The ANSS event ID is uw10770563 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uw10770563/executive.
2009/03/30 07:06:10 47.600 -123.484 43.6 3.6 Washington
USGS/SLU Moment Tensor Solution ENS 2009/03/30 07:06:10:0 47.60 -123.48 43.6 3.6 Washington Stations used: US.NLWA UW.STOR XU.BS11 XU.C04A XU.W030 XU.W040 XU.W060 YW.FACB YW.FACC Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 Best Fitting Double Couple Mo = 7.76e+21 dyne-cm Mw = 3.86 Z = 46 km Plane Strike Dip Rake NP1 185 60 -65 NP2 322 38 -126 Principal Axes: Axis Value Plunge Azimuth T 7.76e+21 12 257 N 0.00e+00 21 352 P -7.76e+21 65 141 Moment Tensor: (dyne-cm) Component Value Mxx -4.47e+20 Mxy 2.27e+21 Mxz 1.94e+21 Myy 6.54e+21 Myz -3.36e+21 Mzz -6.09e+21 -------####### ----------############ ###########---############## ###########-------############ ############-----------########### #############-------------########## #############----------------######### #############------------------######### #############-------------------######## ##############--------------------######## #############----------------------####### #############-----------------------###### # #########---------- ----------###### T #########---------- P ----------##### #########---------- ----------##### ############----------------------#### ###########----------------------### ##########----------------------## #########--------------------# #########------------------# #######--------------- ####---------- Global CMT Convention Moment Tensor: R T P -6.09e+21 1.94e+21 3.36e+21 1.94e+21 -4.47e+20 -2.27e+21 3.36e+21 -2.27e+21 6.54e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20090330070610/index.html |
STK = 185 DIP = 60 RAKE = -65 MW = 3.86 HS = 46.0
The NDK file is 20090330070610.ndk The waveform inversion is preferred.
Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.
Left: ML computed using the IASPEI formula for Horizontal components. Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
Left: ML computed using the IASPEI formula for Vertical components (research). Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot.
Right: Residuals from new relation as a function of distance and azimuth.
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The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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:
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 2.0 195 50 -55 3.24 0.3567 WVFGRD96 4.0 30 90 20 3.29 0.3628 WVFGRD96 6.0 65 35 40 3.37 0.4065 WVFGRD96 8.0 65 35 45 3.45 0.4630 WVFGRD96 10.0 65 35 50 3.47 0.4901 WVFGRD96 12.0 65 40 50 3.47 0.5048 WVFGRD96 14.0 35 50 -45 3.47 0.5109 WVFGRD96 16.0 35 50 -45 3.49 0.5398 WVFGRD96 18.0 35 50 -45 3.51 0.5572 WVFGRD96 20.0 35 50 -45 3.52 0.5662 WVFGRD96 22.0 200 55 -55 3.57 0.5766 WVFGRD96 24.0 205 60 -50 3.59 0.5866 WVFGRD96 26.0 205 60 -50 3.61 0.5913 WVFGRD96 28.0 25 50 -60 3.61 0.6048 WVFGRD96 30.0 0 40 -90 3.63 0.6243 WVFGRD96 32.0 -5 35 -100 3.65 0.6439 WVFGRD96 34.0 185 55 -80 3.66 0.6684 WVFGRD96 36.0 185 55 -75 3.69 0.6867 WVFGRD96 38.0 185 55 -70 3.71 0.7025 WVFGRD96 40.0 180 55 -75 3.81 0.7412 WVFGRD96 42.0 180 55 -75 3.83 0.7501 WVFGRD96 44.0 185 60 -65 3.84 0.7516 WVFGRD96 46.0 185 60 -65 3.86 0.7534 WVFGRD96 48.0 185 60 -65 3.86 0.7493 WVFGRD96 50.0 185 60 -65 3.87 0.7431 WVFGRD96 52.0 185 65 -60 3.89 0.7395 WVFGRD96 54.0 185 65 -60 3.89 0.7342 WVFGRD96 56.0 185 65 -65 3.89 0.7264 WVFGRD96 58.0 185 65 -65 3.90 0.7154 WVFGRD96 60.0 180 65 -70 3.90 0.7034 WVFGRD96 62.0 185 70 -65 3.91 0.6959 WVFGRD96 64.0 185 70 -65 3.92 0.6866 WVFGRD96 66.0 180 70 -75 3.92 0.6764 WVFGRD96 68.0 180 70 -75 3.92 0.6671 WVFGRD96 70.0 180 70 -75 3.92 0.6565 WVFGRD96 72.0 175 70 -90 3.93 0.6461 WVFGRD96 74.0 45 35 -30 3.97 0.6443 WVFGRD96 76.0 45 35 -30 3.98 0.6375 WVFGRD96 78.0 50 40 -20 3.99 0.6340 WVFGRD96 80.0 50 40 -20 4.00 0.6295 WVFGRD96 82.0 50 40 -20 4.00 0.6244 WVFGRD96 84.0 50 40 -20 4.01 0.6166 WVFGRD96 86.0 50 40 -20 4.01 0.6058 WVFGRD96 88.0 50 40 -20 4.01 0.5927 WVFGRD96 90.0 50 40 -20 4.01 0.5776 WVFGRD96 92.0 55 45 -15 4.03 0.5630 WVFGRD96 94.0 55 45 -15 4.03 0.5496 WVFGRD96 96.0 55 50 -10 4.03 0.5261 WVFGRD96 98.0 50 60 5 4.03 0.4969
The best solution is
WVFGRD96 46.0 185 60 -65 3.86 0.7534
The mechanism corresponding 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 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3
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Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample. |
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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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:
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.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows (The format is in the model96 format of Computer Programs in Seismology).
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