2006/03/29 03:37:04 66.41N 142.23W 10 4.6 Alaska
2006/03/29 03:37:05 66.29N 142.23W 5.0g 4.5Mw PGC 280 km NW of Dawson, YT NCAN
http://earthquakescanada.nrcan.gc.ca/recent_eq/maps/index_e.php
USGS Felt map for this earthquake
USGS Felt reports page for Alaska
SLU Moment Tensor Solution
2006/03/29 03:37:04 66.41N 142.23W 10 4.6 Alaska
Best Fitting Double Couple
Mo = 3.16e+22 dyne-cm
Mw = 4.30
Z = 6 km
Plane Strike Dip Rake
NP1 130 76 159
NP2 225 70 15
Principal Axes:
Axis Value Plunge Azimuth
T 3.16e+22 24 86
N 0.00e+00 65 277
P -3.16e+22 4 178
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.13e+22
Mxy 2.63e+21
Mxz 2.95e+21
Myy 2.61e+22
Myz 1.18e+22
Mzz 5.26e+21
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####------------------##############
######---------------#################
########-----------#####################
##########-------#######################
#############----################## ####
################################### T ####
#############----################## ####
############-------#######################
##########----------####################
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---------- ---------
------ P -----
Harvard Convention
Moment Tensor:
R T F
5.26e+21 2.95e+21 -1.18e+22
2.95e+21 -3.13e+22 -2.63e+21
-1.18e+22 -2.63e+21 2.61e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/NEW/20060329033654/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 = 225
DIP = 70
RAKE = 15
MW = 4.30
HS = 6
The location given is from USGS NEIC. This is preferred to the automatic solution from Alaska, which has since been revised by AEIC. Using the CUS modeli and elocate we have the following solution:
elocate
CHOOSE VELOCITY MODEL
TELE = Model( 1) P S
BEAM = Model( 2) P
HALF = Model( 3) P S
CUS = Model( 4) P S Lg
UPL = Model( 5) P S Lg
EMBN = Model( 6) P Ps Sp S
WHICH MODEL ? 1 - 6
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STA IWT ARRIVAL TIME PhIDQL PHASE FM CHAN
COLD 0 20060329033757.501 1 0 i P C Z
COLD 2 20060329033846.755 3 0 e Lg X Z
DAWY 0 20060329033744.667 1 0 i P C Z
DAWY 2 20060329033823.817 3 0 e Lg X Z
HARP 2 20060329033809.332 1 0 e P X Z
INK 0 20060329033804.816 1 0 i P C Z
INK 2 20060329033850.653 2 0 e S X Z
INK 2 20060329033910.843 3 0 e Lg X Z
WHY 0 20060329033840.457 1 0 i P C Z
enter depth, depth < 0 is fixed at abs(depth)
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64.0655 -139.3909 10.00 20060329033707.863 13203.42
66.4479 -142.6068 15.00 20060329033704.869 108.86
66.2422 -142.2910 14.88 20060329033705.716 12.29
66.2459 -142.2943 14.75 20060329033705.696 12.23
66.2462 -142.2932 13.71 20060329033705.525 6.72
66.2359 -142.3045 13.05 20060329033705.460 6.16
66.2320 -142.3166 13.13 20060329033705.454 5.97
66.2300 -142.3260 13.22 20060329033705.432 5.83
66.2292 -142.3337 13.30 20060329033705.397 5.73
66.2290 -142.3407 13.34 20060329033705.353 5.65
66.2292 -142.3472 13.35 20060329033705.305 5.56
66.2294 -142.3533 13.35 20060329033705.260 5.46
66.2297 -142.3586 13.37 20060329033705.221 5.35
66.2299 -142.3629 13.41 20060329033705.190 5.25
66.2300 -142.3662 13.46 20060329033705.168 5.17
66.2300 -142.3686 13.51 20060329033705.153 5.10
66.2300 -142.3703 13.57 20060329033705.144 5.06
66.2300 -142.3714 13.61 20060329033705.138 5.03
66.2300 -142.3721 13.65 20060329033705.134 5.00
66.2299 -142.3726 13.68 20060329033705.132 4.99
9 phases used
STA COMP DIS(K) AZM AIN ARR TIME RES(SEC) WT QFM PHASE WGT
DAWY Z 278.46 149. 93. 20060329033823.817 0.15 2 eX Lg 0.07
DAWY Z 278.46 149. 51. 20060329033744.667 -0.75 0 iC P 0.06
COLD Z 361.75 291. 93. 20060329033846.755 -0.35 2 eX Lg 0.04
COLD Z 361.75 291. 51. 20060329033757.501 1.87 0 iC P 0.02
INK Z 445.19 55. 92. 20060329033910.843 0.25 2 eX Lg 0.04
INK Z 445.19 55. 51. 20060329033804.816 -1.05 0 iC P 0.03
INK Z 445.19 55. 51. 20060329033850.653 0.25 2 eX S 0.04
HARP Z 446.20 199. 51. 20060329033809.332 3.34 2 eX P 0.00
WHY Z 722.69 146. 51. 20060329033840.457 0.54 0 iC P 0.03
Error Ellipse X= 2.1145 km Y= 2.6331 km Theta = 134.3993 deg
RMS Error : 0.998 sec
Travel_Time_Table: CUS
Latitude : 66.2299 +- 0.0214 N 2.3933 km
Longitude : -142.3729 +- 0.0541 E 2.3825 km
Depth : 13.70 +- 5.36 km
Epoch Time : 1143603425.131 +- 0.47 sec
Event Time : 20060329033705.131 +- 0.47 sec
HYPO71 Quality : DD
Gap : 123 deg
which is similar to the preliminary USGS solution. The current AEIC solution is
Wednesday, March 29, 2006 at 03:36:52 (UTC) 67.150N, 141.035W 11.8 km (7.3 miles) (poorly constrained) NORTHERN ALASKA horizontal +/- 21.5 km (13.4 miles); depth +/- 194.3 km (120.7 miles)I do not like that solution since it does not predict the arrivals as well at the nearby Canadian stations.
The surface-wave solution is preferred on the basis of its depth sensitivity, even though it does not fit the waveforms as nicely as the direct wavefrom inversion.
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 3 lp c 0.10 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 45 80 -10 4.14 0.5679
WVFGRD96 1.0 45 80 -10 4.16 0.5837
WVFGRD96 2.0 80 80 5 4.20 0.5951
WVFGRD96 3.0 80 80 5 4.23 0.6091
WVFGRD96 4.0 80 70 0 4.26 0.6131
WVFGRD96 5.0 80 65 0 4.28 0.6158
WVFGRD96 6.0 260 65 0 4.29 0.6302
WVFGRD96 7.0 260 65 0 4.30 0.6434
WVFGRD96 8.0 260 65 0 4.31 0.6532
WVFGRD96 9.0 260 70 0 4.32 0.6594
WVFGRD96 10.0 260 65 5 4.33 0.6656
WVFGRD96 11.0 260 70 5 4.33 0.6712
WVFGRD96 12.0 260 70 5 4.34 0.6773
WVFGRD96 13.0 260 70 5 4.35 0.6808
WVFGRD96 14.0 260 70 5 4.35 0.6821
WVFGRD96 15.0 260 75 5 4.36 0.6834
WVFGRD96 16.0 260 75 5 4.37 0.6839
WVFGRD96 17.0 260 80 10 4.37 0.6835
WVFGRD96 18.0 260 80 10 4.38 0.6823
WVFGRD96 19.0 260 80 10 4.39 0.6803
The best solution is
WVFGRD96 16.0 260 75 5 4.37 0.6839
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 3 lp c 0.10 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= 129.75
DIP= 75.92
RAKE= 159.36
OR
STK= 224.99
DIP= 70.00
RAKE= 15.00
DEPTH = 6.0 km
Mw = 4.30
Best Fit 0.7416 - 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 DAWY 152 294 iP_C COLD 288 362 iP_C INK 57 430 iP_C HARP 199 469 eP_X WHY 147 738 iP_C DLBC 139 1087 eP_X FNBB 122 1286 eP_X LUPN 79 1392 eP_+ YKW2 96 1392 iP_C YNEN 81 1424 iP_C
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.
The velocity model used for the search is a modified Utah model .
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. |
Sta Az(deg) Dist(km) DAWY 152 294 COLD 288 362 INK 57 430 HARP 199 469 WHY 147 738 DLBC 139 1087 FNBB 122 1286 LUPN 79 1392 YKW2 96 1392 YNEN 82 1424 EDM 119 2155 WALA 126 2524
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 velocity model used for the waveform fit is a modified Utah model .
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 0.02 3 lp c 0.10 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:
