The ANSS event ID is usp000gnrd and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000gnrd/executive.
2008/11/15 10:52:50 47.740 -69.713 20.0 3.6 Quebec, Canada
USGS/SLU Moment Tensor Solution
ENS 2008/11/15 10:52:50:0 47.74 -69.71 20.0 3.6 Quebec, Canada
Stations used:
CN.A16 CN.A21 CN.A54 CN.A64 CN.GGN CN.ICQ CN.KGNO CN.MNT
CN.VLDQ LD.ACCN LD.FRNY US.LBNH US.LONY US.PKME
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2
Best Fitting Double Couple
Mo = 2.85e+21 dyne-cm
Mw = 3.57
Z = 14 km
Plane Strike Dip Rake
NP1 175 55 70
NP2 27 40 116
Principal Axes:
Axis Value Plunge Azimuth
T 2.85e+21 72 34
N 0.00e+00 16 187
P -2.85e+21 8 279
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.20e+20
Mxy 5.68e+20
Mxz 6.37e+20
Myy -2.64e+21
Myz 8.64e+20
Mzz 2.52e+21
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---------########### T #########------
P ---------########### #########-------
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Global CMT Convention Moment Tensor:
R T P
2.52e+21 6.37e+20 -8.64e+20
6.37e+20 1.20e+20 -5.68e+20
-8.64e+20 -5.68e+20 -2.64e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081115105250/index.html
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STK = 175
DIP = 55
RAKE = 70
MW = 3.57
HS = 14.0
The NDK file is 20081115105250.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:
hp c 0.02 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 0.5 345 35 -95 3.44 0.4087
WVFGRD96 1.0 185 65 -85 3.55 0.4097
WVFGRD96 2.0 115 30 -70 3.51 0.4127
WVFGRD96 3.0 160 35 -20 3.48 0.3994
WVFGRD96 4.0 170 30 -10 3.46 0.4137
WVFGRD96 5.0 155 70 60 3.51 0.4455
WVFGRD96 6.0 165 65 70 3.53 0.4765
WVFGRD96 7.0 165 65 70 3.52 0.4966
WVFGRD96 8.0 175 60 70 3.53 0.5112
WVFGRD96 9.0 175 60 70 3.53 0.5208
WVFGRD96 10.0 175 60 75 3.56 0.5243
WVFGRD96 11.0 170 60 70 3.55 0.5292
WVFGRD96 12.0 180 55 75 3.57 0.5322
WVFGRD96 13.0 175 55 70 3.57 0.5341
WVFGRD96 14.0 175 55 70 3.57 0.5345
WVFGRD96 15.0 175 55 70 3.58 0.5318
WVFGRD96 16.0 175 55 70 3.59 0.5287
WVFGRD96 17.0 175 55 70 3.59 0.5233
WVFGRD96 18.0 175 50 70 3.60 0.5179
WVFGRD96 19.0 175 50 70 3.61 0.5119
WVFGRD96 20.0 175 50 70 3.64 0.5024
WVFGRD96 21.0 175 50 70 3.65 0.4945
WVFGRD96 22.0 175 50 70 3.65 0.4875
WVFGRD96 23.0 175 50 70 3.66 0.4800
WVFGRD96 24.0 175 50 70 3.66 0.4713
WVFGRD96 25.0 170 50 65 3.67 0.4631
WVFGRD96 26.0 180 45 70 3.68 0.4553
WVFGRD96 27.0 175 45 70 3.69 0.4470
WVFGRD96 28.0 175 45 70 3.69 0.4399
WVFGRD96 29.0 175 45 70 3.70 0.4322
The best solution is
WVFGRD96 14.0 175 55 70 3.57 0.5345
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
hp c 0.02 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