The SLU location is
2010/09/16 21:41:33.598 35.616 -97.256 4.66 km
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2010/09/16 21:41:34:0 35.63 -97.22 5.0 3.8 Oklahoma Stations used: AG.HHAR AG.LCAR AG.WHAR TA.O35A TA.O36A TA.P34A TA.P35A TA.P36A TA.Q31A TA.Q32A TA.Q33A TA.Q34A TA.Q35A TA.Q36A TA.Q37A TA.R31A TA.R32A TA.R34A TA.R36A TA.R37A TA.S31A TA.S33A TA.S34A TA.S35A TA.T32A TA.T33A TA.T34A TA.T36A TA.T37A TA.TUL1 TA.U33A TA.U34A TA.V33A TA.V34A TA.V35A TA.W31A TA.W34A TA.W35A TA.W36A TA.W37A TA.W38A TA.X34A TA.X35A TA.X36A TA.X37A TA.X38A TA.Y37A US.WMOK Filtering commands used: hp c 0.02 n 4 lp c 0.10 n 4 Best Fitting Double Couple Mo = 1.48e+21 dyne-cm Mw = 3.38 Z = 4 km Plane Strike Dip Rake NP1 285 85 10 NP2 194 80 175 Principal Axes: Axis Value Plunge Azimuth T 1.48e+21 11 150 N 0.00e+00 79 311 P -1.48e+21 3 59 Moment Tensor: (dyne-cm) Component Value Mxx 6.84e+20 Mxy -1.27e+21 Mxz -2.77e+20 Myy -7.29e+20 Myz 5.72e+19 Mzz 4.46e+19 ############-- ###############------- #################----------- #################------------- ##################--------------- ##################---------------- P ###################---------------- ###################--------------------- -----##############--------------------- ---------------####----------------------- -------------------###-------------------- ------------------###########------------- ------------------#################------- ----------------######################-- ----------------######################## ---------------####################### -------------####################### ------------###################### ----------############# #### ---------############# T ### ------############# --############ Global CMT Convention Moment Tensor: R T P 4.46e+19 -2.77e+20 -5.72e+19 -2.77e+20 6.84e+20 1.27e+21 -5.72e+19 1.27e+21 -7.29e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100916214134/index.html |
STK = 285 DIP = 85 RAKE = 10 MW = 3.38 HS = 4.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2010/09/16 21:41:34:0 35.63 -97.22 5.0 3.8 Oklahoma Stations used: AG.HHAR AG.LCAR AG.WHAR TA.O35A TA.O36A TA.P34A TA.P35A TA.P36A TA.Q31A TA.Q32A TA.Q33A TA.Q34A TA.Q35A TA.Q36A TA.Q37A TA.R31A TA.R32A TA.R34A TA.R36A TA.R37A TA.S31A TA.S33A TA.S34A TA.S35A TA.T32A TA.T33A TA.T34A TA.T36A TA.T37A TA.TUL1 TA.U33A TA.U34A TA.V33A TA.V34A TA.V35A TA.W31A TA.W34A TA.W35A TA.W36A TA.W37A TA.W38A TA.X34A TA.X35A TA.X36A TA.X37A TA.X38A TA.Y37A US.WMOK Filtering commands used: hp c 0.02 n 4 lp c 0.10 n 4 Best Fitting Double Couple Mo = 1.48e+21 dyne-cm Mw = 3.38 Z = 4 km Plane Strike Dip Rake NP1 285 85 10 NP2 194 80 175 Principal Axes: Axis Value Plunge Azimuth T 1.48e+21 11 150 N 0.00e+00 79 311 P -1.48e+21 3 59 Moment Tensor: (dyne-cm) Component Value Mxx 6.84e+20 Mxy -1.27e+21 Mxz -2.77e+20 Myy -7.29e+20 Myz 5.72e+19 Mzz 4.46e+19 ############-- ###############------- #################----------- #################------------- ##################--------------- ##################---------------- P ###################---------------- ###################--------------------- -----##############--------------------- ---------------####----------------------- -------------------###-------------------- ------------------###########------------- ------------------#################------- ----------------######################-- ----------------######################## ---------------####################### -------------####################### ------------###################### ----------############# #### ---------############# T ### ------############# --############ Global CMT Convention Moment Tensor: R T P 4.46e+19 -2.77e+20 -5.72e+19 -2.77e+20 6.84e+20 1.27e+21 -5.72e+19 1.27e+21 -7.29e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100916214134/index.html |
First motions plot using the waveform inversion nodal planes and the elcoate takeoff angles and azimuths. Symbols: o strong compression, + weak compression, Delta strong dilatation, - weak dilatation, X undetermined polarity. |
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 4 lp c 0.10 n 4The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 0.5 285 60 5 3.22 0.3282 WVFGRD96 1.0 285 75 0 3.22 0.3476 WVFGRD96 2.0 105 90 -20 3.31 0.3944 WVFGRD96 3.0 285 80 -5 3.34 0.4161 WVFGRD96 4.0 285 85 10 3.38 0.4199 WVFGRD96 5.0 285 80 10 3.40 0.4163 WVFGRD96 6.0 285 85 15 3.43 0.4116 WVFGRD96 7.0 285 85 15 3.45 0.4094 WVFGRD96 8.0 105 85 25 3.49 0.4097 WVFGRD96 9.0 105 85 25 3.51 0.4078 WVFGRD96 10.0 105 85 25 3.53 0.4055 WVFGRD96 11.0 105 90 25 3.54 0.4031 WVFGRD96 12.0 105 90 25 3.56 0.4009 WVFGRD96 13.0 105 90 25 3.57 0.3990 WVFGRD96 14.0 285 90 -25 3.59 0.3960 WVFGRD96 15.0 285 90 -25 3.60 0.3917 WVFGRD96 16.0 285 90 -25 3.61 0.3867 WVFGRD96 17.0 285 90 -25 3.62 0.3810 WVFGRD96 18.0 285 90 -25 3.63 0.3741 WVFGRD96 19.0 285 90 -25 3.64 0.3667 WVFGRD96 20.0 285 90 -25 3.65 0.3586 WVFGRD96 21.0 105 85 25 3.66 0.3501 WVFGRD96 22.0 105 85 25 3.67 0.3419 WVFGRD96 23.0 105 85 25 3.68 0.3338 WVFGRD96 24.0 285 90 -25 3.68 0.3243 WVFGRD96 25.0 105 85 25 3.69 0.3196 WVFGRD96 26.0 105 85 25 3.70 0.3134 WVFGRD96 27.0 285 90 -25 3.70 0.3053 WVFGRD96 28.0 15 70 5 3.70 0.3068 WVFGRD96 29.0 15 75 5 3.70 0.3087
The best solution is
WVFGRD96 4.0 285 85 10 3.38 0.4199
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 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 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 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 4 lp c 0.10 n 4
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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. |
A check on the asusmed 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 shifst 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.
This earthquake was recorded by NetQuake accelerographs in the epicentral area. Although this earthquake was too small for the accelerometer signals to be low-pass filtered for use in the broadband moment tensor inversion, we were able to filter the traces near 1 Hz and comapre them to Grene's functions predicted using the moment tensor solution. This was done with care:
Both the predicted and observed ground velocities were filtered using the gsac command:
hp c 0.5 n 4 lp c 1.00 n 4
triangle w 1.0
Comparison of filtered observed (red) and predicted (blue) ground velocities in units of m/s. In general there is a agreement in the corresponding amplitudes. Even at these frequencies, the low frequency noise is significant. The difference in amplitude at short distance may be due to differences in distance and azimuth between the true location and the assumed NEIC location. |
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 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 Sep 20 20:14:41 CDT 2010