2011/03/03 15:55:25 35.241 -92.388 6.0 3.70 Arkansas
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution ENS 2011/03/03 15:55:25:0 35.24 -92.39 6.0 3.7 Arkansas Stations used: AG.FCAR AG.WHAR NM.UALR NM.X102 NM.X201 TA.T37A TA.T38A TA.T39A TA.T40A TA.TUL1 TA.U38A TA.U39A TA.U40A TA.V39A TA.W36A TA.W38A TA.W39A TA.W40A TA.X40A Filtering commands used: hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 4.17e+21 dyne-cm Mw = 3.68 Z = 6 km Plane Strike Dip Rake NP1 209 79 134 NP2 310 45 15 Principal Axes: Axis Value Plunge Azimuth T 4.17e+21 39 158 N 0.00e+00 43 19 P -4.17e+21 22 267 Moment Tensor: (dyne-cm) Component Value Mxx 2.17e+21 Mxy -1.03e+21 Mxz -1.83e+21 Myy -3.25e+21 Myz 2.18e+21 Mzz 1.08e+21 ############## #####################- ######################------ -------------########--------- -------------------###------------ ---------------------##------------- ---------------------######----------- ---------------------########----------- --------------------###########--------- -------------------##############--------- --- ------------#################------- --- P -----------###################------ --- ----------####################------ ---------------#####################---- --------------######################---- ------------#######################--- ----------########### ##########-- --------############ T ##########- ------############ ######### ----######################## -##################### ############## Global CMT Convention Moment Tensor: R T P 1.08e+21 -1.83e+21 -2.18e+21 -1.83e+21 2.17e+21 1.03e+21 -2.18e+21 1.03e+21 -3.25e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110303155525/index.html |
STK = 310 DIP = 45 RAKE = 15 MW = 3.68 HS = 6.0
The NDK file is 20110303155525.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2011/03/03 15:55:24:0 35.24 -92.39 6.0 3.7 Arkansas Stations used: AG.FCAR AG.WHAR NM.UALR NM.X102 NM.X201 TA.T37A TA.T38A TA.T39A TA.T40A TA.TUL1 TA.U38A TA.U39A TA.U40A TA.V39A TA.W36A TA.W38A TA.W39A TA.W40A TA.X40A Filtering commands used: hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 2.24e+21 dyne-cm Mw = 3.50 Z = 4 km Plane Strike Dip Rake NP1 217 80 -170 NP2 125 80 -10 Principal Axes: Axis Value Plunge Azimuth T 2.24e+21 0 351 N 0.00e+00 76 260 P -2.24e+21 14 81 Moment Tensor: (dyne-cm) Component Value Mxx 2.13e+21 Mxy -6.80e+20 Mxz -7.97e+19 Myy -2.00e+21 Myz -5.23e+20 Mzz -1.33e+20 ## T ######### ###### ############# #########################--- ########################------ ########################---------- --#####################------------- -----##################--------------- --------##############------------------ ----------##########---------------- - -------------#######----------------- P -- ---------------####------------------ -- -----------------#------------------------ ----------------#####--------------------- --------------########------------------ -------------############--------------- ----------##################---------- --------######################------ ------############################ ----########################## --########################## ###################### ############## Global CMT Convention Moment Tensor: R T P -1.33e+20 -7.97e+19 5.23e+20 -7.97e+19 2.13e+21 6.80e+20 5.23e+20 6.80e+20 -2.00e+21 Details of the solution is found at http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20110303155524/index.html USGS/SLU Moment Tensor Solution ENS 2011/03/03 15:55:25:0 35.24 -92.39 6.0 3.7 Arkansas Stations used: AG.FCAR AG.WHAR NM.UALR NM.X102 NM.X201 TA.T37A TA.T38A TA.T39A TA.T40A TA.TUL1 TA.U38A TA.U39A TA.U40A TA.V39A TA.W36A TA.W38A TA.W39A TA.W40A TA.X40A Filtering commands used: hp c 0.03 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 4.17e+21 dyne-cm Mw = 3.68 Z = 6 km Plane Strike Dip Rake NP1 209 79 134 NP2 310 45 15 Principal Axes: Axis Value Plunge Azimuth T 4.17e+21 39 158 N 0.00e+00 43 19 P -4.17e+21 22 267 Moment Tensor: (dyne-cm) Component Value Mxx 2.17e+21 Mxy -1.03e+21 Mxz -1.83e+21 Myy -3.25e+21 Myz 2.18e+21 Mzz 1.08e+21 ############## #####################- ######################------ -------------########--------- -------------------###------------ ---------------------##------------- ---------------------######----------- ---------------------########----------- --------------------###########--------- -------------------##############--------- --- ------------#################------- --- P -----------###################------ --- ----------####################------ ---------------#####################---- --------------######################---- ------------#######################--- ----------########### ##########-- --------############ T ##########- ------############ ######### ----######################## -##################### ############## Global CMT Convention Moment Tensor: R T P 1.08e+21 -1.83e+21 -2.18e+21 -1.83e+21 2.17e+21 1.03e+21 -2.18e+21 1.03e+21 -3.25e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110303155525/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 0.03 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 0.5 305 55 -5 3.39 0.6772 WVFGRD96 1.0 305 70 -10 3.38 0.7052 WVFGRD96 2.0 120 75 -15 3.43 0.7342 WVFGRD96 3.0 125 80 -10 3.45 0.7560 WVFGRD96 4.0 125 80 -10 3.50 0.7597 WVFGRD96 5.0 305 90 10 3.51 0.7464 WVFGRD96 6.0 305 80 10 3.53 0.7254 WVFGRD96 7.0 305 75 10 3.55 0.7013 WVFGRD96 8.0 305 70 10 3.56 0.6774 WVFGRD96 9.0 305 70 10 3.58 0.6550 WVFGRD96 10.0 310 60 10 3.60 0.6310 WVFGRD96 11.0 305 60 15 3.61 0.6070 WVFGRD96 12.0 305 60 15 3.61 0.5837 WVFGRD96 13.0 305 60 15 3.62 0.5624 WVFGRD96 14.0 305 60 15 3.63 0.5426 WVFGRD96 15.0 305 60 15 3.63 0.5260 WVFGRD96 16.0 305 60 15 3.64 0.5116 WVFGRD96 17.0 305 60 15 3.64 0.4987 WVFGRD96 18.0 305 60 15 3.65 0.4869 WVFGRD96 19.0 305 60 15 3.66 0.4771 WVFGRD96 20.0 310 55 15 3.68 0.4681 WVFGRD96 21.0 310 55 15 3.69 0.4592 WVFGRD96 22.0 310 55 15 3.69 0.4513 WVFGRD96 23.0 310 60 20 3.69 0.4461 WVFGRD96 24.0 310 60 20 3.70 0.4409 WVFGRD96 25.0 320 60 10 3.73 0.4374 WVFGRD96 26.0 320 60 10 3.74 0.4339 WVFGRD96 27.0 320 60 15 3.74 0.4304 WVFGRD96 28.0 320 60 10 3.76 0.4270 WVFGRD96 29.0 320 60 10 3.76 0.4243
The best solution is
WVFGRD96 4.0 125 80 -10 3.50 0.7597
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 0.03 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: