The ANSS event ID is nn00239974 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/nn00239974/executive.
2008/04/01 13:16:17 41.225 -114.830 9.5 4.1 Nevada
USGS/SLU Moment Tensor Solution
ENS 2008/04/01 13:16:17:0 41.22 -114.83 9.5 4.1 Nevada
Stations used:
IW.DCID1 IW.DLMT IW.IMW IW.LOHW IW.REDW IW.RRI2 IW.SNOW
IW.TPAW TA.D10A TA.D13A TA.D14A TA.D15A TA.D16A TA.E10A
TA.E11A TA.E14A TA.E15A TA.E16A TA.F08A TA.F09A TA.F10A
TA.F12A TA.F13A TA.F14A TA.F15A TA.F16A TA.G06A TA.G08A
TA.G09A TA.G10A TA.G11A TA.G13A TA.G14A TA.G15A TA.G16A
TA.G17A TA.H08A TA.H09A TA.H10A TA.H11A TA.H12A TA.H13A
TA.H14A TA.H15A TA.H16A TA.I07A TA.I08A TA.I09A TA.I10A
TA.I11A TA.I13A TA.I14A TA.I15A TA.I16A TA.I17A TA.I18A
TA.J06A TA.J07A TA.J08A TA.J09A TA.J10A TA.J11A TA.J14A
TA.J17A TA.J18A TA.K05A TA.K07A TA.K08A TA.K09A TA.K10A
TA.K11A TA.K12A TA.K13A TA.K14A TA.K15A TA.K16A TA.K17A
TA.K18A TA.K19A TA.K20A TA.L07A TA.L08A TA.L09A TA.L10A
TA.L11A TA.L12A TA.L13A TA.L14A TA.L15A TA.L16A TA.L17A
TA.L18A TA.L19A TA.L20A TA.M07A TA.M08A TA.M09A TA.M10A
TA.M11A TA.M12A TA.M14A TA.M15A TA.M17A TA.M18A TA.M19A
TA.M20A TA.N06A TA.N10A TA.N11A TA.N12A TA.N13A TA.N14A
TA.N15A TA.N16A TA.N17A TA.N18A TA.N19A TA.N20A TA.O10A
TA.O11A TA.O12A TA.O13A TA.O15A TA.O16A TA.O17A TA.O18A
TA.O19A TA.O20A TA.P10A TA.P11A TA.P12A TA.P13A TA.P14A
TA.P15A TA.P16A TA.P17A TA.P19A TA.P20A TA.Q10A TA.Q11A
TA.Q12A TA.Q13A TA.Q14A TA.Q15A TA.Q16A TA.Q18A TA.Q19A
TA.Q20A TA.Q21A TA.R10A TA.R11A TA.R12A TA.R13A TA.R14A
TA.R15A TA.R16A TA.R17A TA.R18A TA.R19A TA.S10A TA.S11A
TA.S12A TA.S13A TA.S14A TA.S17A TA.S18A TA.S19A TA.T11A
TA.T12A TA.T13A TA.T14A TA.T15A TA.T16A TA.T17A TA.T18A
TA.U10A TA.U13A TA.U14A TA.U15A TA.U16A TA.U17A TA.V11A
TA.V12A TA.V14A TA.V15A TA.W12A TA.W13A US.AHID US.BMO
US.BW06 US.DUG US.ELK US.HLID US.HWUT US.WVOR UU.CCUT
UU.CTU UU.MPU UU.NLU UU.NOQ UU.SPU UU.SRU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.91e+22 dyne-cm
Mw = 4.12
Z = 12 km
Plane Strike Dip Rake
NP1 185 79 -139
NP2 85 50 -15
Principal Axes:
Axis Value Plunge Azimuth
T 1.91e+22 18 309
N 0.00e+00 48 198
P -1.91e+22 36 53
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.37e+21
Mxy -1.43e+22
Mxz -1.88e+21
Myy 2.49e+21
Myz -1.17e+22
Mzz -4.86e+21
########------
###########-----------
##############--------------
##############----------------
## ###########------------------
### T ##########----------- ------
#### ##########----------- P -------
##################----------- --------
##################----------------------
##################------------------------
##################-----------------------#
##################----------------------##
-#################--------------------####
--###############------------------#####
----#############----------------#######
-------#########------------##########
---------------#####################
--------------####################
------------##################
-----------#################
---------#############
-----#########
Global CMT Convention Moment Tensor:
R T P
-4.86e+21 -1.88e+21 1.17e+22
-1.88e+21 2.37e+21 1.43e+22
1.17e+22 1.43e+22 2.49e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080401131617/index.html
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STK = 85
DIP = 50
RAKE = -15
MW = 4.12
HS = 12.0
The NDK file is 20080401131617.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:
hp c 0.02 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 215 45 -90 3.69 0.2912
WVFGRD96 1.0 250 55 -40 3.68 0.2575
WVFGRD96 2.0 225 45 -75 3.87 0.3401
WVFGRD96 3.0 260 55 -20 3.85 0.3402
WVFGRD96 4.0 95 45 15 3.91 0.3877
WVFGRD96 5.0 95 45 15 3.94 0.4329
WVFGRD96 6.0 95 50 15 3.96 0.4718
WVFGRD96 7.0 90 55 15 3.99 0.5047
WVFGRD96 8.0 80 40 -25 4.06 0.5409
WVFGRD96 9.0 85 45 -15 4.07 0.5616
WVFGRD96 10.0 85 50 -15 4.09 0.5753
WVFGRD96 11.0 85 50 -15 4.11 0.5830
WVFGRD96 12.0 85 50 -15 4.12 0.5842
WVFGRD96 14.0 85 55 -15 4.15 0.5649
WVFGRD96 15.0 85 55 -15 4.16 0.5542
WVFGRD96 16.0 85 55 -15 4.17 0.5402
WVFGRD96 17.0 85 55 -15 4.18 0.5238
WVFGRD96 18.0 85 55 -15 4.19 0.5059
WVFGRD96 19.0 85 55 -15 4.20 0.4866
WVFGRD96 20.0 85 55 -15 4.20 0.4667
WVFGRD96 21.0 85 55 -15 4.21 0.4474
WVFGRD96 22.0 85 55 -15 4.22 0.4274
WVFGRD96 23.0 85 55 -10 4.22 0.4077
WVFGRD96 24.0 85 55 -10 4.23 0.3887
WVFGRD96 25.0 85 55 -10 4.23 0.3700
WVFGRD96 26.0 85 55 -10 4.23 0.3519
WVFGRD96 27.0 85 55 -10 4.24 0.3346
WVFGRD96 28.0 85 55 -10 4.24 0.3183
WVFGRD96 29.0 85 55 -10 4.24 0.3031
WVFGRD96 13.0 85 55 -15 4.14 0.5811
WVFGRD96 8.0 80 40 -25 4.06 0.5410
WVFGRD96 9.0 85 45 -15 4.07 0.5616
WVFGRD96 10.0 85 50 -15 4.09 0.5753
WVFGRD96 11.0 85 50 -15 4.11 0.5830
WVFGRD96 12.0 85 50 -15 4.12 0.5842
WVFGRD96 13.0 85 55 -15 4.14 0.5811
WVFGRD96 8.0 80 40 -25 4.06 0.5410
WVFGRD96 9.0 85 45 -15 4.07 0.5616
WVFGRD96 10.0 85 50 -15 4.09 0.5753
WVFGRD96 11.0 85 50 -15 4.11 0.5830
WVFGRD96 12.0 85 50 -15 4.12 0.5842
WVFGRD96 13.0 85 55 -15 4.14 0.5811
The best solution is
WVFGRD96 12.0 85 50 -15 4.12 0.5842
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
hp c 0.02 n 3 lp c 0.10 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 following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES
STK= 344.64
DIP= 67.48
RAKE= 135.90
OR
STK= 94.99
DIP= 50.00
RAKE= 30.00
DEPTH = 9.0 km
Mw = 4.17
Best Fit 0.9105 - P-T axis plot gives solutions with FIT greater than FIT90
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Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave radiation pattern search program srfgrd96.
Digital data were collected, instrument response removed and traces converted
to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh- and Love-wave spectral amplitudes, respectively.
These were input to the search program which examined all depths between 1 and 25 km
and all possible mechanisms.
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| Pressure-tension axis trends. Since the surface-wave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and T-axes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here. |
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| Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled. |
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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