Location

2015/05/09 10:15:49 61.512 -146.562 14.7 4.1 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  2015/05/09 10:15:49:0  61.51 -146.56  14.7 4.1 Alaska
 
 Stations used:
   AK.BARN AK.BMR AK.BWN AK.CRQ AK.CTG AK.CUT AK.DOT AK.FID 
   AK.GHO AK.GLB AK.GLI AK.GRNC AK.HIN AK.KLU AK.KNK AK.KTH 
   AK.MCAR AK.MCK AK.MLY AK.PAX AK.PPLA AK.RC01 AK.RND AK.SAW 
   AK.SCM AK.SKN AK.TRF AK.VRDI AK.WAT3 AK.WAT4 AK.WAT5 AK.WRH 
   AK.YAH AT.PMR TA.I23K TA.M24K TA.N25K TA.POKR 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 2.43e+22 dyne-cm
  Mw = 4.19 
  Z  = 42 km
  Plane   Strike  Dip  Rake
   NP1       55    80    87
   NP2      250    10   105
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.43e+22     55     322
    N   0.00e+00      3      55
    P  -2.43e+22     35     147

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -6.38e+21
       Mxy     3.41e+21
       Mxz     1.86e+22
       Myy    -1.64e+21
       Myz    -1.33e+22
       Mzz     8.02e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----###############---              
              ---#######################--           
             --###########################-          
           --###############################-        
          --################################--       
         -###########   ##################-----      
        --########### T ################--------     
        -############   ##############----------     
       -############################-------------    
       -#########################----------------    
       -#######################------------------    
       -####################---------------------    
        ##################----------------------     
        ###############-------------------------     
         ##########----------------------------      
          ######------------------   ---------       
           ----------------------- P --------        
             ---------------------   ------          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  8.02e+21   1.86e+22   1.33e+22 
  1.86e+22  -6.38e+21  -3.41e+21 
  1.33e+22  -3.41e+21  -1.64e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150509101549/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 = 250
      DIP = 10
     RAKE = 105
       MW = 4.19
       HS = 42.0

The NDK file is 20150509101549.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  2015/05/09 10:15:49:0  61.51 -146.56  14.7 4.1 Alaska
 
 Stations used:
   AK.BARN AK.BMR AK.BWN AK.CRQ AK.CTG AK.CUT AK.DOT AK.FID 
   AK.GHO AK.GLB AK.GLI AK.GRNC AK.HIN AK.KLU AK.KNK AK.KTH 
   AK.MCAR AK.MCK AK.MLY AK.PAX AK.PPLA AK.RC01 AK.RND AK.SAW 
   AK.SCM AK.SKN AK.TRF AK.VRDI AK.WAT3 AK.WAT4 AK.WAT5 AK.WRH 
   AK.YAH AT.PMR TA.I23K TA.M24K TA.N25K TA.POKR 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 2.43e+22 dyne-cm
  Mw = 4.19 
  Z  = 42 km
  Plane   Strike  Dip  Rake
   NP1       55    80    87
   NP2      250    10   105
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.43e+22     55     322
    N   0.00e+00      3      55
    P  -2.43e+22     35     147

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -6.38e+21
       Mxy     3.41e+21
       Mxz     1.86e+22
       Myy    -1.64e+21
       Myz    -1.33e+22
       Mzz     8.02e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----###############---              
              ---#######################--           
             --###########################-          
           --###############################-        
          --################################--       
         -###########   ##################-----      
        --########### T ################--------     
        -############   ##############----------     
       -############################-------------    
       -#########################----------------    
       -#######################------------------    
       -####################---------------------    
        ##################----------------------     
        ###############-------------------------     
         ##########----------------------------      
          ######------------------   ---------       
           ----------------------- P --------        
             ---------------------   ------          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  8.02e+21   1.86e+22   1.33e+22 
  1.86e+22  -6.38e+21  -3.41e+21 
  1.33e+22  -3.41e+21  -1.64e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150509101549/index.html
	
Regional Moment Tensor (Mwr)
Moment	2.617e+15 N-m
Magnitude	4.21
Depth	43.0 km
Percent DC	79%
Half Duration	–
Catalog	AK (ak11588180)
Data Source	US3
Contributor	US3
Nodal Planes
Plane	Strike	Dip	Rake
NP1	243°	11°	99°
NP2	54°	79°	88°
Principal Axes
Axis	Value	Plunge	Azimuth
T	2.461	56°	322°
N	0.289	2°	55°
P	-2.750	34°	146°

        

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 o DIST/3.3 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.07 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    50    45    90   3.59 0.2946
WVFGRD96    4.0   230    45    95   3.66 0.2319
WVFGRD96    6.0   165    70   -15   3.67 0.2292
WVFGRD96    8.0   160    60   -25   3.73 0.2545
WVFGRD96   10.0    50    80    80   3.70 0.2931
WVFGRD96   12.0    45    80    70   3.72 0.3394
WVFGRD96   14.0    50    75    75   3.75 0.3854
WVFGRD96   16.0    45    75    65   3.79 0.4292
WVFGRD96   18.0    50    70    70   3.82 0.4706
WVFGRD96   20.0    50    75    70   3.84 0.5071
WVFGRD96   22.0    50    75    75   3.87 0.5408
WVFGRD96   24.0    50    75    75   3.89 0.5716
WVFGRD96   26.0    50    80    80   3.92 0.5994
WVFGRD96   28.0    50    80    80   3.94 0.6288
WVFGRD96   30.0    55    80    85   3.96 0.6545
WVFGRD96   32.0    55    80    85   3.98 0.6752
WVFGRD96   34.0    55    80    85   4.00 0.6903
WVFGRD96   36.0    55    80    85   4.01 0.6990
WVFGRD96   38.0    55    80    85   4.02 0.7041
WVFGRD96   40.0    50    85    85   4.17 0.7063
WVFGRD96   42.0   250    10   105   4.19 0.7099
WVFGRD96   44.0   240    10    95   4.20 0.7098
WVFGRD96   46.0   235    10    90   4.21 0.7061
WVFGRD96   48.0    55    80    90   4.22 0.7003
WVFGRD96   50.0    55    80    90   4.23 0.6937
WVFGRD96   52.0    55    80    90   4.24 0.6844
WVFGRD96   54.0    55    80    90   4.24 0.6733
WVFGRD96   56.0   230    10    85   4.25 0.6608
WVFGRD96   58.0    50    85    85   4.25 0.6496
WVFGRD96   60.0   250     5   105   4.26 0.6374
WVFGRD96   62.0    55    85    85   4.26 0.6241
WVFGRD96   64.0    55    85    85   4.27 0.6103
WVFGRD96   66.0    55    85    85   4.27 0.5961
WVFGRD96   68.0   230    90   -80   4.27 0.5788
WVFGRD96   70.0    50    85    80   4.28 0.5674
WVFGRD96   72.0    50    85    80   4.28 0.5531
WVFGRD96   74.0    50    85    80   4.29 0.5386
WVFGRD96   76.0    50    85    80   4.29 0.5246
WVFGRD96   78.0    50    85    75   4.30 0.5114
WVFGRD96   80.0    45    85    70   4.30 0.5005
WVFGRD96   82.0    45    85    70   4.30 0.4906
WVFGRD96   84.0    45    85    70   4.31 0.4811
WVFGRD96   86.0    45    85    70   4.31 0.4715
WVFGRD96   88.0    45    85    70   4.31 0.4618
WVFGRD96   90.0    45    85    65   4.32 0.4520
WVFGRD96   92.0    45    85    65   4.32 0.4388
WVFGRD96   94.0    40    85    60   4.32 0.4222
WVFGRD96   96.0    40    90    55   4.33 0.4088
WVFGRD96   98.0   180    65   -85   4.29 0.3960

The best solution is

WVFGRD96   42.0   250    10   105   4.19 0.7099

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 -30 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.07 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 00:03:09 CST 2015