The ANSS event ID is nm605762 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nm605762/executive.
2005/06/02 11:35:10 36.150 -89.474 15.0 4 Tennessee
USGS/SLU Moment Tensor Solution ENS 2005/06/02 11:35:10:0 36.15 -89.47 15.0 4.0 Tennessee Stations used: NM.BLO NM.FVM NM.MPH NM.OLIL NM.PLAL NM.PVMO NM.SLM NM.UALR NM.USIN NM.UTMT US.LRAL US.OXF US.WVT Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 7.00e+21 dyne-cm Mw = 3.83 Z = 15 km Plane Strike Dip Rake NP1 145 70 60 NP2 24 36 144 Principal Axes: Axis Value Plunge Azimuth T 7.00e+21 55 17 N 0.00e+00 28 156 P -7.00e+21 19 257 Moment Tensor: (dyne-cm) Component Value Mxx 1.81e+21 Mxy -7.06e+20 Mxz 3.64e+21 Myy -5.70e+21 Myz 3.12e+21 Mzz 3.90e+21 ############## #####################- --#######################--- ---########################--- ------########################---- -------############ ##########---- ---------########### T ##########----- -----------########## ##########------ -----------#######################------ -------------######################------- --------------#####################------- ---------------####################------- --- -----------#################-------- -- P ------------################------- -- --------------#############-------- -------------------###########-------- --------------------########-------- ---------------------####--------- ------------------------------ ------------------#####----- -----------########### ############## Global CMT Convention Moment Tensor: R T P 3.90e+21 3.64e+21 -3.12e+21 3.64e+21 1.81e+21 7.06e+20 -3.12e+21 7.06e+20 -5.70e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20050602113510/index.html |
STK = 145 DIP = 70 RAKE = 60 MW = 3.83 HS = 15.0
The NDK file is 20050602113510.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 2005/06/02 11:35:10:0 36.15 -89.47 15.0 4.0 Tennessee Stations used: NM.BLO NM.FVM NM.MPH NM.OLIL NM.PLAL NM.PVMO NM.SLM NM.UALR NM.USIN NM.UTMT US.LRAL US.OXF US.WVT Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 7.00e+21 dyne-cm Mw = 3.83 Z = 15 km Plane Strike Dip Rake NP1 145 70 60 NP2 24 36 144 Principal Axes: Axis Value Plunge Azimuth T 7.00e+21 55 17 N 0.00e+00 28 156 P -7.00e+21 19 257 Moment Tensor: (dyne-cm) Component Value Mxx 1.81e+21 Mxy -7.06e+20 Mxz 3.64e+21 Myy -5.70e+21 Myz 3.12e+21 Mzz 3.90e+21 ############## #####################- --#######################--- ---########################--- ------########################---- -------############ ##########---- ---------########### T ##########----- -----------########## ##########------ -----------#######################------ -------------######################------- --------------#####################------- ---------------####################------- --- -----------#################-------- -- P ------------################------- -- --------------#############-------- -------------------###########-------- --------------------########-------- ---------------------####--------- ------------------------------ ------------------#####----- -----------########### ############## Global CMT Convention Moment Tensor: R T P 3.90e+21 3.64e+21 -3.12e+21 3.64e+21 1.81e+21 7.06e+20 -3.12e+21 7.06e+20 -5.70e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20050602113510/index.html |
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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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 335 50 80 3.65 0.3572 WVFGRD96 2.0 330 60 75 3.74 0.3353 WVFGRD96 3.0 320 70 65 3.72 0.3198 WVFGRD96 4.0 130 85 -65 3.68 0.3459 WVFGRD96 5.0 315 90 65 3.68 0.3724 WVFGRD96 6.0 320 85 65 3.69 0.3955 WVFGRD96 7.0 320 85 65 3.69 0.4142 WVFGRD96 8.0 320 80 65 3.70 0.4290 WVFGRD96 9.0 155 65 70 3.74 0.4444 WVFGRD96 10.0 150 65 70 3.78 0.4680 WVFGRD96 11.0 155 60 75 3.81 0.4866 WVFGRD96 12.0 155 60 75 3.82 0.5013 WVFGRD96 13.0 155 60 75 3.82 0.5102 WVFGRD96 14.0 145 70 60 3.82 0.5163 WVFGRD96 15.0 145 70 60 3.83 0.5198 WVFGRD96 16.0 145 70 60 3.84 0.5195 WVFGRD96 17.0 150 70 65 3.84 0.5165 WVFGRD96 18.0 150 70 65 3.85 0.5109 WVFGRD96 19.0 150 70 65 3.86 0.5030 WVFGRD96 20.0 150 70 65 3.89 0.4960 WVFGRD96 21.0 150 70 65 3.90 0.4852 WVFGRD96 22.0 150 75 65 3.90 0.4731 WVFGRD96 23.0 150 75 70 3.91 0.4628 WVFGRD96 24.0 150 75 70 3.91 0.4513 WVFGRD96 25.0 150 75 70 3.92 0.4383 WVFGRD96 26.0 155 75 75 3.92 0.4245 WVFGRD96 27.0 155 80 80 3.92 0.4130 WVFGRD96 28.0 155 80 75 3.93 0.4020 WVFGRD96 29.0 155 80 75 3.93 0.3911
The best solution is
WVFGRD96 15.0 145 70 60 3.83 0.5198
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 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 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