Location

2014/05/05 04:59:44 60.655 -149.549 32.8 4.7 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  2014/05/05 04:59:44:0  60.65 -149.55  32.8 4.7 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ 
   AK.CTG AK.DHY AK.DOT AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI 
   AK.HDA AK.HIN AK.HOM AK.KNK AK.KTH AK.MCAR AK.MCK AK.MLY 
   AK.NEA AK.PPLA AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.SCRK 
   AK.TGL AK.TRF AK.WRH AT.MENT AT.PMR IM.IL31 IU.COLA 
 
 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 = 7.33e+22 dyne-cm
  Mw = 4.51 
  Z  = 46 km
  Plane   Strike  Dip  Rake
   NP1       60    55   -65
   NP2      201    42   -121
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.33e+22      7     132
    N   0.00e+00     20     225
    P  -7.33e+22     69      25

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.48e+22
       Mxy    -3.97e+22
       Mxz    -2.86e+22
       Myy     3.76e+22
       Myz    -4.03e+21
       Mzz    -6.24e+22
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ############----------              
              ###########-----------------           
             ##########--------------------          
           ##########------------------------        
          ##########--------------------------       
         ##########---------------------------#      
        ##########-----------   -------------###     
        #########------------ P ------------####     
       #########-------------   -----------######    
       #########--------------------------#######    
       ########--------------------------########    
       ########------------------------##########    
        #######----------------------###########     
        #######-------------------##############     
         ######----------------################      
          ######-----------###################       
           -----########################   ##        
             ----####################### T           
              ----######################             
                 --####################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -6.24e+22  -2.86e+22   4.03e+21 
 -2.86e+22   2.48e+22   3.97e+22 
  4.03e+21   3.97e+22   3.76e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140505045944/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 = 60
      DIP = 55
     RAKE = -65
       MW = 4.51
       HS = 46.0

The NDK file is 20140505045944.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  2014/05/05 04:59:44:0  60.65 -149.55  32.8 4.7 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ 
   AK.CTG AK.DHY AK.DOT AK.EYAK AK.FID AK.GHO AK.GLB AK.GLI 
   AK.HDA AK.HIN AK.HOM AK.KNK AK.KTH AK.MCAR AK.MCK AK.MLY 
   AK.NEA AK.PPLA AK.RC01 AK.RIDG AK.RND AK.SAW AK.SCM AK.SCRK 
   AK.TGL AK.TRF AK.WRH AT.MENT AT.PMR IM.IL31 IU.COLA 
 
 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 = 7.33e+22 dyne-cm
  Mw = 4.51 
  Z  = 46 km
  Plane   Strike  Dip  Rake
   NP1       60    55   -65
   NP2      201    42   -121
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.33e+22      7     132
    N   0.00e+00     20     225
    P  -7.33e+22     69      25

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.48e+22
       Mxy    -3.97e+22
       Mxz    -2.86e+22
       Myy     3.76e+22
       Myz    -4.03e+21
       Mzz    -6.24e+22
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ############----------              
              ###########-----------------           
             ##########--------------------          
           ##########------------------------        
          ##########--------------------------       
         ##########---------------------------#      
        ##########-----------   -------------###     
        #########------------ P ------------####     
       #########-------------   -----------######    
       #########--------------------------#######    
       ########--------------------------########    
       ########------------------------##########    
        #######----------------------###########     
        #######-------------------##############     
         ######----------------################      
          ######-----------###################       
           -----########################   ##        
             ----####################### T           
              ----######################             
                 --####################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -6.24e+22  -2.86e+22   4.03e+21 
 -2.86e+22   2.48e+22   3.97e+22 
  4.03e+21   3.97e+22   3.76e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140505045944/index.html
	
Regional Moment Tensor (Mwr)

Moment magnitude derived from a moment tensor 
inversion of complete waveforms at regional 
distances (less than ~8 degrees), generally 
used for the analysis of small to moderate 
size earthquakes (typically Mw 3.5-6.0) crust 
or upper mantle earthquakes.

Moment      7.64e+15 N-m
Magnitude   4.5
Percent DC  93%
Depth       48.0 km
Updated     2014-05-05 05:28:41 UTC
Author      us
Catalog     us
Contributor us
Code us_b000qa69_mwr

Principal Axes
Axis	Value	Plunge	Azimuth
T	7.518	9	134
N	0.244	27	229
P	-7.762	62	27
Nodal Planes
Plane	Strike	Dip	Rake
NP1	66	60	-59
NP2	196	43	-131

        

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 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   230    45    90   3.92 0.3445
WVFGRD96    4.0   125    40   -90   3.94 0.3147
WVFGRD96    6.0   155    85    15   3.95 0.2983
WVFGRD96    8.0   355    35    25   4.01 0.3007
WVFGRD96   10.0     0    30    30   4.02 0.3348
WVFGRD96   12.0    65    80   -60   4.04 0.3761
WVFGRD96   14.0    65    75   -60   4.06 0.4211
WVFGRD96   16.0    65    70   -60   4.09 0.4634
WVFGRD96   18.0    65    70   -60   4.11 0.5026
WVFGRD96   20.0    65    70   -55   4.14 0.5373
WVFGRD96   22.0    65    70   -55   4.17 0.5690
WVFGRD96   24.0    65    70   -55   4.20 0.5973
WVFGRD96   26.0    65    65   -60   4.21 0.6224
WVFGRD96   28.0    65    65   -60   4.23 0.6451
WVFGRD96   30.0    65    65   -60   4.25 0.6633
WVFGRD96   32.0    65    65   -60   4.27 0.6781
WVFGRD96   34.0    65    60   -60   4.28 0.6928
WVFGRD96   36.0    65    60   -60   4.30 0.7041
WVFGRD96   38.0    65    55   -60   4.32 0.7094
WVFGRD96   40.0    60    55   -65   4.46 0.7353
WVFGRD96   42.0    60    55   -65   4.48 0.7464
WVFGRD96   44.0    60    55   -65   4.49 0.7515
WVFGRD96   46.0    60    55   -65   4.51 0.7520
WVFGRD96   48.0    60    55   -60   4.53 0.7499
WVFGRD96   50.0    60    55   -60   4.54 0.7439
WVFGRD96   52.0    60    55   -60   4.55 0.7347
WVFGRD96   54.0    60    55   -60   4.56 0.7227
WVFGRD96   56.0    65    55   -55   4.56 0.7097
WVFGRD96   58.0    65    55   -55   4.57 0.6947
WVFGRD96   60.0    65    55   -55   4.58 0.6779
WVFGRD96   62.0    65    60   -55   4.58 0.6599
WVFGRD96   64.0    70    60   -50   4.58 0.6440
WVFGRD96   66.0    70    60   -50   4.59 0.6284
WVFGRD96   68.0    70    60   -50   4.59 0.6128
WVFGRD96   70.0    70    60   -50   4.60 0.5968
WVFGRD96   72.0    70    60   -50   4.61 0.5801
WVFGRD96   74.0    75    65   -50   4.60 0.5655
WVFGRD96   76.0    75    65   -45   4.60 0.5522
WVFGRD96   78.0    75    65   -45   4.61 0.5389
WVFGRD96   80.0    70    65   -45   4.62 0.5255
WVFGRD96   82.0    70    65   -45   4.63 0.5129
WVFGRD96   84.0    70    65   -45   4.63 0.4998
WVFGRD96   86.0    70    65   -40   4.64 0.4877
WVFGRD96   88.0    70    70   -45   4.63 0.4795
WVFGRD96   90.0    70    70   -45   4.64 0.4715
WVFGRD96   92.0    70    70   -45   4.65 0.4636
WVFGRD96   94.0    70    70   -40   4.65 0.4559
WVFGRD96   96.0    70    70   -40   4.66 0.4488
WVFGRD96   98.0    70    75   -40   4.65 0.4426

The best solution is

WVFGRD96   46.0    60    55   -65   4.51 0.7520

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 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 00:11:40 CST 2015