2007/11/03 15:35:32 66.32 -135.43 20.0 4.6 Yukon, Canada
USGS Felt map for this earthquake
SLU Moment Tensor Solution 2007/11/03 15:35:32 66.32 -135.43 20.0 4.6 state Best Fitting Double Couple Mo = 9.02e+22 dyne-cm Mw = 4.57 Z = 6 km Plane Strike Dip Rake NP1 333 71 159 NP2 70 70 20 Principal Axes: Axis Value Plunge Azimuth T 9.02e+22 28 291 N 0.00e+00 62 113 P -9.02e+22 1 22 Moment Tensor: (dyne-cm) Component Value Mxx -6.87e+22 Mxy -5.46e+22 Mxz 1.23e+22 Myy 4.89e+22 Myz -3.53e+22 Mzz 1.98e+22 ------------ P ###------------- --- ########-------------------- ###########------------------- ###############------------------- #################------------------- ####################------------------ #### ###############-----------------# #### T ################--------------### ##### #################-----------###### ##########################--------######## ###########################----########### ########################################## ######################-----############# ################------------############ ---------------------------########### ---------------------------######### --------------------------######## ------------------------###### ------------------------#### ---------------------# -------------- Harvard Convention Moment Tensor: R T F 1.98e+22 1.23e+22 3.53e+22 1.23e+22 -6.87e+22 5.46e+22 3.53e+22 5.46e+22 4.89e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071103153532/index.html |
STK = 70 DIP = 70 RAKE = 20 MW = 4.57 HS = 6
The depth control is poor. The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution 2007/11/03 15:35:32 66.32 -135.43 20.0 4.6 state Best Fitting Double Couple Mo = 9.02e+22 dyne-cm Mw = 4.57 Z = 6 km Plane Strike Dip Rake NP1 333 71 159 NP2 70 70 20 Principal Axes: Axis Value Plunge Azimuth T 9.02e+22 28 291 N 0.00e+00 62 113 P -9.02e+22 1 22 Moment Tensor: (dyne-cm) Component Value Mxx -6.87e+22 Mxy -5.46e+22 Mxz 1.23e+22 Myy 4.89e+22 Myz -3.53e+22 Mzz 1.98e+22 ------------ P ###------------- --- ########-------------------- ###########------------------- ###############------------------- #################------------------- ####################------------------ #### ###############-----------------# #### T ################--------------### ##### #################-----------###### ##########################--------######## ###########################----########### ########################################## ######################-----############# ################------------############ ---------------------------########### ---------------------------######### --------------------------######## ------------------------###### ------------------------#### ---------------------# -------------- Harvard Convention Moment Tensor: R T F 1.98e+22 1.23e+22 3.53e+22 1.23e+22 -6.87e+22 5.46e+22 3.53e+22 5.46e+22 4.89e+22 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20071103153532/index.html |
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 0.02 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 55 60 -40 4.57 0.3619 WVFGRD96 1.0 235 65 -45 4.59 0.3694 WVFGRD96 2.0 225 60 -60 4.64 0.3760 WVFGRD96 3.0 65 75 5 4.48 0.3872 WVFGRD96 4.0 70 70 20 4.53 0.4179 WVFGRD96 5.0 70 70 20 4.55 0.4376 WVFGRD96 6.0 70 70 20 4.57 0.4456 WVFGRD96 7.0 70 70 15 4.57 0.4450 WVFGRD96 8.0 65 75 10 4.56 0.4395 WVFGRD96 9.0 65 75 10 4.57 0.4364 WVFGRD96 10.0 65 75 5 4.57 0.4324 WVFGRD96 11.0 70 75 30 4.61 0.4334 WVFGRD96 12.0 70 80 25 4.61 0.4353 WVFGRD96 13.0 70 80 25 4.61 0.4375 WVFGRD96 14.0 70 80 20 4.62 0.4401 WVFGRD96 15.0 65 85 20 4.61 0.4400 WVFGRD96 16.0 65 80 20 4.61 0.4423 WVFGRD96 17.0 65 80 20 4.62 0.4415 WVFGRD96 18.0 65 80 20 4.62 0.4400 WVFGRD96 19.0 65 80 20 4.63 0.4409 WVFGRD96 20.0 65 80 20 4.64 0.4382 WVFGRD96 21.0 65 80 20 4.65 0.4366 WVFGRD96 22.0 65 80 20 4.65 0.4329 WVFGRD96 23.0 65 85 15 4.66 0.4288 WVFGRD96 24.0 65 80 15 4.66 0.4255 WVFGRD96 25.0 65 80 15 4.66 0.4204 WVFGRD96 26.0 65 85 15 4.67 0.4157 WVFGRD96 27.0 245 90 -15 4.68 0.4069 WVFGRD96 28.0 245 90 -15 4.69 0.4016 WVFGRD96 29.0 245 90 -15 4.69 0.3964
The best solution is
WVFGRD96 6.0 70 70 20 4.57 0.4456
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 0.02 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= 248.26 DIP= 85.29 RAKE= -20.07 OR STK= 339.97 DIP= 70.00 RAKE= -174.99 DEPTH = 5.0 km Mw = 4.56 Best Fit 0.8067 - P-T axis plot gives solutions with FIT greater than FIT90
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion INK 19 236 -12345 DAWY 218 312 -12345 EGAK 240 315 -12345 DOT 238 504 -12345 WHY 177 632 -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. |
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 19 236 DAWY 218 312 EGAK 240 315 DOT 238 504 PAX 237 607 WHY 177 632 COLD 286 657 MCK 252 697 BPAW 258 767 PNL 197 768 TRF 252 771 SAW 237 803 ROMN 97 839 PPLA 252 885 RC01 237 913 DLBC 160 921 CTLN 94 923 FIB 238 924 SWD 232 984 FNBB 137 1041 JERN 81 1075 COWN 85 1109 WRAK 170 1115 BMBC 142 1344 BBB 162 1626 RES 40 1724 PHC 162 1797 YBKN 79 1820 STLN 67 1832 BULN 70 1858 EDB 161 1892 EDM 130 1894 CBB 158 1903 LLLB 150 1910 KUGN 64 1927 SLEB 142 1947 SHB 155 1977 NUNN 73 1993 OZB 159 2016 WAGN 70 2034 JOSN 79 2075 ARVN 86 2083 SEDN 79 2085 PNT 147 2100 QILN 66 2129 LAIN 58 2151 SRLN 60 2178 GIFN 55 2195 ILON 57 2207 FCC 92 2237 NEW 143 2274 WALA 137 2285 HAWA 149 2410 ULM 109 2850 MUMO 100 2883 KASO 96 2884 SILO 92 2973 PKLO 101 2979 EPLO 108 2993 ATKO 106 3161 LDIO 104 3216 NANO 99 3228 PNPO 101 3413 OTRO 94 3481 KAPO 96 3505 VLDQ 93 3829
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:
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 0.02 n 3 lp c 0.06 n 3
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=Sat Nov 3 14:32:23 CDT 2007