Location

2011/01/08 19:33:40 59.355 -135.024 1.0 4.20 Alaska

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  2011/01/08 19:33:40:0  59.35 -135.02   1.0 4.2 Alaska
 
 Stations used:
   AK.BAL AK.BMR AK.DCPH AK.EYAK AK.PIN AK.PNL AK.RAG AT.SKAG 
   AT.YKU2 CN.BVCY CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY 
   CN.YUK5 US.WRAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 6.10e+21 dyne-cm
  Mw = 3.79 
  Z  = 2 km
  Plane   Strike  Dip  Rake
   NP1      180    45    90
   NP2      360    45    90
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.10e+21     90     145
    N   0.00e+00     -0       0
    P  -6.10e+21     -0     270

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     0.00e+00
       Mxy    -1.88e+14
       Mxz     1.88e+14
       Myy    -6.10e+21
       Myz    -2.66e+14
       Mzz     6.10e+21
                                                     
                                                     
                                                     
                                                     
                     -----####-----                  
                 -------########-------              
              --------############--------           
             --------##############--------          
           ---------################---------        
          ---------##################---------       
         ---------####################---------      
        ----------####################----------     
        ---------######################---------     
       ----------######################----------    
         --------##########   #########----------    
       P --------########## T #########----------    
         --------##########   #########----------    
        ---------######################---------     
        ----------####################----------     
         ---------####################---------      
          ---------##################---------       
           ---------################---------        
             --------##############--------          
              --------############--------           
                 -------########-------              
                     -----####-----                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  6.10e+21   1.88e+14   2.66e+14 
  1.88e+14   0.00e+00   1.88e+14 
  2.66e+14   1.88e+14  -6.10e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110108193340/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 = 0
      DIP = 45
     RAKE = 90
       MW = 3.79
       HS = 2.0

The NDK file is 20110108193340.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2011/01/08 19:33:40:0  59.35 -135.02   1.0 4.2 Alaska
 
 Stations used:
   AK.BAL AK.BMR AK.DCPH AK.EYAK AK.PIN AK.PNL AK.RAG AT.SKAG 
   AT.YKU2 CN.BVCY CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY 
   CN.YUK5 US.WRAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 6.10e+21 dyne-cm
  Mw = 3.79 
  Z  = 2 km
  Plane   Strike  Dip  Rake
   NP1      180    45    90
   NP2      360    45    90
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.10e+21     90     145
    N   0.00e+00     -0       0
    P  -6.10e+21     -0     270

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     0.00e+00
       Mxy    -1.88e+14
       Mxz     1.88e+14
       Myy    -6.10e+21
       Myz    -2.66e+14
       Mzz     6.10e+21
                                                     
                                                     
                                                     
                                                     
                     -----####-----                  
                 -------########-------              
              --------############--------           
             --------##############--------          
           ---------################---------        
          ---------##################---------       
         ---------####################---------      
        ----------####################----------     
        ---------######################---------     
       ----------######################----------    
         --------##########   #########----------    
       P --------########## T #########----------    
         --------##########   #########----------    
        ---------######################---------     
        ----------####################----------     
         ---------####################---------      
          ---------##################---------       
           ---------################---------        
             --------##############--------          
              --------############--------           
                 -------########-------              
                     -----####-----                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  6.10e+21   1.88e+14   2.66e+14 
  1.88e+14   0.00e+00   1.88e+14 
  2.66e+14   1.88e+14  -6.10e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110108193340/index.html
	


First motions and takeoff angles from an elocate run.

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 0.02 n 3
lp c 0.06 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     0    45    90   3.69 0.6476
WVFGRD96    1.0   160    60    45   3.71 0.5627
WVFGRD96    2.0     0    45    90   3.79 0.6500
WVFGRD96    3.0   175    40    80   3.84 0.5841
WVFGRD96    4.0   160    30    55   3.90 0.5265
WVFGRD96    5.0   170    80    85   3.94 0.5333
WVFGRD96    6.0   170    80    85   3.92 0.5721
WVFGRD96    7.0   170    80    85   3.89 0.5911
WVFGRD96    8.0   170    80    85   3.96 0.6058
WVFGRD96    9.0   170    80    80   3.94 0.6172
WVFGRD96   10.0   170    80    80   3.92 0.6243
WVFGRD96   11.0   165    85    80   3.92 0.6263
WVFGRD96   12.0   165    85    80   3.91 0.6287
WVFGRD96   13.0   345    90   -75   3.91 0.6253
WVFGRD96   14.0   165    85    75   3.91 0.6285
WVFGRD96   15.0   165    90    75   3.91 0.6268
WVFGRD96   16.0   345    90   -80   3.91 0.6259
WVFGRD96   17.0   345    90   -80   3.91 0.6241
WVFGRD96   18.0   350    85   -85   3.90 0.6235
WVFGRD96   19.0   350    85   -85   3.91 0.6220
WVFGRD96   20.0   350    80   -90   3.92 0.6203
WVFGRD96   21.0   180    10   -85   3.93 0.6182
WVFGRD96   22.0   195    15   -70   3.95 0.6173
WVFGRD96   23.0   200    15   -65   3.95 0.6160
WVFGRD96   24.0   200    15   -65   3.96 0.6136
WVFGRD96   25.0   200    15   -65   3.97 0.6102
WVFGRD96   26.0   200    15   -70   3.97 0.6058
WVFGRD96   27.0   200    15   -70   3.98 0.6003
WVFGRD96   28.0   205    15   -65   3.98 0.5936
WVFGRD96   29.0   200    15   -70   3.99 0.5858
WVFGRD96   30.0   210    15   -60   4.00 0.5766
WVFGRD96   31.0   210    15   -60   4.00 0.5665
WVFGRD96   32.0   210    15   -60   4.01 0.5555
WVFGRD96   33.0   215    15   -55   4.02 0.5435
WVFGRD96   34.0   220    15   -50   4.02 0.5312
WVFGRD96   35.0   225    15   -45   4.02 0.5185
WVFGRD96   36.0   225    15   -45   4.03 0.5066
WVFGRD96   37.0   230    15   -40   4.03 0.4954
WVFGRD96   38.0   205    10   -65   4.02 0.4850
WVFGRD96   39.0   210    10   -60   4.02 0.4778
WVFGRD96   40.0   210     5   -55   4.17 0.4689
WVFGRD96   41.0   215     5   -50   4.18 0.4597
WVFGRD96   42.0   210     5   -55   4.18 0.4504
WVFGRD96   43.0   220     5   -45   4.18 0.4408
WVFGRD96   44.0   220     5   -45   4.19 0.4310
WVFGRD96   45.0   220     5   -45   4.19 0.4211
WVFGRD96   46.0   230     5   -35   4.20 0.4111
WVFGRD96   47.0    40    30   -40   4.17 0.4046
WVFGRD96   48.0    40    30   -40   4.18 0.4003
WVFGRD96   49.0    45    35   -40   4.18 0.3962

The best solution is

WVFGRD96    2.0     0    45    90   3.79 0.6500

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
br c 0.12 0.25 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 Mon Dec 7 03:03:18 CST 2015