The ANSS event ID is usp000h6hu and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000h6hu/executive.
2010/01/23 22:01:27 43.511 -110.241 8.0 3.5 Wyoming
USGS/SLU Moment Tensor Solution
ENS 2010/01/23 22:01:27:0 43.51 -110.24 8.0 3.5 Wyoming
Stations used:
IW.FLWY IW.LOHW IW.MOOW IW.REDW IW.SNOW TA.F21A TA.G20A
TA.H19A TA.H20A TA.H21A TA.I17A TA.I19A TA.I20A TA.I22A
TA.I23A TA.J19A TA.J20A TA.K24A XV.BB3 XV.BH1A XV.BH1C
XV.BH2A XV.BH3A XV.BH3D XV.BH3E XV.BH4A XV.BHM5
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 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.66e+21 dyne-cm
Mw = 3.55
Z = 9 km
Plane Strike Dip Rake
NP1 347 69 -103
NP2 200 25 -60
Principal Axes:
Axis Value Plunge Azimuth
T 2.66e+21 22 87
N 0.00e+00 12 352
P -2.66e+21 64 236
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.55e+20
Mxy -1.37e+20
Mxz 6.26e+20
Myy 1.92e+21
Myz 1.80e+21
Mzz -1.77e+21
###------#####
#######--#############
#######------###############
######----------##############
######-------------###############
######--------------################
#####-----------------################
######------------------################
#####-------------------################
#####---------------------########## ###
#####---------------------########## T ###
#####----------------------######### ###
#####-------- -----------###############
####-------- P -----------##############
####-------- -----------##############
####----------------------############
###----------------------###########
###--------------------###########
##-------------------#########
###-----------------########
#----------------#####
------------##
Global CMT Convention Moment Tensor:
R T P
-1.77e+21 6.26e+20 -1.80e+21
6.26e+20 -1.55e+20 1.37e+20
-1.80e+21 1.37e+20 1.92e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100123220127/index.html
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STK = 200
DIP = 25
RAKE = -60
MW = 3.55
HS = 9.0
The NDK file is 20100123220127.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 0.10 n 3 br c 0.12 0.25 n 4 p 2The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 10 45 -75 3.12 0.2411
WVFGRD96 2.0 10 50 -75 3.33 0.4000
WVFGRD96 3.0 30 70 -50 3.37 0.3685
WVFGRD96 4.0 230 30 -10 3.45 0.4427
WVFGRD96 5.0 225 20 -30 3.48 0.5419
WVFGRD96 6.0 210 20 -50 3.49 0.6120
WVFGRD96 7.0 205 25 -55 3.50 0.6482
WVFGRD96 8.0 190 20 -75 3.55 0.6696
WVFGRD96 9.0 200 25 -60 3.55 0.6732
WVFGRD96 10.0 210 25 -45 3.54 0.6685
WVFGRD96 11.0 215 30 -40 3.54 0.6628
WVFGRD96 12.0 220 30 -30 3.53 0.6564
WVFGRD96 13.0 225 35 -20 3.54 0.6495
WVFGRD96 14.0 240 40 15 3.56 0.6432
WVFGRD96 15.0 240 40 15 3.56 0.6377
WVFGRD96 16.0 240 40 15 3.57 0.6309
WVFGRD96 17.0 240 40 15 3.58 0.6234
WVFGRD96 18.0 240 40 15 3.58 0.6149
WVFGRD96 19.0 240 40 15 3.59 0.6051
WVFGRD96 20.0 245 40 25 3.60 0.5950
WVFGRD96 21.0 245 35 20 3.61 0.5848
WVFGRD96 22.0 245 35 20 3.61 0.5743
WVFGRD96 23.0 245 35 20 3.62 0.5633
WVFGRD96 24.0 250 30 20 3.62 0.5527
WVFGRD96 25.0 255 30 30 3.64 0.5419
WVFGRD96 26.0 255 30 30 3.64 0.5314
WVFGRD96 27.0 255 30 30 3.65 0.5198
WVFGRD96 28.0 260 30 35 3.65 0.5089
WVFGRD96 29.0 260 30 35 3.66 0.4968
The best solution is
WVFGRD96 9.0 200 25 -60 3.55 0.6732
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 0.10 n 3 br c 0.12 0.25 n 4 p 2
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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