Location

2004/07/12 16:45:00 44.3290 -124.4900 29.0 4.90 Oregon

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
 2004/07/12 16:45:00  44.3290  -124.4900  29.0  4.90 Oregon
 
 Best Fitting Double Couple
    Mo = 1.27e+23 dyne-cm
    Mw = 4.67 
    Z  = 15 km
     Plane   Strike  Dip  Rake
      NP1      186    71    97
      NP2      345    20    70
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   1.27e+23     63     107
     N   0.00e+00      7       4
     P  -1.27e+23     26     271



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     2.30e+21
       Mxy    -6.33e+21
       Mxz    -1.58e+22
       Myy    -7.92e+22
       Myz     9.91e+22
       Mzz     7.69e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 -----------######-----              
              -------------##########-----           
             -------------#############----          
           ---------------##############-----        
          ---------------#################----       
         ----------------##################----      
        ----------------####################----     
        ----------------####################----     
       ----   ----------#####################----    
       ---- P ---------######################----    
       ----   ---------##########   #########----    
       ----------------########## T #########----    
        ---------------##########   #########---     
        ---------------#####################----     
         --------------#####################---      
          -------------####################---       
           ------------###################---        
             -----------#################--          
              ----------###############---           
                 -------#############--              
                     ----##########                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
  7.69e+22  -1.58e+22  -9.91e+22 
 -1.58e+22   2.30e+21   6.33e+21 
 -9.91e+22   6.33e+21  -7.92e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20040712164500/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 = 345
      DIP = 20
     RAKE = 70
       MW = 4.67
       HS = 15.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
GCMT
UCB
 SLU Moment Tensor Solution
 2004/07/12 16:45:00  44.3290  -124.4900  29.0  4.90 Oregon
 
 Best Fitting Double Couple
    Mo = 1.27e+23 dyne-cm
    Mw = 4.67 
    Z  = 15 km
     Plane   Strike  Dip  Rake
      NP1      186    71    97
      NP2      345    20    70
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   1.27e+23     63     107
     N   0.00e+00      7       4
     P  -1.27e+23     26     271



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx     2.30e+21
       Mxy    -6.33e+21
       Mxz    -1.58e+22
       Myy    -7.92e+22
       Myz     9.91e+22
       Mzz     7.69e+22
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 -----------######-----              
              -------------##########-----           
             -------------#############----          
           ---------------##############-----        
          ---------------#################----       
         ----------------##################----      
        ----------------####################----     
        ----------------####################----     
       ----   ----------#####################----    
       ---- P ---------######################----    
       ----   ---------##########   #########----    
       ----------------########## T #########----    
        ---------------##########   #########---     
        ---------------#####################----     
         --------------#####################---      
          -------------####################---       
           ------------###################---        
             -----------#################--          
              ----------###############---           
                 -------#############--              
                     ----##########                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
  7.69e+22  -1.58e+22  -9.91e+22 
 -1.58e+22   2.30e+21   6.33e+21 
 -9.91e+22   6.33e+21  -7.92e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20040712164500/index.html
	
071204B  NEAR COAST OF OREGON

  Date: 2004/ 7/12   Centroid Time: 16:45: 3.7 GMT
  Lat=  44.30  Lon=-124.71
  Depth= 20.0   Half duration= 0.7
  Centroid time minus hypocenter time:  3.0
  Moment Tensor: Expo=23  1.960 0.051 -2.010 0.254 -1.650 -0.397 
  Mw = 4.9    mb = 4.9    Ms = 4.1   Scalar Moment = 2.62e+23
  Fault plane:  strike=23    dip=27   slip=112
  Fault plane:  strike=178    dip=65   slip=79


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


        
ofor04194   0  07/12/2004 16:45:00.0 44.332 -124.520    4.9 29.1 7121645
            2    191   58         100  353     34    74        8   0.0 2.15e23 4.8 3
           -2 0.02 0.05 OT01 OT04 OT06 OT08 HUMO YBH (uw7121645)

STK 191
DIP  59
RAKE 100 

Mo=2.15E+23 dyne-cm
Mw=4.8
H=8



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


        

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   205    45   -85   4.20 0.2137
WVFGRD96    1.0   205    45   -85   4.25 0.2051
WVFGRD96    2.0   205    45   -85   4.38 0.2428
WVFGRD96    3.0   225    20   -60   4.41 0.1521
WVFGRD96    4.0   255    10   -30   4.41 0.2057
WVFGRD96    5.0   270    10   -15   4.42 0.2631
WVFGRD96    6.0   280    10     0   4.43 0.3137
WVFGRD96    7.0   295    10    15   4.44 0.3539
WVFGRD96    8.0   305    10    25   4.54 0.3837
WVFGRD96    9.0   325    15    45   4.56 0.4206
WVFGRD96   10.0   340    20    60   4.59 0.4543
WVFGRD96   11.0   345    20    65   4.61 0.4854
WVFGRD96   12.0   350    20    75   4.63 0.5079
WVFGRD96   13.0   350    25    70   4.65 0.5242
WVFGRD96   14.0   350    20    75   4.66 0.5322
WVFGRD96   15.0   345    20    70   4.67 0.5344
WVFGRD96   16.0   345    20    65   4.68 0.5328
WVFGRD96   17.0   345    20    65   4.69 0.5261
WVFGRD96   18.0   340    15    60   4.69 0.5162
WVFGRD96   19.0   340    15    60   4.71 0.5062
WVFGRD96   20.0   340    15    60   4.72 0.4943
WVFGRD96   21.0   335    15    55   4.74 0.4818
WVFGRD96   22.0   325    15    45   4.75 0.4670
WVFGRD96   23.0   335    10    55   4.75 0.4525
WVFGRD96   24.0   330    10    50   4.76 0.4371
WVFGRD96   25.0   330    10    50   4.77 0.4203
WVFGRD96   26.0   330    10    50   4.78 0.4021
WVFGRD96   27.0   330    10    50   4.79 0.3824
WVFGRD96   28.0   325    10    45   4.79 0.3608
WVFGRD96   29.0   325    10    45   4.80 0.3374

The best solution is

WVFGRD96   15.0   345    20    70   4.67 0.5344

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 0.02 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.

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=Thu Dec 18 13:00:00 CST 2008

Last Changed 2004/07/12