Location

SLU Location

2010/12/10 05:42:34 59.357 -135.165 1.0 4.60 Alaska

The event was relocation using arrival times from nearby ANSS and NRCAN stations. This solution provided a better fit than the initial solution in that the nearby waveforms were correctly rotated into certical, raidla and transverse components of gorund motion. The detailed relocation is in elocate.txt.

USGS Initial Location

2010/12/10 05:42:37 59.448 -135.051 14.0 4.60 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  2010/12/10 05:42:34:0  59.36 -135.16   1.0 4.6 Alaska
 
 Stations used:
   AK.BAL AK.BMR AK.CRQ AK.CTG AK.DCPH AT.CRAG AT.SKAG CN.BVCY 
   CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY CN.YUK1 CN.YUK2 
   CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 US.WRAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 4.68e+22 dyne-cm
  Mw = 4.38 
  Z  = 1 km
  Plane   Strike  Dip  Rake
   NP1        7    50    94
   NP2      180    40    85
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.68e+22     84     306
    N   0.00e+00      3     184
    P  -4.68e+22      5      94

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.58e+14
       Mxy     2.62e+21
       Mxz     3.12e+21
       Myy    -4.59e+22
       Myz    -8.09e+21
       Mzz     4.59e+22
                                                     
                                                     
                                                     
                                                     
                     ----#######---                  
                 ------##########------              
              -------##############-------           
             -------################-------          
           --------#################---------        
          --------###################---------       
         --------#####################---------      
        --------######################----------     
        --------######################----------     
       ---------#########   ##########-----------    
       ---------######### T ##########--------       
       ---------#########   ##########-------- P     
       ---------######################--------       
        --------#####################-----------     
        --------#####################-----------     
         --------###################-----------      
          --------#################-----------       
           --------################----------        
             -------#############----------          
              -------###########----------           
                 ------#######---------              
                     ----###-------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.59e+22   3.12e+21   8.09e+21 
  3.12e+21  -4.58e+14  -2.62e+21 
  8.09e+21  -2.62e+21  -4.59e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101210054234/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 = 180
      DIP = 40
     RAKE = 85
       MW = 4.38
       HS = 1.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2010/12/10 05:42:34:0  59.36 -135.16   1.0 4.6 Alaska
 
 Stations used:
   AK.BAL AK.BMR AK.CRQ AK.CTG AK.DCPH AT.CRAG AT.SKAG CN.BVCY 
   CN.DAWY CN.DLBC CN.HYT CN.PLBC CN.WHY CN.YUK1 CN.YUK2 
   CN.YUK3 CN.YUK4 CN.YUK5 CN.YUK6 CN.YUK7 US.WRAK 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
 
 Best Fitting Double Couple
  Mo = 4.68e+22 dyne-cm
  Mw = 4.38 
  Z  = 1 km
  Plane   Strike  Dip  Rake
   NP1        7    50    94
   NP2      180    40    85
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   4.68e+22     84     306
    N   0.00e+00      3     184
    P  -4.68e+22      5      94

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -4.58e+14
       Mxy     2.62e+21
       Mxz     3.12e+21
       Myy    -4.59e+22
       Myz    -8.09e+21
       Mzz     4.59e+22
                                                     
                                                     
                                                     
                                                     
                     ----#######---                  
                 ------##########------              
              -------##############-------           
             -------################-------          
           --------#################---------        
          --------###################---------       
         --------#####################---------      
        --------######################----------     
        --------######################----------     
       ---------#########   ##########-----------    
       ---------######### T ##########--------       
       ---------#########   ##########-------- P     
       ---------######################--------       
        --------#####################-----------     
        --------#####################-----------     
         --------###################-----------      
          --------#################-----------       
           --------################----------        
             -------#############----------          
              -------###########----------           
                 ------#######---------              
                     ----###-------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  4.59e+22   3.12e+21   8.09e+21 
  3.12e+21  -4.58e+14  -2.62e+21 
  8.09e+21  -2.62e+21  -4.59e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101210054234/index.html
	


First motions and takeoff angles from an elocate run.

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:

hp c 0.02 n 3
lp c 0.10 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    0.5     5    50    95   4.34 0.7073
WVFGRD96    1.0   180    40    85   4.38 0.7074
WVFGRD96    2.0   180    25    80   4.48 0.6234
WVFGRD96    3.0     0    70    85   4.46 0.5599
WVFGRD96    4.0   175    70    85   4.44 0.5449
WVFGRD96    5.0    15    20   110   4.42 0.5442
WVFGRD96    6.0   175    75    85   4.40 0.5530
WVFGRD96    7.0   175    80    80   4.39 0.5594
WVFGRD96    8.0   315    10    55   4.39 0.5652
WVFGRD96    9.0   305    10    45   4.39 0.5681
WVFGRD96   10.0   300    10    40   4.43 0.5674
WVFGRD96   11.0   175    85    80   4.43 0.5647
WVFGRD96   12.0   355    90   -80   4.43 0.5572
WVFGRD96   13.0   355    90   -80   4.44 0.5491
WVFGRD96   14.0   210    30   -70   4.46 0.5502
WVFGRD96   15.0   210    30   -70   4.47 0.5496
WVFGRD96   16.0   215    30   -65   4.47 0.5468
WVFGRD96   17.0   215    30   -65   4.48 0.5401
WVFGRD96   18.0   215    30   -65   4.49 0.5315
WVFGRD96   19.0   225    30   -55   4.49 0.5204
WVFGRD96   20.0   215    25   -65   4.52 0.5067
WVFGRD96   21.0   215    25   -65   4.53 0.4942
WVFGRD96   22.0   220    25   -60   4.53 0.4808
WVFGRD96   23.0   220    25   -60   4.54 0.4653
WVFGRD96   24.0   220    25   -60   4.54 0.4492
WVFGRD96   25.0   225    25   -55   4.55 0.4328
WVFGRD96   26.0   230    25   -50   4.55 0.4150
WVFGRD96   27.0   160    80   -85   4.60 0.4064
WVFGRD96   28.0   160    80   -85   4.60 0.4013
WVFGRD96   29.0   160    80   -85   4.61 0.3950

The best solution is

WVFGRD96    1.0   180    40    85   4.38 0.7074

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

hp c 0.02 n 3
lp c 0.10 n 3
Figure 3. Waveform comparison for selected depth
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

The Future

Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.

Acknowledgements

Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
CUS Model with Q from simple gamma values
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
  1.0000  5.0000  2.8900  2.5000 0.172E-02 0.387E-02 0.00  0.00  1.00  1.00 
  9.0000  6.1000  3.5200  2.7300 0.160E-02 0.363E-02 0.00  0.00  1.00  1.00 
 10.0000  6.4000  3.7000  2.8200 0.149E-02 0.336E-02 0.00  0.00  1.00  1.00 
 20.0000  6.7000  3.8700  2.9020 0.000E-04 0.000E-04 0.00  0.00  1.00  1.00 
  0.0000  8.1500  4.7000  3.3640 0.194E-02 0.431E-02 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:

DATE=Fri Dec 10 11:38:21 CST 2010

Last Changed 2010/12/10