Location

ANSS Location

elocate (SLU) Location

We use the program elocate and the WUS model, given below, with our own reading from the broadband stations. The output of the program is elocate.txt

Felt Map

USGS Felt map for this earthquake

USGS Felt reports main page

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2010/06/17 14:23:24:0 46.12 -120.75 2.0 4.2 Washington Stations used: HW.CCRK IU.COR US.HAWA US.NEW US.NLWA UW.BLOW UW.DAVN UW.LRIV UW.LTY UW.MRBL UW.OMAK UW.PASS UW.STOR UW.TREE UW.WOLL UW.YACT Filtering commands used: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 7.24e+21 dyne-cm Mw = 3.84 Z = 12 km Plane Strike Dip Rake NP1 283 85 160 NP2 15 70 5 Principal Axes: Axis Value Plunge Azimuth T 7.24e+21 17 237 N 0.00e+00 69 91 P -7.24e+21 11 331 Moment Tensor: (dyne-cm) Component Value Mxx -3.42e+21 Mxy 5.97e+21 Mxz -2.26e+21 Myy 3.01e+21 Myz -1.11e+21 Mzz 4.06e+20 -------------# --------------##### --- P --------------######## ---- ---------------######## ------------------------########## -------------------------########### --------------------------############ --------------------------############## #-------------------------############## ##############-------------############### ######################----################ ##########################---############# ##########################----------###### ########################---------------- #######################----------------- ### ################---------------- ## T ###############---------------- # ##############---------------- ###############--------------- #############--------------- ########-------------- ##------------ Global CMT Convention Moment Tensor: R T P 4.06e+20 -2.26e+21 1.11e+21 -2.26e+21 -3.42e+21 -5.97e+21 1.11e+21 -5.97e+21 3.01e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100617142324/index.html

Preferred Solution

      STK = 15
      DIP = 70
     RAKE = 5
       MW = 3.84
       HS = 12.0

This was very difficult to do. The Rayleigh wave signals were poor while the SH signals were large. The solution with significant strike slip at a depth of 12 km is compatible with this excitation. The SLU elocate location, using hand picked waveforms is compatible with the deeper depth rather than the published U. Washington PNW depth of 2.2 km. The lower Mw is certainly more compatible with the intensity responses. We provide the elocate solution for reference since it provides the takeoff angles for the first motion data.

The PNW P-wave first motion focal mechanism has more observations than out hand pick because of the availability of short period. Although the solution depends heavily on the takeoff angle, there is rough agreement in the mechanisms in the general orientations of the compression and dilatation quadrants.

Moment Tensor Comparison

The following compares this source inversion to others

SLU	SLUFM	UW
USGS/SLU Moment Tensor Solution ENS 2010/06/17 14:23:24:0 46.12 -120.75 2.0 4.2 Washington Stations used: HW.CCRK IU.COR US.HAWA US.NEW US.NLWA UW.BLOW UW.DAVN UW.LRIV UW.LTY UW.MRBL UW.OMAK UW.PASS UW.STOR UW.TREE UW.WOLL UW.YACT Filtering commands used: hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 7.24e+21 dyne-cm Mw = 3.84 Z = 12 km Plane Strike Dip Rake NP1 283 85 160 NP2 15 70 5 Principal Axes: Axis Value Plunge Azimuth T 7.24e+21 17 237 N 0.00e+00 69 91 P -7.24e+21 11 331 Moment Tensor: (dyne-cm) Component Value Mxx -3.42e+21 Mxy 5.97e+21 Mxz -2.26e+21 Myy 3.01e+21 Myz -1.11e+21 Mzz 4.06e+20 -------------# --------------##### --- P --------------######## ---- ---------------######## ------------------------########## -------------------------########### --------------------------############ --------------------------############## #-------------------------############## ##############-------------############### ######################----################ ##########################---############# ##########################----------###### ########################---------------- #######################----------------- ### ################---------------- ## T ###############---------------- # ##############---------------- ###############--------------- #############--------------- ########-------------- ##------------ Global CMT Convention Moment Tensor: R T P 4.06e+20 -2.26e+21 1.11e+21 -2.26e+21 -3.42e+21 -5.97e+21 1.11e+21 -5.97e+21 3.01e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100617142324/index.html

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 0.05 n 3

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    0.5    25    60    20   3.52 0.3325
WVFGRD96    1.0    20    70    15   3.51 0.3539
WVFGRD96    2.0    25    65    25   3.63 0.4364
WVFGRD96    3.0    20    65    15   3.66 0.4778
WVFGRD96    4.0    20    70    15   3.68 0.5070
WVFGRD96    5.0    15    80     5   3.70 0.5293
WVFGRD96    6.0    15    80     5   3.72 0.5443
WVFGRD96    7.0    15    80     5   3.75 0.5552
WVFGRD96    8.0    20    65    15   3.79 0.5733
WVFGRD96    9.0    20    65    15   3.80 0.5788
WVFGRD96   10.0    15    70    10   3.82 0.5833
WVFGRD96   11.0    15    70    10   3.83 0.5869
WVFGRD96   12.0    15    70     5   3.84 0.5877
WVFGRD96   13.0    15    70     5   3.85 0.5870
WVFGRD96   14.0    15    85    15   3.85 0.5854
WVFGRD96   15.0    15    85    15   3.86 0.5872
WVFGRD96   16.0    15    85    15   3.87 0.5865
WVFGRD96   17.0    15    85    15   3.88 0.5839
WVFGRD96   18.0    15    85    15   3.88 0.5794
WVFGRD96   19.0    15    90    15   3.89 0.5737

The best solution is

WVFGRD96   12.0    15    70     5   3.84 0.5877

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 0.05 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=Fri Jun 18 02:51:36 CDT 2010