The ANSS event ID is usp000j7x7 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000j7x7/executive.
2011/09/11 12:27:45 32.848 -100.769 5.0 4.3 Texas
USGS/SLU Moment Tensor Solution ENS 2011/09/11 12:27:45:0 32.85 -100.77 5.0 4.3 Texas Stations used: EP.KIDD IU.ANMO TA.136A TA.137A TA.233A TA.234A TA.236A TA.333A TA.334A TA.335A TA.336A TA.433A TA.434A TA.435B TA.436A TA.534A TA.535A TA.536A TA.633A TA.634A TA.635A TA.733A TA.ABTX TA.MSTX TA.T25A TA.TUL1 TA.U32A TA.U35A TA.V36A TA.W35A TA.W36A TA.W37B TA.WHTX TA.X35A TA.X36A TA.X37A TA.Y35A TA.Y36A TA.Y37A TA.Y38A TA.Z33A TA.Z36A US.AMTX US.JCT US.MNTX US.WMOK Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 4.68e+22 dyne-cm Mw = 4.38 Z = 13 km Plane Strike Dip Rake NP1 207 85 -160 NP2 115 70 -5 Principal Axes: Axis Value Plunge Azimuth T 4.68e+22 11 339 N 0.00e+00 69 219 P -4.68e+22 17 73 Moment Tensor: (dyne-cm) Component Value Mxx 3.57e+22 Mxy -2.71e+22 Mxz 3.90e+21 Myy -3.31e+22 Myz -1.58e+22 Mzz -2.62e+21 ############ ### T ##############-- ###### ############------- #####################--------- ######################------------ ######################-------------- ######################---------------- ---###################------------- -- ----#################-------------- P -- -------##############--------------- --- ----------##########---------------------- ------------#######----------------------- ---------------###------------------------ ----------------##---------------------- ----------------######------------------ --------------##############---------- ------------######################## ----------######################## -------####################### ------###################### --#################### ############## Global CMT Convention Moment Tensor: R T P -2.62e+21 3.90e+21 1.58e+22 3.90e+21 3.57e+22 2.71e+22 1.58e+22 2.71e+22 -3.31e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110911122745/index.html |
STK = 115 DIP = 70 RAKE = -5 MW = 4.38 HS = 13.0
The NDK file is 20110911122745.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 2011/09/11 12:27:45:0 32.85 -100.77 5.0 4.3 Texas Stations used: EP.KIDD IU.ANMO TA.136A TA.137A TA.233A TA.234A TA.236A TA.333A TA.334A TA.335A TA.336A TA.433A TA.434A TA.435B TA.436A TA.534A TA.535A TA.536A TA.633A TA.634A TA.635A TA.733A TA.ABTX TA.MSTX TA.T25A TA.TUL1 TA.U32A TA.U35A TA.V36A TA.W35A TA.W36A TA.W37B TA.WHTX TA.X35A TA.X36A TA.X37A TA.Y35A TA.Y36A TA.Y37A TA.Y38A TA.Z33A TA.Z36A US.AMTX US.JCT US.MNTX US.WMOK Filtering commands used: cut o DIST/3.3 -30 o DIST/3.3 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 4.68e+22 dyne-cm Mw = 4.38 Z = 13 km Plane Strike Dip Rake NP1 207 85 -160 NP2 115 70 -5 Principal Axes: Axis Value Plunge Azimuth T 4.68e+22 11 339 N 0.00e+00 69 219 P -4.68e+22 17 73 Moment Tensor: (dyne-cm) Component Value Mxx 3.57e+22 Mxy -2.71e+22 Mxz 3.90e+21 Myy -3.31e+22 Myz -1.58e+22 Mzz -2.62e+21 ############ ### T ##############-- ###### ############------- #####################--------- ######################------------ ######################-------------- ######################---------------- ---###################------------- -- ----#################-------------- P -- -------##############--------------- --- ----------##########---------------------- ------------#######----------------------- ---------------###------------------------ ----------------##---------------------- ----------------######------------------ --------------##############---------- ------------######################## ----------######################## -------####################### ------###################### --#################### ############## Global CMT Convention Moment Tensor: R T P -2.62e+21 3.90e+21 1.58e+22 3.90e+21 3.57e+22 2.71e+22 1.58e+22 2.71e+22 -3.31e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110911122745/index.html |
USGS/SLU Regional Moment Solution WESTERN TEXAS 11/09/11 12:27:45.27 Epicenter: 32.855 -100.899 MW 4.3 USGS/SLU REGIONAL MOMENT TENSOR Depth 6 No. of sta: 17 Moment Tensor; Scale 10**15 Nm Mrr=-0.55 Mtt= 3.29 Mpp=-2.74 Mrt=-0.71 Mrp=-0.66 Mtp= 1.78 Principal axes: T Val= 3.94 Plg=11 Azm=164 N -0.64 75 26 P -3.30 10 256 Best Double Couple:Mo=3.7*10**15 NP1:Strike=210 Dip=89 Slip= 165 NP2: 300 75 1 |
eptember 11, 2011, WESTERN TEXAS, MW=4.5 Meredith Nettles CENTROID-MOMENT-TENSOR SOLUTION GCMT EVENT: S201109111227A DATA: IU II LD G CU TA US BK SURFACE WAVES: 80S, 107C, T= 50 TIMESTAMP: Q-20110911220257 CENTROID LOCATION: ORIGIN TIME: 12:27:45.8 0.5 LAT:32.83N 0.03;LON:100.80W 0.02 DEP: 12.0 FIX;TRIANG HDUR: 0.4 MOMENT TENSOR: SCALE 10**22 D-CM RR=-1.600 0.242; TT= 5.360 0.252 PP=-3.760 0.237; RT= 1.570 0.873 RP= 2.710 0.786; TP= 3.420 0.214 PRINCIPAL AXES: 1.(T) VAL= 7.156;PLG=16;AZM=339 2.(N) -1.166; 58; 223 3.(P) -5.990; 28; 77 BEST DBLE.COUPLE:M0= 6.57*10**22 NP1: STRIKE=115;DIP=59;SLIP= -9 NP2: STRIKE=210;DIP=82;SLIP=-148 ######### ### T ###########-- ##### ##########----- ##################--------- ##################----------- -#################------------- -###############---------- -- ----############----------- P --- -----##########------------ --- -------#######------------------- ---------####-------------------- ------------------------------- ----------#####---------------- --------#############----#### -------#################### ----################### -################## ########### |
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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 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 300 85 0 4.09 0.4294 WVFGRD96 2.0 300 80 0 4.17 0.5166 WVFGRD96 3.0 120 80 5 4.20 0.5509 WVFGRD96 4.0 115 70 -10 4.24 0.5749 WVFGRD96 5.0 115 70 -10 4.27 0.5947 WVFGRD96 6.0 115 70 -10 4.29 0.6118 WVFGRD96 7.0 115 70 -10 4.31 0.6275 WVFGRD96 8.0 115 65 -10 4.34 0.6431 WVFGRD96 9.0 115 65 -5 4.35 0.6493 WVFGRD96 10.0 115 65 -5 4.36 0.6534 WVFGRD96 11.0 115 65 -5 4.37 0.6557 WVFGRD96 12.0 115 70 -5 4.38 0.6570 WVFGRD96 13.0 115 70 -5 4.38 0.6571 WVFGRD96 14.0 115 70 -5 4.39 0.6558 WVFGRD96 15.0 115 70 -5 4.40 0.6531 WVFGRD96 16.0 115 70 -5 4.41 0.6491 WVFGRD96 17.0 115 70 -5 4.41 0.6440 WVFGRD96 18.0 120 80 25 4.44 0.6388 WVFGRD96 19.0 120 80 25 4.44 0.6349 WVFGRD96 20.0 120 80 25 4.45 0.6299 WVFGRD96 21.0 120 80 25 4.46 0.6236 WVFGRD96 22.0 120 85 25 4.47 0.6169 WVFGRD96 23.0 120 85 25 4.47 0.6107 WVFGRD96 24.0 120 85 25 4.48 0.6037 WVFGRD96 25.0 120 85 25 4.48 0.5959 WVFGRD96 26.0 300 75 -5 4.48 0.5877 WVFGRD96 27.0 300 75 -5 4.48 0.5793 WVFGRD96 28.0 300 75 -5 4.49 0.5703 WVFGRD96 29.0 300 75 -5 4.50 0.5610
The best solution is
WVFGRD96 13.0 115 70 -5 4.38 0.6571
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 +70 rtr taper w 0.1 hp c 0.02 n 3 lp c 0.05 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 CUS.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 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