2006/03/05 10:42:16 64.93N 129.26W 10 5.6 Canada
USGS Felt map for this earthquake
USGS Felt reports page for northwestern, Canada
SLU Moment Tensor Solution
2006/03/05 10:42:16 64.93N 129.26W 10 5.6 Canada
Best Fitting Double Couple
Mo = 1.51e+24 dyne-cm
Mw = 5.42
Z = 2 km
Plane Strike Dip Rake
NP1 117 45 95
NP2 290 45 85
Principal Axes:
Axis Value Plunge Azimuth
T 1.51e+24 86 112
N 0.00e+00 4 294
P -1.51e+24 0 204
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.27e+24
Mxy -5.56e+23
Mxz -3.19e+22
Myy -2.36e+23
Myz 8.77e+22
Mzz 1.51e+24
--------------
----------------------
----------------------------
------------------------------
--------#######-------------------
---####################-------------
############################----------
--#############################---------
--###############################-------
----################################------
-----################# #############----
------################ T ##############---
-------############### ##############---
--------###############################-
----------#############################-
-----------###########################
-------------######################-
-----------------#############----
------------------------------
----------------------------
--- ----------------
P ------------
Harvard Convention
Moment Tensor:
R T F
1.51e+24 -3.19e+22 -8.77e+22
-3.19e+22 -1.27e+24 5.56e+23
-8.77e+22 5.56e+23 -2.36e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/NEW/20060305104216/index.html
|
March 5, 2006, NORTHWEST TERRITORIES, CANADA, MW=5.5
Natasha Maternovskaya
CENTROID, MOMENT TENSOR SOLUTION
HARVARD EVENT-FILE NAME C030506B
DATA USED: GSN
L.P. BODY WAVES: 61S,123C, T= 40
SURFACE WAVES: 81S,181C, T= 50
CENTROID LOCATION:
ORIGIN TIME 10:42:19.6 0.1
LAT 65.05N 0.01;LON 129.19W 0.03
DEP 12.0 FIX;HALF-DURATION 1.3
MOMENT TENSOR; SCALE 10**24 D-CM
MRR= 1.88 0.03; MTT=-1.68 0.02
MPP=-0.21 0.02; MRT= 0.13 0.07
MRP=-0.13 0.07; MTP= 0.70 0.02
PRINCIPAL AXES:
1.(T) VAL= 1.89;PLG=87;AZM= 64
2.(N) 0.07; 2; 292
3.(P) -1.96; 2; 202
BEST DOUBLE COUPLE:M0=1.9*10**24
NP1:STRIKE=289;DIP=43;SLIP= 87
NP2:STRIKE=114;DIP=48;SLIP= 93
-----------
-------------------
-----------------------
---------------------------
---################----------
-######################--------
-#########################-----
--############## ##########----
---############# T ###########---
----############ ############--
------##########################-
-------########################
----------#####################
------------###############--
---------------------------
-----------------------
-- --------------
P ----------
|
The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.
|
|
|
|
STK = 290
DIP = 45
RAKE = 85
MW = 5.42
HS = 2
The waveform solution is preferred. It agrees with the surface-wave solution.
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 0.016 3 lp c 0.06 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 275 45 60 5.33 0.5207
WVFGRD96 1.0 280 50 70 5.35 0.5400
WVFGRD96 2.0 290 45 85 5.42 0.5721
WVFGRD96 3.0 295 45 90 5.46 0.5479
WVFGRD96 4.0 285 30 80 5.49 0.4986
WVFGRD96 5.0 280 30 75 5.48 0.4778
WVFGRD96 6.0 280 30 75 5.47 0.4631
WVFGRD96 7.0 290 25 85 5.45 0.4529
WVFGRD96 8.0 55 50 -25 5.38 0.4630
WVFGRD96 9.0 55 55 -25 5.39 0.4754
WVFGRD96 10.0 100 25 75 5.45 0.4775
WVFGRD96 11.0 50 50 -35 5.42 0.4896
WVFGRD96 12.0 50 50 -35 5.43 0.5030
WVFGRD96 13.0 50 50 -35 5.43 0.5142
WVFGRD96 14.0 55 55 -35 5.44 0.5236
WVFGRD96 15.0 55 55 -35 5.44 0.5314
WVFGRD96 16.0 55 55 -35 5.45 0.5376
WVFGRD96 17.0 55 55 -30 5.45 0.5426
WVFGRD96 18.0 55 55 -30 5.46 0.5464
WVFGRD96 19.0 50 55 -35 5.47 0.5494
WVFGRD96 20.0 50 55 -35 5.49 0.5430
WVFGRD96 21.0 50 55 -35 5.49 0.5425
WVFGRD96 22.0 55 55 -30 5.49 0.5413
WVFGRD96 23.0 55 55 -30 5.50 0.5391
WVFGRD96 24.0 85 45 50 5.51 0.5392
WVFGRD96 25.0 85 45 50 5.51 0.5386
WVFGRD96 26.0 75 50 35 5.52 0.5370
WVFGRD96 27.0 75 50 35 5.52 0.5352
WVFGRD96 28.0 75 50 35 5.53 0.5326
WVFGRD96 29.0 75 50 35 5.54 0.5292
The best solution is
WVFGRD96 2.0 290 45 85 5.42 0.5721
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 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 0.016 3 lp c 0.06 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. |
NODAL PLANES
STK= 302.15
DIP= 55.61
RAKE= 96.94
OR
STK= 109.99
DIP= 35.00
RAKE= 79.99
DEPTH = 2.0 km
Mw = 5.46
Best Fit 0.8362 - 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 335 421 eP_- DAWY 263 497 eP_- WHY 214 557 eP_X GALN 94 580 eP_X SKAG 210 688 eP_+ DOT 265 731 eP_- FNBB 151 750 eP_X BESE 205 768 eP_- PNL 226 788 eP_- DCPH 220 802 eP_X PAX 262 823 eP_X HARP 258 835 eP_X LUPN 76 841 eP_- BMR 247 894 eP_X MLON 88 936 eP_X SIT 203 938 -12345 MCK 271 959 -12345 EYAK 247 972 eP_X COLD 295 978 eP_D TRF 270 1032 eP_+ BPAW 275 1044 eP_+ KTH 272 1059 eP_+ PMR 259 1062 -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.
|
|
|
|
| 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 335 421 DAWY 263 497 WHY 214 557 GALN 94 580 SKAG 210 688 DOT 265 731 FNBB 151 750 BESE 205 768 YKW2 104 776 YKW1 104 779 PNL 226 788 DCPH 220 802 PAX 262 823 HARP 258 835 LUPN 76 841 BMR 247 894 DIV 251 935 MLON 88 936 SIT 203 938 MCK 271 959 EYAK 247 972 COLD 294 978 TRF 270 1032 BPAW 275 1044 KTH 272 1059 PMR 259 1062 BMBC 155 1065 CRAG 193 1077 CHUM 274 1114 RC01 257 1118 FIB 258 1134 PPLA 269 1143 EDM 138 1584 LLLB 161 1654 RES 35 1674 TNA 290 1783 PNT 157 1832 OFR 169 1918 OCWA 168 1940 FCC 94 1948 NEW 153 1995 SDPT 253 2009 D03A 168 2014 E04A 166 2083 HAWA 159 2150 EGMT 139 2216 MSO 148 2221 HEBO 169 2224 G04A 166 2238 H02A 169 2281 TOLO 169 2288 COR 168 2298 AKUT 257 2346 DGMT 129 2361 I03A 168 2365 WIFE 165 2372 TAKO 170 2383 UNV 257 2403 BOZ 145 2405 I06A 162 2406 LAO 134 2465 K01A 171 2484 HUMO 168 2519 K06A 163 2531 ULM 114 2532 HLID 152 2556 NIKO 258 2585 WVOR 160 2595 YBH 168 2618 M04C 166 2622 MOD 163 2628 M02C 168 2654 JCC 170 2707 AHID 146 2721 HATC 166 2733 BILL 306 2756 BW06 144 2763 HWUT 148 2832 BMN 158 2837 ORV 166 2871 SUTB 167 2904 HOPS 169 2917 DUG 151 2952 TPH 159 3093 ISCO 140 3187 KAPO 100 3206 BAK 163 3364 SUMG 36 3400 GSC 160 3403 SDCO 141 3404 CBKS 132 3482 WUAZ 151 3486 NEE 156 3494 VLDQ 97 3537 KSU1 128 3566 Y22C 145 3751 AAM 109 3795 TUC 152 3844 SLM 120 3863 CCM 122 3879 FVM 121 3919 WMOK 134 3932 BLO 115 3966 SIUC 120 3995 LONY 97 4001 ACSO 110 4020 USIN 118 4035 MNTX 144 4045 NCB 98 4076 PVMO 121 4103 MIAR 127 4138 UTMT 120 4144 ACCN 98 4155 BINY 101 4155 LBNH 95 4160 UALR 126 4162 WRPS 104 4198 WVT 119 4208 MCWV 107 4214 MPH 122 4222 OXF 122 4304 HRV 96 4334 JCT 138 4340 MVL 103 4342 LTX 143 4344 TZTN 114 4349 BRNJ 101 4361 PAL 100 4362 SDMD 104 4375 FOR 100 4376 CPNY 100 4379 NATX 130 4382 BLA 110 4422 CBN 106 4464 HKT 133 4526 LRAL 120 4549 LTL 126 4652 NHSC 113 4831 DWPF 117 5272
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 0.016 3 lp c 0.06 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 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 modified Utah 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.
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
 |
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
