------------###-----              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  3.06e+23   8.97e+22  -1.55e+23 
  8.97e+22  -1.11e+21   5.70e+22 
 -1.55e+23   5.70e+22  -3.05e+23 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140410174910/index.html
	

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 180
rtr
taper w 0.1
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    2.0   160    40   -90   4.72 0.4468
WVFGRD96    4.0   350    80   -85   4.83 0.3597
WVFGRD96    6.0   165    90    80   4.82 0.4970
WVFGRD96    8.0   165    90    85   4.89 0.5806
WVFGRD96   10.0   165    80    80   4.90 0.6589
WVFGRD96   12.0   165    70    85   4.93 0.7266
WVFGRD96   14.0   165    65    85   4.95 0.7748
WVFGRD96   16.0   165    60    85   4.96 0.7977
WVFGRD96   18.0   160    60    80   4.97 0.7995
WVFGRD96   20.0   160    60    80   4.97 0.7852
WVFGRD96   22.0   160    60    80   4.99 0.7627
WVFGRD96   24.0   160    65    80   4.99 0.7326
WVFGRD96   26.0   160    65    80   4.99 0.6980
WVFGRD96   28.0   155    65    75   5.00 0.6600
WVFGRD96   30.0   155    65    75   5.00 0.6193
WVFGRD96   32.0   155    65    75   5.01 0.5759
WVFGRD96   34.0   155    65    75   5.01 0.5310
WVFGRD96   36.0   155    65    75   5.02 0.4858
WVFGRD96   38.0   160    70    75   5.01 0.4451
WVFGRD96   40.0   160    75    80   5.14 0.4129
WVFGRD96   42.0   160    75    80   5.14 0.3726
WVFGRD96   44.0   150    70    70   5.14 0.3379
WVFGRD96   46.0   150    70    70   5.14 0.3084
WVFGRD96   48.0   150    70    70   5.14 0.2813
WVFGRD96   50.0   305    75    50   5.19 0.2585
WVFGRD96   52.0   305    75    50   5.19 0.2430
WVFGRD96   54.0   305    70    45   5.20 0.2300
WVFGRD96   56.0   300    75    40   5.20 0.2177
WVFGRD96   58.0   300    80    40   5.20 0.2075
WVFGRD96   60.0   300    80    40   5.21 0.2011
WVFGRD96   62.0   300    75    40   5.21 0.1955
WVFGRD96   64.0   300    75    40   5.21 0.1886
WVFGRD96   66.0   300    75    35   5.21 0.1842
WVFGRD96   68.0   295    80    30   5.22 0.1820
WVFGRD96   70.0   295    85    25   5.23 0.1818
WVFGRD96   72.0   140    50    45   5.20 0.1787
WVFGRD96   74.0   145    50    55   5.20 0.1793
WVFGRD96   76.0   145    50    55   5.21 0.1812
WVFGRD96   78.0   150    50    60   5.21 0.1815
WVFGRD96   80.0   335    65    70   5.19 0.1895
WVFGRD96   82.0   335    65    70   5.20 0.1888
WVFGRD96   84.0   335    60    70   5.21 0.2008
WVFGRD96   86.0   335    60    70   5.21 0.2059
WVFGRD96   88.0   340    55    75   5.22 0.2145
WVFGRD96   90.0   340    55    75   5.23 0.2208
WVFGRD96   92.0   340    55    75   5.23 0.2321
WVFGRD96   94.0   340    55    75   5.24 0.2358
WVFGRD96   96.0   345    50    80   5.24 0.2389
WVFGRD96   98.0   340    50    80   5.25 0.2517
WVFGRD96  100.0   335    50    75   5.26 0.2542
WVFGRD96  102.0   335    50    75   5.26 0.2577
WVFGRD96  104.0   340    45    80   5.27 0.2684
WVFGRD96  106.0   340    45    80   5.27 0.2724
WVFGRD96  108.0   340    40    80   5.28 0.2749

The best solution is

WVFGRD96   18.0   160    60    80   4.97 0.7995

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 180
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.06 n 3 
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 WUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
Model after     8 iterations
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
     1.9000     3.4065     2.0089     2.2150  0.302E-02  0.679E-02   0.00       0.00       1.00       1.00    
     6.1000     5.5445     3.2953     2.6089  0.349E-02  0.784E-02   0.00       0.00       1.00       1.00    
    13.0000     6.2708     3.7396     2.7812  0.212E-02  0.476E-02   0.00       0.00       1.00       1.00    
    19.0000     6.4075     3.7680     2.8223  0.111E-02  0.249E-02   0.00       0.00       1.00       1.00    
     0.0000     7.9000     4.6200     3.2760  0.164E-10  0.370E-10   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 Thu Apr 10 20:29:03 CDT 2014