The ANSS event ID is se60400186 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/se60400186/executive.
2022/06/18 08:05:23 32.453 -82.141 0.8 3.9 Georgia
USGS/SLU Moment Tensor Solution ENS 2022/06/18 08:05:23:0 32.45 -82.14 0.8 3.9 Georgia Stations used: CO.BIRD CO.CASEE CO.CSB CO.HODGE CO.JSC CO.PAULI CO.TEEBA ET.CPCT ET.FPAL IM.TKL N4.152A N4.154A N4.250A N4.257A N4.352A N4.456A N4.656A N4.KMSC N4.TIGA N4.V53A N4.V55A N4.W50A N4.W52A N4.W57A N4.X51A N4.X58A N4.Y49A N4.Y52A N4.Y57A N4.Y58A N4.Y60A US.GOGA US.NHSC 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 = 8.32e+21 dyne-cm Mw = 3.88 Z = 16 km Plane Strike Dip Rake NP1 176 64 134 NP2 290 50 35 Principal Axes: Axis Value Plunge Azimuth T 8.32e+21 50 136 N 0.00e+00 39 333 P -8.32e+21 8 236 Moment Tensor: (dyne-cm) Component Value Mxx -7.94e+20 Mxy -5.51e+21 Mxz -2.28e+21 Myy -3.90e+21 Myz 3.83e+21 Mzz 4.70e+21 ####---------- #######--------------- ##########------------------ ##########-------------------- ###########----------------------- ####--------#######----------------- #------------############------------- -------------################----------- -------------###################-------- --------------#####################------- --------------#######################----- --------------########################---- ---------------########################--- --------------########### ###########- --------------########### T ###########- - ----------########## ########### P ----------####################### -----------##################### ------------################## ------------################ ----------############ -------####### Global CMT Convention Moment Tensor: R T P 4.70e+21 -2.28e+21 -3.83e+21 -2.28e+21 -7.94e+20 5.51e+21 -3.83e+21 5.51e+21 -3.90e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220618080523/index.html |
STK = 290 DIP = 50 RAKE = 35 MW = 3.88 HS = 16.0
The NDK file is 20220618080523.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 2022/06/18 08:05:23:0 32.45 -82.14 0.8 3.9 Georgia Stations used: CO.BIRD CO.CASEE CO.CSB CO.HODGE CO.JSC CO.PAULI CO.TEEBA ET.CPCT ET.FPAL IM.TKL N4.152A N4.154A N4.250A N4.257A N4.352A N4.456A N4.656A N4.KMSC N4.TIGA N4.V53A N4.V55A N4.W50A N4.W52A N4.W57A N4.X51A N4.X58A N4.Y49A N4.Y52A N4.Y57A N4.Y58A N4.Y60A US.GOGA US.NHSC 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 = 8.32e+21 dyne-cm Mw = 3.88 Z = 16 km Plane Strike Dip Rake NP1 176 64 134 NP2 290 50 35 Principal Axes: Axis Value Plunge Azimuth T 8.32e+21 50 136 N 0.00e+00 39 333 P -8.32e+21 8 236 Moment Tensor: (dyne-cm) Component Value Mxx -7.94e+20 Mxy -5.51e+21 Mxz -2.28e+21 Myy -3.90e+21 Myz 3.83e+21 Mzz 4.70e+21 ####---------- #######--------------- ##########------------------ ##########-------------------- ###########----------------------- ####--------#######----------------- #------------############------------- -------------################----------- -------------###################-------- --------------#####################------- --------------#######################----- --------------########################---- ---------------########################--- --------------########### ###########- --------------########### T ###########- - ----------########## ########### P ----------####################### -----------##################### ------------################## ------------################ ----------############ -------####### Global CMT Convention Moment Tensor: R T P 4.70e+21 -2.28e+21 -3.83e+21 -2.28e+21 -7.94e+20 5.51e+21 -3.83e+21 5.51e+21 -3.90e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220618080523/index.html |
Regional Moment Tensor (Mwr) Moment 8.461e+14 N-m Magnitude 3.88 Mwr Depth 16.0 km Percent DC 80% Half Duration - Catalog US Data Source US 4 Contributor US 4 Nodal Planes Plane Strike Dip Rake NP1 292 55 39 NP2 177 59 137 Principal Axes Axis Value Plunge Azimuth T 7.983e+14 N-m 51 142 N 0.887e+14 N-m 39 327 P -8.870e+14 N-m 2 235 |
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 -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 90 60 -30 3.68 0.4833 WVFGRD96 2.0 80 50 -50 3.75 0.4966 WVFGRD96 3.0 280 50 0 3.71 0.4839 WVFGRD96 4.0 285 50 10 3.71 0.5010 WVFGRD96 5.0 285 50 10 3.72 0.5189 WVFGRD96 6.0 285 50 15 3.73 0.5391 WVFGRD96 7.0 285 50 20 3.74 0.5632 WVFGRD96 8.0 290 50 25 3.75 0.5904 WVFGRD96 9.0 290 50 30 3.77 0.6187 WVFGRD96 10.0 290 50 30 3.80 0.6429 WVFGRD96 11.0 290 50 30 3.82 0.6645 WVFGRD96 12.0 290 50 30 3.83 0.6813 WVFGRD96 13.0 290 50 30 3.84 0.6932 WVFGRD96 14.0 290 50 35 3.86 0.7011 WVFGRD96 15.0 290 50 35 3.87 0.7051 WVFGRD96 16.0 290 50 35 3.88 0.7056 WVFGRD96 17.0 290 50 30 3.88 0.7031 WVFGRD96 18.0 290 50 30 3.89 0.6980 WVFGRD96 19.0 290 50 30 3.90 0.6907 WVFGRD96 20.0 290 50 30 3.93 0.6794 WVFGRD96 21.0 290 50 30 3.93 0.6675 WVFGRD96 22.0 290 50 30 3.94 0.6533 WVFGRD96 23.0 290 50 30 3.95 0.6369 WVFGRD96 24.0 295 45 30 3.95 0.6192 WVFGRD96 25.0 295 45 30 3.95 0.6004 WVFGRD96 26.0 295 45 30 3.96 0.5804 WVFGRD96 27.0 295 45 30 3.96 0.5598 WVFGRD96 28.0 290 45 25 3.96 0.5387 WVFGRD96 29.0 290 45 20 3.97 0.5185
The best solution is
WVFGRD96 16.0 290 50 35 3.88 0.7056
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