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.
The ANSS event ID is tx2025nlxbop and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/tx2025nlxbop/executive.
2025/07/10 14:37:52 32.440 -102.064 8.4 3.7 Texas
USGS/SLU Moment Tensor Solution
ENS 2025/07/10 14:37:52.0 32.44 -102.06 8.4 3.7 Texas
Stations used:
4O.BW01 4O.CW01 4O.DB03 4O.DB04 4O.EE01 4O.EE04 4O.FOR01
4O.GV02 4O.GV03 4O.GV04 4O.MBBB2 4O.MG01 4O.MID01 4O.MID02
4O.MID03 4O.OE01 4O.OE02 4O.SD01 4O.SE01 4O.SM02 4O.SM03
4O.SM05 4O.SM06 4O.VW01 4O.WW01 4T.NM01 4T.NM03 TX.DKNS
TX.MB01 TX.MB03 TX.MB05 TX.MB08 TX.MB09 TX.MB10 TX.MB11
TX.MB12 TX.MB13 TX.MB15 TX.MB16 TX.MB18 TX.MB19 TX.MB21
TX.MB22 TX.MB23 TX.MB25 TX.MB27 TX.MNHN TX.ODSA TX.PB04
TX.PB06 TX.PB07 TX.PB08 TX.PB16 TX.PB17 TX.PB18 TX.PB19
TX.PB21 TX.PB22 TX.PB30 TX.PB46 TX.PB47 TX.PB51 TX.PB54
TX.POST TX.SN02 TX.SN03 TX.SN04
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +30
rtr
taper w 0.1
hp c 0.05 n 3
lp c 0.15 n 3
Best Fitting Double Couple
Mo = 1.43e+21 dyne-cm
Mw = 3.37
Z = 5 km
Plane Strike Dip Rake
NP1 218 61 -132
NP2 100 50 -40
Principal Axes:
Axis Value Plunge Azimuth
T 1.43e+21 6 337
N 0.00e+00 36 243
P -1.43e+21 53 75
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.16e+21
Mxy -6.33e+20
Mxz -3.49e+19
Myy -2.60e+20
Myz -7.21e+20
Mzz -9.05e+20
#############
## T #################
##### ###############-----
####################----------
###################---------------
#################-------------------
################----------------------
################------------------------
##############-------------- ---------
-#############--------------- P ----------
--###########---------------- ----------
---########-------------------------------
-----######-------------------------------
------###------------------------------#
--------#----------------------------###
-------#####---------------------#####
-----#############-------###########
----##############################
--############################
-###########################
######################
##############
Global CMT Convention Moment Tensor:
R T P
-9.05e+20 -3.49e+19 7.21e+20
-3.49e+19 1.16e+21 6.33e+20
7.21e+20 6.33e+20 -2.60e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250710143752/index.html
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STK = 100
DIP = 50
RAKE = -40
MW = 3.37
HS = 5.0
The NDK file is 20250710143752.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 -30 o DIST/3.3 +30 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 1.0 105 50 10 3.01 0.2419
WVFGRD96 2.0 115 45 25 3.21 0.3209
WVFGRD96 3.0 100 45 -35 3.29 0.3804
WVFGRD96 4.0 100 55 -40 3.33 0.4248
WVFGRD96 5.0 100 50 -40 3.37 0.4447
WVFGRD96 6.0 105 55 -35 3.39 0.4446
WVFGRD96 7.0 105 55 -30 3.42 0.4319
WVFGRD96 8.0 105 50 -35 3.49 0.4159
WVFGRD96 9.0 105 55 -30 3.50 0.3940
WVFGRD96 10.0 110 55 -30 3.52 0.3723
WVFGRD96 11.0 110 55 -30 3.54 0.3494
WVFGRD96 12.0 110 55 -30 3.56 0.3278
WVFGRD96 13.0 110 55 -30 3.57 0.3073
WVFGRD96 14.0 110 55 -30 3.58 0.2893
WVFGRD96 15.0 110 55 -30 3.59 0.2748
WVFGRD96 16.0 110 55 -35 3.61 0.2637
WVFGRD96 17.0 110 50 -40 3.63 0.2567
WVFGRD96 18.0 110 50 -40 3.64 0.2518
WVFGRD96 19.0 110 50 -40 3.65 0.2474
WVFGRD96 20.0 110 50 -40 3.66 0.2441
WVFGRD96 21.0 360 55 -50 3.62 0.2446
WVFGRD96 22.0 0 55 -50 3.63 0.2479
WVFGRD96 23.0 -5 55 -55 3.64 0.2519
WVFGRD96 24.0 -5 55 -55 3.65 0.2551
WVFGRD96 25.0 0 60 -50 3.65 0.2584
WVFGRD96 26.0 5 55 -45 3.66 0.2621
WVFGRD96 27.0 5 55 -45 3.66 0.2657
WVFGRD96 28.0 5 55 -50 3.67 0.2696
WVFGRD96 29.0 5 55 -50 3.68 0.2722
The best solution is
WVFGRD96 5.0 100 50 -40 3.37 0.4447
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 -30 o DIST/3.3 +30 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