The ANSS event ID is us20005d4q and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us20005d4q/executive.
2016/03/29 10:19:44 35.989 -97.573 5.6 3.6 Oklahoma
USGS/SLU Moment Tensor Solution ENS 2016/03/29 10:19:44:0 35.99 -97.57 5.6 3.6 Oklahoma Stations used: GS.KAN06 GS.KAN12 GS.KAN14 GS.KAN16 GS.KAN17 GS.OK025 GS.OK029 GS.OK030 GS.OK032 GS.OK033 GS.OK036 GS.OK038 GS.OK039 GS.OK040 GS.OK042 GS.OK043 N4.T35B OK.BCOK OK.CCOK OK.U32A OK.X37A TA.TUL1 TA.W39A US.KSU1 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 0.10 n 3 Best Fitting Double Couple Mo = 2.75e+21 dyne-cm Mw = 3.56 Z = 4 km Plane Strike Dip Rake NP1 13 81 -160 NP2 280 70 -10 Principal Axes: Axis Value Plunge Azimuth T 2.75e+21 7 145 N 0.00e+00 68 37 P -2.75e+21 21 238 Moment Tensor: (dyne-cm) Component Value Mxx 1.17e+21 Mxy -2.34e+21 Mxz 2.00e+20 Myy -8.62e+20 Myz 9.77e+20 Mzz -3.07e+20 ############-- ################------ ###################--------- ####################---------- ######################------------ ######################-------------- #######################--------------- ########################---------------- ##-------------------------------------- ------------------------#######----------- ------------------------###########------- -----------------------###############---- -----------------------##################- ---------------------################### ---- --------------################### --- P -------------################### -- -------------################## ----------------################## -------------############ ## -----------############# T # --------############# ---########### Global CMT Convention Moment Tensor: R T P -3.07e+20 2.00e+20 -9.77e+20 2.00e+20 1.17e+21 2.34e+21 -9.77e+20 2.34e+21 -8.62e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160329101944/index.html |
STK = 280 DIP = 70 RAKE = -10 MW = 3.56 HS = 4.0
The NDK file is 20160329101944.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: 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:
cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 280 65 -5 3.33 0.4538 WVFGRD96 2.0 100 80 -10 3.45 0.5823 WVFGRD96 3.0 280 70 -10 3.52 0.6313 WVFGRD96 4.0 280 70 -10 3.56 0.6435 WVFGRD96 5.0 280 80 5 3.58 0.6385 WVFGRD96 6.0 280 80 5 3.61 0.6270 WVFGRD96 7.0 280 75 5 3.65 0.6122 WVFGRD96 8.0 280 75 10 3.69 0.5937 WVFGRD96 9.0 280 75 10 3.71 0.5709 WVFGRD96 10.0 280 75 10 3.72 0.5473 WVFGRD96 11.0 280 75 10 3.74 0.5229 WVFGRD96 12.0 280 75 10 3.75 0.4989 WVFGRD96 13.0 280 75 10 3.76 0.4755 WVFGRD96 14.0 285 75 10 3.77 0.4524 WVFGRD96 15.0 285 75 10 3.78 0.4291 WVFGRD96 16.0 280 75 5 3.79 0.4067 WVFGRD96 17.0 280 75 5 3.79 0.3855 WVFGRD96 18.0 280 75 5 3.80 0.3648 WVFGRD96 19.0 280 75 0 3.80 0.3456 WVFGRD96 20.0 280 80 -5 3.79 0.3289 WVFGRD96 21.0 280 85 -15 3.78 0.3135 WVFGRD96 22.0 100 85 15 3.78 0.3010 WVFGRD96 23.0 100 85 20 3.78 0.2903 WVFGRD96 24.0 10 65 15 3.81 0.2836 WVFGRD96 25.0 10 70 10 3.81 0.2889 WVFGRD96 26.0 10 80 -10 3.80 0.2967 WVFGRD96 27.0 10 80 -10 3.81 0.3039 WVFGRD96 28.0 195 80 15 3.84 0.3125 WVFGRD96 29.0 195 80 15 3.84 0.3198
The best solution is
WVFGRD96 4.0 280 70 -10 3.56 0.6435
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 0.10 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