The ANSS event ID is us7000qun8 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us7000qun8/executive.
2025/09/08 02:50:27 39.489 -99.283 12.3 3.3 Kansas
USGS/SLU Moment Tensor Solution
ENS 2025/09/08 02:50:27.0 39.49 -99.28 12.3 3.3 Kansas
Stations used:
C0.LAMA GS.KS28 GS.OK051 N4.BGNE N4.R32B N4.T35B O2.PW05
O2.SC16 O2.SC19 TX.DRZT US.CBKS US.KSU1
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +40
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 1.29e+21 dyne-cm
Mw = 3.34
Z = 2 km
Plane Strike Dip Rake
NP1 150 65 -40
NP2 260 54 -149
Principal Axes:
Axis Value Plunge Azimuth
T 1.29e+21 6 207
N 0.00e+00 44 303
P -1.29e+21 45 110
Moment Tensor: (dyne-cm)
Component Value
Mxx 9.33e+20
Mxy 7.22e+20
Mxz 9.51e+19
Myy -2.99e+20
Myz -6.69e+20
Mzz -6.34e+20
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-##############--------------- ---------
###############-------------- P --------
#################------------ --------
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# T ################--
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Global CMT Convention Moment Tensor:
R T P
-6.34e+20 9.51e+19 6.69e+20
9.51e+19 9.33e+20 -7.22e+20
6.69e+20 -7.22e+20 -2.99e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20250908025027/index.html
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STK = 150
DIP = 65
RAKE = -40
MW = 3.34
HS = 2.0
The NDK file is 20250908025027.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: 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 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 150 70 -35 3.28 0.5465
WVFGRD96 2.0 150 65 -40 3.34 0.5671
WVFGRD96 3.0 160 75 -40 3.39 0.5398
WVFGRD96 4.0 350 80 20 3.36 0.5051
WVFGRD96 5.0 350 70 20 3.36 0.4984
WVFGRD96 6.0 175 65 35 3.38 0.5116
WVFGRD96 7.0 175 65 35 3.38 0.5193
WVFGRD96 8.0 165 70 35 3.37 0.5251
WVFGRD96 9.0 165 70 35 3.37 0.5276
WVFGRD96 10.0 170 65 40 3.40 0.5288
WVFGRD96 11.0 165 70 35 3.40 0.5274
WVFGRD96 12.0 165 70 35 3.40 0.5240
WVFGRD96 13.0 165 70 35 3.41 0.5185
WVFGRD96 14.0 165 70 35 3.42 0.5120
WVFGRD96 15.0 165 70 35 3.42 0.5035
WVFGRD96 16.0 345 75 35 3.44 0.4959
WVFGRD96 17.0 345 75 35 3.45 0.4936
WVFGRD96 18.0 345 75 35 3.46 0.4902
WVFGRD96 19.0 345 75 35 3.47 0.4848
WVFGRD96 20.0 345 75 40 3.49 0.4761
WVFGRD96 21.0 340 85 40 3.49 0.4695
WVFGRD96 22.0 155 85 -45 3.49 0.4648
WVFGRD96 23.0 155 85 -45 3.50 0.4595
WVFGRD96 24.0 150 80 -50 3.50 0.4525
WVFGRD96 25.0 150 80 -50 3.51 0.4462
WVFGRD96 26.0 150 80 -50 3.51 0.4384
WVFGRD96 27.0 150 80 -50 3.52 0.4299
WVFGRD96 28.0 150 80 -50 3.52 0.4208
WVFGRD96 29.0 155 80 -45 3.53 0.4134
The best solution is
WVFGRD96 2.0 150 65 -40 3.34 0.5671
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 +40 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.08 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