The ANSS event ID is uw10530748 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/uw10530748/executive.
2001/02/28 18:54:33 47.149 -122.727 51.8 6.8 Washington
USGS/SLU Moment Tensor Solution
ENS 2001/02/28 18:54:33:0 47.15 -122.73 51.8 6.8 Washington
Stations used:
BK.CMB CI.MLAC CI.TIN CN.LLLB IU.COR US.AHID US.BW06 US.DUG
US.HAWA US.HLID US.NEW US.OCWA US.WVOR UW.ERW UW.LTY UW.SQM
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.11e+26 dyne-cm
Mw = 6.63
Z = 52 km
Plane Strike Dip Rake
NP1 17 70 -105
NP2 235 25 -55
Principal Axes:
Axis Value Plunge Azimuth
T 1.11e+26 23 119
N 0.00e+00 14 23
P -1.11e+26 62 264
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.14e+25
Mxy -4.19e+25
Mxz -1.48e+25
Myy 4.82e+25
Myz 8.07e+25
Mzz -6.96e+25
#############-
##################----
##########-----------####---
#######---------------#######-
#######-----------------##########
######-------------------###########
#####---------------------############
#####----------------------#############
####----------------------##############
####-----------------------###############
###--------- ------------###############
###--------- P -----------################
###--------- -----------################
##----------------------################
##---------------------########## ####
#--------------------########### T ###
-------------------############ ##
-----------------#################
--------------################
------------################
-------###############
-#############
Global CMT Convention Moment Tensor:
R T P
-6.96e+25 -1.48e+25 -8.07e+25
-1.48e+25 2.14e+25 4.19e+25
-8.07e+25 4.19e+25 4.82e+25
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20010228185433/index.html
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STK = 235
DIP = 25
RAKE = -55
MW = 6.63
HS = 52.0
The NDK file is 20010228185433.ndk The waveform inversion is preferred.
The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
USGS/SLU Moment Tensor Solution
ENS 2001/02/28 18:54:33:0 47.15 -122.73 51.8 6.8 Washington
Stations used:
BK.CMB CI.MLAC CI.TIN CN.LLLB IU.COR US.AHID US.BW06 US.DUG
US.HAWA US.HLID US.NEW US.OCWA US.WVOR UW.ERW UW.LTY UW.SQM
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +70
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.06 n 3
Best Fitting Double Couple
Mo = 1.11e+26 dyne-cm
Mw = 6.63
Z = 52 km
Plane Strike Dip Rake
NP1 17 70 -105
NP2 235 25 -55
Principal Axes:
Axis Value Plunge Azimuth
T 1.11e+26 23 119
N 0.00e+00 14 23
P -1.11e+26 62 264
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.14e+25
Mxy -4.19e+25
Mxz -1.48e+25
Myy 4.82e+25
Myz 8.07e+25
Mzz -6.96e+25
#############-
##################----
##########-----------####---
#######---------------#######-
#######-----------------##########
######-------------------###########
#####---------------------############
#####----------------------#############
####----------------------##############
####-----------------------###############
###--------- ------------###############
###--------- P -----------################
###--------- -----------################
##----------------------################
##---------------------########## ####
#--------------------########### T ###
-------------------############ ##
-----------------#################
--------------################
------------################
-------###############
-#############
Global CMT Convention Moment Tensor:
R T P
-6.96e+25 -1.48e+25 -8.07e+25
-1.48e+25 2.14e+25 4.19e+25
-8.07e+25 4.19e+25 4.82e+25
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20010228185433/index.html
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Global CMT
Best Fitting Double Couple
Mo = 1.78e+26 dyne-cm
Mw = 6.80
Z = 48 km
Plane Strike Dip Rake
NP1 2 73 -88
NP2 176 17 -96
Principal Axes:
Axis Value Plunge Azimuth
T 1.78e+26 28 91
N 0.00e+00 2 182
P -1.78e+26 62 275
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.75e+23
Mxy 1.50e+24
Mxz -7.50e+24
Myy 9.92e+25
Myz 1.48e+26
Mzz -9.89e+25
##------######
##-----------#########
###--------------###########
##----------------############
###------------------#############
###-------------------##############
###--------------------###############
###---------------------################
###---------------------################
####-------- ----------#################
####-------- P ----------########## ####
####-------- ----------########## T ####
####---------------------########## ####
###---------------------################
####--------------------################
###-------------------################
###------------------###############
###-----------------##############
###--------------#############
####------------############
###---------##########
###----#######
Harvard Convention
Moment Tensor:
R T F
-9.89e+25 -7.50e+24 -1.48e+26
-7.50e+24 -2.75e+23 -1.50e+24
-1.48e+26 -1.50e+24 9.92e+25
---------------------
Event name: 022801L
Region name: WASHINGTON
Date (y/m/d): 2001/2/28
Information on data used in inversion
Wave nsta nrec cutoff
Body 68 178 45
Mantle 66 161 135
Surface 0 0 0
Timing and location information
hr min sec lat lon depth mb Ms
PDE 18 54 32.80 47.15 -122.73 51.9 6.5 6.6
CMT 18 54 37.30 47.14 -122.53 46.8
Error 0.10 0.01 0.01 0.3
Assumed half duration: 6.1
Mechanism information
Exponent for moment tensor: 26 units: dyne-cm
Mrr Mtt Mpp Mrt Mrp Mtp
CMT -0.960 -0.054 1.013 -0.060 -1.453 -0.019
Error 0.006 0.004 0.005 0.009 0.013 0.004
Mw = 6.8 Scalar Moment = 1.76e+26
Fault plane: strike=176 dip=17 slip=-96
Fault plane: strike=2 dip=73 slip=-88
Eigenvector: eigenvalue: 1.78 plunge: 28 azimuth: 90
Eigenvector: eigenvalue: -0.05 plunge: 2 azimuth: 181
Eigenvector: eigenvalue: -1.73 plunge: 62 azimuth: 275
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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 +70 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 2.0 25 45 90 5.98 0.3031
WVFGRD96 4.0 30 45 90 6.09 0.2841
WVFGRD96 6.0 150 80 5 6.13 0.2325
WVFGRD96 8.0 150 75 0 6.18 0.2175
WVFGRD96 10.0 315 25 20 6.04 0.2315
WVFGRD96 12.0 310 25 15 6.06 0.2732
WVFGRD96 14.0 305 25 10 6.08 0.3108
WVFGRD96 16.0 305 25 10 6.10 0.3452
WVFGRD96 18.0 305 25 10 6.13 0.3771
WVFGRD96 20.0 295 20 0 6.15 0.4065
WVFGRD96 22.0 295 20 0 6.18 0.4341
WVFGRD96 24.0 290 20 -5 6.21 0.4606
WVFGRD96 26.0 290 20 -5 6.23 0.4847
WVFGRD96 28.0 285 15 -10 6.25 0.5061
WVFGRD96 30.0 285 15 -10 6.27 0.5245
WVFGRD96 32.0 280 15 -15 6.29 0.5394
WVFGRD96 34.0 280 15 -15 6.31 0.5511
WVFGRD96 36.0 270 15 -20 6.34 0.5603
WVFGRD96 38.0 265 20 -25 6.35 0.5683
WVFGRD96 40.0 260 15 -30 6.50 0.5701
WVFGRD96 42.0 250 20 -40 6.52 0.5825
WVFGRD96 44.0 250 25 -40 6.55 0.5969
WVFGRD96 46.0 245 25 -45 6.57 0.6110
WVFGRD96 48.0 240 25 -50 6.59 0.6215
WVFGRD96 50.0 235 25 -55 6.61 0.6276
WVFGRD96 52.0 235 25 -55 6.63 0.6289
WVFGRD96 54.0 230 25 -60 6.64 0.6260
WVFGRD96 56.0 230 25 -60 6.66 0.6185
WVFGRD96 58.0 230 25 -65 6.65 0.6083
WVFGRD96 60.0 235 25 -60 6.66 0.5959
WVFGRD96 62.0 235 25 -60 6.67 0.5804
WVFGRD96 64.0 240 25 -55 6.68 0.5625
WVFGRD96 66.0 225 20 -70 6.67 0.5461
WVFGRD96 68.0 230 20 -65 6.68 0.5286
The best solution is
WVFGRD96 52.0 235 25 -55 6.63 0.6289
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 +70 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