The ANSS event ID is usp000h81j and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000h81j/executive.
2010/02/27 22:22:27 35.553 -96.752 5.0 4.1 Oklahoma
USGS/SLU Moment Tensor Solution ENS 2010/02/27 22:22:27:0 35.55 -96.75 5.0 4.1 Oklahoma Stations used: NM.MGMO TA.133A TA.134A TA.135A TA.137A TA.234A TA.237A TA.333A TA.334A TA.335A TA.336A TA.P31A TA.P32A TA.P33A TA.Q31A TA.Q32A TA.Q33A TA.R30A TA.R31A TA.R32A TA.R33A TA.S30A TA.S31A TA.S32A TA.S33A TA.T32A TA.T33A TA.TUL1 TA.U31A TA.U32A TA.U33A TA.U34A TA.V33A TA.V34A TA.W33A TA.W34A TA.WHTX TA.X34A TA.Y31A TA.Y34A TA.Z31A TA.Z33A TA.Z34A TA.Z35A US.KSU1 US.MIAR X9.CLEF1 X9.NLKCG X9.OBC01 Filtering commands used: cut o DIST/3.3 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 1.97e+22 dyne-cm Mw = 4.13 Z = 8 km Plane Strike Dip Rake NP1 219 85 165 NP2 310 75 5 Principal Axes: Axis Value Plunge Azimuth T 1.97e+22 14 173 N 0.00e+00 74 21 P -1.97e+22 7 265 Moment Tensor: (dyne-cm) Component Value Mxx 1.82e+22 Mxy -3.72e+21 Mxz -4.41e+21 Myy -1.90e+22 Myz 2.94e+21 Mzz 8.60e+20 ############## ###################### ##########################-- ##########################---- -----#####################-------- ----------###############----------- --------------##########-------------- ------------------######---------------- --------------------##------------------ ----------------------##------------------ -----------------######---------------- P ----------------#########-------------- --------------#############------------ ---------------###############---------- -------------###################-------- -----------#####################------ ---------#######################---- -------#########################-- ---########################### -############## ########## ############ T ####### ######## ### Global CMT Convention Moment Tensor: R T P 8.60e+20 -4.41e+21 -2.94e+21 -4.41e+21 1.82e+22 3.72e+21 -2.94e+21 3.72e+21 -1.90e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100227222227/index.html |
STK = 310 DIP = 75 RAKE = 5 MW = 4.13 HS = 8.0
The NDK file is 20100227222227.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 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 130 90 -5 3.80 0.3442 WVFGRD96 2.0 130 85 0 3.92 0.4362 WVFGRD96 3.0 130 90 0 3.97 0.4732 WVFGRD96 4.0 130 90 0 4.00 0.4901 WVFGRD96 5.0 310 90 0 4.03 0.4960 WVFGRD96 6.0 310 75 5 4.07 0.4989 WVFGRD96 7.0 310 75 5 4.09 0.5011 WVFGRD96 8.0 310 75 5 4.13 0.5015 WVFGRD96 9.0 310 90 20 4.15 0.4967 WVFGRD96 10.0 310 90 20 4.16 0.4918 WVFGRD96 11.0 130 80 -15 4.17 0.4869 WVFGRD96 12.0 130 80 -15 4.19 0.4797 WVFGRD96 13.0 130 80 -15 4.20 0.4719 WVFGRD96 14.0 130 80 -15 4.21 0.4625 WVFGRD96 15.0 130 80 -15 4.22 0.4522 WVFGRD96 16.0 130 80 -15 4.23 0.4411 WVFGRD96 17.0 130 85 -15 4.24 0.4293 WVFGRD96 18.0 130 85 -15 4.25 0.4172 WVFGRD96 19.0 130 85 -15 4.26 0.4042 WVFGRD96 20.0 130 85 -15 4.26 0.3909 WVFGRD96 21.0 130 85 -15 4.27 0.3778 WVFGRD96 22.0 130 85 -15 4.27 0.3644 WVFGRD96 23.0 130 85 -15 4.28 0.3514 WVFGRD96 24.0 315 80 15 4.28 0.3406 WVFGRD96 25.0 315 75 15 4.28 0.3285 WVFGRD96 26.0 315 75 15 4.28 0.3168 WVFGRD96 27.0 220 85 -20 4.29 0.3025 WVFGRD96 28.0 220 85 -20 4.30 0.3061 WVFGRD96 29.0 220 85 -15 4.30 0.3095
The best solution is
WVFGRD96 8.0 310 75 5 4.13 0.5015
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 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 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