The ANSS event ID is usb000s3ni and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usb000s3ni/executive.
2014/08/18 01:25:57 36.840 -98.254 3.0 3.7 Oklahoma
USGS/SLU Moment Tensor Solution ENS 2014/08/18 01:25:57:0 36.84 -98.25 3.0 3.7 Oklahoma Stations used: GS.KAN10 GS.KAN11 GS.KAN12 GS.OK025 GS.OK026 GS.OK027 GS.OK028 GS.OK029 N4.N33B N4.R32B N4.T35B N4.Z35B N4.Z38B OK.BCOK OK.CROK OK.FNO OK.X34A OK.X37A TA.TUL1 TA.WHTX US.CBKS US.KSU1 US.MIAR 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 0.08 n 3 Best Fitting Double Couple Mo = 2.02e+21 dyne-cm Mw = 3.47 Z = 3 km Plane Strike Dip Rake NP1 290 65 -60 NP2 56 38 -137 Principal Axes: Axis Value Plunge Azimuth T 2.02e+21 15 359 N 0.00e+00 27 96 P -2.02e+21 59 243 Moment Tensor: (dyne-cm) Component Value Mxx 1.77e+21 Mxy -2.70e+20 Mxz 9.10e+20 Myy -4.31e+20 Myz 7.85e+20 Mzz -1.34e+21 ##### ###### ######### T ########## ############ ############# ############################## ################################## ###################################- ####-------##########################- ---------------------#################-- -------------------------############--- ------------------------------########---- ---------------------------------####----- ------------ --------------------##----- ------------ P ---------------------#----- ----------- -------------------#####-- --------------------------------#######- -----------------------------######### --------------------------########## ----------------------############ ##-------------############### ############################ ###################### ############## Global CMT Convention Moment Tensor: R T P -1.34e+21 9.10e+20 -7.85e+20 9.10e+20 1.77e+21 2.70e+20 -7.85e+20 2.70e+20 -4.31e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140818012557/index.html |
STK = 290 DIP = 65 RAKE = -60 MW = 3.47 HS = 3.0
The NDK file is 20140818012557.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 2014/08/18 01:25:57:0 36.84 -98.25 3.0 3.7 Oklahoma Stations used: GS.KAN10 GS.KAN11 GS.KAN12 GS.OK025 GS.OK026 GS.OK027 GS.OK028 GS.OK029 N4.N33B N4.R32B N4.T35B N4.Z35B N4.Z38B OK.BCOK OK.CROK OK.FNO OK.X34A OK.X37A TA.TUL1 TA.WHTX US.CBKS US.KSU1 US.MIAR 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 0.08 n 3 Best Fitting Double Couple Mo = 2.02e+21 dyne-cm Mw = 3.47 Z = 3 km Plane Strike Dip Rake NP1 290 65 -60 NP2 56 38 -137 Principal Axes: Axis Value Plunge Azimuth T 2.02e+21 15 359 N 0.00e+00 27 96 P -2.02e+21 59 243 Moment Tensor: (dyne-cm) Component Value Mxx 1.77e+21 Mxy -2.70e+20 Mxz 9.10e+20 Myy -4.31e+20 Myz 7.85e+20 Mzz -1.34e+21 ##### ###### ######### T ########## ############ ############# ############################## ################################## ###################################- ####-------##########################- ---------------------#################-- -------------------------############--- ------------------------------########---- ---------------------------------####----- ------------ --------------------##----- ------------ P ---------------------#----- ----------- -------------------#####-- --------------------------------#######- -----------------------------######### --------------------------########## ----------------------############ ##-------------############### ############################ ###################### ############## Global CMT Convention Moment Tensor: R T P -1.34e+21 9.10e+20 -7.85e+20 9.10e+20 1.77e+21 2.70e+20 -7.85e+20 2.70e+20 -4.31e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140818012557/index.html |
Moment 4.47e+14 N-m Magnitude 3.7 Percent DC 86% Depth 3.0 km Updated 2014-08-18 01:47:01 UTC Author us Catalog us Contributor us Code us_b000s3ni_mwr Principal Axes Axis Value Plunge Azimuth T 4.317 13 347 N 0.295 7 255 P -4.612 75 135 Nodal Planes Plane Strike Dip Rake NP1 250 58 -99 NP2 86 33 -76 |
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 +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 1.0 120 40 -35 3.30 0.4117 WVFGRD96 2.0 120 35 -35 3.43 0.4661 WVFGRD96 3.0 290 65 -60 3.47 0.4807 WVFGRD96 4.0 290 65 -50 3.49 0.4689 WVFGRD96 5.0 300 75 -40 3.47 0.4308 WVFGRD96 6.0 320 50 10 3.44 0.4136 WVFGRD96 7.0 315 60 -35 3.47 0.4092 WVFGRD96 8.0 325 45 15 3.50 0.3968 WVFGRD96 9.0 320 50 15 3.52 0.3896 WVFGRD96 10.0 325 50 20 3.52 0.3826 WVFGRD96 11.0 320 55 25 3.55 0.3763 WVFGRD96 12.0 320 55 25 3.56 0.3696 WVFGRD96 13.0 320 55 25 3.57 0.3617 WVFGRD96 14.0 320 55 25 3.58 0.3530 WVFGRD96 15.0 315 60 25 3.60 0.3441 WVFGRD96 16.0 145 60 35 3.59 0.3352 WVFGRD96 17.0 145 60 35 3.60 0.3312 WVFGRD96 18.0 155 55 50 3.63 0.3272 WVFGRD96 19.0 160 55 55 3.64 0.3250 WVFGRD96 20.0 160 55 60 3.66 0.3229 WVFGRD96 21.0 160 55 65 3.69 0.3201 WVFGRD96 22.0 160 55 65 3.70 0.3183 WVFGRD96 23.0 165 55 70 3.71 0.3161 WVFGRD96 24.0 165 55 75 3.73 0.3149 WVFGRD96 25.0 165 55 75 3.74 0.3140 WVFGRD96 26.0 165 55 75 3.74 0.3127 WVFGRD96 27.0 160 60 75 3.76 0.3101 WVFGRD96 28.0 160 60 75 3.77 0.3080 WVFGRD96 29.0 50 60 35 3.69 0.3054
The best solution is
WVFGRD96 3.0 290 65 -60 3.47 0.4807
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 0.08 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