The ANSS event ID is usp000hq2d and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000hq2d/executive.
2010/11/24 22:48:30 35.612 -97.246 5.0 3.9 Oklahoma
USGS/SLU Moment Tensor Solution
ENS 2010/11/24 22:48:30:0 35.61 -97.25 5.0 3.9 Oklahoma
Stations used:
AG.HHAR AG.WHAR NM.MGMO NM.UALR TA.133A TA.134A TA.135A
TA.336A TA.ABTX TA.P31A TA.P32A TA.P33A TA.P36A TA.Q31A
TA.Q32A TA.Q33A TA.Q35A TA.Q36A TA.Q37A TA.R29A TA.R30A
TA.R31A TA.R32A TA.R33A TA.R34A TA.R36A TA.R37A TA.S28A
TA.S30A TA.S31A TA.S32A TA.S33A TA.S34A TA.S35A TA.S36A
TA.S37A TA.T29A TA.T30A TA.T31A TA.T32A TA.T33A TA.T34A
TA.T35A TA.T36A TA.T37A TA.TUL1 TA.U29A TA.U30A TA.U31A
TA.U32A TA.U33A TA.U34A TA.U35A TA.U36A TA.U37A TA.U38A
TA.V30A TA.V31A TA.V32A TA.V33A TA.V34A TA.V35A TA.V36A
TA.V37A TA.V38A TA.W30A TA.W31A TA.W33A TA.W34A TA.W35A
TA.W36A TA.W38A TA.X30A TA.X31A TA.X32A TA.X34A TA.X35A
TA.X36A TA.X38A TA.Y31A TA.Y32A TA.Y33A TA.Y34A TA.Y35A
TA.Y36A TA.Y38A TA.Y39A TA.Z31A TA.Z32A TA.Z33A TA.Z34A
TA.Z35A TA.Z37A TA.Z39A US.AMTX US.CBKS US.KSU1 US.MIAR
US.WMOK
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 9.89e+21 dyne-cm
Mw = 3.93
Z = 3 km
Plane Strike Dip Rake
NP1 190 90 180
NP2 280 90 -0
Principal Axes:
Axis Value Plunge Azimuth
T 9.89e+21 -0 325
N 0.00e+00 90 190
P -9.89e+21 -0 55
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.38e+21
Mxy -9.29e+21
Mxz -7.50e+13
Myy -3.38e+21
Myz 4.26e+14
Mzz -0.00e+00
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T ############--------
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Global CMT Convention Moment Tensor:
R T P
-0.00e+00 -7.50e+13 -4.26e+14
-7.50e+13 3.38e+21 9.29e+21
-4.26e+14 9.29e+21 -3.38e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101124224830/index.html
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STK = 100
DIP = 90
RAKE = 0
MW = 3.93
HS = 3.0
The NDK file is 20101124224830.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:
hp c 0.02 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 0.5 280 80 -5 3.83 0.4760
WVFGRD96 1.0 280 80 -5 3.86 0.5038
WVFGRD96 2.0 100 90 0 3.90 0.5359
WVFGRD96 3.0 100 90 0 3.93 0.5410
WVFGRD96 4.0 100 80 10 3.95 0.5331
WVFGRD96 5.0 100 85 20 3.97 0.5270
WVFGRD96 6.0 100 85 20 3.98 0.5229
WVFGRD96 7.0 100 85 20 3.98 0.5199
WVFGRD96 8.0 100 85 20 3.99 0.5188
WVFGRD96 9.0 100 70 5 4.00 0.5210
WVFGRD96 10.0 100 70 10 4.01 0.5226
WVFGRD96 11.0 100 70 10 4.02 0.5240
WVFGRD96 12.0 100 70 10 4.03 0.5237
WVFGRD96 13.0 100 75 10 4.03 0.5231
WVFGRD96 14.0 100 80 15 4.04 0.5219
WVFGRD96 15.0 100 80 15 4.05 0.5206
WVFGRD96 16.0 100 80 15 4.05 0.5182
WVFGRD96 17.0 100 80 15 4.06 0.5151
WVFGRD96 18.0 100 80 15 4.07 0.5116
WVFGRD96 19.0 100 85 15 4.08 0.5072
WVFGRD96 20.0 100 85 15 4.09 0.5020
WVFGRD96 21.0 100 85 15 4.10 0.4979
WVFGRD96 22.0 280 90 -15 4.10 0.4935
WVFGRD96 23.0 280 90 -15 4.11 0.4889
WVFGRD96 24.0 280 90 -15 4.12 0.4833
WVFGRD96 25.0 100 90 15 4.12 0.4772
WVFGRD96 26.0 100 90 15 4.13 0.4701
WVFGRD96 27.0 100 90 15 4.14 0.4623
WVFGRD96 28.0 10 75 5 4.14 0.4532
WVFGRD96 29.0 10 75 5 4.15 0.4490
The best solution is
WVFGRD96 3.0 100 90 0 3.93 0.5410
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 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 CUS.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 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00