The ANSS event ID is nn00833903 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00833903/executive.
2022/02/15 21:16:24 38.181 -117.783 4.1 4.7 Nevada
USGS/SLU Moment Tensor Solution
ENS 2022/02/15 21:16:24:0 38.18 -117.78 4.1 4.7 Nevada
Stations used:
BK.BUCR BK.DANT BK.EAGL BK.HATC BK.HELL BK.MZTA BK.SUTB
BK.WINE CI.BFS CI.CCC CI.CLC CI.CWC CI.DTP CI.FUR CI.GRA
CI.GSC CI.HAR CI.LRL CI.LUC2 CI.MTP CI.OSI CI.RAG CI.SHO
CI.TEH CI.TIN CI.TPO CI.VES IM.NV31 LB.BMN LB.TPH NC.AFD
NC.BBGB NC.LDH NN.BEK NN.DIX NN.GMN NN.GWY NN.KVN NN.LHV
NN.MPK NN.PAH NN.PIO NN.PNT NN.PYM2 NN.REDF NN.SHP NN.WAK
NN.WDEM NN.YER SN.HEL US.ELK US.TPNV UU.FOR1 UU.LCMT
UU.PSUT UU.SWUT UU.SZCU UU.VRUT
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.08 n 3
Best Fitting Double Couple
Mo = 2.43e+22 dyne-cm
Mw = 4.19
Z = 10 km
Plane Strike Dip Rake
NP1 260 90 30
NP2 170 60 180
Principal Axes:
Axis Value Plunge Azimuth
T 2.43e+22 21 129
N 0.00e+00 60 260
P -2.43e+22 21 31
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.19e+21
Mxy -1.97e+22
Mxz -1.19e+22
Myy 7.19e+21
Myz 2.11e+21
Mzz -1.06e+15
###-----------
######----------------
########------------- ----
########-------------- P -----
##########-------------- -------
##########--------------------------
###########---------------------------
############----------------------------
############----------------------------
#############------------------------#####
#############-------------################
#############---##########################
#####---------############################
-------------###########################
--------------##########################
-------------################# #####
-------------################ T ####
-------------############### ###
------------##################
------------################
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Global CMT Convention Moment Tensor:
R T P
-1.06e+15 -1.19e+22 -2.11e+21
-1.19e+22 -7.19e+21 1.97e+22
-2.11e+21 1.97e+22 7.19e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20220215211624/index.html
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STK = 260
DIP = 90
RAKE = 30
MW = 4.19
HS = 10.0
The NDK file is 20220215211624.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 -40 o DIST/3.3 +50 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 80 75 -20 3.81 0.3962
WVFGRD96 2.0 260 70 -20 3.93 0.4983
WVFGRD96 3.0 260 85 40 4.03 0.5453
WVFGRD96 4.0 260 85 40 4.06 0.5960
WVFGRD96 5.0 260 85 35 4.08 0.6348
WVFGRD96 6.0 260 90 35 4.10 0.6651
WVFGRD96 7.0 75 85 -30 4.12 0.6894
WVFGRD96 8.0 75 85 -35 4.17 0.7047
WVFGRD96 9.0 260 90 30 4.18 0.7066
WVFGRD96 10.0 260 90 30 4.19 0.7080
WVFGRD96 11.0 260 90 30 4.21 0.7034
WVFGRD96 12.0 260 90 30 4.22 0.6939
WVFGRD96 13.0 80 90 -25 4.23 0.6808
WVFGRD96 14.0 80 90 -25 4.24 0.6666
WVFGRD96 15.0 80 90 -25 4.25 0.6508
WVFGRD96 16.0 80 90 -25 4.26 0.6337
WVFGRD96 17.0 260 85 25 4.26 0.6161
WVFGRD96 18.0 260 90 25 4.27 0.5989
WVFGRD96 19.0 80 90 -25 4.28 0.5817
WVFGRD96 20.0 80 90 -25 4.28 0.5650
WVFGRD96 21.0 80 90 -25 4.29 0.5482
WVFGRD96 22.0 80 90 -25 4.30 0.5318
WVFGRD96 23.0 260 85 25 4.30 0.5164
WVFGRD96 24.0 80 90 -25 4.31 0.5016
WVFGRD96 25.0 80 90 -25 4.31 0.4871
WVFGRD96 26.0 80 90 -25 4.32 0.4727
WVFGRD96 27.0 80 90 -25 4.32 0.4583
WVFGRD96 28.0 80 90 -25 4.33 0.4442
WVFGRD96 29.0 80 90 -25 4.33 0.4307
The best solution is
WVFGRD96 10.0 260 90 30 4.19 0.7080
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 0.03 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 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