The ANSS event ID is uw61504942 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uw61504942/executive.
2018/11/19 11:09:13 47.698 -123.552 39.3 4.07 Washington
USGS/SLU Moment Tensor Solution
ENS 2018/11/19 11:09:13:0 47.70 -123.55 39.3 4.1 Washington
Stations used:
CC.JRO CN.CBB CN.CLRS CN.OZB CN.PGC UO.MARQ US.NLWA UW.CCRK
UW.FORK UW.GNW UW.LON UW.OMAK UW.STOR
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 = 1.17e+22 dyne-cm
Mw = 3.98
Z = 40 km
Plane Strike Dip Rake
NP1 342 50 -113
NP2 195 45 -65
Principal Axes:
Axis Value Plunge Azimuth
T 1.17e+22 3 88
N 0.00e+00 17 357
P -1.17e+22 72 186
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.04e+21
Mxy 3.79e+20
Mxz 3.39e+21
Myy 1.17e+22
Myz 9.09e+20
Mzz -1.06e+22
##--------####
######################
###########----#############
##########--------############
##########------------############
##########--------------############
##########----------------############
##########------------------############
##########-------------------###########
##########---------------------#########
##########---------------------######### T
#########-----------------------########
#########---------- ----------##########
########---------- P ----------#########
########---------- ----------#########
########----------------------########
#######----------------------#######
######---------------------#######
#####--------------------#####
#####------------------#####
###----------------###
#-------------
Global CMT Convention Moment Tensor:
R T P
-1.06e+22 3.39e+21 -9.09e+20
3.39e+21 -1.04e+21 -3.79e+20
-9.09e+20 -3.79e+20 1.17e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20181119110913/index.html
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STK = 195
DIP = 45
RAKE = -65
MW = 3.98
HS = 40.0
The NDK file is 20181119110913.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 2.0 0 45 90 3.40 0.4815
WVFGRD96 4.0 335 40 55 3.45 0.3550
WVFGRD96 6.0 120 25 15 3.48 0.4781
WVFGRD96 8.0 130 20 30 3.55 0.5203
WVFGRD96 10.0 125 25 25 3.54 0.5348
WVFGRD96 12.0 125 25 20 3.54 0.5347
WVFGRD96 14.0 125 30 20 3.55 0.5322
WVFGRD96 16.0 130 30 25 3.57 0.5286
WVFGRD96 18.0 130 30 30 3.58 0.5213
WVFGRD96 20.0 135 30 35 3.60 0.5120
WVFGRD96 22.0 140 30 40 3.63 0.5013
WVFGRD96 24.0 15 60 -65 3.66 0.5012
WVFGRD96 26.0 0 50 -80 3.69 0.5129
WVFGRD96 28.0 0 50 -80 3.72 0.5247
WVFGRD96 30.0 175 40 -90 3.75 0.5340
WVFGRD96 32.0 180 40 -85 3.78 0.5462
WVFGRD96 34.0 180 40 -85 3.81 0.5652
WVFGRD96 36.0 185 40 -80 3.84 0.5796
WVFGRD96 38.0 185 40 -80 3.86 0.5979
WVFGRD96 40.0 195 45 -65 3.98 0.6441
WVFGRD96 42.0 195 45 -65 4.00 0.6270
WVFGRD96 44.0 195 45 -65 4.01 0.6000
WVFGRD96 46.0 180 35 -85 3.98 0.5740
WVFGRD96 48.0 175 30 -90 3.97 0.5646
WVFGRD96 50.0 215 35 -55 4.00 0.5608
WVFGRD96 52.0 215 30 -55 3.99 0.5581
WVFGRD96 54.0 215 30 -50 4.00 0.5559
WVFGRD96 56.0 215 30 -50 4.01 0.5525
WVFGRD96 58.0 215 30 -50 4.01 0.5465
WVFGRD96 60.0 215 30 -45 4.02 0.5393
WVFGRD96 62.0 215 30 -45 4.02 0.5302
WVFGRD96 64.0 215 30 -40 4.03 0.5218
WVFGRD96 66.0 215 30 -40 4.03 0.5113
WVFGRD96 68.0 25 60 -65 3.98 0.5073
WVFGRD96 70.0 25 60 -65 3.98 0.5077
WVFGRD96 72.0 25 60 -65 3.99 0.5063
WVFGRD96 74.0 30 60 -60 4.00 0.5041
WVFGRD96 76.0 30 60 -60 4.00 0.5030
WVFGRD96 78.0 30 60 -60 4.01 0.4997
The best solution is
WVFGRD96 40.0 195 45 -65 3.98 0.6441
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