Location

2014/09/25 17:51:17 61.953 -151.785 102.8 6.2 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  2014/09/25 17:51:17:0  61.95 -151.79 102.8 6.2 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.COLD 
   AK.CRQ AK.CTG AK.DHY AK.DOT AK.EYAK AK.FID AK.GLB AK.GLI 
   AK.HDA AK.HIN AK.HMT AK.KAI AK.KLU AK.KTH AK.MCAR AK.MCK 
   AK.MDM AK.MESA AK.PAX AK.PPLA AK.RAG AK.RIDG AK.RND AK.SAW 
   AK.SCM AK.SWD AK.TGL AK.TRF AK.VRDI AK.WAX AK.WRH AK.YAH 
   AT.MENT AT.PMR AT.SVW2 AT.TTA IU.COLA TA.M24K 
 
 Filtering commands used:
   cut a -30 a 210
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.04 n 3 
 
 Best Fitting Double Couple
  Mo = 2.69e+25 dyne-cm
  Mw = 6.22 
  Z  = 104 km
  Plane   Strike  Dip  Rake
   NP1      310    76   159
   NP2       45    70    15
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.69e+25     24     266
    N   0.00e+00     65      97
    P  -2.69e+25      4     358

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.67e+25
       Mxy     2.24e+24
       Mxz    -2.51e+24
       Myy     2.22e+25
       Myz    -1.01e+25
       Mzz     4.48e+24
                                                     
                                                     
                                                     
                                                     
                     ----- P ------                  
                 ---------   ----------              
              ----------------------------           
             ------------------------------          
           #####--------------------------###        
          ##########---------------------#####       
         ##############------------------######      
        #################---------------########     
        ####################----------##########     
       #######################-------############    
       ####   ##################----#############    
       #### T ###################################    
       ####   ##################----#############    
        #######################-------##########     
        #####################-----------########     
         #################---------------######      
          ##############------------------####       
           ##########----------------------##        
             ###---------------------------          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.48e+24  -2.51e+24   1.01e+25 
 -2.51e+24  -2.67e+25  -2.24e+24 
  1.01e+25  -2.24e+24   2.22e+25 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140925175117/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 = 45
      DIP = 70
     RAKE = 15
       MW = 6.22
       HS = 104.0

The NDK file is 20140925175117.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
GCMT
 USGS/SLU Moment Tensor Solution
 ENS  2014/09/25 17:51:17:0  61.95 -151.79 102.8 6.2 Alaska
 
 Stations used:
   AK.BAL AK.BARN AK.BPAW AK.BRLK AK.BWN AK.CCB AK.CNP AK.COLD 
   AK.CRQ AK.CTG AK.DHY AK.DOT AK.EYAK AK.FID AK.GLB AK.GLI 
   AK.HDA AK.HIN AK.HMT AK.KAI AK.KLU AK.KTH AK.MCAR AK.MCK 
   AK.MDM AK.MESA AK.PAX AK.PPLA AK.RAG AK.RIDG AK.RND AK.SAW 
   AK.SCM AK.SWD AK.TGL AK.TRF AK.VRDI AK.WAX AK.WRH AK.YAH 
   AT.MENT AT.PMR AT.SVW2 AT.TTA IU.COLA TA.M24K 
 
 Filtering commands used:
   cut a -30 a 210
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.04 n 3 
 
 Best Fitting Double Couple
  Mo = 2.69e+25 dyne-cm
  Mw = 6.22 
  Z  = 104 km
  Plane   Strike  Dip  Rake
   NP1      310    76   159
   NP2       45    70    15
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.69e+25     24     266
    N   0.00e+00     65      97
    P  -2.69e+25      4     358

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.67e+25
       Mxy     2.24e+24
       Mxz    -2.51e+24
       Myy     2.22e+25
       Myz    -1.01e+25
       Mzz     4.48e+24
                                                     
                                                     
                                                     
                                                     
                     ----- P ------                  
                 ---------   ----------              
              ----------------------------           
             ------------------------------          
           #####--------------------------###        
          ##########---------------------#####       
         ##############------------------######      
        #################---------------########     
        ####################----------##########     
       #######################-------############    
       ####   ##################----#############    
       #### T ###################################    
       ####   ##################----#############    
        #######################-------##########     
        #####################-----------########     
         #################---------------######      
          ##############------------------####       
           ##########----------------------##        
             ###---------------------------          
              ----------------------------           
                 ----------------------              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.48e+24  -2.51e+24   1.01e+25 
 -2.51e+24  -2.67e+25  -2.24e+24 
  1.01e+25  -2.24e+24   2.22e+25 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140925175117/index.html
	
Method Mw H (km) S1, D1, R1 S2, D2, R2 Catalog Source us
Mwr 6.3 100.0 km 310, 76, 161 45, 72, 15 us us us
Mwb 6.3 102.0 km 303, 73, 160 39, 71, 18 us us us
Mww 6.3 110.5 km 46, 79, 13 314, 77, 169 us us us
Mwc 6.3 111.6 km 315, 82, 164 47, 75, 9 gcmt gcmt us
CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     C201409251751A
DATA: II LD IU G  DK CU MN IC GE
 XF KP
L.P.BODY WAVES:179S, 431C, T= 40
MANTLE WAVES:  144S, 244C, T=125
SURFACE WAVES: 177S, 419C, T= 50
TIMESTAMP:      Q-20140926082604
CENTROID LOCATION:
ORIGIN TIME:      17:51:22.7 0.1
LAT:62.02N 0.00;LON:151.80W 0.01
DEP:111.6  0.3;TRIANG HDUR:  3.5
MOMENT TENSOR: SCALE 10**25 D-CM
RR= 0.274 0.013; TT=-3.560 0.016
PP= 3.280 0.016; RT=-0.299 0.012
RP= 1.000 0.011; TP= 0.139 0.014
PRINCIPAL AXES:
1.(T) VAL=  3.583;PLG=17;AZM=270
2.(N)       0.002;    72;    108
3.(P)      -3.590;     5;      2
BEST DBLE.COUPLE:M0= 3.59*10**25
NP1: STRIKE= 47;DIP=75;SLIP=   9
NP2: STRIKE=315;DIP=82;SLIP= 164

            ----- P ---
        ---------   -------
      -----------------------
    ####---------------------##
   ########-----------------####
  ###########--------------######
  #############-----------#######
 #   ############-------##########
 # T ##############----###########
 #   #############################
 ##################---############
  ###############-------#########
  #############-----------#######
   #########---------------#####
    ####--------------------###
      -----------------------
        -------------------
            -----------
        

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 210
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.04 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   125    75   -35   5.44 0.2496
WVFGRD96    4.0   130    75   -20   5.47 0.2718
WVFGRD96    6.0   130    80   -10   5.49 0.2803
WVFGRD96    8.0   135    85   -10   5.55 0.2850
WVFGRD96   10.0   135    80    -5   5.57 0.2748
WVFGRD96   12.0   135    65    15   5.58 0.2606
WVFGRD96   14.0   135    65    15   5.59 0.2569
WVFGRD96   16.0   135    70    20   5.60 0.2563
WVFGRD96   18.0   135    65    15   5.61 0.2571
WVFGRD96   20.0   135    65    15   5.62 0.2587
WVFGRD96   22.0    35    65   -10   5.62 0.2610
WVFGRD96   24.0    35    60   -10   5.64 0.2698
WVFGRD96   26.0    35    65   -10   5.66 0.2789
WVFGRD96   28.0    35    65   -10   5.68 0.2893
WVFGRD96   30.0    35    65   -10   5.70 0.2998
WVFGRD96   32.0    35    65   -10   5.72 0.3112
WVFGRD96   34.0    35    65   -10   5.74 0.3245
WVFGRD96   36.0    35    70   -10   5.77 0.3395
WVFGRD96   38.0    40    75    -5   5.83 0.3611
WVFGRD96   40.0    40    70    -5   5.89 0.3895
WVFGRD96   42.0    40    70    -5   5.91 0.4075
WVFGRD96   44.0    40    70    -5   5.93 0.4257
WVFGRD96   46.0    40    75   -10   5.96 0.4450
WVFGRD96   48.0    40    75   -10   5.98 0.4644
WVFGRD96   50.0    40    75    -5   5.99 0.4838
WVFGRD96   52.0    40    75    -5   6.01 0.5037
WVFGRD96   54.0    40    75    -5   6.03 0.5230
WVFGRD96   56.0    40    75    -5   6.04 0.5419
WVFGRD96   58.0    40    75    -5   6.06 0.5600
WVFGRD96   60.0    40    75     0   6.07 0.5778
WVFGRD96   62.0    40    75     0   6.08 0.5951
WVFGRD96   64.0    40    75     0   6.10 0.6122
WVFGRD96   66.0    40    75     0   6.11 0.6286
WVFGRD96   68.0    40    75     5   6.12 0.6443
WVFGRD96   70.0    40    75     5   6.13 0.6614
WVFGRD96   72.0    40    75     5   6.14 0.6772
WVFGRD96   74.0    45    75     5   6.16 0.6926
WVFGRD96   76.0    45    75     5   6.17 0.7074
WVFGRD96   78.0    45    75     5   6.17 0.7208
WVFGRD96   80.0    45    75     5   6.18 0.7324
WVFGRD96   82.0    45    75    10   6.19 0.7445
WVFGRD96   84.0    45    75    10   6.19 0.7552
WVFGRD96   86.0    45    75    10   6.20 0.7644
WVFGRD96   88.0    45    70    10   6.20 0.7728
WVFGRD96   90.0    45    70    10   6.20 0.7791
WVFGRD96   92.0    45    70    10   6.21 0.7852
WVFGRD96   94.0    45    70    10   6.21 0.7900
WVFGRD96   96.0    45    70    10   6.22 0.7936
WVFGRD96   98.0    45    70    10   6.22 0.7961
WVFGRD96  100.0    45    70    15   6.22 0.7973
WVFGRD96  102.0    45    70    15   6.22 0.7986
WVFGRD96  104.0    45    70    15   6.22 0.7995
WVFGRD96  106.0    45    70    15   6.23 0.7993
WVFGRD96  108.0    45    70    15   6.23 0.7984
WVFGRD96  110.0    45    70    15   6.23 0.7960
WVFGRD96  112.0    45    70    15   6.23 0.7939
WVFGRD96  114.0    45    70    15   6.23 0.7909
WVFGRD96  116.0    45    70    15   6.23 0.7877
WVFGRD96  118.0    45    70    15   6.24 0.7839
WVFGRD96  120.0    45    70    20   6.23 0.7804
WVFGRD96  122.0    45    70    20   6.23 0.7763
WVFGRD96  124.0    45    70    20   6.23 0.7722
WVFGRD96  126.0    45    70    20   6.23 0.7678
WVFGRD96  128.0    45    70    20   6.24 0.7627
WVFGRD96  130.0    45    70    20   6.24 0.7578
WVFGRD96  132.0    45    70    20   6.24 0.7524
WVFGRD96  134.0    45    70    20   6.24 0.7468
WVFGRD96  136.0    45    70    20   6.24 0.7414
WVFGRD96  138.0    45    70    20   6.24 0.7356

The best solution is

WVFGRD96  104.0    45    70    15   6.22 0.7995

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 210
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.04 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 00:15:59 CST 2015