Location

2014/11/29 21:06:49 62.556 -148.106 59.9 4.6 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  2014/11/29 21:06:49:0  62.56 -148.11  59.9 4.6 Alaska
 
 Stations used:
   AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CNP AK.CRQ AK.CTG AK.DHY 
   AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT 
   AK.ISLE AK.KLU AK.KNK AK.KTH AK.MDM AK.MESA AK.PAX AK.PPLA 
   AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.SUCK AK.SWD 
   AK.TGL AK.TRF AK.WRH AK.YAH AT.PMR AT.TTA CN.HYT IM.IL31 
   IU.COLA TA.I23K TA.M24K TA.N25K TA.POKR US.EGAK 
 
 Filtering commands used:
   cut o DIST/3.3 -50 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 1.19e+23 dyne-cm
  Mw = 4.65 
  Z  = 74 km
  Plane   Strike  Dip  Rake
   NP1      220    73   -148
   NP2      120    60   -20
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.19e+23      8     348
    N   0.00e+00     54     246
    P  -1.19e+23     34      84

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.10e+23
       Mxy    -3.31e+22
       Mxz     1.03e+22
       Myy    -7.50e+22
       Myz    -5.85e+22
       Mzz    -3.52e+22
                                                     
                                                     
                                                     
                                                     
                     # T ##########                  
                 #####   ##############              
              ###########################-           
             ########################------          
           #######################-----------        
          ######################--------------       
         --###################-----------------      
        ---#################--------------------     
        ----##############----------------------     
       ------############---------------   ------    
       --------########----------------- P ------    
       ----------#####------------------   ------    
       ------------#-----------------------------    
        -----------##---------------------------     
        ----------######------------------------     
         --------###########-------------------      
          ------#################-------------       
           -----#############################        
             --############################          
              -###########################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.52e+22   1.03e+22   5.85e+22 
  1.03e+22   1.10e+23   3.31e+22 
  5.85e+22   3.31e+22  -7.50e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141129210649/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 = 120
      DIP = 60
     RAKE = -20
       MW = 4.65
       HS = 74.0

The NDK file is 20141129210649.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
 USGS/SLU Moment Tensor Solution
 ENS  2014/11/29 21:06:49:0  62.56 -148.11  59.9 4.6 Alaska
 
 Stations used:
   AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CNP AK.CRQ AK.CTG AK.DHY 
   AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI AK.HDA AK.HIN AK.HMT 
   AK.ISLE AK.KLU AK.KNK AK.KTH AK.MDM AK.MESA AK.PAX AK.PPLA 
   AK.RIDG AK.RND AK.SAW AK.SCM AK.SKN AK.SSN AK.SUCK AK.SWD 
   AK.TGL AK.TRF AK.WRH AK.YAH AT.PMR AT.TTA CN.HYT IM.IL31 
   IU.COLA TA.I23K TA.M24K TA.N25K TA.POKR US.EGAK 
 
 Filtering commands used:
   cut o DIST/3.3 -50 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 1.19e+23 dyne-cm
  Mw = 4.65 
  Z  = 74 km
  Plane   Strike  Dip  Rake
   NP1      220    73   -148
   NP2      120    60   -20
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.19e+23      8     348
    N   0.00e+00     54     246
    P  -1.19e+23     34      84

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.10e+23
       Mxy    -3.31e+22
       Mxz     1.03e+22
       Myy    -7.50e+22
       Myz    -5.85e+22
       Mzz    -3.52e+22
                                                     
                                                     
                                                     
                                                     
                     # T ##########                  
                 #####   ##############              
              ###########################-           
             ########################------          
           #######################-----------        
          ######################--------------       
         --###################-----------------      
        ---#################--------------------     
        ----##############----------------------     
       ------############---------------   ------    
       --------########----------------- P ------    
       ----------#####------------------   ------    
       ------------#-----------------------------    
        -----------##---------------------------     
        ----------######------------------------     
         --------###########-------------------      
          ------#################-------------       
           -----#############################        
             --############################          
              -###########################           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -3.52e+22   1.03e+22   5.85e+22 
  1.03e+22   1.10e+23   3.31e+22 
  5.85e+22   3.31e+22  -7.50e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20141129210649/index.html
	
Type Magnitude Depth NP1 NP2 Author Catalog Contributor
Mww 4.6 60.5 km 214, 75, -144 114, 55, -18 us us
Mwr 4.7 70.0 km 222, 70, -145 119, 58, -24 us us
        

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:

cut o DIST/3.3 -50 o DIST/3.3 +70
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   225    60    45   3.90 0.2799
WVFGRD96    4.0   290    55   -35   3.97 0.2928
WVFGRD96    6.0   295    70   -20   3.99 0.3268
WVFGRD96    8.0   295    70   -20   4.05 0.3567
WVFGRD96   10.0   110    70   -20   4.09 0.3687
WVFGRD96   12.0   125    65    25   4.11 0.3794
WVFGRD96   14.0   125    65    25   4.13 0.3905
WVFGRD96   16.0   125    70    25   4.15 0.4008
WVFGRD96   18.0   125    70    20   4.17 0.4098
WVFGRD96   20.0   305    70    20   4.19 0.4219
WVFGRD96   22.0   305    70    20   4.21 0.4342
WVFGRD96   24.0   305    75    20   4.23 0.4452
WVFGRD96   26.0   305    75    20   4.25 0.4557
WVFGRD96   28.0   120    75   -15   4.27 0.4684
WVFGRD96   30.0   120    75   -15   4.29 0.4821
WVFGRD96   32.0   120    75   -15   4.31 0.4937
WVFGRD96   34.0   115    75   -20   4.33 0.5068
WVFGRD96   36.0   115    75   -20   4.36 0.5203
WVFGRD96   38.0   120    80   -15   4.39 0.5340
WVFGRD96   40.0   115    65   -20   4.45 0.5469
WVFGRD96   42.0   115    65   -20   4.47 0.5549
WVFGRD96   44.0   115    65   -25   4.49 0.5656
WVFGRD96   46.0   115    65   -20   4.51 0.5809
WVFGRD96   48.0   115    60   -25   4.53 0.5976
WVFGRD96   50.0   115    60   -25   4.54 0.6169
WVFGRD96   52.0   115    60   -25   4.56 0.6358
WVFGRD96   54.0   115    60   -25   4.57 0.6531
WVFGRD96   56.0   115    60   -25   4.59 0.6699
WVFGRD96   58.0   115    60   -25   4.60 0.6850
WVFGRD96   60.0   115    55   -30   4.61 0.6982
WVFGRD96   62.0   115    55   -30   4.62 0.7109
WVFGRD96   64.0   115    55   -30   4.63 0.7196
WVFGRD96   66.0   115    55   -30   4.64 0.7258
WVFGRD96   68.0   115    55   -25   4.64 0.7300
WVFGRD96   70.0   115    55   -25   4.65 0.7325
WVFGRD96   72.0   120    60   -20   4.65 0.7336
WVFGRD96   74.0   120    60   -20   4.65 0.7347
WVFGRD96   76.0   120    60   -20   4.66 0.7338
WVFGRD96   78.0   120    60   -20   4.66 0.7315
WVFGRD96   80.0   120    60   -20   4.66 0.7279
WVFGRD96   82.0   120    60   -20   4.66 0.7237
WVFGRD96   84.0   120    60   -20   4.66 0.7189
WVFGRD96   86.0   120    60   -15   4.67 0.7140
WVFGRD96   88.0   120    60   -15   4.67 0.7095
WVFGRD96   90.0   120    60   -15   4.67 0.7041
WVFGRD96   92.0   120    65   -15   4.67 0.6989
WVFGRD96   94.0   125    65   -10   4.68 0.6936
WVFGRD96   96.0   125    65   -10   4.68 0.6899
WVFGRD96   98.0   125    65   -10   4.68 0.6860

The best solution is

WVFGRD96   74.0   120    60   -20   4.65 0.7347

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 o DIST/3.3 -50 o DIST/3.3 +70
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 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 00:19:09 CST 2015