The ANSS event ID is usp000hhkt and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000hhkt/executive.
2010/08/05 14:59:28 43.645 -110.383 5.0 4.2 Wyoming
USGS/SLU Moment Tensor Solution
ENS 2010/08/05 14:59:28:0 43.65 -110.38 5.0 4.2 Wyoming
Stations used:
IW.DLMT IW.FLWY IW.FXWY IW.IMW IW.MFID IW.MOOW IW.PHWY
IW.REDW IW.SNOW IW.TPAW TA.E21A TA.E22A TA.F20A TA.F21A
TA.F22A TA.G20A TA.G23A TA.H17A TA.H19A TA.H20A TA.H24A
TA.H25A TA.I19A TA.I22A TA.I24A TA.J19A TA.J20A TA.J22A
TA.K23A TA.K24A TA.N23A US.AHID US.BOZ US.DUG US.HLID
US.HWUT US.LAO US.LKWY US.MSO US.RLMT UU.BGU UU.HVU UU.MPU
UU.NLU UU.NOQ UU.RDMU UU.TCU XV.BB3 XV.BH1A XV.BH1B XV.BH1D
XV.BH1E XV.BH1H XV.BH2A XV.BH2C XV.BH2G XV.BH3A XV.BH4A
XV.BH4C XV.BH4G XV.BHM3 XV.BHM4 XV.BHM5 XV.BHM6 XV.BHM7
YX.A02 YX.A03 YX.B02 YX.B04 YX.B12 YX.B15 YX.B17 YX.B18
YX.C14 YX.D02 Z2.BRWY Z2.CFWY Z2.CSR Z2.EHMT Z2.SNFF
Filtering commands used:
cut o DIST/3.3 -30 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 = 2.51e+22 dyne-cm
Mw = 4.20
Z = 9 km
Plane Strike Dip Rake
NP1 40 80 -30
NP2 136 61 -168
Principal Axes:
Axis Value Plunge Azimuth
T 2.51e+22 13 91
N 0.00e+00 59 203
P -2.51e+22 28 354
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.93e+22
Mxy 1.60e+21
Mxz -1.05e+22
Myy 2.36e+22
Myz 6.61e+21
Mzz -4.30e+21
--------------
-------- -----------
----------- P -------------#
------------ ------------###
###--------------------------#####
####-------------------------#######
#####-----------------------##########
#######---------------------############
########-------------------#############
##########----------------################
###########--------------############# #
############------------############## T #
#############---------################ #
##############-----#####################
################--######################
###############--#####################
############-------#################
#########------------#############
#####------------------#######
#---------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-4.30e+21 -1.05e+22 -6.61e+21
-1.05e+22 -1.93e+22 -1.60e+21
-6.61e+21 -1.60e+21 2.36e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100805145928/index.html
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STK = 40
DIP = 80
RAKE = -30
MW = 4.20
HS = 9.0
The NDK file is 20100805145928.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 -30 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 45 80 5 3.87 0.3829
WVFGRD96 2.0 45 75 10 3.98 0.4707
WVFGRD96 3.0 45 85 5 4.01 0.4992
WVFGRD96 4.0 40 80 -25 4.08 0.5226
WVFGRD96 5.0 40 80 -30 4.11 0.5442
WVFGRD96 6.0 40 80 -30 4.13 0.5604
WVFGRD96 7.0 40 80 -25 4.15 0.5716
WVFGRD96 8.0 40 80 -30 4.19 0.5797
WVFGRD96 9.0 40 80 -30 4.20 0.5807
WVFGRD96 10.0 40 80 -30 4.21 0.5772
WVFGRD96 11.0 40 80 -25 4.22 0.5707
WVFGRD96 12.0 40 80 -25 4.23 0.5622
WVFGRD96 13.0 40 80 -25 4.24 0.5523
WVFGRD96 14.0 40 75 -25 4.25 0.5428
WVFGRD96 15.0 40 75 -25 4.25 0.5348
WVFGRD96 16.0 40 75 -20 4.26 0.5254
WVFGRD96 17.0 40 80 -20 4.27 0.5161
WVFGRD96 18.0 40 80 -20 4.27 0.5061
WVFGRD96 19.0 40 80 -20 4.28 0.4953
WVFGRD96 20.0 40 80 -20 4.28 0.4843
WVFGRD96 21.0 40 80 -20 4.29 0.4729
WVFGRD96 22.0 40 80 -20 4.29 0.4615
WVFGRD96 23.0 40 80 -20 4.30 0.4504
WVFGRD96 24.0 45 90 -25 4.29 0.4393
WVFGRD96 25.0 45 90 -25 4.30 0.4297
WVFGRD96 26.0 45 90 -25 4.30 0.4202
WVFGRD96 27.0 45 90 -25 4.30 0.4112
WVFGRD96 28.0 225 85 30 4.31 0.4038
WVFGRD96 29.0 225 85 30 4.31 0.3966
The best solution is
WVFGRD96 9.0 40 80 -30 4.20 0.5807
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 -30 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 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