The ANSS event ID is nn00911076 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00911076/executive.
2026/02/23 03:57:18 37.111 -115.306 8.5 3.7 Nevada
USGS/SLU Moment Tensor Solution
ENS 2026/02/23 03:57:18.0 37.11 -115.31 8.5 3.7 Nevada
Stations used:
AE.BABIT AE.DOVA AE.LOGN AE.PRCT AE.U15A AE.W13A AE.Y14B
BK.HELL BK.MMI BK.OVRO BK.PATT CI.BC3 CI.BEL CI.BFS CI.BLY
CI.CCC CI.CFT CI.CKP CI.CWC CI.DAN CI.DSC CI.DTP CI.FUR
CI.GRA CI.GSC CI.HAR CI.IRM CI.ISA CI.LRL CI.LUC2 CI.MPM
CI.MTP CI.NEE2 CI.OSI CI.PALA CI.PDM CI.RAG CI.RMM CI.RPK
CI.SBB2 CI.SHO CI.SLA CI.TEH CI.TPO CI.VES CI.WRC2 LB.BMN
NN.BFC NN.DIX NN.GMN NN.GWY NN.KVN NN.LHV NN.PRN NN.Q09A
NN.QSM NN.R11B NN.S11A NN.SHP NN.WAK NN.YER US.DUG US.ELK
US.TPNV US.WUAZ UU.CCUT UU.CVRU UU.ECUT UU.EKU UU.FOR1
UU.FSU UU.KNB UU.LCMT UU.NLU UU.SZCU UU.TMU UU.VRUT UU.ZNPU
Filtering commands used:
cut o DIST/3.3 -20 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 5.13e+21 dyne-cm
Mw = 3.74
Z = 4 km
Plane Strike Dip Rake
NP1 147 81 160
NP2 240 70 10
Principal Axes:
Axis Value Plunge Azimuth
T 5.13e+21 21 102
N 0.00e+00 68 303
P -5.13e+21 7 195
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.54e+21
Mxy -2.13e+21
Mxz 2.73e+20
Myy 3.97e+21
Myz 1.84e+21
Mzz 5.72e+20
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#########----------------------#####
###########--------------#############
#############--------###################
##############----######################
##########################################
#############-----########################
###########--------################# ###
#########-----------################ T ###
######--------------############### ##
####------------------##################
##--------------------################
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----- --------------
- P ----------
Global CMT Convention Moment Tensor:
R T P
5.72e+20 2.73e+20 -1.84e+21
2.73e+20 -4.54e+21 2.13e+21
-1.84e+21 2.13e+21 3.97e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260223035718/index.html
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STK = 240
DIP = 70
RAKE = 10
MW = 3.74
HS = 4.0
The NDK file is 20260223035718.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 -20 o DIST/3.3 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 240 85 5 3.61 0.5399
WVFGRD96 2.0 240 80 5 3.68 0.6286
WVFGRD96 3.0 240 80 10 3.71 0.6436
WVFGRD96 4.0 240 70 10 3.74 0.6459
WVFGRD96 5.0 240 60 10 3.78 0.6455
WVFGRD96 6.0 235 60 -5 3.79 0.6444
WVFGRD96 7.0 235 60 -5 3.80 0.6435
WVFGRD96 8.0 55 85 -45 3.87 0.6397
WVFGRD96 9.0 240 85 45 3.87 0.6405
WVFGRD96 10.0 240 85 45 3.88 0.6386
WVFGRD96 11.0 240 85 40 3.88 0.6372
WVFGRD96 12.0 240 85 40 3.88 0.6347
WVFGRD96 13.0 240 85 35 3.88 0.6314
WVFGRD96 14.0 240 85 35 3.89 0.6285
WVFGRD96 15.0 240 85 35 3.90 0.6250
WVFGRD96 16.0 240 85 35 3.91 0.6207
WVFGRD96 17.0 240 85 30 3.91 0.6155
WVFGRD96 18.0 240 85 30 3.92 0.6103
WVFGRD96 19.0 240 85 30 3.92 0.6044
WVFGRD96 20.0 240 85 30 3.93 0.5980
WVFGRD96 21.0 240 85 30 3.94 0.5911
WVFGRD96 22.0 240 85 30 3.95 0.5837
WVFGRD96 23.0 240 80 25 3.95 0.5759
WVFGRD96 24.0 240 80 25 3.96 0.5681
WVFGRD96 25.0 240 80 25 3.96 0.5598
WVFGRD96 26.0 240 80 25 3.97 0.5512
WVFGRD96 27.0 240 80 25 3.98 0.5428
WVFGRD96 28.0 240 80 20 3.98 0.5344
WVFGRD96 29.0 240 80 20 3.99 0.5259
The best solution is
WVFGRD96 4.0 240 70 10 3.74 0.6459
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 +50 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.06 n 3 br c 0.12 0.25 n 4 p 2
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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