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 usb000jx58 and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usb000jx58/executive.
2013/09/21 14:48:23 49.767 -65.915 18.0 4.2 Quebec
USGS/SLU Moment Tensor Solution
ENS 2013/09/21 14:48:23:0 49.77 -65.92 18.0 4.2 Quebec
Stations used:
CN.A11 CN.A16 CN.A21 CN.A54 CN.A61 CN.A64 CN.BATG CN.DMCQ
CN.DRLN CN.ICQ CN.NATG CN.SCHQ NE.EMMW NE.PQI NE.WVL
PO.CHGQ PO.LATQ TA.D58A TA.D59A TA.D60A TA.D61A TA.E58A
TA.E59A TA.E60A TA.E61A TA.F59A TA.F60A TA.F61A TA.H65A
Filtering commands used:
cut a -30 a 210
rtr
taper w 0.1
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 = 1.10e+22 dyne-cm
Mw = 3.96
Z = 27 km
Plane Strike Dip Rake
NP1 135 50 60
NP2 357 48 121
Principal Axes:
Axis Value Plunge Azimuth
T 1.10e+22 67 338
N 0.00e+00 23 155
P -1.10e+22 1 246
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.76e+20
Mxy -4.68e+21
Mxz 3.66e+21
Myy -8.88e+21
Myz -1.33e+21
Mzz 9.35e+21
########------
##############--------
###################---------
#####################---------
--######################----------
---#######################----------
----########### ##########----------
-----########### T ##########-----------
------########## ###########----------
-------########################-----------
--------#######################-----------
---------######################-----------
----------#####################-----------
-----------###################----------
---------##################----------
P -----------################---------
-------------#############---------
----------------#########---------
------------------####--------
--------------------########
----------------######
----------####
Global CMT Convention Moment Tensor:
R T P
9.35e+21 3.66e+21 1.33e+21
3.66e+21 -4.76e+20 4.68e+21
1.33e+21 4.68e+21 -8.88e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130921144823/index.html
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STK = 135
DIP = 50
RAKE = 60
MW = 3.96
HS = 27.0
The NDK file is 20130921144823.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 a -30 a 210 rtr taper w 0.1 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 0.5 300 45 -95 3.64 0.5769
WVFGRD96 1.0 305 45 -90 3.68 0.5995
WVFGRD96 2.0 325 45 -90 3.75 0.6009
WVFGRD96 3.0 190 65 -30 3.83 0.5238
WVFGRD96 4.0 20 65 5 3.85 0.4751
WVFGRD96 5.0 200 30 -10 3.77 0.5010
WVFGRD96 6.0 205 30 -5 3.75 0.5296
WVFGRD96 7.0 210 30 0 3.74 0.5516
WVFGRD96 8.0 210 45 20 3.80 0.5685
WVFGRD96 9.0 210 45 20 3.79 0.5827
WVFGRD96 10.0 215 35 15 3.78 0.5913
WVFGRD96 11.0 210 45 20 3.82 0.6031
WVFGRD96 12.0 210 45 20 3.83 0.6138
WVFGRD96 13.0 215 45 30 3.84 0.6240
WVFGRD96 14.0 215 45 30 3.85 0.6332
WVFGRD96 15.0 215 45 30 3.85 0.6411
WVFGRD96 16.0 215 45 30 3.86 0.6480
WVFGRD96 17.0 220 40 25 3.84 0.6543
WVFGRD96 18.0 210 50 30 3.89 0.6597
WVFGRD96 19.0 210 50 30 3.90 0.6644
WVFGRD96 20.0 220 35 20 3.88 0.6658
WVFGRD96 21.0 225 30 20 3.87 0.6684
WVFGRD96 22.0 135 60 60 3.91 0.6764
WVFGRD96 23.0 140 55 60 3.92 0.6841
WVFGRD96 24.0 135 55 55 3.94 0.6900
WVFGRD96 25.0 135 55 55 3.95 0.6944
WVFGRD96 26.0 130 55 55 3.96 0.6962
WVFGRD96 27.0 135 50 60 3.96 0.6964
WVFGRD96 28.0 135 50 60 3.97 0.6954
WVFGRD96 29.0 135 50 60 3.98 0.6921
WVFGRD96 30.0 130 50 55 4.00 0.6882
WVFGRD96 31.0 130 50 55 4.01 0.6821
WVFGRD96 32.0 130 50 55 4.03 0.6738
WVFGRD96 33.0 135 45 60 4.03 0.6650
WVFGRD96 34.0 135 45 60 4.04 0.6543
WVFGRD96 35.0 135 45 60 4.05 0.6417
WVFGRD96 36.0 135 45 55 4.08 0.6283
WVFGRD96 37.0 130 45 55 4.09 0.6122
WVFGRD96 38.0 130 45 55 4.11 0.5947
WVFGRD96 39.0 145 40 60 4.12 0.5750
WVFGRD96 40.0 305 70 -70 4.16 0.5656
WVFGRD96 41.0 305 70 -70 4.17 0.5488
WVFGRD96 42.0 310 70 -65 4.17 0.5340
WVFGRD96 43.0 310 70 -65 4.17 0.5206
WVFGRD96 44.0 310 70 -60 4.18 0.5080
WVFGRD96 45.0 310 70 -60 4.18 0.4821
WVFGRD96 46.0 310 70 -60 4.18 0.4709
WVFGRD96 47.0 310 70 -55 4.20 0.4601
WVFGRD96 48.0 310 70 -55 4.20 0.4500
WVFGRD96 49.0 310 70 -55 4.21 0.4401
WVFGRD96 50.0 310 70 -55 4.21 0.4304
The best solution is
WVFGRD96 27.0 135 50 60 3.96 0.6964
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 a -30 a 210 rtr taper w 0.1 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