The ANSS event ID is tx2023wzka and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/tx2023wzka/executive.
2023/11/23 23:14:34 32.409 -102.019 7.6 4.2 Texas
USGS/SLU Moment Tensor Solution ENS 2023/11/23 23:14:34:0 32.41 -102.02 7.6 4.2 Texas Stations used: 4O.BP01 4O.CV01 4O.DB02 4O.DB03 4O.DB04 4O.MBBB2 4O.MID01 4O.MID02 4O.MID03 4O.WB08 4O.WB10 4T.NM01 TX.435B TX.ALPN TX.BRDY TX.DKNS TX.FW01 TX.MB01 TX.MB04 TX.MB06 TX.MB07 TX.MB08 TX.MB09 TX.MB10 TX.MB11 TX.MB13 TX.MB14 TX.MB15 TX.MB17 TX.MB18 TX.MB19 TX.MB21 TX.MB22 TX.MB23 TX.MNHN TX.ODSA TX.OZNA TX.PB04 TX.PB07 TX.PB16 TX.PB17 TX.PB18 TX.PB19 TX.PB21 TX.PB22 TX.PB25 TX.PB35 TX.PB43 TX.PB44 TX.PB51 TX.PLPT TX.POST TX.SAND TX.SGCY TX.SMWD TX.SN03 TX.SN08 TX.SN10 TX.WTFS Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 4.17e+21 dyne-cm Mw = 3.68 Z = 7 km Plane Strike Dip Rake NP1 100 85 -35 NP2 193 55 -174 Principal Axes: Axis Value Plunge Azimuth T 4.17e+21 20 152 N 0.00e+00 55 273 P -4.17e+21 28 51 Moment Tensor: (dyne-cm) Component Value Mxx 1.57e+21 Mxy -3.13e+21 Mxz -2.27e+21 Myy -1.15e+21 Myz -7.02e+20 Mzz -4.15e+20 ##########---- ############---------- #############--------------- ############------------------ #############-------------- ---- #############--------------- P ----- #############---------------- ------ #############--------------------------- ############---------------------------- ---##########----------------------------- ----------##------------------------------ ------------#######----------------------- ------------###################----------- -----------############################# -----------############################# ----------############################ ---------########################### --------########################## -------############### ##### ------############### T #### ----############## # --############ Global CMT Convention Moment Tensor: R T P -4.15e+20 -2.27e+21 7.02e+20 -2.27e+21 1.57e+21 3.13e+21 7.02e+20 3.13e+21 -1.15e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20231123231434/index.html |
STK = 100 DIP = 85 RAKE = -35 MW = 3.68 HS = 7.0
The NDK file is 20231123231434.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 2023/11/23 23:14:34:0 32.41 -102.02 7.6 4.2 Texas Stations used: 4O.BP01 4O.CV01 4O.DB02 4O.DB03 4O.DB04 4O.MBBB2 4O.MID01 4O.MID02 4O.MID03 4O.WB08 4O.WB10 4T.NM01 TX.435B TX.ALPN TX.BRDY TX.DKNS TX.FW01 TX.MB01 TX.MB04 TX.MB06 TX.MB07 TX.MB08 TX.MB09 TX.MB10 TX.MB11 TX.MB13 TX.MB14 TX.MB15 TX.MB17 TX.MB18 TX.MB19 TX.MB21 TX.MB22 TX.MB23 TX.MNHN TX.ODSA TX.OZNA TX.PB04 TX.PB07 TX.PB16 TX.PB17 TX.PB18 TX.PB19 TX.PB21 TX.PB22 TX.PB25 TX.PB35 TX.PB43 TX.PB44 TX.PB51 TX.PLPT TX.POST TX.SAND TX.SGCY TX.SMWD TX.SN03 TX.SN08 TX.SN10 TX.WTFS Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.04 n 3 lp c 0.08 n 3 Best Fitting Double Couple Mo = 4.17e+21 dyne-cm Mw = 3.68 Z = 7 km Plane Strike Dip Rake NP1 100 85 -35 NP2 193 55 -174 Principal Axes: Axis Value Plunge Azimuth T 4.17e+21 20 152 N 0.00e+00 55 273 P -4.17e+21 28 51 Moment Tensor: (dyne-cm) Component Value Mxx 1.57e+21 Mxy -3.13e+21 Mxz -2.27e+21 Myy -1.15e+21 Myz -7.02e+20 Mzz -4.15e+20 ##########---- ############---------- #############--------------- ############------------------ #############-------------- ---- #############--------------- P ----- #############---------------- ------ #############--------------------------- ############---------------------------- ---##########----------------------------- ----------##------------------------------ ------------#######----------------------- ------------###################----------- -----------############################# -----------############################# ----------############################ ---------########################### --------########################## -------############### ##### ------############### T #### ----############## # --############ Global CMT Convention Moment Tensor: R T P -4.15e+20 -2.27e+21 7.02e+20 -2.27e+21 1.57e+21 3.13e+21 7.02e+20 3.13e+21 -1.15e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20231123231434/index.html |
Regional Moment Tensor (Mwr) Moment 6.511e+14 N-m Magnitude 3.81 Mwr Depth 4.0 km Percent DC 55% Half Duration - Catalog US Data Source US 2 Contributor US 2 Nodal Planes Plane Strike Dip Rake NP1 87 77 -49 NP2 192 43 -161 Principal Axes Axis Value Plunge Azimuth T 7.164e+14 21 148 N -1.607e+14 40 257 P -5.557e+14 42 36 |
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.
![]() |
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.
![]() |
|
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 0.04 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 280 80 10 3.35 0.3455 WVFGRD96 2.0 280 90 25 3.49 0.4296 WVFGRD96 3.0 95 80 -45 3.60 0.4837 WVFGRD96 4.0 95 80 -45 3.64 0.5281 WVFGRD96 5.0 95 80 -40 3.65 0.5528 WVFGRD96 6.0 95 80 -35 3.67 0.5627 WVFGRD96 7.0 100 85 -35 3.68 0.5637 WVFGRD96 8.0 95 80 -40 3.74 0.5581 WVFGRD96 9.0 100 90 -35 3.74 0.5483 WVFGRD96 10.0 285 80 35 3.76 0.5357 WVFGRD96 11.0 100 90 -30 3.76 0.5190 WVFGRD96 12.0 100 90 -30 3.77 0.5024 WVFGRD96 13.0 280 85 25 3.78 0.4870 WVFGRD96 14.0 100 90 -25 3.79 0.4698 WVFGRD96 15.0 100 90 -25 3.80 0.4549 WVFGRD96 16.0 280 85 25 3.81 0.4417 WVFGRD96 17.0 280 85 25 3.81 0.4276 WVFGRD96 18.0 280 85 25 3.82 0.4143 WVFGRD96 19.0 280 85 25 3.82 0.4021 WVFGRD96 20.0 280 85 25 3.83 0.3907 WVFGRD96 21.0 100 90 -25 3.83 0.3799 WVFGRD96 22.0 100 90 -25 3.84 0.3711 WVFGRD96 23.0 100 90 -25 3.84 0.3628 WVFGRD96 24.0 100 90 -25 3.85 0.3562 WVFGRD96 25.0 100 90 -25 3.86 0.3507 WVFGRD96 26.0 100 90 -25 3.86 0.3465 WVFGRD96 27.0 100 85 -25 3.86 0.3436 WVFGRD96 28.0 100 85 -25 3.87 0.3425 WVFGRD96 29.0 100 85 -20 3.88 0.3422
The best solution is
WVFGRD96 7.0 100 85 -35 3.68 0.5637
The mechanism corresponding to the best fit is
![]() |
|
The best fit as a function of depth is given in the following figure:
![]() |
|
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 0.04 n 3 lp c 0.08 n 3
![]() |
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. |
![]() |
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 WUS.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 Model after 8 iterations 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 1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00 6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00 13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00 19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00 0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 0.00 0.00 1.00 1.00