Location

2016/01/24 10:30:30 59.658 -153.452 127.8 7.1 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  2016/01/24 10:30:30:0  59.66 -153.45 127.8 7.1 Alaska
 
 Stations used:
   AK.CAST AK.DIV AK.KTH AK.MCK AK.PPLA AT.OHAK AT.PMR AT.TTA 
   II.KDAK TA.L19K TA.N19K TA.O18K TA.O19K TA.P18K 
 
 Filtering commands used:
   cut o DIST/3.3 -60 o DIST/3.3 +180
   rtr
   taper w 0.1
   hp c 0.01 n 3 
   lp c 0.025 n 3 
 
 Best Fitting Double Couple
  Mo = 4.42e+26 dyne-cm
  Mw = 7.03 
  Z  = 114 km
  Plane   Strike  Dip  Rake
   NP1       55    65    30
   NP2      311    63   152
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.42e+26     38     274
    N   0.00e+00     52      91
    P  -4.42e+26      1     183

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.39e+26
       Mxy    -3.91e+25
       Mxz     2.36e+25
       Myy     2.70e+26
       Myz    -2.14e+26
       Mzz     1.69e+26
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             ------------------------------          
           ###########-----------------------        
          ###############--------------------#       
         ###################----------------###      
        #######################------------#####     
        #########################---------######     
       #######   ##################-----#########    
       ####### T ####################--##########    
       #######   ####################-###########    
       ############################-----#########    
        ########################---------#######     
        ######################------------######     
         ##################---------------#####      
          ############---------------------###       
           -##-----------------------------##        
             ------------------------------          
              ----------------------------           
                 ---------   ----------              
                     ----- P ------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.69e+26   2.36e+25   2.14e+26 
  2.36e+25  -4.39e+26   3.91e+25 
  2.14e+26   3.91e+25   2.70e+26 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160124103030/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 = 55
      DIP = 65
     RAKE = 30
       MW = 7.03
       HS = 114.0

The NDK file is 20160124103030.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
GCMT
USGSW
 USGS/SLU Moment Tensor Solution
 ENS  2016/01/24 10:30:30:0  59.66 -153.45 127.8 7.1 Alaska
 
 Stations used:
   AK.CAST AK.DIV AK.KTH AK.MCK AK.PPLA AT.OHAK AT.PMR AT.TTA 
   II.KDAK TA.L19K TA.N19K TA.O18K TA.O19K TA.P18K 
 
 Filtering commands used:
   cut o DIST/3.3 -60 o DIST/3.3 +180
   rtr
   taper w 0.1
   hp c 0.01 n 3 
   lp c 0.025 n 3 
 
 Best Fitting Double Couple
  Mo = 4.42e+26 dyne-cm
  Mw = 7.03 
  Z  = 114 km
  Plane   Strike  Dip  Rake
   NP1       55    65    30
   NP2      311    63   152
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.42e+26     38     274
    N   0.00e+00     52      91
    P  -4.42e+26      1     183

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.39e+26
       Mxy    -3.91e+25
       Mxz     2.36e+25
       Myy     2.70e+26
       Myz    -2.14e+26
       Mzz     1.69e+26
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ----------------------              
              ----------------------------           
             ------------------------------          
           ###########-----------------------        
          ###############--------------------#       
         ###################----------------###      
        #######################------------#####     
        #########################---------######     
       #######   ##################-----#########    
       ####### T ####################--##########    
       #######   ####################-###########    
       ############################-----#########    
        ########################---------#######     
        ######################------------######     
         ##################---------------#####      
          ############---------------------###       
           -##-----------------------------##        
             ------------------------------          
              ----------------------------           
                 ---------   ----------              
                     ----- P ------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.69e+26   2.36e+25   2.14e+26 
  2.36e+25  -4.39e+26   3.91e+25 
  2.14e+26   3.91e+25   2.70e+26 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160124103030/index.html
	
Body-wave Moment Tensor (Mwb)
Moment	3.867e+19 N-m
Magnitude	6.99
Depth	117.0 km
Percent DC	60%
Half Duration	–
Catalog	US (us10004gqp)
Data Source	US3
Contributor	US3
Nodal Planes
Plane	Strike	Dip	Rake
NP1	302	50	153
NP2	50	70	43
Principal Axes
Axis	Value	Plunge	Azimuth
T	4.217	45	274
N	-0.837	43	70
P	-3.381	12	172

        
January 24, 2016, SOUTHERN ALASKA, MW=7.1

Meredith Nettles

CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     C201601241030A
DATA: II IU CU IC
L.P.BODY WAVES:109S, 304C, T= 50
MANTLE WAVES:  105S, 258C, T=150
SURFACE WAVES: 110S, 283C, T= 50
TIMESTAMP:      Q-20160124105219
CENTROID LOCATION:
ORIGIN TIME:      10:30:37.7 0.1
LAT:59.73N 0.01;LON:153.30W 0.01
DEP:111.6  0.5;TRIANG HDUR:  8.8
MOMENT TENSOR: SCALE 10**26 D-CM
RR= 2.270 0.031; TT=-5.530 0.024
PP= 3.260 0.022; RT= 0.734 0.024
RP= 3.110 0.022; TP= 0.880 0.016
PRINCIPAL AXES:
1.(T) VAL=  6.028;PLG=40;AZM=277
2.(N)      -0.384;    50;     90
3.(P)      -5.644;     4;    184
BEST DBLE.COUPLE:M0= 5.84*10**26
NP1: STRIKE=313;DIP=60;SLIP= 152
NP2: STRIKE= 58;DIP=66;SLIP=  33

            -----------
        -------------------
      -----------------------
    #########------------------
   ##############--------------#
  #################------------##
  ###################---------###
 #####   ##############-----######
 ##### T ################--#######
 #####   ################-########
 #####################-----#######
  #################---------#####
  ##############-------------####
   ########------------------###
    --------------------------#
      -----------------------
        -------   ---------
            --- P -----
        
W-phase Moment Tensor (Mww)
Moment	6.005e+19 N-m
Magnitude	7.12
Depth	110.5 km
Percent DC	98%
Half Duration	–
Catalog	US (us10004gqp)
Data Source	US3
Contributor	US3
Nodal Planes
Plane	Strike	Dip	Rake
NP1	313	61	152
NP2	58	66	33
Principal Axes
Axis	Value	Plunge	Azimuth
T	5.979	40	277
N	0.050	50	91
P	-6.030	3	185

        

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 o DIST/3.3 -60 o DIST/3.3 +180
rtr
taper w 0.1
hp c 0.01 n 3 
lp c 0.025 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   110    40   -70   6.27 0.1895
WVFGRD96    4.0   100    40   -85   6.35 0.2190
WVFGRD96    6.0   110    45   -65   6.38 0.2218
WVFGRD96    8.0   105    45   -75   6.43 0.2338
WVFGRD96   10.0   105    40   -70   6.43 0.2129
WVFGRD96   12.0   110    40   -65   6.42 0.1842
WVFGRD96   14.0   270    85   -55   6.37 0.1723
WVFGRD96   16.0   270    85   -55   6.38 0.1829
WVFGRD96   18.0    90    90    50   6.38 0.1887
WVFGRD96   20.0   265    80   -55   6.40 0.2028
WVFGRD96   22.0   265    80   -55   6.41 0.2137
WVFGRD96   24.0   265    80   -55   6.43 0.2249
WVFGRD96   26.0   265    80   -50   6.43 0.2354
WVFGRD96   28.0   265    80   -50   6.45 0.2472
WVFGRD96   30.0   265    80   -50   6.46 0.2585
WVFGRD96   32.0   265    80   -50   6.47 0.2686
WVFGRD96   34.0   265    80   -45   6.49 0.2791
WVFGRD96   36.0   260    75   -45   6.50 0.2887
WVFGRD96   38.0   260    75   -40   6.51 0.2974
WVFGRD96   40.0   260    75   -55   6.60 0.2990
WVFGRD96   42.0   260    75   -55   6.61 0.3052
WVFGRD96   44.0   260    75   -50   6.62 0.3107
WVFGRD96   46.0   260    75   -50   6.62 0.3155
WVFGRD96   48.0   260    75   -50   6.63 0.3189
WVFGRD96   50.0   260    75   -50   6.64 0.3210
WVFGRD96   52.0   255    75   -45   6.64 0.3229
WVFGRD96   54.0   255    75   -50   6.64 0.3245
WVFGRD96   56.0   255    75   -40   6.65 0.3289
WVFGRD96   58.0   250    75   -45   6.65 0.3366
WVFGRD96   60.0    80    50    70   6.76 0.3523
WVFGRD96   62.0    75    55    65   6.77 0.3742
WVFGRD96   64.0    75    55    65   6.79 0.3999
WVFGRD96   66.0    65    55    50   6.81 0.4274
WVFGRD96   68.0    65    55    50   6.83 0.4561
WVFGRD96   70.0    65    55    50   6.84 0.4842
WVFGRD96   72.0    65    55    50   6.86 0.5110
WVFGRD96   74.0    65    55    50   6.87 0.5363
WVFGRD96   76.0    65    55    50   6.89 0.5597
WVFGRD96   78.0    60    60    40   6.89 0.5862
WVFGRD96   80.0    60    60    40   6.90 0.6121
WVFGRD96   82.0    60    60    40   6.92 0.6361
WVFGRD96   84.0    60    60    40   6.93 0.6581
WVFGRD96   86.0    60    60    40   6.94 0.6778
WVFGRD96   88.0    60    60    40   6.95 0.6948
WVFGRD96   90.0    60    60    40   6.96 0.7093
WVFGRD96   92.0    60    60    40   6.97 0.7220
WVFGRD96   94.0    60    65    40   6.97 0.7343
WVFGRD96   96.0    60    65    40   6.98 0.7455
WVFGRD96   98.0    60    65    40   6.98 0.7553
WVFGRD96  100.0    60    65    40   6.99 0.7634
WVFGRD96  102.0    60    65    35   7.00 0.7721
WVFGRD96  104.0    60    65    35   7.01 0.7792
WVFGRD96  106.0    60    65    35   7.01 0.7842
WVFGRD96  108.0    60    65    35   7.02 0.7873
WVFGRD96  110.0    60    65    35   7.02 0.7885
WVFGRD96  112.0    55    65    30   7.03 0.7908
WVFGRD96  114.0    55    65    30   7.03 0.7913
WVFGRD96  116.0    55    70    30   7.03 0.7911
WVFGRD96  118.0    55    70    30   7.03 0.7912
WVFGRD96  120.0    55    70    30   7.04 0.7898
WVFGRD96  122.0    55    70    30   7.04 0.7871
WVFGRD96  124.0    55    70    30   7.04 0.7833
WVFGRD96  126.0    55    70    30   7.04 0.7786
WVFGRD96  128.0    55    70    30   7.05 0.7730
WVFGRD96  130.0    50    70    25   7.05 0.7684
WVFGRD96  132.0    50    70    25   7.06 0.7645
WVFGRD96  134.0    50    70    25   7.06 0.7599
WVFGRD96  136.0    50    70    25   7.06 0.7546
WVFGRD96  138.0    50    75    25   7.05 0.7500

The best solution is

WVFGRD96  114.0    55    65    30   7.03 0.7913

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 -60 o DIST/3.3 +180
rtr
taper w 0.1
hp c 0.01 n 3 
lp c 0.025 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 Sun Jan 24 11:20:34 CST 2016