SLU location using NRCAN data A54 Z 10.32 28. 156. 20060407083145.753 -0.01 0 iC P 0.98 A54 Z 10.32 28. 156. 20060407083148.867 0.05 2 eX S 0.45 LMQ Z 22.36 30. 134. 20060407083146.848 0.02 0 iC P 0.96 LMQ Z 22.36 30. 134. 20060407083150.714 0.06 2 eX S 0.45 A11 Z 25.69 125. 130. 20060407083147.190 -0.01 0 iC P 0.98 A11 Z 25.69 125. 130. 20060407083151.223 -0.08 0 iX S 0.86 A16 Z 37.00 73. 118. 20060407083153.797 0.05 0 iX S 0.91 A16 Z 37.00 73. 118. 20060407083148.678 0.06 0 iC P 0.88 A64 Z 66.70 41. 102. 20060407083200.882 -0.14 0 iX S 0.57 A64 Z 66.70 41. 101. 20060407083152.457 -0.36 0 iC P 0.41 A21 Z 69.55 58. 101. 20060407083202.024 0.27 0 iX S 0.44 A21 Z 69.55 58. 101. 20060407083153.152 -0.08 2 e- P 0.31 MNT Z 318.72 230. 95. 20060407083305.299 -6.33 2 eX Lg 0.00 MNT Z 318.72 230. 55. 20060407083229.636 3.78 2 eX P 0.00 MNT Z 318.72 230. 55. 20060407083259.368 1.06 2 eX S 0.02 MNT Z 318.72 230. 95. 20060407083236.119 1.26 2 eX Pg 0.02 ICQ Z 336.15 44. 55. 20060407083228.110 0.11 2 eX P 0.06 Error Ellipse X= 0.5840 km Y= 0.7854 km Theta = 177.9083 deg RMS Error : 0.042 sec Travel_Time_Table: CUS Latitude : 47.3748 +- 0.0052 N 0.5843 km Longitude : -70.4769 +- 0.0105 E 0.7851 km Depth : 24.02 +- 0.91 km Epoch Time : 1144398701.589 +- 0.16 sec Event Time : 20060407083141.589 +- 0.16 sec HYPO71 Quality : BC Gap : 157 deg
2006/04/07 08:31:41 47.38N 70.46W 25. 4.1 Quebec, Canada
USGS Felt map for this earthquake
USGS Felt reports page for Southeastern Canada
SLU Moment Tensor Solution
2006/04/07 08:31:41 47.38N 70.46W 25. 4.1 Quebec, Canada
Best Fitting Double Couple
Mo = 5.07e+21 dyne-cm
Mw = 3.77
Z = 25 km
Plane Strike Dip Rake
NP1 15 55 85
NP2 204 35 97
Principal Axes:
Axis Value Plunge Azimuth
T 5.07e+21 79 266
N 0.00e+00 4 18
P -5.07e+21 10 109
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.99e+20
Mxy 1.50e+21
Mxz 2.02e+20
Myy -4.25e+21
Myz -1.73e+21
Mzz 4.75e+21
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---------#################--------
--------###################---------
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--------######################----------
-------#######################----------
--------######################------------
-------######### ###########------------
-------######### T ###########------------
-------######### ##########-------------
------######################-------- -
------#####################--------- P -
-----####################----------
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---###############------------
---############-------------
-#########------------
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Harvard Convention
Moment Tensor:
R T F
4.75e+21 2.02e+20 1.73e+21
2.02e+20 -4.99e+20 -1.50e+21
1.73e+21 -1.50e+21 -4.25e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/NEW/20060407083140/index.html
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The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.
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STK = 15
DIP = 55
RAKE = 85
MW = 3.77
HS = 25
The waveform inversion solution is the preferred. This was possible because of the fine broadband stations available in the region through NRCanada. There were too few surface-wave spectral data to get a mechanism, other than to say that the moment magnitude is appropriate.
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:
hp c 0.05 3 lp c 0.50 3 br c 0.12 0.25 n 4 p 2The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 170 0 75 3.38 0.5173
WVFGRD96 1.0 360 85 80 3.36 0.5451
WVFGRD96 2.0 10 80 70 3.34 0.5592
WVFGRD96 3.0 20 65 70 3.38 0.5621
WVFGRD96 4.0 185 90 -75 3.38 0.5307
WVFGRD96 5.0 30 25 -65 3.48 0.5233
WVFGRD96 6.0 40 35 -50 3.51 0.4902
WVFGRD96 7.0 55 30 -40 3.59 0.4778
WVFGRD96 8.0 180 55 35 3.62 0.4433
WVFGRD96 9.0 50 35 -55 3.68 0.4675
WVFGRD96 10.0 195 45 60 3.68 0.5154
WVFGRD96 11.0 195 50 55 3.70 0.5062
WVFGRD96 12.0 190 50 50 3.71 0.5065
WVFGRD96 13.0 350 75 20 3.62 0.5099
WVFGRD96 14.0 80 50 0 3.70 0.5154
WVFGRD96 15.0 80 50 0 3.71 0.5140
WVFGRD96 16.0 80 55 0 3.73 0.5180
WVFGRD96 17.0 85 55 0 3.77 0.5061
WVFGRD96 18.0 95 50 5 3.79 0.5223
WVFGRD96 19.0 45 50 90 3.60 0.5234
WVFGRD96 20.0 40 50 85 3.66 0.5981
WVFGRD96 21.0 35 50 85 3.69 0.6394
WVFGRD96 22.0 25 55 90 3.71 0.6553
WVFGRD96 23.0 35 50 85 3.72 0.6647
WVFGRD96 24.0 30 50 80 3.75 0.7060
WVFGRD96 25.0 15 55 85 3.77 0.7126
WVFGRD96 26.0 200 35 90 3.76 0.6692
WVFGRD96 27.0 30 50 80 3.76 0.6552
WVFGRD96 28.0 25 50 75 3.78 0.6463
WVFGRD96 29.0 30 50 80 3.77 0.6239
The best solution is
WVFGRD96 25.0 15 55 85 3.77 0.7126
The mechanism correspond 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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was
hp c 0.05 3 lp c 0.50 3 br c 0.12 0.25 n 4 p 2
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| 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. |
NODAL PLANES
STK= 164.99
DIP= 85.00
RAKE= 40.00
OR
STK= 70.80
DIP= 50.19
RAKE= 173.48
DEPTH = 15.0 km
Mw = 3.57
Best Fit 0.9295 - P-T axis plot gives solutions with FIT greater than FIT90
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The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion A54 24 11 iP_C LMQ 29 23 iP_C A11 124 25 iP_C A16 72 37 iP_C A64 40 67 iP_C A21 57 70 eP_- MNT 231 319 eP_X ICQ 43 337 eP_X NCB 219 478 ePn SCHQ 16 869 -12345
Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave 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 Love-wave spectral amplitudes, respectively.
These were input to the search program which examined all depths between 1 and 25 km
and all possible mechanisms.
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| Pressure-tension axis trends. Since the surface-wave 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 T-axes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here. |
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| 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 0-180 degrees are sampled. |
The distribution of broadband stations with azimuth and distance is
Sta Az(deg) Dist(km) A21 57 70 MNT 231 319 ICQ 44 337 NCB 220 471 HRV 190 539 PAL 203 751
Since the analysis of the surface-wave radiation patterns uses only spectral amplitudes and because the surfave-wave radiation patterns have a 180 degree symmetry, each surface-wave solution consists of four possible focal mechanisms corresponding to the interchange of the P- and T-axes and a roation of the mechanism by 180 degrees. To select one mechanism, P-wave first motion can be used. This was not possible in this case because all the P-wave first motions were emergent ( a feature of the P-wave 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:
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This figure shows the fit to the three components of motion (Z - vertical, R-radial 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:
hp c 0.05 3 lp c 0.50 3 br c 0.12 0.25 n 4 p 2
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Should the national backbone of the USGS Advanced National Seismic System (ANSS) be implemented with an interstation separation of 300 km, it is very likely that an earthquake such as this would have been recorded at distances on the order of 100-200 km. This means that the closest station would have information on source depth and mechanism that was lacking here.
Dr. Harley Benz, USGS, provided the USGS USNSN digital data. The digital data used in this study were provided by Natural Resources Canada through their AUTODRM site http://www.seismo.nrcan.gc.ca/nwfa/autodrm/autodrm_req_e.php, and IRIS using their BUD interface
The figures below show the observed spectral amplitudes (units of cm-sec) at each station and the
theoretical predictions as a function of period for the mechanism given above. The CUS model earth model
was used to define the Green's functions. For each station, the Love and Rayleigh wave spectrail amplitudes are plotted with the same scaling so that one can get a sense fo the effects of the effects of the focal mechanism and depth on the excitation of each.
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Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
