The ANSS event ID is tx2024qamq and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/tx2024qamq/executive.
2024/08/15 22:59:30 31.691 -101.701 7.3 3.8 Texas
USGS/SLU Moment Tensor Solution ENS 2024/08/15 22:59:30:0 31.69 -101.70 7.3 3.8 Texas Stations used: 4O.CW01 4O.DB04 4O.EE01 4O.HP01 4O.HP02 4O.MBBB2 4O.MBBB3 4O.MG01 4O.MID02 4O.MID03 4O.OE01 4O.PL01 4O.SD01 4O.SM03 4O.VW01 TX.MB02 TX.MB03 TX.MB06 TX.MB07 TX.MB08 TX.MB10 TX.MB11 TX.MB13 TX.MB15 TX.MB16 TX.MB18 TX.MB19 TX.MB21 TX.MB22 TX.MB23 TX.MB25 TX.MNHN TX.ODSA TX.OZNA TX.PB04 TX.PB08 TX.PB16 TX.PB19 TX.PB21 TX.PB46 TX.PB47 TX.PB51 TX.PB54 TX.SGCY TX.SN02 TX.SN03 TX.SN04 Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.05 n 3 lp c 0.15 n 3 Best Fitting Double Couple Mo = 3.16e+21 dyne-cm Mw = 3.60 Z = 6 km Plane Strike Dip Rake NP1 213 69 -148 NP2 110 60 -25 Principal Axes: Axis Value Plunge Azimuth T 3.16e+21 5 340 N 0.00e+00 52 243 P -3.16e+21 38 74 Moment Tensor: (dyne-cm) Component Value Mxx 2.62e+21 Mxy -1.53e+21 Mxz -1.38e+20 Myy -1.46e+21 Myz -1.58e+21 Mzz -1.16e+21 T ############ ### ################ ######################------ ####################---------- ####################-------------- ###################----------------- ##################-------------------- -#################---------------------- --###############-------------- ------ ----############---------------- P ------- ------#########----------------- ------- -------#######---------------------------- ----------###----------------------------- -----------#---------------------------- -----------#####------------------------ ---------###########----------------## -------############################# ------############################ ----########################## ---######################### ###################### ############## Global CMT Convention Moment Tensor: R T P -1.16e+21 -1.38e+20 1.58e+21 -1.38e+20 2.62e+21 1.53e+21 1.58e+21 1.53e+21 -1.46e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240815225930/index.html |
STK = 110 DIP = 60 RAKE = -25 MW = 3.60 HS = 6.0
The NDK file is 20240815225930.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 2024/08/15 22:59:30:0 31.69 -101.70 7.3 3.8 Texas Stations used: 4O.CW01 4O.DB04 4O.EE01 4O.HP01 4O.HP02 4O.MBBB2 4O.MBBB3 4O.MG01 4O.MID02 4O.MID03 4O.OE01 4O.PL01 4O.SD01 4O.SM03 4O.VW01 TX.MB02 TX.MB03 TX.MB06 TX.MB07 TX.MB08 TX.MB10 TX.MB11 TX.MB13 TX.MB15 TX.MB16 TX.MB18 TX.MB19 TX.MB21 TX.MB22 TX.MB23 TX.MB25 TX.MNHN TX.ODSA TX.OZNA TX.PB04 TX.PB08 TX.PB16 TX.PB19 TX.PB21 TX.PB46 TX.PB47 TX.PB51 TX.PB54 TX.SGCY TX.SN02 TX.SN03 TX.SN04 Filtering commands used: cut o DIST/3.3 -40 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.05 n 3 lp c 0.15 n 3 Best Fitting Double Couple Mo = 3.16e+21 dyne-cm Mw = 3.60 Z = 6 km Plane Strike Dip Rake NP1 213 69 -148 NP2 110 60 -25 Principal Axes: Axis Value Plunge Azimuth T 3.16e+21 5 340 N 0.00e+00 52 243 P -3.16e+21 38 74 Moment Tensor: (dyne-cm) Component Value Mxx 2.62e+21 Mxy -1.53e+21 Mxz -1.38e+20 Myy -1.46e+21 Myz -1.58e+21 Mzz -1.16e+21 T ############ ### ################ ######################------ ####################---------- ####################-------------- ###################----------------- ##################-------------------- -#################---------------------- --###############-------------- ------ ----############---------------- P ------- ------#########----------------- ------- -------#######---------------------------- ----------###----------------------------- -----------#---------------------------- -----------#####------------------------ ---------###########----------------## -------############################# ------############################ ----########################## ---######################### ###################### ############## Global CMT Convention Moment Tensor: R T P -1.16e+21 -1.38e+20 1.58e+21 -1.38e+20 2.62e+21 1.53e+21 1.58e+21 1.53e+21 -1.46e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240815225930/index.html |
Regional Moment Tensor (Mwr) Moment 4.479e+14 N-m Magnitude 3.70 Mwr Depth 4.0 km Percent DC 63% Half Duration - Catalog US Data Source US 2 Contributor US 2 Nodal Planes Plane Strike Dip Rake NP1 222 59 -132 NP2 102 51 -42 Principal Axes Axis Value Plunge Azimuth T 4.864e+14 4 341 N -0.909e+14 35 248 P -3.955e+14 54 77 |
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 0.05 n 3 lp c 0.15 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 20 65 -15 3.20 0.2786 WVFGRD96 2.0 125 50 25 3.42 0.3535 WVFGRD96 3.0 125 40 20 3.50 0.4244 WVFGRD96 4.0 105 45 -35 3.54 0.4738 WVFGRD96 5.0 285 55 -35 3.57 0.4983 WVFGRD96 6.0 110 60 -25 3.60 0.4985 WVFGRD96 7.0 110 65 -25 3.63 0.4826 WVFGRD96 8.0 110 60 -25 3.69 0.4551 WVFGRD96 9.0 110 65 -25 3.71 0.4274 WVFGRD96 10.0 110 65 -20 3.73 0.3970 WVFGRD96 11.0 110 65 -15 3.75 0.3636 WVFGRD96 12.0 115 70 -10 3.77 0.3312 WVFGRD96 13.0 115 70 -10 3.78 0.2986 WVFGRD96 14.0 115 70 -5 3.78 0.2672 WVFGRD96 15.0 115 65 5 3.79 0.2411 WVFGRD96 16.0 115 65 5 3.79 0.2181 WVFGRD96 17.0 115 65 5 3.79 0.1989 WVFGRD96 18.0 115 65 0 3.79 0.1842 WVFGRD96 19.0 115 65 -5 3.79 0.1745 WVFGRD96 20.0 110 60 -10 3.80 0.1698 WVFGRD96 21.0 110 60 -15 3.80 0.1683 WVFGRD96 22.0 110 65 -20 3.81 0.1681 WVFGRD96 23.0 110 65 -20 3.81 0.1681 WVFGRD96 24.0 205 80 20 3.82 0.1722 WVFGRD96 25.0 210 75 20 3.83 0.1826 WVFGRD96 26.0 205 80 20 3.85 0.1935 WVFGRD96 27.0 205 80 20 3.86 0.2042 WVFGRD96 28.0 205 80 15 3.86 0.2149 WVFGRD96 29.0 205 80 15 3.87 0.2260
The best solution is
WVFGRD96 6.0 110 60 -25 3.60 0.4985
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 0.05 n 3 lp c 0.15 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 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