2004/07/22 20:26:27 42.1920 -120.2960 5.0 4.30 Oregon
USGS Felt map for this earthquake
USGS Felt reports page for Pacific Northwest
SLU Moment Tensor Solution 2004/07/22 20:26:27 42.1920 -120.2960 5.0 4.30 Oregon Best Fitting Double Couple Mo = 5.96e+22 dyne-cm Mw = 4.45 Z = 8 km Plane Strike Dip Rake NP1 164 64 -114 NP2 30 35 -50 Principal Axes: Axis Value Plunge Azimuth T 5.96e+22 16 272 N 0.00e+00 22 175 P -5.96e+22 63 35 Moment Tensor: (dyne-cm) Component Value Mxx -8.30e+21 Mxy -7.59e+21 Mxz -1.94e+22 Myy 5.12e+22 Myz -2.92e+22 Mzz -4.29e+22 #------------- ####------------------ #######-------------------## #######---------------------## #########----------------------### ##########----------------------#### ###########----------- ---------#### ############----------- P ---------##### ############----------- ---------##### ## #########----------------------###### ## T #########----------------------###### ## #########---------------------####### ###############--------------------####### ###############------------------####### ###############-----------------######## ###############---------------######## ###############------------######### ###############----------######### ##############-------######### ###############--########### #########----######### ------------## Harvard Convention Moment Tensor: R T F -4.29e+22 -1.94e+22 2.92e+22 -1.94e+22 -8.30e+21 7.59e+21 2.92e+22 7.59e+21 5.12e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20040722202627/index.html |
STK = 30 DIP = 35 RAKE = -50 MW = 4.45 HS = 8.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution 2004/07/22 20:26:27 42.1920 -120.2960 5.0 4.30 Oregon Best Fitting Double Couple Mo = 5.96e+22 dyne-cm Mw = 4.45 Z = 8 km Plane Strike Dip Rake NP1 164 64 -114 NP2 30 35 -50 Principal Axes: Axis Value Plunge Azimuth T 5.96e+22 16 272 N 0.00e+00 22 175 P -5.96e+22 63 35 Moment Tensor: (dyne-cm) Component Value Mxx -8.30e+21 Mxy -7.59e+21 Mxz -1.94e+22 Myy 5.12e+22 Myz -2.92e+22 Mzz -4.29e+22 #------------- ####------------------ #######-------------------## #######---------------------## #########----------------------### ##########----------------------#### ###########----------- ---------#### ############----------- P ---------##### ############----------- ---------##### ## #########----------------------###### ## T #########----------------------###### ## #########---------------------####### ###############--------------------####### ###############------------------####### ###############-----------------######## ###############---------------######## ###############------------######### ###############----------######### ##############-------######### ###############--########### #########----######### ------------## Harvard Convention Moment Tensor: R T F -4.29e+22 -1.94e+22 2.92e+22 -1.94e+22 -8.30e+21 7.59e+21 2.92e+22 7.59e+21 5.12e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20040722202627/index.html |
lake04204 0 07/22/2004 20:26:27.0 42.212 -120.283 5.0 4.3 uslfbr 2 176 64 -101 20 28 -69 8 0.0 8.08e22 4.6 4 -2 0.02 0.05 HUMO ORV WDC YBH (uslfbr) STK 176 DIP 64 RAKE -101 H 8 Mw 4.6 UC Berkeley Moment Tensor Best Fitting Double Couple Mo = 8.91e+22 dyne-cm Mw = 4.60 Z = 8 km Plane Strike Dip Rake NP1 176 64 -101 NP2 20 28 -69 Principal Axes: Axis Value Plunge Azimuth T 8.91e+22 18 274 N 0.00e+00 10 181 P -8.91e+22 69 64 Moment Tensor: (dyne-cm) Component Value Mxx -1.79e+21 Mxy -1.03e+22 Mxz -1.12e+22 Myy 7.07e+22 Myz -5.32e+22 Mzz -6.89e+22 #####--------- #######-------------## ##########---------------### ##########-----------------### ###########-------------------#### ############--------------------#### #############---------------------#### #############----------------------##### #############----------- --------##### ## #########----------- P ---------##### ## T #########----------- ---------##### ## #########----------------------###### ###############---------------------###### ##############--------------------###### ##############--------------------###### ##############------------------###### #############-----------------###### #############--------------####### ############------------###### ############--------######## ##########----######## ####---####### Harvard Convention Moment Tensor: R T F -6.89e+22 -1.12e+22 5.32e+22 -1.12e+22 -1.79e+21 1.03e+22 5.32e+22 1.03e+22 7.07e+22 |
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.
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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 0.06 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 20 35 -85 4.15 0.3724 WVFGRD96 1.0 10 40 -90 4.17 0.3577 WVFGRD96 2.0 190 55 -95 4.27 0.4167 WVFGRD96 3.0 40 30 -30 4.35 0.4073 WVFGRD96 4.0 35 25 -40 4.37 0.4431 WVFGRD96 5.0 35 30 -40 4.37 0.4948 WVFGRD96 6.0 35 35 -45 4.38 0.5287 WVFGRD96 7.0 30 35 -50 4.39 0.5481 WVFGRD96 8.0 30 35 -50 4.45 0.5781 WVFGRD96 9.0 30 35 -50 4.45 0.5775 WVFGRD96 10.0 35 40 -40 4.44 0.5710 WVFGRD96 11.0 40 45 -30 4.43 0.5597 WVFGRD96 12.0 45 45 -20 4.42 0.5502 WVFGRD96 13.0 45 50 -15 4.43 0.5400 WVFGRD96 14.0 50 50 -10 4.42 0.5280 WVFGRD96 15.0 50 50 -10 4.42 0.5157 WVFGRD96 16.0 55 65 25 4.46 0.5081 WVFGRD96 17.0 55 65 20 4.46 0.5021 WVFGRD96 18.0 60 60 25 4.45 0.4947 WVFGRD96 19.0 60 60 25 4.45 0.4874 WVFGRD96 20.0 60 60 25 4.46 0.4793 WVFGRD96 21.0 60 60 25 4.47 0.4691 WVFGRD96 22.0 65 55 25 4.46 0.4608 WVFGRD96 23.0 65 55 25 4.46 0.4522 WVFGRD96 24.0 65 55 25 4.47 0.4442 WVFGRD96 25.0 70 55 25 4.47 0.4362 WVFGRD96 26.0 70 55 25 4.47 0.4279 WVFGRD96 27.0 70 50 25 4.47 0.4200 WVFGRD96 28.0 70 50 25 4.48 0.4121 WVFGRD96 29.0 70 50 25 4.48 0.4044
The best solution is
WVFGRD96 8.0 30 35 -50 4.45 0.5781
The mechanism correspond to the best fit is
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The best fit as a function of depth is given in the following figure:
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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 0.06 n 3
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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. |
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.
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.
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
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 20:36:22 CST 2008