The ANSS event ID is uw61293181 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uw61293181/executive.
2017/06/16 03:55:26 47.840 -122.886 56.5 3.69 Washington
USGS/SLU Moment Tensor Solution ENS 2017/06/16 03:55:26:0 47.84 -122.89 56.5 3.7 Washington Stations used: CN.CLRS CN.PGC US.HAWA US.NLWA UW.DOSE UW.GNW UW.KENT UW.LON UW.LTY UW.SP2 UW.STOR UW.WISH Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 7.24e+21 dyne-cm Mw = 3.84 Z = 46 km Plane Strike Dip Rake NP1 37 83 -135 NP2 300 45 -10 Principal Axes: Axis Value Plunge Azimuth T 7.24e+21 24 160 N 0.00e+00 44 44 P -7.24e+21 36 269 Moment Tensor: (dyne-cm) Component Value Mxx 5.31e+21 Mxy -1.98e+21 Mxz -2.52e+21 Myy -4.05e+21 Myz 4.37e+21 Mzz -1.26e+21 ############## ###################### ##########################-- ##########################---- ##----------------#########------- -----------------------####--------- -------------------------------------- ---------------------------###---------- --------------------------######-------- -------------------------##########------- ------ ---------------############------ ------ P --------------##############----- ------ ------------#################---- -------------------##################--- -----------------#####################-- ---------------######################- ------------######################## ---------######################### -----############## ######## --################ T ####### ############### #### ############## Global CMT Convention Moment Tensor: R T P -1.26e+21 -2.52e+21 -4.37e+21 -2.52e+21 5.31e+21 1.98e+21 -4.37e+21 1.98e+21 -4.05e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20170616035526/index.html |
STK = 300 DIP = 45 RAKE = -10 MW = 3.84 HS = 46.0
The NDK file is 20170616035526.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 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 2.0 10 45 -90 3.23 0.3471 WVFGRD96 4.0 115 60 0 3.25 0.3951 WVFGRD96 6.0 295 55 5 3.36 0.4536 WVFGRD96 8.0 290 50 -5 3.44 0.4853 WVFGRD96 10.0 290 55 -5 3.46 0.4929 WVFGRD96 12.0 290 55 -10 3.48 0.4871 WVFGRD96 14.0 310 60 -20 3.41 0.4780 WVFGRD96 16.0 330 50 25 3.45 0.4837 WVFGRD96 18.0 330 50 25 3.47 0.4872 WVFGRD96 20.0 335 45 25 3.49 0.4947 WVFGRD96 22.0 335 40 25 3.52 0.5036 WVFGRD96 24.0 330 40 25 3.56 0.5119 WVFGRD96 26.0 330 35 30 3.60 0.5194 WVFGRD96 28.0 325 35 25 3.62 0.5229 WVFGRD96 30.0 315 35 15 3.64 0.5254 WVFGRD96 32.0 310 40 5 3.64 0.5274 WVFGRD96 34.0 310 40 5 3.66 0.5250 WVFGRD96 36.0 305 45 0 3.68 0.5292 WVFGRD96 38.0 300 50 -5 3.70 0.5413 WVFGRD96 40.0 300 40 -5 3.80 0.5510 WVFGRD96 42.0 300 40 -5 3.82 0.5568 WVFGRD96 44.0 300 45 -10 3.82 0.5600 WVFGRD96 46.0 300 45 -10 3.84 0.5618 WVFGRD96 48.0 300 45 -10 3.85 0.5614 WVFGRD96 50.0 300 45 -15 3.86 0.5594 WVFGRD96 52.0 300 45 -15 3.87 0.5564 WVFGRD96 54.0 300 50 -15 3.87 0.5524 WVFGRD96 56.0 300 50 -20 3.88 0.5487 WVFGRD96 58.0 300 50 -20 3.89 0.5451 WVFGRD96 60.0 300 50 -25 3.89 0.5399 WVFGRD96 62.0 300 50 -25 3.89 0.5356 WVFGRD96 64.0 300 50 -25 3.90 0.5288 WVFGRD96 66.0 300 50 -25 3.91 0.5217 WVFGRD96 68.0 300 55 -30 3.90 0.5155 WVFGRD96 70.0 300 55 -30 3.90 0.5088 WVFGRD96 72.0 300 55 -30 3.91 0.5012 WVFGRD96 74.0 300 55 -35 3.91 0.4954 WVFGRD96 76.0 300 50 -50 3.92 0.4880 WVFGRD96 78.0 300 50 -50 3.92 0.4839 WVFGRD96 80.0 300 50 -50 3.93 0.4794 WVFGRD96 82.0 300 50 -50 3.93 0.4746 WVFGRD96 84.0 300 50 -50 3.94 0.4699 WVFGRD96 86.0 305 55 -50 3.93 0.4655 WVFGRD96 88.0 300 55 -55 3.93 0.4613 WVFGRD96 90.0 300 55 -55 3.93 0.4570 WVFGRD96 92.0 300 55 -55 3.94 0.4531 WVFGRD96 94.0 300 55 -55 3.94 0.4485 WVFGRD96 96.0 300 55 -55 3.94 0.4443 WVFGRD96 98.0 300 55 -60 3.95 0.4395
The best solution is
WVFGRD96 46.0 300 45 -10 3.84 0.5618
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 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2
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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