The ANSS event ID is uu60272922 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uu60272922/executive.
2018/02/28 14:11:47 37.670 -112.531 11.4 3.64 Utah
USGS/SLU Moment Tensor Solution
ENS 2018/02/28 14:11:47:0 37.67 -112.53 11.4 3.6 Utah
Stations used:
AE.BABIT AE.PRCT AE.U15A AE.X16A AE.X18A AE.Y14A CI.LDF
LB.MVU LB.TPH NN.GMN NN.MZPB NN.PIO NN.Q09A NN.QSM NN.S11A
NN.SHP NN.WLDB SN.HEL TA.R11B TA.W18A US.DUG US.ELK US.MVCO
US.WUAZ UU.BGU UU.BRPU UU.BSUT UU.CCUT UU.CVRU UU.HMU
UU.KNB UU.LCMT UU.MPU UU.MTPU UU.NLU UU.PNSU UU.PSUT
UU.RDMU UU.SPU UU.SRU UU.SWUT UU.SZCU UU.TCRU
Filtering commands used:
cut o DIST/3.3 -30 o DIST/3.3 +40
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 = 3.63e+21 dyne-cm
Mw = 3.64
Z = 15 km
Plane Strike Dip Rake
NP1 146 64 -106
NP2 0 30 -60
Principal Axes:
Axis Value Plunge Azimuth
T 3.63e+21 18 248
N 0.00e+00 14 153
P -3.63e+21 67 27
Moment Tensor: (dyne-cm)
Component Value
Mxx 0.00e+00
Mxy 9.08e+20
Mxz -1.57e+21
Myy 2.72e+21
Myz -1.57e+21
Mzz -2.72e+21
----------####
-----------------#####
##--------------------######
###----------------------#####
#####-----------------------######
#######-----------------------######
########------------------------######
##########----------- ----------######
##########----------- P ----------######
############---------- -----------######
#############-----------------------######
##############----------------------######
###############---------------------######
## ##########-------------------######
## T ############-----------------######
# #############---------------######
##################------------######
###################---------######
###################------#####
#####################-######
#################-----
##########----
Global CMT Convention Moment Tensor:
R T P
-2.72e+21 -1.57e+21 1.57e+21
-1.57e+21 0.00e+00 -9.08e+20
1.57e+21 -9.08e+20 2.72e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20180228141147/index.html
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STK = 0
DIP = 30
RAKE = -60
MW = 3.64
HS = 15.0
The NDK file is 20180228141147.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 +40 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 1.0 250 90 0 3.34 0.3039
WVFGRD96 2.0 140 45 -90 3.43 0.3583
WVFGRD96 3.0 70 90 -5 3.49 0.3256
WVFGRD96 4.0 45 25 -5 3.50 0.3089
WVFGRD96 5.0 40 20 -10 3.53 0.4086
WVFGRD96 6.0 35 20 -15 3.53 0.4737
WVFGRD96 7.0 30 20 -20 3.52 0.5085
WVFGRD96 8.0 25 20 -25 3.60 0.5257
WVFGRD96 9.0 10 20 -45 3.60 0.5421
WVFGRD96 10.0 5 25 -50 3.61 0.5545
WVFGRD96 11.0 0 25 -55 3.61 0.5650
WVFGRD96 12.0 0 30 -60 3.63 0.5730
WVFGRD96 13.0 -5 30 -65 3.63 0.5789
WVFGRD96 14.0 0 30 -60 3.63 0.5819
WVFGRD96 15.0 0 30 -60 3.64 0.5827
WVFGRD96 16.0 5 35 -55 3.65 0.5821
WVFGRD96 17.0 0 35 -60 3.66 0.5802
WVFGRD96 18.0 0 35 -60 3.67 0.5769
WVFGRD96 19.0 360 35 -60 3.67 0.5725
WVFGRD96 20.0 360 35 -60 3.68 0.5666
WVFGRD96 21.0 355 35 -60 3.70 0.5591
WVFGRD96 22.0 355 35 -60 3.70 0.5501
WVFGRD96 23.0 355 35 -60 3.71 0.5392
WVFGRD96 24.0 355 35 -60 3.72 0.5265
WVFGRD96 25.0 355 35 -60 3.73 0.5120
WVFGRD96 26.0 355 35 -60 3.73 0.4959
WVFGRD96 27.0 355 35 -60 3.74 0.4781
WVFGRD96 28.0 355 35 -60 3.74 0.4600
WVFGRD96 29.0 355 35 -60 3.75 0.4412
The best solution is
WVFGRD96 15.0 0 30 -60 3.64 0.5827
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 +40 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