2011/02/18 08:13:35 35.271 -92.377 6.3 4.30 Arkansas
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2011/02/18 08:13:35:0 35.27 -92.38 6.3 4.3 Arkansas Stations used: AG.CCAR AG.FCAR AG.HHAR AG.LCAR AG.WHAR AG.WLAR IU.WVT NM.MGMO NM.MPH NM.OLIL NM.SIUC NM.SLM NM.UALR NM.USIN NM.X102 NM.X201 TA.139A TA.140A TA.141A TA.236A TA.O34A TA.O36A TA.O38A TA.O39A TA.O40A TA.P33A TA.P34A TA.P35A TA.P36A TA.P38A TA.P39A TA.P40A TA.Q33A TA.Q34A TA.Q35A TA.Q36A TA.Q37A TA.Q38A TA.Q39A TA.R32A TA.R33A TA.R34A TA.R35A TA.R36A TA.R37A TA.R38A TA.R39A TA.R40A TA.S32A TA.S33A TA.S34A TA.S35A TA.S36A TA.S37A TA.S38A TA.S39A TA.S40A TA.T32A TA.T33A TA.T34A TA.T35A TA.T36A TA.T37A TA.T38A TA.T39A TA.T40A TA.TUL1 TA.U31A TA.U32A TA.U33A TA.U34A TA.U35A TA.U36A TA.U37A TA.U38A TA.U39A TA.U40A TA.V32A TA.V33A TA.V34A TA.V35A TA.V36A TA.V37A TA.V38A TA.V39A TA.W33A TA.W34A TA.W35A TA.W36A TA.W37B TA.W38A TA.W39A TA.W40A TA.WHTX TA.X33A TA.X36A TA.X37A TA.X38A TA.X40A TA.Y36A TA.Y37A TA.Y38A TA.Y39A TA.Y40A TA.Z37A TA.Z38A TA.Z39A TA.Z40A US.KSU1 US.LRAL US.MIAR US.OXF 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 = 1.60e+22 dyne-cm Mw = 4.07 Z = 8 km Plane Strike Dip Rake NP1 197 81 160 NP2 290 70 10 Principal Axes: Axis Value Plunge Azimuth T 1.60e+22 21 152 N 0.00e+00 68 353 P -1.60e+22 7 245 Moment Tensor: (dyne-cm) Component Value Mxx 7.96e+21 Mxy -1.19e+22 Mxz -3.85e+21 Myy -9.75e+21 Myz 4.35e+21 Mzz 1.79e+21 #############- ###############------- #################----------- ##################------------ ###################--------------- ###################----------------- ###################------------------- ----------------####-------------------- -------------------###------------------ -------------------#########-------------- -------------------############----------- ------------------################-------- ------------------##################------ ----------------#####################--- - ------------#######################- P -----------######################## -----------####################### ------------########### ######## ---------############ T ###### --------############ ##### -----################# -############# Global CMT Convention Moment Tensor: R T P 1.79e+21 -3.85e+21 -4.35e+21 -3.85e+21 7.96e+21 1.19e+22 -4.35e+21 1.19e+22 -9.75e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110218081335/index.html |
STK = 290 DIP = 70 RAKE = 10 MW = 4.07 HS = 8.0
The NDK file is 20110218081335.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2011/02/18 08:13:35:0 35.27 -92.38 6.3 4.3 Arkansas Stations used: AG.CCAR AG.FCAR AG.HHAR AG.LCAR AG.WHAR AG.WLAR IU.WVT NM.MGMO NM.MPH NM.OLIL NM.SIUC NM.SLM NM.UALR NM.USIN NM.X102 NM.X201 TA.139A TA.140A TA.141A TA.236A TA.O34A TA.O36A TA.O38A TA.O39A TA.O40A TA.P33A TA.P34A TA.P35A TA.P36A TA.P38A TA.P39A TA.P40A TA.Q33A TA.Q34A TA.Q35A TA.Q36A TA.Q37A TA.Q38A TA.Q39A TA.R32A TA.R33A TA.R34A TA.R35A TA.R36A TA.R37A TA.R38A TA.R39A TA.R40A TA.S32A TA.S33A TA.S34A TA.S35A TA.S36A TA.S37A TA.S38A TA.S39A TA.S40A TA.T32A TA.T33A TA.T34A TA.T35A TA.T36A TA.T37A TA.T38A TA.T39A TA.T40A TA.TUL1 TA.U31A TA.U32A TA.U33A TA.U34A TA.U35A TA.U36A TA.U37A TA.U38A TA.U39A TA.U40A TA.V32A TA.V33A TA.V34A TA.V35A TA.V36A TA.V37A TA.V38A TA.V39A TA.W33A TA.W34A TA.W35A TA.W36A TA.W37B TA.W38A TA.W39A TA.W40A TA.WHTX TA.X33A TA.X36A TA.X37A TA.X38A TA.X40A TA.Y36A TA.Y37A TA.Y38A TA.Y39A TA.Y40A TA.Z37A TA.Z38A TA.Z39A TA.Z40A US.KSU1 US.LRAL US.MIAR US.OXF 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 = 1.60e+22 dyne-cm Mw = 4.07 Z = 8 km Plane Strike Dip Rake NP1 197 81 160 NP2 290 70 10 Principal Axes: Axis Value Plunge Azimuth T 1.60e+22 21 152 N 0.00e+00 68 353 P -1.60e+22 7 245 Moment Tensor: (dyne-cm) Component Value Mxx 7.96e+21 Mxy -1.19e+22 Mxz -3.85e+21 Myy -9.75e+21 Myz 4.35e+21 Mzz 1.79e+21 #############- ###############------- #################----------- ##################------------ ###################--------------- ###################----------------- ###################------------------- ----------------####-------------------- -------------------###------------------ -------------------#########-------------- -------------------############----------- ------------------################-------- ------------------##################------ ----------------#####################--- - ------------#######################- P -----------######################## -----------####################### ------------########### ######## ---------############ T ###### --------############ ##### -----################# -############# Global CMT Convention Moment Tensor: R T P 1.79e+21 -3.85e+21 -4.35e+21 -3.85e+21 7.96e+21 1.19e+22 -4.35e+21 1.19e+22 -9.75e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110218081335/index.html |
(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.
(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.
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 0.5 110 85 -25 3.94 0.4731 WVFGRD96 1.0 110 85 -15 3.95 0.5072 WVFGRD96 2.0 290 90 10 3.99 0.5532 WVFGRD96 3.0 290 90 5 4.01 0.5684 WVFGRD96 4.0 290 90 10 4.03 0.5699 WVFGRD96 5.0 290 80 10 4.04 0.5674 WVFGRD96 6.0 295 70 15 4.06 0.5691 WVFGRD96 7.0 290 70 10 4.07 0.5704 WVFGRD96 8.0 290 70 10 4.07 0.5712 WVFGRD96 9.0 290 75 10 4.08 0.5705 WVFGRD96 10.0 290 70 10 4.09 0.5701 WVFGRD96 11.0 290 70 10 4.10 0.5675 WVFGRD96 12.0 290 75 10 4.11 0.5643 WVFGRD96 13.0 290 75 10 4.11 0.5608 WVFGRD96 14.0 290 75 10 4.12 0.5563 WVFGRD96 15.0 290 75 10 4.13 0.5513 WVFGRD96 16.0 290 75 10 4.14 0.5460 WVFGRD96 17.0 290 75 10 4.14 0.5398 WVFGRD96 18.0 290 75 10 4.15 0.5326 WVFGRD96 19.0 290 75 10 4.16 0.5249 WVFGRD96 20.0 290 75 10 4.17 0.5160 WVFGRD96 21.0 290 75 10 4.17 0.5076 WVFGRD96 22.0 290 75 10 4.18 0.4989 WVFGRD96 23.0 290 75 10 4.19 0.4899 WVFGRD96 24.0 290 75 10 4.19 0.4808 WVFGRD96 25.0 290 75 10 4.20 0.4715 WVFGRD96 26.0 290 75 10 4.20 0.4620 WVFGRD96 27.0 290 75 10 4.21 0.4521 WVFGRD96 28.0 290 75 10 4.21 0.4421 WVFGRD96 29.0 290 70 10 4.22 0.4325
The best solution is
WVFGRD96 8.0 290 70 10 4.07 0.5712
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 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. |
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.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.
The CUS model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: