Location

2015/07/06 00:50:34 62.135 -150.784 67.3 4.8 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  2015/07/06 00:50:34:0  62.13 -150.78  67.3 4.8 Alaska
 
 Stations used:
   AK.BARN AK.BMR AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ AK.CTG 
   AK.CUT AK.DOT AK.EYAK AK.FID AK.GLB AK.GLI AK.HDA AK.HIN 
   AK.HMT AK.ISLE AK.KLU AK.KNK AK.KTH AK.LOGN AK.MCAR AK.MCK 
   AK.MDM AK.MLY AK.NEA2 AK.PAX AK.PPD AK.PPLA AK.PWL AK.RC01 
   AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN AK.SWD AK.TGL 
   AK.TRF AK.VRDI AK.WAX AK.WRH AT.MENT AT.MID AT.PMR II.KDAK 
   IM.IL31 IU.COLA TA.I23K TA.K27K TA.L27K TA.M24K TA.N25K 
   TA.POKR 
 
 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 = 2.82e+23 dyne-cm
  Mw = 4.90 
  Z  = 76 km
  Plane   Strike  Dip  Rake
   NP1      337    84   130
   NP2       75    40    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.82e+23     38     282
    N   0.00e+00     39     152
    P  -2.82e+23     28      37

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.34e+23
       Mxy    -1.42e+23
       Mxz    -6.32e+22
       Myy     8.60e+22
       Myz    -2.03e+23
       Mzz     4.82e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ####------------------              
              ########--------------------           
             ##########-------------   ----          
           #############------------ P ------        
          ###############-----------   -------       
         #################---------------------      
        ###################---------------------     
        ######   ###########--------------------     
       ####### T ############-------------------#    
       #######   ############------------------##    
       #######################----------------###    
       ########################--------------####    
        ########################-----------#####     
        -#######################----------######     
         --######################------########      
          ----####################--##########       
           -------#############---###########        
             ----------------------########          
              ---------------------#######           
                 -------------------###              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.82e+22  -6.32e+22   2.03e+23 
 -6.32e+22  -1.34e+23   1.42e+23 
  2.03e+23   1.42e+23   8.60e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150706005034/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 = 75
      DIP = 40
     RAKE = 10
       MW = 4.90
       HS = 76.0

The NDK file is 20150706005034.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  2015/07/06 00:50:34:0  62.13 -150.78  67.3 4.8 Alaska
 
 Stations used:
   AK.BARN AK.BMR AK.BRLK AK.BWN AK.CCB AK.CNP AK.CRQ AK.CTG 
   AK.CUT AK.DOT AK.EYAK AK.FID AK.GLB AK.GLI AK.HDA AK.HIN 
   AK.HMT AK.ISLE AK.KLU AK.KNK AK.KTH AK.LOGN AK.MCAR AK.MCK 
   AK.MDM AK.MLY AK.NEA2 AK.PAX AK.PPD AK.PPLA AK.PWL AK.RC01 
   AK.RND AK.SAW AK.SCM AK.SCRK AK.SKN AK.SSN AK.SWD AK.TGL 
   AK.TRF AK.VRDI AK.WAX AK.WRH AT.MENT AT.MID AT.PMR II.KDAK 
   IM.IL31 IU.COLA TA.I23K TA.K27K TA.L27K TA.M24K TA.N25K 
   TA.POKR 
 
 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 = 2.82e+23 dyne-cm
  Mw = 4.90 
  Z  = 76 km
  Plane   Strike  Dip  Rake
   NP1      337    84   130
   NP2       75    40    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.82e+23     38     282
    N   0.00e+00     39     152
    P  -2.82e+23     28      37

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.34e+23
       Mxy    -1.42e+23
       Mxz    -6.32e+22
       Myy     8.60e+22
       Myz    -2.03e+23
       Mzz     4.82e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ####------------------              
              ########--------------------           
             ##########-------------   ----          
           #############------------ P ------        
          ###############-----------   -------       
         #################---------------------      
        ###################---------------------     
        ######   ###########--------------------     
       ####### T ############-------------------#    
       #######   ############------------------##    
       #######################----------------###    
       ########################--------------####    
        ########################-----------#####     
        -#######################----------######     
         --######################------########      
          ----####################--##########       
           -------#############---###########        
             ----------------------########          
              ---------------------#######           
                 -------------------###              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.82e+22  -6.32e+22   2.03e+23 
 -6.32e+22  -1.34e+23   1.42e+23 
  2.03e+23   1.42e+23   8.60e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150706005034/index.html
	
Regional Moment Tensor (Mwr)
Moment	2.579e+16 N-m
Magnitude	4.87
Depth	65.0 km
Percent DC	90%
Half Duration	–
Catalog	US (us10002nkt)
Data Source	US2
Contributor	US2
Nodal Planes
Plane	Strike	Dip	Rake
NP1	338	77	132
NP2	82	44	19
Principal Axes
Axis	Value	Plunge	Azimuth
T	2.511	42	288
N	0.132	41	146
P	-2.642	21	38

        

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 -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    65    45   -60   4.10 0.2045
WVFGRD96    4.0    70    75    -5   4.15 0.2333
WVFGRD96    6.0    70    70     0   4.22 0.2600
WVFGRD96    8.0    70    70     5   4.28 0.2873
WVFGRD96   10.0    70    70     5   4.32 0.3042
WVFGRD96   12.0    70    75    10   4.35 0.3141
WVFGRD96   14.0    70    75    15   4.37 0.3222
WVFGRD96   16.0    70    75    10   4.39 0.3306
WVFGRD96   18.0    70    70    10   4.40 0.3410
WVFGRD96   20.0    75    70    15   4.41 0.3550
WVFGRD96   22.0    75    70    15   4.43 0.3702
WVFGRD96   24.0    75    70    15   4.45 0.3846
WVFGRD96   26.0    75    70    15   4.47 0.3992
WVFGRD96   28.0    75    70    15   4.49 0.4141
WVFGRD96   30.0    75    70    15   4.51 0.4289
WVFGRD96   32.0    75    65    15   4.52 0.4450
WVFGRD96   34.0    75    65    15   4.55 0.4627
WVFGRD96   36.0    70    70    10   4.59 0.4823
WVFGRD96   38.0    70    70    10   4.62 0.5064
WVFGRD96   40.0    70    60    10   4.69 0.5187
WVFGRD96   42.0    70    60    10   4.71 0.5316
WVFGRD96   44.0    70    55     5   4.72 0.5475
WVFGRD96   46.0    70    55     5   4.74 0.5651
WVFGRD96   48.0    70    55    10   4.76 0.5828
WVFGRD96   50.0    75    50    10   4.77 0.6039
WVFGRD96   52.0    75    50    15   4.79 0.6230
WVFGRD96   54.0    75    50    15   4.80 0.6433
WVFGRD96   56.0    75    50    15   4.82 0.6609
WVFGRD96   58.0    75    50    15   4.83 0.6772
WVFGRD96   60.0    75    45    15   4.84 0.6940
WVFGRD96   62.0    75    45    15   4.85 0.7090
WVFGRD96   64.0    75    45    15   4.86 0.7215
WVFGRD96   66.0    75    45    15   4.87 0.7314
WVFGRD96   68.0    75    45    15   4.88 0.7392
WVFGRD96   70.0    75    45    15   4.89 0.7446
WVFGRD96   72.0    75    45    15   4.89 0.7480
WVFGRD96   74.0    75    40    10   4.90 0.7509
WVFGRD96   76.0    75    40    10   4.90 0.7520
WVFGRD96   78.0    75    40    10   4.91 0.7517
WVFGRD96   80.0    75    40    10   4.91 0.7496
WVFGRD96   82.0    75    40    10   4.92 0.7455
WVFGRD96   84.0    75    40    10   4.92 0.7404
WVFGRD96   86.0    75    40    10   4.92 0.7334
WVFGRD96   88.0    80    35    10   4.92 0.7263
WVFGRD96   90.0    80    35    10   4.92 0.7180
WVFGRD96   92.0    80    35    10   4.93 0.7108
WVFGRD96   94.0    80    35    10   4.93 0.7024
WVFGRD96   96.0    80    35    10   4.93 0.6925
WVFGRD96   98.0    80    35    10   4.93 0.6815

The best solution is

WVFGRD96   76.0    75    40    10   4.90 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 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 00:05:18 CST 2015