Location

1999/07/03 01:43:54 47.076 -123.463 40.0 5.40 Washington

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for Pacific Northwest

Focal Mechanism

 SLU Moment Tensor Solution
 1999/07/03 01:43:54  47.076  -123.463  40.0  5.40 Washington
 
 Best Fitting Double Couple
    Mo = 4.95e+24 dyne-cm
    Mw = 5.73 
    Z  = 45 km
     Plane   Strike  Dip  Rake
      NP1      165    50   -95
      NP2      353    40   -84
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   4.95e+24      5     259
     N   0.00e+00      4     168
     P  -4.95e+24     84      40



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     1.60e+23
       Mxy     9.29e+23
       Mxz    -4.90e+23
       Myy     4.70e+24
       Myz    -7.56e+23
       Mzz    -4.86e+24
                                                     
                                                     
                                                     
                                                     
                     #------#######                  
                 ####----------########              
              ######--------------########           
             ######----------------########          
           #######-------------------########        
          ########--------------------########       
         ########---------------------#########      
        #########----------------------#########     
        #########------------   --------########     
       ##########------------ P --------#########    
       ###########-----------   --------#########    
       ###########----------------------#########    
          ########----------------------#########    
        T #########---------------------########     
          ##########--------------------########     
         ###########--------------------#######      
          ###########------------------#######       
           ############---------------#######        
             ###########-------------######          
              ############----------######           
                 ###########------#####              
                     ##############                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -4.86e+24  -4.90e+23   7.56e+23 
 -4.90e+23   1.60e+23  -9.29e+23 
  7.56e+23  -9.29e+23   4.70e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/19990703014354/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 = 165
      DIP = 50
     RAKE = -95
       MW = 5.73
       HS = 45.0

The waveform inversion is preferred. The fits for the filter band 0.02 - 0.10 were very good for the detail match of the body waves at COR and other short distances.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
GCMT
 SLU Moment Tensor Solution
 1999/07/03 01:43:54  47.076  -123.463  40.0  5.40 Washington
 
 Best Fitting Double Couple
    Mo = 4.95e+24 dyne-cm
    Mw = 5.73 
    Z  = 45 km
     Plane   Strike  Dip  Rake
      NP1      165    50   -95
      NP2      353    40   -84
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   4.95e+24      5     259
     N   0.00e+00      4     168
     P  -4.95e+24     84      40



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     1.60e+23
       Mxy     9.29e+23
       Mxz    -4.90e+23
       Myy     4.70e+24
       Myz    -7.56e+23
       Mzz    -4.86e+24
                                                     
                                                     
                                                     
                                                     
                     #------#######                  
                 ####----------########              
              ######--------------########           
             ######----------------########          
           #######-------------------########        
          ########--------------------########       
         ########---------------------#########      
        #########----------------------#########     
        #########------------   --------########     
       ##########------------ P --------#########    
       ###########-----------   --------#########    
       ###########----------------------#########    
          ########----------------------#########    
        T #########---------------------########     
          ##########--------------------########     
         ###########--------------------#######      
          ###########------------------#######       
           ############---------------#######        
             ###########-------------######          
              ############----------######           
                 ###########------#####              
                     ##############                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -4.86e+24  -4.90e+23   7.56e+23 
 -4.90e+23   1.60e+23  -9.29e+23 
  7.56e+23  -9.29e+23   4.70e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/19990703014354/index.html
	
 Global CMT

 Best Fitting Double Couple
    Mo = 5.62e+24 dyne-cm
    Mw = 5.80
    Z  = 45 km
     Plane   Strike  Dip  Rake
      NP1      345    61   -108
      NP2      199    34   -61
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   5.62e+24     14      88
     N   0.00e+00     16     354
     P  -5.62e+24     69     218



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx    -4.55e+23
       Mxy    -2.02e+23
       Mxz     1.54e+24
       Myy     5.02e+24
       Myz     2.48e+24
       Mzz    -4.56e+24




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




 Harvard Convention
 Moment Tensor:
      R          T          F
 -4.56e+24   1.54e+24  -2.48e+24
  1.54e+24  -4.55e+23   2.02e+23
 -2.48e+24   2.02e+23   5.02e+24

        

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 0.01 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    0.5   345    40    90   4.99 0.2413
WVFGRD96    1.0   170    45    90   5.05 0.2709
WVFGRD96    2.0   170    45    90   5.14 0.3333
WVFGRD96    3.0   185    45   100   5.23 0.3753
WVFGRD96    4.0   190    45   105   5.28 0.3555
WVFGRD96    5.0   330    55    40   5.27 0.3034
WVFGRD96    6.0   320    75    10   5.28 0.2721
WVFGRD96    7.0   320    80     0   5.30 0.2508
WVFGRD96    8.0   315    75   -10   5.30 0.2363
WVFGRD96    9.0   130    50   -10   5.28 0.2380
WVFGRD96   10.0   120    35     5   5.23 0.2528
WVFGRD96   11.0   120    35     5   5.24 0.2693
WVFGRD96   12.0   115    30    15   5.23 0.2863
WVFGRD96   13.0   110    30    15   5.24 0.3024
WVFGRD96   14.0   115    30    20   5.26 0.3173
WVFGRD96   15.0   115    30    20   5.27 0.3324
WVFGRD96   16.0   110    30    20   5.28 0.3457
WVFGRD96   17.0    60    50    40   5.43 0.3595
WVFGRD96   18.0    60    50    40   5.44 0.3749
WVFGRD96   19.0    60    50    40   5.45 0.3890
WVFGRD96   20.0    60    50    40   5.47 0.4026
WVFGRD96   21.0    60    50    40   5.49 0.4176
WVFGRD96   22.0    60    45    40   5.51 0.4301
WVFGRD96   23.0    60    45    40   5.52 0.4416
WVFGRD96   24.0    60    45    40   5.53 0.4529
WVFGRD96   25.0    60    45    40   5.54 0.4636
WVFGRD96   26.0    60    45    40   5.55 0.4735
WVFGRD96   27.0    10    50   -60   5.46 0.4931
WVFGRD96   28.0    10    50   -60   5.47 0.5126
WVFGRD96   29.0    15    50   -55   5.49 0.5307
WVFGRD96   30.0    15    50   -55   5.50 0.5477
WVFGRD96   31.0    15    50   -55   5.51 0.5623
WVFGRD96   32.0    10    45   -60   5.51 0.5757
WVFGRD96   33.0    10    45   -60   5.52 0.5877
WVFGRD96   34.0    10    45   -60   5.54 0.5974
WVFGRD96   35.0   370    45   -60   5.55 0.6048
WVFGRD96   36.0   370    45   -60   5.56 0.6115
WVFGRD96   37.0   355    40   -75   5.57 0.6186
WVFGRD96   38.0   355    40   -75   5.58 0.6261
WVFGRD96   39.0   350    40   -80   5.60 0.6339
WVFGRD96   40.0   160    50  -105   5.69 0.6181
WVFGRD96   41.0   160    50  -105   5.71 0.6302
WVFGRD96   42.0   345    45  -100   5.71 0.6379
WVFGRD96   43.0   345    45  -105   5.72 0.6434
WVFGRD96   44.0   165    50   -95   5.73 0.6469
WVFGRD96   45.0   165    50   -95   5.73 0.6483
WVFGRD96   46.0   355    40   -80   5.74 0.6475
WVFGRD96   47.0   165    50   -95   5.75 0.6464
WVFGRD96   48.0   350    40   -90   5.75 0.6434
WVFGRD96   49.0   165    50   -95   5.76 0.6397
WVFGRD96   50.0   350    40   -90   5.76 0.6342

The best solution is

WVFGRD96   45.0   165    50   -95   5.73 0.6483

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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was

hp c 0.01 n 3
lp c 0.06 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.

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 WUS 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:

DATE=Sat Dec 20 14:50:51 CST 2008

Last Changed 1999/07/03