Location

2011/07/24 12:19:28 47.708 -123.178 42 3.70 Washington

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  2011/07/24 12:19:28:0  47.71 -123.18  42.0 3.7 Washington
 
 Stations used:
   IU.COR UW.DAVN UW.LEBA UW.LON UW.LTY UW.MRBL UW.OMAK 
   UW.STOR UW.TUCA UW.WOLL UW.YACT 
 
 Filtering commands used:
   hp c 0.03 n 3
   lp c 0.06 n 3
   br c 0.12 0.20 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 5.89e+21 dyne-cm
  Mw = 3.78 
  Z  = 44 km
  Plane   Strike  Dip  Rake
   NP1      285    50   -60
   NP2       63    48   -121
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.89e+21      1     354
    N   0.00e+00     23      85
    P  -5.89e+21     67     262

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.81e+21
       Mxy    -6.98e+20
       Mxz     3.66e+20
       Myy    -7.91e+20
       Myz     2.06e+21
       Mzz    -5.02e+21
                                                     
                                                     
                                                     
                                                     
                     ### T ########                  
                 #######   ############              
              ############################           
             ##############################          
           ##################################        
          #######------------#################       
         ###-----------------------###########-      
        #-----------------------------########--     
        ---------------------------------#####--     
       ------------------------------------##----    
       --------------   --------------------#----    
       -------------- P -------------------###---    
       --------------   -----------------######--    
        -------------------------------#########     
        -----------------------------###########     
         -------------------------#############      
          #--------------------###############       
           #####---------####################        
             ##############################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.02e+21   3.66e+20  -2.06e+21 
  3.66e+20   5.81e+21   6.98e+20 
 -2.06e+21   6.98e+20  -7.91e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110724121928/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 = 285
      DIP = 50
     RAKE = -60
       MW = 3.78
       HS = 44.0

The NDK file is 20110724121928.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2011/07/24 12:19:28:0  47.71 -123.18  42.0 3.7 Washington
 
 Stations used:
   IU.COR UW.DAVN UW.LEBA UW.LON UW.LTY UW.MRBL UW.OMAK 
   UW.STOR UW.TUCA UW.WOLL UW.YACT 
 
 Filtering commands used:
   hp c 0.03 n 3
   lp c 0.06 n 3
   br c 0.12 0.20 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 5.89e+21 dyne-cm
  Mw = 3.78 
  Z  = 44 km
  Plane   Strike  Dip  Rake
   NP1      285    50   -60
   NP2       63    48   -121
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.89e+21      1     354
    N   0.00e+00     23      85
    P  -5.89e+21     67     262

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.81e+21
       Mxy    -6.98e+20
       Mxz     3.66e+20
       Myy    -7.91e+20
       Myz     2.06e+21
       Mzz    -5.02e+21
                                                     
                                                     
                                                     
                                                     
                     ### T ########                  
                 #######   ############              
              ############################           
             ##############################          
           ##################################        
          #######------------#################       
         ###-----------------------###########-      
        #-----------------------------########--     
        ---------------------------------#####--     
       ------------------------------------##----    
       --------------   --------------------#----    
       -------------- P -------------------###---    
       --------------   -----------------######--    
        -------------------------------#########     
        -----------------------------###########     
         -------------------------#############      
          #--------------------###############       
           #####---------####################        
             ##############################          
              ############################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.02e+21   3.66e+20  -2.06e+21 
  3.66e+20   5.81e+21   6.98e+20 
 -2.06e+21   6.98e+20  -7.91e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110724121928/index.html
	

Magnitudes

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 0.03 n 3
lp c 0.06 n 3
br c 0.12 0.20 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    75    45    90   3.10 0.2730
WVFGRD96    1.0    75    45    90   3.13 0.2733
WVFGRD96    2.0    80    45    95   3.23 0.3421
WVFGRD96    3.0    75    45    90   3.28 0.3416
WVFGRD96    4.0   255    45    85   3.31 0.3187
WVFGRD96    5.0   235    60    60   3.30 0.3193
WVFGRD96    6.0    50    75    55   3.30 0.3274
WVFGRD96    7.0    50    75    50   3.29 0.3335
WVFGRD96    8.0    55    70    65   3.37 0.3445
WVFGRD96    9.0    55    70    65   3.37 0.3492
WVFGRD96   10.0    60    65    65   3.37 0.3533
WVFGRD96   11.0    55    65    60   3.37 0.3567
WVFGRD96   12.0    55    65    55   3.37 0.3677
WVFGRD96   13.0    55    60    55   3.38 0.3793
WVFGRD96   14.0    55    60    50   3.39 0.3888
WVFGRD96   15.0    55    60    50   3.39 0.3970
WVFGRD96   16.0    55    60    45   3.40 0.4034
WVFGRD96   17.0    55    60    45   3.41 0.4092
WVFGRD96   18.0    55    60    45   3.42 0.4133
WVFGRD96   19.0    55    60    45   3.42 0.4165
WVFGRD96   20.0    55    60    45   3.43 0.4189
WVFGRD96   21.0    55    60    45   3.44 0.4204
WVFGRD96   22.0   105    50   -45   3.44 0.4215
WVFGRD96   23.0   105    50   -45   3.45 0.4276
WVFGRD96   24.0   110    50   -40   3.46 0.4335
WVFGRD96   25.0   110    50   -40   3.47 0.4394
WVFGRD96   26.0   295    55   -40   3.49 0.4507
WVFGRD96   27.0   295    55   -40   3.50 0.4623
WVFGRD96   28.0   295    55   -40   3.51 0.4733
WVFGRD96   29.0   295    55   -40   3.52 0.4838
WVFGRD96   30.0   300    60   -40   3.54 0.4937
WVFGRD96   31.0   300    60   -40   3.55 0.5036
WVFGRD96   32.0   300    60   -40   3.56 0.5129
WVFGRD96   33.0   300    60   -40   3.57 0.5214
WVFGRD96   34.0   300    60   -40   3.59 0.5298
WVFGRD96   35.0   300    60   -40   3.60 0.5378
WVFGRD96   36.0   300    60   -40   3.61 0.5453
WVFGRD96   37.0   300    60   -40   3.62 0.5524
WVFGRD96   38.0   300    60   -40   3.63 0.5590
WVFGRD96   39.0   295    55   -45   3.64 0.5646
WVFGRD96   40.0   290    50   -55   3.74 0.5776
WVFGRD96   41.0   290    50   -55   3.75 0.5832
WVFGRD96   42.0   290    50   -55   3.76 0.5864
WVFGRD96   43.0   290    50   -55   3.77 0.5879
WVFGRD96   44.0   285    50   -60   3.78 0.5880
WVFGRD96   45.0   285    50   -60   3.78 0.5874
WVFGRD96   46.0   285    50   -60   3.79 0.5855
WVFGRD96   47.0   285    50   -60   3.80 0.5824
WVFGRD96   48.0   280    50   -60   3.80 0.5788
WVFGRD96   49.0   280    50   -65   3.81 0.5750
WVFGRD96   50.0   275    50   -65   3.81 0.5706
WVFGRD96   51.0   275    50   -65   3.82 0.5661
WVFGRD96   52.0   275    50   -70   3.83 0.5615
WVFGRD96   53.0   275    50   -70   3.83 0.5561
WVFGRD96   54.0   270    50   -70   3.83 0.5506
WVFGRD96   55.0   270    50   -75   3.84 0.5452
WVFGRD96   56.0   270    50   -75   3.84 0.5392
WVFGRD96   57.0   270    50   -75   3.85 0.5331
WVFGRD96   58.0   270    50   -75   3.85 0.5265
WVFGRD96   59.0   265    50   -80   3.86 0.5200
WVFGRD96   60.0   270    55   -70   3.85 0.5144
WVFGRD96   61.0   270    55   -70   3.85 0.5099
WVFGRD96   62.0   270    55   -70   3.85 0.5048
WVFGRD96   63.0   270    55   -70   3.86 0.4999
WVFGRD96   64.0   270    55   -75   3.86 0.4944
WVFGRD96   65.0   270    55   -75   3.87 0.4890
WVFGRD96   66.0   325    75   -50   3.86 0.4825
WVFGRD96   67.0   325    75   -50   3.86 0.4809
WVFGRD96   68.0   325    75   -50   3.86 0.4786
WVFGRD96   69.0   325    75   -50   3.87 0.4759

The best solution is

WVFGRD96   44.0   285    50   -60   3.78 0.5880

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 0.03 n 3
lp c 0.06 n 3
br c 0.12 0.20 n 4 p 2
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 WUS model 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 Sun Dec 6 20:50:07 CST 2015