The ANSS event ID is uu50338750 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uu50338750/executive.
2007/06/11 01:03:46 37.485 -114.004 4.0 3.93 Utah
USGS/SLU Moment Tensor Solution
ENS 2007/06/11 01:03:46:0 37.49 -114.00 4.0 3.9 Utah
Stations used:
AZ.KNW CI.BC3 CI.CHF CI.CWC CI.FUR CI.GLA CI.GMR CI.GRA
CI.GSC CI.MLAC CI.MPM CI.MWC CI.PASC CI.RCT CI.SHO CI.SLA
CI.TIN CI.TUQ CI.VES II.PFO IM.NV31 LB.TPH TA.113A TA.HELL
TA.L11A TA.L12A TA.L13A TA.M11A TA.M14A TA.M15A TA.N08A
TA.N12A TA.N13A TA.N14A TA.O07A TA.O08A TA.O09A TA.O10A
TA.O11A TA.O12A TA.O13A TA.P10A TA.P12A TA.P13A TA.P15A
TA.P16A TA.Q08A TA.Q12A TA.Q13A TA.Q16A TA.R06C TA.R08A
TA.R09A TA.R10A TA.R11A TA.R13A TA.R14A TA.R15A TA.S06C
TA.S08C TA.S09A TA.S10A TA.S11A TA.S12A TA.S14A TA.S15A
TA.T06C TA.T11A TA.T13A TA.T15A TA.T16A TA.U10A TA.U11A
TA.U13A TA.U14A TA.U15A TA.U17A TA.V14A TA.V15A TA.W12A
TA.W13A TA.W14A TA.W16A TA.W18A TA.W19A TA.X13A TA.X14A
TA.Y13A TA.Y14A TA.Y15A TA.Y16A TA.Y18A TA.Z14A US.DUG
US.MVCO US.TPNV UU.BGU UU.CCUT UU.SRU XE.SNP63 XE.SNP75
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 0.06 n 3
Best Fitting Double Couple
Mo = 5.13e+21 dyne-cm
Mw = 3.74
Z = 9 km
Plane Strike Dip Rake
NP1 163 85 155
NP2 255 65 5
Principal Axes:
Axis Value Plunge Azimuth
T 5.13e+21 21 116
N 0.00e+00 65 333
P -5.13e+21 14 212
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.63e+21
Mxy -3.92e+21
Mxz 2.81e+20
Myy 2.29e+21
Myz 2.16e+21
Mzz 3.42e+20
#-------------
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#################---#################---
##############---#######################
###########--------#######################
#######-------------######################
#####---------------######################
###------------------#####################
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---------------------############ ####
---------------------########### T ###
--------------------########### ##
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---- ------------###########
--- P ------------##########
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Global CMT Convention Moment Tensor:
R T P
3.42e+20 2.81e+20 -2.16e+21
2.81e+20 -2.63e+21 3.92e+21
-2.16e+21 3.92e+21 2.29e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20070611010346/index.html
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STK = 255
DIP = 65
RAKE = 5
MW = 3.74
HS = 9.0
The NDK file is 20070611010346.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 0.06 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 250 90 0 3.43 0.4608
WVFGRD96 2.0 250 70 -15 3.55 0.5827
WVFGRD96 3.0 250 60 -10 3.61 0.6376
WVFGRD96 4.0 250 60 -10 3.64 0.6796
WVFGRD96 5.0 250 65 -10 3.65 0.7092
WVFGRD96 6.0 255 65 0 3.67 0.7312
WVFGRD96 7.0 255 70 0 3.69 0.7474
WVFGRD96 8.0 255 65 5 3.72 0.7593
WVFGRD96 9.0 255 65 5 3.74 0.7637
WVFGRD96 10.0 255 65 5 3.75 0.7633
WVFGRD96 11.0 255 70 5 3.76 0.7605
WVFGRD96 12.0 255 70 5 3.77 0.7557
WVFGRD96 13.0 255 70 5 3.78 0.7486
WVFGRD96 14.0 255 70 5 3.79 0.7398
WVFGRD96 15.0 255 70 5 3.80 0.7298
WVFGRD96 16.0 255 70 5 3.80 0.7188
WVFGRD96 17.0 255 70 5 3.81 0.7072
WVFGRD96 18.0 255 70 5 3.82 0.6955
WVFGRD96 19.0 255 75 5 3.82 0.6836
WVFGRD96 20.0 255 75 10 3.83 0.6721
WVFGRD96 21.0 255 75 10 3.84 0.6603
WVFGRD96 22.0 255 75 10 3.84 0.6484
WVFGRD96 23.0 255 75 10 3.85 0.6365
WVFGRD96 24.0 255 75 10 3.86 0.6247
WVFGRD96 25.0 255 75 10 3.86 0.6131
WVFGRD96 26.0 255 75 10 3.87 0.6015
WVFGRD96 27.0 255 75 5 3.87 0.5903
WVFGRD96 28.0 255 75 5 3.88 0.5793
WVFGRD96 29.0 255 75 5 3.88 0.5686
The best solution is
WVFGRD96 9.0 255 65 5 3.74 0.7637
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 0.06 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= 157.87
DIP= 85.47
RAKE= 154.92
OR
STK= 249.98
DIP= 65.00
RAKE= 5.00
DEPTH = 9.0 km
Mw = 3.81
Best Fit 0.8809 - 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