Left: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated. Right: residuals as a function of distance and azimuth.
The ANSS event ID is us6000np1d and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/us6000np1d/executive.
2024/09/01 09:43:36 46.044 -72.755 1.1 3.8 Quebec, Canada
USGS/SLU Moment Tensor Solution
ENS 2024/09/01 09:43:36:0 46.04 -72.75 1.1 3.8 Quebec, Canada
Stations used:
C8.ELNB CN.A16 CN.A21 CN.A61 CN.BCLQ CN.CALQ CN.DPQ CN.GGN
CN.HSNB CN.KILO CN.KIPQ CN.LDAQ CN.LMQ CN.MCNB CN.ORIO
CN.OTT CN.TRQ CN.VLDQ CN.WBO GS.NJ05 IU.HRV N4.D62A N4.E62A
N4.G62A N4.G65A N4.H62A N4.I62A N4.I63A N4.J55A N4.J57A
N4.J59A N4.J61A N4.K57A N4.K62A N4.L59A N4.L61B N4.L64A
N4.N62A NE.BCX NE.EMMW NE.HNH NE.TRY NE.WES NE.WSPT NE.WVL
PE.PAMP PE.PAPL PE.PSWB PO.MATQ US.BINY
Filtering commands used:
cut o DIST/3.3 -40 o DIST/3.3 +30
rtr
taper w 0.1
hp c 0.03 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 6.53e+21 dyne-cm
Mw = 3.81
Z = 5 km
Plane Strike Dip Rake
NP1 90 80 15
NP2 357 75 170
Principal Axes:
Axis Value Plunge Azimuth
T 6.53e+21 18 314
N 0.00e+00 72 123
P -6.53e+21 3 223
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.78e+20
Mxy -6.21e+21
Mxz 1.59e+21
Myy -5.43e+14
Myz -1.10e+21
Mzz 5.78e+20
#######-------
############----------
###############-------------
# #############-------------
### T #############---------------
#### ##############---------------
######################----------------
#######################-----------------
#######################-----------------
#########################-----------------
#########################-----------------
---######################--------------###
-------------------------#################
------------------------################
------------------------################
-----------------------###############
----------------------##############
- ----------------##############
P ----------------############
----------------###########
-------------#########
---------#####
Global CMT Convention Moment Tensor:
R T P
5.78e+20 1.59e+21 1.10e+21
1.59e+21 -5.78e+20 6.21e+21
1.10e+21 6.21e+21 -5.43e+14
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20240901094336/index.html
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STK = 90
DIP = 80
RAKE = 15
MW = 3.81
HS = 5.0
The NDK file is 20240901094336.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: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated.
Right: residuals as a function of distance and azimuth.
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 +30 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 n 3The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 85 75 -30 3.75 0.6467
WVFGRD96 2.0 85 90 25 3.77 0.6990
WVFGRD96 3.0 90 80 20 3.79 0.7318
WVFGRD96 4.0 90 80 20 3.81 0.7476
WVFGRD96 5.0 90 80 15 3.81 0.7481
WVFGRD96 6.0 90 80 15 3.82 0.7413
WVFGRD96 7.0 270 80 15 3.83 0.7295
WVFGRD96 8.0 270 85 20 3.83 0.7291
WVFGRD96 9.0 270 85 15 3.85 0.7283
WVFGRD96 10.0 270 80 20 3.86 0.7270
WVFGRD96 11.0 270 80 20 3.87 0.7218
WVFGRD96 12.0 270 80 20 3.88 0.7150
WVFGRD96 13.0 270 80 15 3.88 0.7063
WVFGRD96 14.0 270 80 15 3.89 0.6955
WVFGRD96 15.0 270 80 15 3.90 0.6830
WVFGRD96 16.0 270 80 15 3.91 0.6694
WVFGRD96 17.0 270 80 15 3.91 0.6549
WVFGRD96 18.0 270 80 20 3.92 0.6394
WVFGRD96 19.0 270 80 20 3.92 0.6247
WVFGRD96 20.0 270 80 20 3.94 0.6110
WVFGRD96 21.0 270 80 20 3.94 0.5964
WVFGRD96 22.0 270 80 20 3.95 0.5818
WVFGRD96 23.0 270 80 20 3.95 0.5683
WVFGRD96 24.0 270 80 20 3.96 0.5551
WVFGRD96 25.0 270 80 20 3.96 0.5435
WVFGRD96 26.0 270 80 20 3.97 0.5343
WVFGRD96 27.0 265 90 20 3.97 0.5257
WVFGRD96 28.0 265 90 20 3.98 0.5186
WVFGRD96 29.0 265 90 20 3.99 0.5119
The best solution is
WVFGRD96 5.0 90 80 15 3.81 0.7481
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 +30 rtr taper w 0.1 hp c 0.03 n 3 lp c 0.10 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 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