The ANSS event ID is usp000e2bp and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000e2bp/executive.
2005/10/20 21:16:28 44.677 -80.482 11.0 4.2 Quebec, Canada
USGS/SLU Moment Tensor Solution
ENS 2005/10/20 21:16:28:0 44.68 -80.48 11.0 4.2 Quebec, Canada
Stations used:
CN.ALGO CN.BANO CN.BRCO CN.BUKO CN.DELO CN.ELFO CN.GAC
CN.KAPO CN.KGNO CN.MEDO CN.MNT CN.PECO CN.PKRO CN.PLIO
CN.RSPO CN.SADO
Filtering commands used:
cut o DIST/3.3 -40 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 = 3.27e+21 dyne-cm
Mw = 3.61
Z = 10 km
Plane Strike Dip Rake
NP1 167 67 99
NP2 325 25 70
Principal Axes:
Axis Value Plunge Azimuth
T 3.27e+21 67 94
N 0.00e+00 8 343
P -3.27e+21 21 250
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.31e+20
Mxy -9.45e+20
Mxz 3.03e+20
Myy -2.03e+21
Myz 2.20e+21
Mzz 2.36e+21
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---------------########## T ##########----
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--- ---------######################---
--- P ----------#####################---
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Global CMT Convention Moment Tensor:
R T P
2.36e+21 3.03e+20 -2.20e+21
3.03e+20 -3.31e+20 9.45e+20
-2.20e+21 9.45e+20 -2.03e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20051020211628/index.html
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STK = 325
DIP = 25
RAKE = 70
MW = 3.61
HS = 10.0
The NDK file is 20051020211628.ndk The waveform inversion is preferred.
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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 +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 1.0 165 45 85 3.47 0.5069
WVFGRD96 2.0 160 50 80 3.55 0.4507
WVFGRD96 3.0 350 90 -80 3.59 0.4894
WVFGRD96 4.0 175 80 75 3.59 0.5693
WVFGRD96 5.0 175 75 75 3.60 0.6226
WVFGRD96 6.0 325 20 70 3.60 0.6618
WVFGRD96 7.0 330 25 75 3.62 0.6871
WVFGRD96 8.0 325 25 70 3.60 0.7016
WVFGRD96 9.0 320 30 65 3.61 0.7065
WVFGRD96 10.0 325 25 70 3.61 0.7071
WVFGRD96 11.0 320 30 65 3.62 0.7050
WVFGRD96 12.0 320 30 65 3.62 0.7002
WVFGRD96 13.0 320 30 60 3.62 0.6947
WVFGRD96 14.0 315 30 55 3.61 0.6876
WVFGRD96 15.0 315 30 55 3.61 0.6799
WVFGRD96 16.0 315 30 55 3.62 0.6709
WVFGRD96 17.0 315 30 55 3.62 0.6608
WVFGRD96 18.0 310 30 50 3.62 0.6498
WVFGRD96 19.0 310 30 50 3.63 0.6376
WVFGRD96 20.0 310 30 50 3.66 0.6265
WVFGRD96 21.0 310 30 50 3.67 0.6111
WVFGRD96 22.0 305 30 45 3.68 0.5944
WVFGRD96 23.0 305 30 45 3.68 0.5761
WVFGRD96 24.0 310 25 50 3.68 0.5565
WVFGRD96 25.0 310 25 50 3.69 0.5357
WVFGRD96 26.0 155 65 55 3.73 0.5151
WVFGRD96 27.0 215 55 -40 3.78 0.5034
WVFGRD96 28.0 215 55 -35 3.79 0.4893
WVFGRD96 29.0 215 55 -35 3.80 0.4755
The best solution is
WVFGRD96 10.0 325 25 70 3.61 0.7071
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 +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 CUS.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 CUS Model with Q from simple gamma values 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 1.0000 5.0000 2.8900 2.5000 0.172E-02 0.387E-02 0.00 0.00 1.00 1.00 9.0000 6.1000 3.5200 2.7300 0.160E-02 0.363E-02 0.00 0.00 1.00 1.00 10.0000 6.4000 3.7000 2.8200 0.149E-02 0.336E-02 0.00 0.00 1.00 1.00 20.0000 6.7000 3.8700 2.9020 0.000E-04 0.000E-04 0.00 0.00 1.00 1.00 0.0000 8.1500 4.7000 3.3640 0.194E-02 0.431E-02 0.00 0.00 1.00 1.00