The ANSS event ID is tx2024hjyp and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/tx2024hjyp/executive.
2024/04/15 01:23:47 31.619 -104.485 4.0 3.3 Texas
USGS/SLU Moment Tensor Solution ENS 2024/04/15 01:23:47:0 31.62 -104.49 4.0 3.3 Texas Stations used: 4O.CV01 4O.LWM1 4O.SA02 4O.SA04 4O.SA07 4O.WB03 4O.WB04 4T.NM01 TX.PB03 TX.PB04 TX.PB07 TX.PB09 TX.PB10 TX.PB12 TX.PB13 TX.PB18 TX.PB24 TX.PB25 TX.PB26 TX.PB29 TX.PB31 TX.PB33 TX.PB34 TX.PB37 TX.PB38 TX.PB40 TX.PB46 TX.PECS TX.VHRN Filtering commands used: cut o DIST/3.3 -20 o DIST/3.3 +30 rtr taper w 0.1 hp c 0.05 n 3 lp c 0.20 n 3 Best Fitting Double Couple Mo = 8.81e+20 dyne-cm Mw = 3.23 Z = 7 km Plane Strike Dip Rake NP1 42 63 -104 NP2 250 30 -65 Principal Axes: Axis Value Plunge Azimuth T 8.81e+20 17 142 N 0.00e+00 12 48 P -8.81e+20 69 284 Moment Tensor: (dyne-cm) Component Value Mxx 4.91e+20 Mxy -3.65e+20 Mxz -2.65e+20 Myy 2.01e+20 Myz 4.40e+20 Mzz -6.92e+20 ############## ###################### ############################ ##########---------------####- ########-------------------------- ######-------------------------####- #####---------------------------###### #####---------------------------######## ###----------------------------######### ###----------- --------------########### ###----------- P -------------############ ##------------ ------------############# ##--------------------------############## -------------------------############### -----------------------################# --------------------################## -----------------################### -------------############# ##### --------################ T ### ####################### ## ###################### ############## Global CMT Convention Moment Tensor: R T P -6.92e+20 -2.65e+20 -4.40e+20 -2.65e+20 4.91e+20 3.65e+20 -4.40e+20 3.65e+20 2.01e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240415012347/index.html |
STK = 250 DIP = 30 RAKE = -65 MW = 3.23 HS = 7.0
The NDK file is 20240415012347.ndk The waveform inversion is preferred.
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 -20 o DIST/3.3 +30 rtr taper w 0.1 hp c 0.05 n 3 lp c 0.20 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 325 70 25 2.68 0.1617 WVFGRD96 2.0 325 75 35 2.91 0.2116 WVFGRD96 3.0 280 25 -30 3.03 0.3166 WVFGRD96 4.0 275 25 -35 3.08 0.4055 WVFGRD96 5.0 255 25 -55 3.14 0.4584 WVFGRD96 6.0 255 25 -55 3.18 0.4872 WVFGRD96 7.0 250 30 -65 3.23 0.4962 WVFGRD96 8.0 230 25 -85 3.33 0.4841 WVFGRD96 9.0 220 25 -95 3.36 0.4659 WVFGRD96 10.0 50 65 -80 3.40 0.4387 WVFGRD96 11.0 50 65 -70 3.43 0.4051 WVFGRD96 12.0 175 55 100 3.38 0.3707 WVFGRD96 13.0 340 35 80 3.40 0.3485 WVFGRD96 14.0 345 35 90 3.42 0.3235 WVFGRD96 15.0 170 60 90 3.42 0.2973 WVFGRD96 16.0 185 60 60 3.48 0.2773 WVFGRD96 17.0 190 65 60 3.48 0.2614 WVFGRD96 18.0 190 65 60 3.49 0.2495 WVFGRD96 19.0 120 30 50 3.42 0.2522 WVFGRD96 20.0 120 30 50 3.43 0.2615 WVFGRD96 21.0 155 30 70 3.44 0.2709 WVFGRD96 22.0 155 30 70 3.45 0.2756 WVFGRD96 23.0 150 35 60 3.47 0.2797 WVFGRD96 24.0 110 35 40 3.49 0.2812 WVFGRD96 25.0 115 35 40 3.49 0.2852 WVFGRD96 26.0 120 35 40 3.49 0.2865 WVFGRD96 27.0 120 35 40 3.50 0.2886 WVFGRD96 28.0 25 70 -60 3.51 0.2905 WVFGRD96 29.0 25 70 -60 3.52 0.2920
The best solution is
WVFGRD96 7.0 250 30 -65 3.23 0.4962
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 -20 o DIST/3.3 +30 rtr taper w 0.1 hp c 0.05 n 3 lp c 0.20 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