Location

2015/07/29 02:35:58 59.897 -153.072 118 6.3 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  2015/07/29 02:35:58:0  59.90 -153.07 118.0 6.3 Alaska
 
 Stations used:
   AK.BPAW AK.BRLK AK.BWN AK.CUT AK.EYAK AK.FID AK.GLI AK.HIN 
   AK.KLU AK.KNK AK.KTH AK.MCK AK.PPLA AK.PWL AK.RAG AK.RND 
   AK.SAW AK.SCM AK.SII AK.SKN AK.SSN AK.SWD AK.TRF AT.MID 
   AT.OHAK AT.PMR AT.SVW2 II.KDAK TA.N25K TA.Q23K 
 
 Filtering commands used:
   cut o DIST/3.4 -50 o DIST/3.4 +100
   rtr
   taper w 0.1
   hp c 0.01 n 3 
   lp c 0.05 n 3 
 
 Best Fitting Double Couple
  Mo = 3.31e+25 dyne-cm
  Mw = 6.28 
  Z  = 114 km
  Plane   Strike  Dip  Rake
   NP1      321    60   145
   NP2       70    60    35
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.31e+25     45     285
    N   0.00e+00     45     106
    P  -3.31e+25      0      15

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.96e+25
       Mxy    -1.27e+25
       Mxz     4.29e+24
       Myy     1.32e+25
       Myz    -1.60e+25
       Mzz     1.64e+25
                                                     
                                                     
                                                     
                                                     
                     ----------- P                   
                 ---------------   ----              
              ####------------------------           
             ##########--------------------          
           ###############-------------------        
          ##################------------------       
         ######################----------------      
        ########################---------------#     
        ########   ###############------------##     
       ######### T ################----------####    
       #########   ##################------######    
       ###############################----#######    
       ##########################################    
        ############################---#########     
        ########################--------########     
         --################--------------######      
          -------------------------------#####       
           ------------------------------####        
             ----------------------------##          
              ---------------------------#           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.64e+25   4.29e+24   1.60e+25 
  4.29e+24  -2.96e+25   1.27e+25 
  1.60e+25   1.27e+25   1.32e+25 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150729023558/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 = 70
      DIP = 60
     RAKE = 35
       MW = 6.28
       HS = 114.0

The NDK file is 20150729023558.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSW
 USGS/SLU Moment Tensor Solution
 ENS  2015/07/29 02:35:58:0  59.90 -153.07 118.0 6.3 Alaska
 
 Stations used:
   AK.BPAW AK.BRLK AK.BWN AK.CUT AK.EYAK AK.FID AK.GLI AK.HIN 
   AK.KLU AK.KNK AK.KTH AK.MCK AK.PPLA AK.PWL AK.RAG AK.RND 
   AK.SAW AK.SCM AK.SII AK.SKN AK.SSN AK.SWD AK.TRF AT.MID 
   AT.OHAK AT.PMR AT.SVW2 II.KDAK TA.N25K TA.Q23K 
 
 Filtering commands used:
   cut o DIST/3.4 -50 o DIST/3.4 +100
   rtr
   taper w 0.1
   hp c 0.01 n 3 
   lp c 0.05 n 3 
 
 Best Fitting Double Couple
  Mo = 3.31e+25 dyne-cm
  Mw = 6.28 
  Z  = 114 km
  Plane   Strike  Dip  Rake
   NP1      321    60   145
   NP2       70    60    35
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.31e+25     45     285
    N   0.00e+00     45     106
    P  -3.31e+25      0      15

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.96e+25
       Mxy    -1.27e+25
       Mxz     4.29e+24
       Myy     1.32e+25
       Myz    -1.60e+25
       Mzz     1.64e+25
                                                     
                                                     
                                                     
                                                     
                     ----------- P                   
                 ---------------   ----              
              ####------------------------           
             ##########--------------------          
           ###############-------------------        
          ##################------------------       
         ######################----------------      
        ########################---------------#     
        ########   ###############------------##     
       ######### T ################----------####    
       #########   ##################------######    
       ###############################----#######    
       ##########################################    
        ############################---#########     
        ########################--------########     
         --################--------------######      
          -------------------------------#####       
           ------------------------------####        
             ----------------------------##          
              ---------------------------#           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.64e+25   4.29e+24   1.60e+25 
  4.29e+24  -2.96e+25   1.27e+25 
  1.60e+25   1.27e+25   1.32e+25 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150729023558/index.html
	
W-phase Moment Tensor (Mww)
Moment	3.391e+18 N-m
Magnitude	6.29
Depth	120.5 km
Percent DC	83%
Half Duration	–
Catalog	US (us2000314u)
Data Source	US3
Contributor	US3
Nodal Planes
Plane	Strike	Dip	Rake
NP1	323	63	147
NP2	69	61	31
Principal Axes
Axis	Value	Plunge	Azimuth
T	3.527	42	285
N	-0.292	48	108
P	-3.236	1	16

        

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/3.4 -50 o DIST/3.4 +100
rtr
taper w 0.1
hp c 0.01 n 3 
lp c 0.05 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   150    85   -20   5.36 0.1242
WVFGRD96    4.0   330    90    10   5.43 0.1464
WVFGRD96    6.0   150    90   -10   5.48 0.1557
WVFGRD96    8.0   150    85   -15   5.53 0.1611
WVFGRD96   10.0   240    90   -25   5.57 0.1627
WVFGRD96   12.0    65    80    25   5.59 0.1720
WVFGRD96   14.0    65    80    25   5.61 0.1801
WVFGRD96   16.0    65    75    25   5.63 0.1879
WVFGRD96   18.0    65    75    20   5.65 0.1964
WVFGRD96   20.0    65    75    20   5.66 0.2053
WVFGRD96   22.0    65    75    20   5.68 0.2131
WVFGRD96   24.0    65    70    20   5.70 0.2206
WVFGRD96   26.0    65    70    20   5.71 0.2271
WVFGRD96   28.0    65    70    20   5.73 0.2327
WVFGRD96   30.0    65    75    20   5.76 0.2385
WVFGRD96   32.0    65    75    20   5.78 0.2440
WVFGRD96   34.0    65    75    20   5.80 0.2494
WVFGRD96   36.0    65    75    20   5.82 0.2551
WVFGRD96   38.0    65    75    20   5.85 0.2613
WVFGRD96   40.0    65    75    25   5.93 0.2668
WVFGRD96   42.0    65    70    20   5.94 0.2729
WVFGRD96   44.0    65    70    15   5.96 0.2792
WVFGRD96   46.0    65    70    15   5.97 0.2853
WVFGRD96   48.0    65    70    15   5.99 0.2910
WVFGRD96   50.0    65    70    15   6.00 0.2965
WVFGRD96   52.0    65    75    20   6.02 0.3032
WVFGRD96   54.0    65    75    20   6.04 0.3112
WVFGRD96   56.0    65    70    20   6.05 0.3192
WVFGRD96   58.0    65    70    20   6.06 0.3291
WVFGRD96   60.0    65    65    15   6.07 0.3424
WVFGRD96   62.0    65    65    15   6.09 0.3582
WVFGRD96   64.0    65    65    15   6.10 0.3767
WVFGRD96   66.0    65    65    15   6.12 0.3956
WVFGRD96   68.0    65    65    15   6.13 0.4143
WVFGRD96   70.0    65    65    20   6.15 0.4336
WVFGRD96   72.0    65    65    20   6.16 0.4533
WVFGRD96   74.0    65    65    20   6.17 0.4723
WVFGRD96   76.0    65    65    20   6.19 0.4906
WVFGRD96   78.0    65    65    20   6.20 0.5077
WVFGRD96   80.0    65    65    20   6.21 0.5246
WVFGRD96   82.0    65    65    25   6.21 0.5407
WVFGRD96   84.0    65    65    25   6.22 0.5560
WVFGRD96   86.0    65    65    25   6.23 0.5698
WVFGRD96   88.0    65    65    25   6.24 0.5824
WVFGRD96   90.0    70    60    30   6.24 0.5946
WVFGRD96   92.0    70    60    30   6.24 0.6058
WVFGRD96   94.0    70    60    30   6.25 0.6159
WVFGRD96   96.0    70    60    30   6.26 0.6245
WVFGRD96   98.0    70    60    30   6.26 0.6319
WVFGRD96  100.0    70    60    30   6.27 0.6383
WVFGRD96  102.0    70    60    30   6.27 0.6433
WVFGRD96  104.0    70    60    30   6.27 0.6475
WVFGRD96  106.0    70    60    35   6.27 0.6511
WVFGRD96  108.0    70    60    35   6.28 0.6539
WVFGRD96  110.0    70    60    35   6.28 0.6557
WVFGRD96  112.0    70    60    35   6.28 0.6566
WVFGRD96  114.0    70    60    35   6.28 0.6567
WVFGRD96  116.0    70    60    35   6.29 0.6560
WVFGRD96  118.0    70    60    35   6.29 0.6546
WVFGRD96  120.0    70    60    35   6.29 0.6527
WVFGRD96  122.0    70    60    40   6.29 0.6503
WVFGRD96  124.0    70    60    40   6.29 0.6477
WVFGRD96  126.0    70    60    40   6.29 0.6449
WVFGRD96  128.0    70    60    40   6.29 0.6411

The best solution is

WVFGRD96  114.0    70    60    35   6.28 0.6567

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/3.4 -50 o DIST/3.4 +100
rtr
taper w 0.1
hp c 0.01 n 3 
lp c 0.05 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 00:06:10 CST 2015