The ANSS event ID is usp000hkyn and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000hkyn/executive.
2010/09/19 22:01:47 35.611 -97.246 5.0 3.5 Oklahoma
USGS/SLU Moment Tensor Solution ENS 2010/09/19 22:01:47:0 35.61 -97.25 5.0 3.5 Oklahoma Stations used: AG.HHAR TA.S35A TA.T30A TA.T34A TA.TUL1 TA.U33A TA.U34A TA.V33A TA.V34A TA.V35A TA.W33A TA.W35A TA.W36A TA.W37A TA.W38A TA.X34A TA.X35A TA.X36A TA.X37A TA.X38A TA.Y34A TA.Y35A TA.Y37A TA.Y39A TA.Z35A Filtering commands used: hp c 0.02 n 4 lp c 0.08 n 4 Best Fitting Double Couple Mo = 2.02e+21 dyne-cm Mw = 3.47 Z = 3 km Plane Strike Dip Rake NP1 15 90 -160 NP2 285 70 0 Principal Axes: Axis Value Plunge Azimuth T 2.02e+21 14 148 N 0.00e+00 70 15 P -2.02e+21 14 242 Moment Tensor: (dyne-cm) Component Value Mxx 9.48e+20 Mxy -1.64e+21 Mxz -1.79e+20 Myy -9.48e+20 Myz 6.67e+20 Mzz 0.00e+00 ############-- ################------ ##################---------- ###################----------- ####################-------------- #####################--------------- #####################----------------- ####---------#########------------------ ---------------------#------------------ ----------------------#######------------- ---------------------############--------- ---------------------###############------ --------------------##################---- -------------------####################- --- ------------###################### -- P ------------##################### - -----------##################### --------------#################### -----------############ #### ----------############ T ### ------############# --############ Global CMT Convention Moment Tensor: R T P 0.00e+00 -1.79e+20 -6.67e+20 -1.79e+20 9.48e+20 1.64e+21 -6.67e+20 1.64e+21 -9.48e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100919220147/index.html |
STK = 285 DIP = 70 RAKE = 0 MW = 3.47 HS = 3.0
The NDK file is 20100919220147.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution ENS 2010/09/19 22:01:47:0 35.61 -97.25 5.0 3.5 Oklahoma Stations used: AG.HHAR TA.S35A TA.T30A TA.T34A TA.TUL1 TA.U33A TA.U34A TA.V33A TA.V34A TA.V35A TA.W33A TA.W35A TA.W36A TA.W37A TA.W38A TA.X34A TA.X35A TA.X36A TA.X37A TA.X38A TA.Y34A TA.Y35A TA.Y37A TA.Y39A TA.Z35A Filtering commands used: hp c 0.02 n 4 lp c 0.08 n 4 Best Fitting Double Couple Mo = 2.02e+21 dyne-cm Mw = 3.47 Z = 3 km Plane Strike Dip Rake NP1 15 90 -160 NP2 285 70 0 Principal Axes: Axis Value Plunge Azimuth T 2.02e+21 14 148 N 0.00e+00 70 15 P -2.02e+21 14 242 Moment Tensor: (dyne-cm) Component Value Mxx 9.48e+20 Mxy -1.64e+21 Mxz -1.79e+20 Myy -9.48e+20 Myz 6.67e+20 Mzz 0.00e+00 ############-- ################------ ##################---------- ###################----------- ####################-------------- #####################--------------- #####################----------------- ####---------#########------------------ ---------------------#------------------ ----------------------#######------------- ---------------------############--------- ---------------------###############------ --------------------##################---- -------------------####################- --- ------------###################### -- P ------------##################### - -----------##################### --------------#################### -----------############ #### ----------############ T ### ------############# --############ Global CMT Convention Moment Tensor: R T P 0.00e+00 -1.79e+20 -6.67e+20 -1.79e+20 9.48e+20 1.64e+21 -6.67e+20 1.64e+21 -9.48e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100919220147/index.html |
First motions plot using the waveform inversion nodal planes and the elcoate takeoff angles and azimuths. Symbols: o strong compression, + weak compression, Delta strong dilatation, - weak dilatation, X undetermined polarity. |
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: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
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:
hp c 0.02 n 4 lp c 0.08 n 4The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 285 50 5 3.42 0.3902 WVFGRD96 1.0 285 65 5 3.39 0.4050 WVFGRD96 2.0 285 55 0 3.47 0.4386 WVFGRD96 3.0 285 70 0 3.47 0.4502 WVFGRD96 4.0 285 70 0 3.49 0.4498 WVFGRD96 5.0 285 75 10 3.50 0.4441 WVFGRD96 6.0 285 80 15 3.52 0.4377 WVFGRD96 7.0 285 80 15 3.53 0.4315 WVFGRD96 8.0 285 80 20 3.56 0.4247 WVFGRD96 9.0 105 60 5 3.59 0.4185 WVFGRD96 10.0 105 65 10 3.59 0.4160 WVFGRD96 11.0 105 65 10 3.61 0.4136 WVFGRD96 12.0 105 65 10 3.62 0.4110 WVFGRD96 13.0 105 65 10 3.63 0.4075 WVFGRD96 14.0 105 65 10 3.64 0.4042 WVFGRD96 15.0 105 65 5 3.65 0.4001 WVFGRD96 16.0 105 65 10 3.66 0.3955 WVFGRD96 17.0 105 65 10 3.67 0.3903 WVFGRD96 18.0 105 65 10 3.68 0.3847 WVFGRD96 19.0 105 65 10 3.69 0.3787 WVFGRD96 20.0 105 70 10 3.69 0.3724 WVFGRD96 21.0 110 60 25 3.71 0.3669 WVFGRD96 22.0 110 60 25 3.72 0.3616 WVFGRD96 23.0 110 60 25 3.73 0.3561 WVFGRD96 24.0 110 60 25 3.74 0.3503 WVFGRD96 25.0 110 60 25 3.75 0.3441 WVFGRD96 26.0 110 60 25 3.76 0.3376 WVFGRD96 27.0 110 60 25 3.77 0.3306 WVFGRD96 28.0 110 60 30 3.78 0.3234 WVFGRD96 29.0 110 65 30 3.78 0.3163
The best solution is
WVFGRD96 3.0 285 70 0 3.47 0.4502
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
hp c 0.02 n 4 lp c 0.08 n 4
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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