The SLU location is made using the program elocate and arival time picks from the NetQuake instruments in the source region and adjacent TA stations. The output is given in elocate.txt. The solution is the same as the NEIC solution. However we fix the depth to the value derived from the waveform inversion, e.g., 8 km.
2010/03/22 02:37:18 35.542 -96.737 5. 3.70 Oklahoma
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/03/22 02:37:18:0 35.54 -96.74 5.0 3.7 Oklahoma Stations used: NM.UALR TA.133A TA.135A TA.S31A TA.S33A TA.T31A TA.T33A TA.TUL1 TA.U31A TA.U32A TA.U34A TA.V34A TA.W30A TA.W31A TA.W32A TA.W33A TA.W34A TA.X32A TA.X33A TA.X34A TA.Y31A TA.Z32A TA.Z34A 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 = 3.89e+21 dyne-cm Mw = 3.66 Z = 8 km Plane Strike Dip Rake NP1 57 86 -150 NP2 325 60 -5 Principal Axes: Axis Value Plunge Azimuth T 3.89e+21 17 187 N 0.00e+00 60 65 P -3.89e+21 24 285 Moment Tensor: (dyne-cm) Component Value Mxx 3.25e+21 Mxy 1.29e+21 Mxz -1.49e+21 Myy -2.96e+21 Myz 1.25e+21 Mzz -2.94e+20 ############## ###################### -------##################### ------------################## ----------------################## -------------------###############-- ----------------------###########----- --- -------------------#######-------- --- P --------------------###----------- ---- --------------------#-------------- ------------------------#####------------- ----------------------########------------ -------------------############----------- ---------------################--------- -----------####################--------- -------########################------- ---###########################------ #############################----- ###########################--- ########## #############-- ####### T ############ ### ######## Global CMT Convention Moment Tensor: R T P -2.94e+20 -1.49e+21 -1.25e+21 -1.49e+21 3.25e+21 -1.29e+21 -1.25e+21 -1.29e+21 -2.96e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100322023718/index.html |
STK = 325 DIP = 60 RAKE = -5 MW = 3.66 HS = 8.0
The waveform inversion is preferred. This event has well developed short period surface waves that had to be eliminated using the band reject filter. The original data will be very valuable for surface-wave tomography.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/03/22 02:37:18:0 35.54 -96.74 5.0 3.7 Oklahoma Stations used: NM.UALR TA.133A TA.135A TA.S31A TA.S33A TA.T31A TA.T33A TA.TUL1 TA.U31A TA.U32A TA.U34A TA.V34A TA.W30A TA.W31A TA.W32A TA.W33A TA.W34A TA.X32A TA.X33A TA.X34A TA.Y31A TA.Z32A TA.Z34A 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 = 3.89e+21 dyne-cm Mw = 3.66 Z = 8 km Plane Strike Dip Rake NP1 57 86 -150 NP2 325 60 -5 Principal Axes: Axis Value Plunge Azimuth T 3.89e+21 17 187 N 0.00e+00 60 65 P -3.89e+21 24 285 Moment Tensor: (dyne-cm) Component Value Mxx 3.25e+21 Mxy 1.29e+21 Mxz -1.49e+21 Myy -2.96e+21 Myz 1.25e+21 Mzz -2.94e+20 ############## ###################### -------##################### ------------################## ----------------################## -------------------###############-- ----------------------###########----- --- -------------------#######-------- --- P --------------------###----------- ---- --------------------#-------------- ------------------------#####------------- ----------------------########------------ -------------------############----------- ---------------################--------- -----------####################--------- -------########################------- ---###########################------ #############################----- ###########################--- ########## #############-- ####### T ############ ### ######## Global CMT Convention Moment Tensor: R T P -2.94e+20 -1.49e+21 -1.25e+21 -1.49e+21 3.25e+21 -1.29e+21 -1.25e+21 -1.29e+21 -2.96e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100322023718/index.html |
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The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for 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 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 from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 145 80 -5 3.21 0.2442 WVFGRD96 1.0 325 90 5 3.26 0.2831 WVFGRD96 2.0 145 85 -10 3.44 0.4731 WVFGRD96 3.0 145 90 0 3.50 0.5423 WVFGRD96 4.0 325 85 0 3.53 0.5772 WVFGRD96 5.0 325 85 5 3.56 0.5928 WVFGRD96 6.0 325 85 10 3.59 0.5981 WVFGRD96 7.0 325 65 0 3.62 0.6013 WVFGRD96 8.0 325 60 -5 3.66 0.6035 WVFGRD96 9.0 325 65 -5 3.66 0.6016 WVFGRD96 10.0 325 65 -5 3.68 0.5991 WVFGRD96 11.0 325 65 -5 3.69 0.5951 WVFGRD96 12.0 325 65 0 3.70 0.5903 WVFGRD96 13.0 325 70 0 3.71 0.5851 WVFGRD96 14.0 325 70 0 3.72 0.5795 WVFGRD96 15.0 325 70 0 3.73 0.5728 WVFGRD96 16.0 325 70 0 3.74 0.5649 WVFGRD96 17.0 325 70 0 3.75 0.5566 WVFGRD96 18.0 325 70 0 3.76 0.5482 WVFGRD96 19.0 325 65 -5 3.78 0.5394 WVFGRD96 20.0 325 65 -5 3.78 0.5306 WVFGRD96 21.0 325 65 -5 3.79 0.5219 WVFGRD96 22.0 325 60 -5 3.81 0.5132 WVFGRD96 23.0 325 60 -5 3.82 0.5043 WVFGRD96 24.0 325 60 -5 3.82 0.4954 WVFGRD96 25.0 325 60 -5 3.83 0.4862 WVFGRD96 26.0 325 60 -5 3.84 0.4774 WVFGRD96 27.0 325 55 -5 3.85 0.4694 WVFGRD96 28.0 325 55 -5 3.86 0.4613 WVFGRD96 29.0 325 55 -5 3.87 0.4538
The best solution is
WVFGRD96 8.0 325 60 -5 3.66 0.6035
The mechanism correspond 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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 and because the velocity model used in the predictions may not be perfect. 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 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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Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. 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. |
Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The WUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Mon Mar 22 10:14:12 CDT 2010