The ANSS event ID is uu50357770 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uu50357770/executive.
2008/03/25 11:59:38 44.692 -110.017 3.9 4.18 Wyoming
USGS/SLU Moment Tensor Solution
ENS 2008/03/25 11:59:38:0 44.69 -110.02 3.9 4.2 Wyoming
Stations used:
IW.DCID1 IW.DLMT IW.IMW IW.LOHW IW.REDW IW.RRI2 IW.SNOW
IW.TPAW TA.A11A TA.A12A TA.A14A TA.A15A TA.A16A TA.A17A
TA.B10A TA.B11A TA.B12A TA.B15A TA.B16A TA.B17A TA.B18A
TA.C10A TA.C12B TA.C13A TA.C14A TA.C15A TA.C16A TA.C17A
TA.D10A TA.D11A TA.D12A TA.D13A TA.D14A TA.D15A TA.D16A
TA.D17A TA.D18A TA.E09A TA.E10A TA.E11A TA.E13A TA.E14A
TA.E15A TA.E16A TA.E17A TA.E18A TA.F08A TA.F09A TA.F10A
TA.F11A TA.F13A TA.F14A TA.F15A TA.F16A TA.F17A TA.F18A
TA.G09A TA.G10A TA.G11A TA.G13A TA.G14A TA.G15A TA.G16A
TA.G17A TA.G18A TA.H08A TA.H09A TA.H11A TA.H12A TA.H13A
TA.H15A TA.H16A TA.I08A TA.I09A TA.I11A TA.I12A TA.I13A
TA.I15A TA.I16A TA.I18A TA.J10A TA.J12A TA.J13A TA.J17A
TA.J18A TA.K12A TA.K13A TA.K14A TA.K15A TA.K16A TA.K17A
TA.K18A TA.K19A TA.K20A TA.L14A TA.L15A TA.L16A TA.L19A
TA.L20A TA.L21A TA.M12A TA.M13A TA.M14A TA.M15A TA.M16A
TA.M17A TA.M18A TA.M20A TA.M21A TA.M22A TA.N11A TA.N12A
TA.N13A TA.N14A TA.N15A TA.N16A TA.N17A TA.N20A TA.N22A
TA.O12A TA.O13A TA.O16A TA.O17A TA.O18A TA.P13A TA.P15A
TA.P16A TA.P18A US.AHID US.BOZ US.BW06 US.EGMT US.HLID
US.LAO US.MSO US.RLMT UU.BGU UU.SPU
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 0.07 n 3
Best Fitting Double Couple
Mo = 2.60e+22 dyne-cm
Mw = 4.21
Z = 12 km
Plane Strike Dip Rake
NP1 111 64 -146
NP2 5 60 -30
Principal Axes:
Axis Value Plunge Azimuth
T 2.60e+22 3 237
N 0.00e+00 49 144
P -2.60e+22 41 330
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.30e+21
Mxy 1.82e+22
Mxz -1.18e+22
Myy 1.46e+22
Myz 5.49e+21
Mzz -1.13e+22
----------####
---------------#######
-------------------#########
---------------------#########
--------- ------------##########
---------- P ------------###########
----------- ------------############
#---------------------------############
##--------------------------############
#####------------------------#############
#######----------------------#############
#########--------------------#############
############----------------##############
##############-------------#############
###################--------#############
#################################--
T #####################-------------
#####################------------
###################-----------
#################-----------
############----------
#######-------
Global CMT Convention Moment Tensor:
R T P
-1.13e+22 -1.18e+22 -5.49e+21
-1.18e+22 -3.30e+21 -1.82e+22
-5.49e+21 -1.82e+22 1.46e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20080325115938/index.html
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STK = 5
DIP = 60
RAKE = -30
MW = 4.21
HS = 12.0
The NDK file is 20080325115938.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 0.07 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 225 35 65 3.92 0.3116
WVFGRD96 1.0 220 45 60 3.94 0.3215
WVFGRD96 2.0 220 45 60 4.04 0.3862
WVFGRD96 3.0 25 60 40 4.06 0.3937
WVFGRD96 4.0 200 50 25 4.08 0.3906
WVFGRD96 5.0 10 55 -15 4.08 0.4023
WVFGRD96 6.0 10 55 -15 4.09 0.4164
WVFGRD96 7.0 5 60 -25 4.12 0.4323
WVFGRD96 8.0 5 55 -25 4.16 0.4367
WVFGRD96 9.0 5 60 -30 4.18 0.4484
WVFGRD96 10.0 5 60 -30 4.19 0.4571
WVFGRD96 11.0 5 60 -30 4.20 0.4616
WVFGRD96 12.0 5 60 -30 4.21 0.4624
WVFGRD96 13.0 5 60 -30 4.22 0.4602
WVFGRD96 14.0 10 65 -30 4.23 0.4559
WVFGRD96 15.0 10 65 -30 4.24 0.4505
WVFGRD96 16.0 10 65 -30 4.25 0.4436
WVFGRD96 17.0 10 70 -30 4.26 0.4357
WVFGRD96 18.0 10 70 -30 4.26 0.4274
WVFGRD96 19.0 10 70 -30 4.27 0.4186
WVFGRD96 20.0 10 70 -30 4.28 0.4090
WVFGRD96 21.0 10 70 -30 4.29 0.3983
WVFGRD96 22.0 10 70 -30 4.29 0.3881
WVFGRD96 23.0 10 70 -30 4.30 0.3777
WVFGRD96 24.0 10 70 -30 4.30 0.3675
WVFGRD96 25.0 10 70 -30 4.31 0.3572
WVFGRD96 26.0 10 75 -35 4.32 0.3473
WVFGRD96 27.0 10 75 -35 4.32 0.3378
WVFGRD96 28.0 190 60 -25 4.31 0.3295
WVFGRD96 29.0 190 60 -25 4.32 0.3239
The best solution is
WVFGRD96 12.0 5 60 -30 4.21 0.4624
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 0.07 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