2007/11/28 12:58:18 66.19 -135.55 -- 4.5 Richardson Mountains, YT (NRCAN)
2007/11/28 12:58:18 66.16 -135.47 14.0 4.3 Canada (AEIC)
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2007/11/28 12:58:18 66.19 -135.45 10.0 4.5 Canada
Best Fitting Double Couple
Mo = 1.45e+22 dyne-cm
Mw = 4.04
Z = 22 km
Plane Strike Dip Rake
NP1 25 70 -45
NP2 134 48 -153
Principal Axes:
Axis Value Plunge Azimuth
T 1.45e+22 13 84
N 0.00e+00 42 186
P -1.45e+22 45 340
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.18e+21
Mxy 3.66e+21
Mxz -6.48e+21
Myy 1.28e+22
Myz 5.62e+21
Mzz -6.57e+21
--------------
--------------------##
-----------------------#####
------------------------######
##---------- -----------########
##----------- P -----------#########
####---------- ----------###########
#####-----------------------############
#####----------------------#############
#######---------------------########## #
########-------------------########### T #
#########-----------------############ #
##########---------------#################
##########-------------#################
############----------##################
#############-------##################
##############----##################
##################################
############------############
#########-------------------
####------------------
--------------
Harvard Convention
Moment Tensor:
R T F
-6.57e+21 -6.48e+21 -5.62e+21
-6.48e+21 -6.18e+21 -3.66e+21
-5.62e+21 -3.66e+21 1.28e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071128125818/index.html
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STK = 25
DIP = 70
RAKE = -45
MW = 4.04
HS = 22
Both solutions are similar. Not much depth control.
The following compares this source inversion to others
SLU Moment Tensor Solution
2007/11/28 12:58:18 66.19 -135.45 10.0 4.5 Canada
Best Fitting Double Couple
Mo = 1.45e+22 dyne-cm
Mw = 4.04
Z = 22 km
Plane Strike Dip Rake
NP1 25 70 -45
NP2 134 48 -153
Principal Axes:
Axis Value Plunge Azimuth
T 1.45e+22 13 84
N 0.00e+00 42 186
P -1.45e+22 45 340
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.18e+21
Mxy 3.66e+21
Mxz -6.48e+21
Myy 1.28e+22
Myz 5.62e+21
Mzz -6.57e+21
--------------
--------------------##
-----------------------#####
------------------------######
##---------- -----------########
##----------- P -----------#########
####---------- ----------###########
#####-----------------------############
#####----------------------#############
#######---------------------########## #
########-------------------########### T #
#########-----------------############ #
##########---------------#################
##########-------------#################
############----------##################
#############-------##################
##############----##################
##################################
############------############
#########-------------------
####------------------
--------------
Harvard Convention
Moment Tensor:
R T F
-6.57e+21 -6.48e+21 -5.62e+21
-6.48e+21 -6.18e+21 -3.66e+21
-5.62e+21 -3.66e+21 1.28e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071128125818/index.html
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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.
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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 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 0.025 n 3 lp c 0.06 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 225 80 20 3.78 0.3972
WVFGRD96 1.0 45 80 15 3.79 0.4060
WVFGRD96 2.0 225 90 0 3.80 0.4142
WVFGRD96 3.0 235 60 40 3.89 0.4135
WVFGRD96 4.0 40 70 -25 3.86 0.4178
WVFGRD96 5.0 40 70 -25 3.87 0.4201
WVFGRD96 6.0 230 75 55 3.96 0.4249
WVFGRD96 7.0 230 75 55 3.96 0.4326
WVFGRD96 8.0 230 75 55 3.96 0.4392
WVFGRD96 9.0 225 80 50 3.95 0.4459
WVFGRD96 10.0 30 75 -55 3.98 0.4525
WVFGRD96 11.0 30 75 -55 3.99 0.4640
WVFGRD96 12.0 25 70 -55 3.99 0.4739
WVFGRD96 13.0 25 70 -55 3.99 0.4817
WVFGRD96 14.0 25 70 -50 3.99 0.4882
WVFGRD96 15.0 25 70 -50 3.99 0.4934
WVFGRD96 16.0 25 70 -50 4.00 0.4973
WVFGRD96 17.0 25 70 -50 4.00 0.5000
WVFGRD96 18.0 25 70 -45 4.00 0.5022
WVFGRD96 19.0 25 70 -45 4.01 0.5043
WVFGRD96 20.0 25 70 -50 4.03 0.5070
WVFGRD96 21.0 25 70 -45 4.03 0.5080
WVFGRD96 22.0 25 70 -45 4.04 0.5080
WVFGRD96 23.0 25 70 -45 4.04 0.5069
WVFGRD96 24.0 25 70 -45 4.05 0.5050
WVFGRD96 25.0 25 70 -40 4.05 0.5025
WVFGRD96 26.0 30 75 -40 4.06 0.4998
WVFGRD96 27.0 30 75 -40 4.07 0.4964
WVFGRD96 28.0 25 75 -40 4.08 0.4923
WVFGRD96 29.0 25 75 -40 4.08 0.4884
The best solution is
WVFGRD96 22.0 25 70 -45 4.04 0.5080
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 0.025 n 3 lp c 0.06 n 3
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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. |
The following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
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The surface-wave determined focal mechanism is shown here.
NODAL PLANES
STK= 224.99
DIP= 75.00
RAKE= 50.00
OR
STK= 117.84
DIP= 42.28
RAKE= 157.37
DEPTH = 13.0 km
Mw = 4.08
Best Fit 0.8111 - 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 INK 18 254 -12345 DAWY 220 297 -12345 EGAK 242 305 -12345 COLA 262 589 -12345 WHY 177 614 -12345 COLD 287 660 -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) INK 18 254 DAWY 220 297 EGAK 242 305 DOT 239 493 COLA 262 589 PAX 238 596 WHY 177 614 COLD 287 660 MCK 253 690 SKAG 179 747 PNL 197 750 BPAW 260 761 TRF 254 764 KTH 256 786 EYAK 224 808 PMR 239 840 BESE 178 845 PPLA 253 878 DLBC 159 905 CTLN 93 924 SIT 180 1014 FNBB 136 1030 JERN 80 1079 WRAK 170 1098 COWN 84 1112 CRAG 173 1198 BMBC 141 1331 MOBC 171 1463 TNA 282 1467 BBB 162 1610 RES 40 1739 PHC 161 1781 BULN 70 1865 EDB 161 1876 EDM 129 1884 CBB 157 1887 LLLB 149 1896 SLEB 141 1935 SHB 154 1962 PNT 146 2086 NLWA 156 2199 ILON 57 2219 NEW 143 2261 WALA 136 2274 COR 157 2512 EGMT 131 2513 DGMT 122 2671 HLID 142 2824 ULM 109 2846 FRB 63 3022 EYMN 107 3241 ECSD 117 3423 KAPO 96 3505 JFWS 111 3763 KSU1 121 3876 ANMO 137 3956 AAM 104 4105 SLM 114 4176 CCM 116 4192 USIN 112 4349
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 0.025 n 3 lp c 0.06 n 3
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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.
Thanks also to the many seismic network operators whose dedication make this effort possible: University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint L ouis University, Universityof Memphis, Lamont Doehrty Earth Observatory, Boston College, the Iris stations and the Transportable Array of EarthScope.
The CUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Fri Nov 30 14:52:35 CST 2007
