USGS/SLU Moment Tensor Solution ENS 2021/06/10 11:20:15:0 60.18 74.01 10.0 4.6 Quebec Canada Stations used: CN.A16 CN.A54 CN.A61 CN.A64 CN.BCLQ CN.BJBQ CN.BLKN CN.CLRN CN.FCC CN.FRB CN.GTOO CN.ICQ CN.ILON CN.KAPO CN.KILO CN.KIPQ CN.KUQ CN.LDAQ CN.LMQ CN.PKLO CN.PMAQ CN.PNPO CN.POIN CN.SAKN CN.SCHQ CN.SNFQ CN.SUBO CN.VLDQ PO.MATQ Filtering commands used: cut o DIST/3.3 80 o DIST/3.3 +80 rtr taper w 0.1 hp c 0.025 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.14e+22 dynecm Mw = 3.97 Z = 3 km Plane Strike Dip Rake NP1 285 50 90 NP2 105 40 90 Principal Axes: Axis Value Plunge Azimuth T 1.14e+22 85 195 N 0.00e+00 0 285 P 1.14e+22 5 15 Moment Tensor: (dynecm) Component Value Mxx 1.04e+22 Mxy 2.79e+21 Mxz 1.90e+21 Myy 7.49e+20 Myz 5.10e+20 Mzz 1.12e+22  P       ############ ####################### ############################# ################################# ################################### #################################### ################ ################# ############### T ################## ############# ################### ################################# ############################ ###################### #############     Global CMT Convention Moment Tensor: R T P 1.12e+22 1.90e+21 5.10e+20 1.90e+21 1.04e+22 2.79e+21 5.10e+20 2.79e+21 7.49e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20210610112015/index.html 
STK = 285 DIP = 50 RAKE = 90 MW = 3.97 HS = 3.0
The NDK file is 20210610112015.ndk The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution ENS 2021/06/10 11:20:15:0 60.18 74.01 10.0 4.6 Quebec Canada Stations used: CN.A16 CN.A54 CN.A61 CN.A64 CN.BCLQ CN.BJBQ CN.BLKN CN.CLRN CN.FCC CN.FRB CN.GTOO CN.ICQ CN.ILON CN.KAPO CN.KILO CN.KIPQ CN.KUQ CN.LDAQ CN.LMQ CN.PKLO CN.PMAQ CN.PNPO CN.POIN CN.SAKN CN.SCHQ CN.SNFQ CN.SUBO CN.VLDQ PO.MATQ Filtering commands used: cut o DIST/3.3 80 o DIST/3.3 +80 rtr taper w 0.1 hp c 0.025 n 3 lp c 0.05 n 3 Best Fitting Double Couple Mo = 1.14e+22 dynecm Mw = 3.97 Z = 3 km Plane Strike Dip Rake NP1 285 50 90 NP2 105 40 90 Principal Axes: Axis Value Plunge Azimuth T 1.14e+22 85 195 N 0.00e+00 0 285 P 1.14e+22 5 15 Moment Tensor: (dynecm) Component Value Mxx 1.04e+22 Mxy 2.79e+21 Mxz 1.90e+21 Myy 7.49e+20 Myz 5.10e+20 Mzz 1.12e+22  P       ############ ####################### ############################# ################################# ################################### #################################### ################ ################# ############### T ################## ############# ################### ################################# ############################ ###################### #############     Global CMT Convention Moment Tensor: R T P 1.12e+22 1.90e+21 5.10e+20 1.90e+21 1.04e+22 2.79e+21 5.10e+20 2.79e+21 7.49e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20210610112015/index.html 
(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.
(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the and stations used for the waveform inversion are shown in the next figure.

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 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 80 o DIST/3.3 +80 rtr taper w 0.1 hp c 0.025 n 3 lp c 0.05 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT WVFGRD96 1.0 105 45 95 3.85 0.3813 WVFGRD96 2.0 105 40 95 3.90 0.4051 WVFGRD96 3.0 285 50 90 3.97 0.4264 WVFGRD96 4.0 280 50 80 4.02 0.4179 WVFGRD96 5.0 280 50 80 4.04 0.3823 WVFGRD96 6.0 280 50 80 4.05 0.3245 WVFGRD96 7.0 85 25 65 4.01 0.3175 WVFGRD96 8.0 90 20 70 4.06 0.3367 WVFGRD96 9.0 85 20 65 4.05 0.3438 WVFGRD96 10.0 85 20 65 4.04 0.3531 WVFGRD96 11.0 75 25 45 4.04 0.3649 WVFGRD96 12.0 75 25 45 4.04 0.3756 WVFGRD96 13.0 70 25 35 4.03 0.3848 WVFGRD96 14.0 70 25 35 4.04 0.3928 WVFGRD96 15.0 65 30 30 4.04 0.3995 WVFGRD96 16.0 65 30 30 4.04 0.4061 WVFGRD96 17.0 60 30 20 4.04 0.4118 WVFGRD96 18.0 40 35 30 4.06 0.4200
The best solution is
WVFGRD96 3.0 285 50 90 3.97 0.4264
The mechanism correspond to the best fit is

The best fit as a function of depth is given in the following figure:

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 observedpredicted 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 and because the velocity model used in the predictions may not be perfect. 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 80 o DIST/3.3 +80 rtr taper w 0.1 hp c 0.025 n 3 lp c 0.05 n 3

Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to thewavefroms. 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 following figure shows the stations used in the grid search for the best focal mechanism to fit the surfacewave spectral amplitudes of the Love and Rayleigh waves.

The surfacewave determined focal mechanism is shown here.
NODAL PLANES STK= 286.08 DIP= 55.15 RAKE= 86.51 OR STK= 100.00 DIP= 35.00 RAKE= 94.99 DEPTH = 3.0 km Mw = 4.21 Best Fit 0.9474  PT axis plot gives solutions with FIT greater than FIT90
The Pwave first motion data for focal mechanism studies are as follow:
Sta Az Dist First motion
Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surfacewave radiation pattern search program srfgrd96.
Digital data were collected, instrument response removed and traces converted
to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh and Lovewave spectral amplitudes, respectively.
These were input to the search program which examined all depths between 1 and 25 km
and all possible mechanisms.

Pressuretension axis trends. Since the surfacewave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and Taxes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here. 
Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0180 degrees are sampled. 
The distribution of broadband stations with azimuth and distance is
Listing of broadband stations used
Since the analysis of the surfacewave radiation patterns uses only spectral amplitudes and because the surfavewave radiation patterns have a 180 degree symmetry, each surfacewave solution consists of four possible focal mechanisms corresponding to the interchange of the P and Taxes and a roation of the mechanism by 180 degrees. To select one mechanism, Pwave first motion can be used. This was not possible in this case because all the Pwave first motions were emergent ( a feature of the Pwave wave takeoff angle, the station location and the mechanism). The other way to select among the mechanisms is to compute forward synthetics and compare the observed and predicted waveforms.
The fits to the waveforms with the given mechanism are show below:
This figure shows the fit to the three components of motion (Z  vertical, Rradial and T  transverse). For each station and component, the observed traces is shown in red and the model predicted trace in blue. The traces represent filtered ground velocity in units of meters/sec (the peak value is printed adjacent to each trace; each pair of traces to plotted to the same scale to emphasize the difference in levels). Both synthetic and observed traces have been filtered using the SAC commands:
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureau of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Oklahoma Geological Survey, TexNet, the Iris stations, the Transportable Array of EarthScope and other networks.
The WUS.model used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01 Model after 8 iterations ISOTROPIC KGS FLAT EARTH 1D 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 0.302E02 0.679E02 0.00 0.00 1.00 1.00 6.1000 5.5445 3.2953 2.6089 0.349E02 0.784E02 0.00 0.00 1.00 1.00 13.0000 6.2708 3.7396 2.7812 0.212E02 0.476E02 0.00 0.00 1.00 1.00 19.0000 6.4075 3.7680 2.8223 0.111E02 0.249E02 0.00 0.00 1.00 1.00 0.0000 7.9000 4.6200 3.2760 0.164E10 0.370E10 0.00 0.00 1.00 1.00
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files: