Location
SLU Location
To check the ANSS location or to compare the observed P-wave first motions to the moment tensor solution, P- and S-wave first arrival times were manually read together with the P-wave first motions. The subsequent output of the program elocate is given in the file elocate.txt. The first motion plot is shown below.
Location ANSS
The ANSS event ID is us7000subl and the event page is at
https://earthquake.usgs.gov/earthquakes/eventpage/us7000subl/executive.
2026/06/18 14:21:22 48.790 -68.019 10.0 4.4 Quebec, Canada
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2026/06/18 14:21:22.0 48.79 -68.02 10.0 4.4 Quebec, Canada
Stations used:
C8.ELNB CN.A11 CN.A16 CN.A21 CN.A54 CN.A61 CN.A64 CN.BCLQ
CN.BJBQ CN.CACQ CN.CNOQ CN.DPQ CN.GAC CN.GGN CN.HAL CN.HSNB
CN.ICQ CN.LDAQ CN.LMN CN.LMQ CN.MCNB CN.MORQ CN.PMAQ CN.SMQ
CN.SNFQ CN.TRQ N4.D62A N4.G62A N4.G65A N4.H62A N4.I62A
N4.I63A NE.EMMW NE.HNH NE.VT1 NE.WVL US.LBNH US.PKME
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
Best Fitting Double Couple
Mo = 5.56e+22 dyne-cm
Mw = 4.43
Z = 22 km
Plane Strike Dip Rake
NP1 169 52 102
NP2 330 40 75
Principal Axes:
Axis Value Plunge Azimuth
T 5.56e+22 79 129
N 0.00e+00 10 342
P -5.56e+22 6 251
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.21e+21
Mxy -1.83e+22
Mxz -4.88e+21
Myy -4.77e+22
Myz 1.36e+22
Mzz 5.29e+22
##------------
-----##---------------
-------########-------------
-------############-----------
--------###############-----------
---------#################----------
---------###################----------
----------#####################---------
----------######################--------
-----------######################---------
-----------#######################--------
-----------############ #########-------
------------########### T #########-------
--------########### #########------
P ---------######################------
---------######################-----
-----------#####################----
-----------###################----
-----------#################--
-----------###############--
----------############
---------#####
Global CMT Convention Moment Tensor:
R T P
5.29e+22 -4.88e+21 -1.36e+22
-4.88e+21 -5.21e+21 1.83e+22
-1.36e+22 1.83e+22 -4.77e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260618142122/index.html
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Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is
STK = 330
DIP = 40
RAKE = 75
MW = 4.43
HS = 22.0
The NDK file is 20260618142122.ndk
The waveform inversion is preferred.
Moment Tensor Comparison
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.
| SLU |
USGSMWR |
SLUFM |
USGS/SLU Moment Tensor Solution
ENS 2026/06/18 14:21:22.0 48.79 -68.02 10.0 4.4 Quebec, Canada
Stations used:
C8.ELNB CN.A11 CN.A16 CN.A21 CN.A54 CN.A61 CN.A64 CN.BCLQ
CN.BJBQ CN.CACQ CN.CNOQ CN.DPQ CN.GAC CN.GGN CN.HAL CN.HSNB
CN.ICQ CN.LDAQ CN.LMN CN.LMQ CN.MCNB CN.MORQ CN.PMAQ CN.SMQ
CN.SNFQ CN.TRQ N4.D62A N4.G62A N4.G65A N4.H62A N4.I62A
N4.I63A NE.EMMW NE.HNH NE.VT1 NE.WVL US.LBNH US.PKME
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
Best Fitting Double Couple
Mo = 5.56e+22 dyne-cm
Mw = 4.43
Z = 22 km
Plane Strike Dip Rake
NP1 169 52 102
NP2 330 40 75
Principal Axes:
Axis Value Plunge Azimuth
T 5.56e+22 79 129
N 0.00e+00 10 342
P -5.56e+22 6 251
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.21e+21
Mxy -1.83e+22
Mxz -4.88e+21
Myy -4.77e+22
Myz 1.36e+22
Mzz 5.29e+22
##------------
-----##---------------
-------########-------------
-------############-----------
--------###############-----------
---------#################----------
---------###################----------
----------#####################---------
----------######################--------
-----------######################---------
-----------#######################--------
-----------############ #########-------
------------########### T #########-------
--------########### #########------
P ---------######################------
---------######################-----
-----------#####################----
-----------###################----
-----------#################--
-----------###############--
----------############
---------#####
Global CMT Convention Moment Tensor:
R T P
5.29e+22 -4.88e+21 -1.36e+22
-4.88e+21 -5.21e+21 1.83e+22
-1.36e+22 1.83e+22 -4.77e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20260618142122/index.html
|
Regional Moment Tensor (Mwr)
Moment 5.277e+15 N-m
Magnitude 4.41 Mwr
Depth 23.0 km
Percent DC 60%
Half Duration -
Catalog US
Data Source US
Contributor US
Nodal Planes
Plane Strike Dip Rake
NP1 316 65 50
NP2 200 46 144
Principal Axes
Axis Value Plunge Azimuth
T 5.760e+15 52 178
N -1.160e+15 36 336
P -4.601e+15 11 74
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First motions and takeoff angles from an elocate run.
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Magnitudes
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.
mLg Magnitude
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.
ML Magnitude
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.
Map showing station locations used for computing the ML's. No distinction is made whether the vertical (Z) or horizontal (H) components were used.
Context
The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.
Waveform Inversion using wvfgrd96
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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Location of broadband stations used for waveform inversion
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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
The results of this grid search are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 330 45 -90 4.09 0.4603
WVFGRD96 2.0 325 50 -70 4.22 0.4750
WVFGRD96 3.0 340 60 -50 4.25 0.3739
WVFGRD96 4.0 265 45 -40 4.23 0.3557
WVFGRD96 5.0 300 80 -50 4.10 0.3706
WVFGRD96 6.0 305 85 -50 4.10 0.3972
WVFGRD96 7.0 310 90 -50 4.11 0.4221
WVFGRD96 8.0 140 80 55 4.12 0.4491
WVFGRD96 9.0 150 70 55 4.16 0.4778
WVFGRD96 10.0 0 60 85 4.27 0.5100
WVFGRD96 11.0 180 30 90 4.28 0.5506
WVFGRD96 12.0 170 40 85 4.30 0.5923
WVFGRD96 13.0 165 40 80 4.31 0.6323
WVFGRD96 14.0 165 45 85 4.32 0.6682
WVFGRD96 15.0 350 45 90 4.33 0.6983
WVFGRD96 16.0 350 45 90 4.35 0.7239
WVFGRD96 17.0 350 45 90 4.36 0.7444
WVFGRD96 18.0 340 40 80 4.37 0.7640
WVFGRD96 19.0 340 40 80 4.38 0.7809
WVFGRD96 20.0 335 40 80 4.41 0.7909
WVFGRD96 21.0 330 40 75 4.42 0.8021
WVFGRD96 22.0 330 40 75 4.43 0.8076
WVFGRD96 23.0 330 40 75 4.44 0.8064
WVFGRD96 24.0 330 40 75 4.45 0.8014
WVFGRD96 25.0 330 40 75 4.45 0.7891
WVFGRD96 26.0 325 40 70 4.46 0.7727
WVFGRD96 27.0 340 35 80 4.46 0.7526
WVFGRD96 28.0 340 35 80 4.47 0.7296
WVFGRD96 29.0 340 35 80 4.47 0.7029
The best solution is
WVFGRD96 22.0 330 40 75 4.43 0.8076
The mechanism corresponding to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
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Figure 2. Depth sensitivity for waveform mechanism
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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
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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.
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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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
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.
Velocity Model
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
Last Changed Thu Jun 18 17:05:49 CDT 2026
