2008/12/03 02:47:30 60.91 -138.11 5.0 4.30 Yukon, Canada
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/12/03 02:47:30 60.91 -138.11 5.0 4.30 Yukon, Canada
Best Fitting Double Couple
Mo = 2.11e+22 dyne-cm
Mw = 4.15
Z = 6 km
Plane Strike Dip Rake
NP1 125 60 109
NP2 270 35 60
Principal Axes:
Axis Value Plunge Azimuth
T 2.11e+22 69 75
N 0.00e+00 17 295
P -2.11e+22 13 201
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.72e+22
Mxy -6.06e+21
Mxz 6.26e+21
Myy 4.43e+14
Myz 8.66e+21
Mzz 1.72e+22
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--------##################--------
#-----########################------
###-##############################----
###--################################---
##----################################--
#-------################# #############-
#--------################ T #############-
-----------############## ##############
------------##############################
--------------##########################
----------------########################
------------------####################
---------------------###############
--------------------------########
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------ -------------------
--- P ----------------
------------
Harvard Convention
Moment Tensor:
R T F
1.72e+22 6.26e+21 -8.66e+21
6.26e+21 -1.72e+22 6.06e+21
-8.66e+21 6.06e+21 4.43e+14
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081203024730/index.html
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STK = 270
DIP = 35
RAKE = 60
MW = 4.15
HS = 6.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/12/03 02:47:30 60.91 -138.11 5.0 4.30 Yukon, Canada
Best Fitting Double Couple
Mo = 2.11e+22 dyne-cm
Mw = 4.15
Z = 6 km
Plane Strike Dip Rake
NP1 125 60 109
NP2 270 35 60
Principal Axes:
Axis Value Plunge Azimuth
T 2.11e+22 69 75
N 0.00e+00 17 295
P -2.11e+22 13 201
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.72e+22
Mxy -6.06e+21
Mxz 6.26e+21
Myy 4.43e+14
Myz 8.66e+21
Mzz 1.72e+22
--------------
----------------------
----------------------------
------------------------------
--------##################--------
#-----########################------
###-##############################----
###--################################---
##----################################--
#-------################# #############-
#--------################ T #############-
-----------############## ##############
------------##############################
--------------##########################
----------------########################
------------------####################
---------------------###############
--------------------------########
------------------------------
------ -------------------
--- P ----------------
------------
Harvard Convention
Moment Tensor:
R T F
1.72e+22 6.26e+21 -8.66e+21
6.26e+21 -1.72e+22 6.06e+21
-8.66e+21 6.06e+21 4.43e+14
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081203024730/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 0.02 n 3 lp c 0.08 n 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 0.5 250 65 30 3.99 0.5117
WVFGRD96 1.0 245 70 30 3.98 0.5143
WVFGRD96 2.0 260 35 30 4.12 0.5355
WVFGRD96 3.0 260 45 35 4.08 0.5534
WVFGRD96 4.0 265 40 45 4.11 0.5663
WVFGRD96 5.0 270 35 55 4.15 0.5854
WVFGRD96 6.0 270 35 60 4.15 0.5960
WVFGRD96 7.0 260 40 50 4.11 0.5957
WVFGRD96 8.0 255 40 45 4.10 0.5914
WVFGRD96 9.0 245 45 35 4.08 0.5840
WVFGRD96 10.0 245 45 35 4.10 0.5844
WVFGRD96 11.0 245 45 30 4.09 0.5776
WVFGRD96 12.0 240 50 25 4.09 0.5708
WVFGRD96 13.0 240 50 20 4.09 0.5640
WVFGRD96 14.0 240 50 20 4.10 0.5586
WVFGRD96 15.0 240 50 20 4.10 0.5517
WVFGRD96 16.0 240 50 20 4.11 0.5434
WVFGRD96 17.0 235 55 15 4.12 0.5358
WVFGRD96 18.0 235 55 15 4.12 0.5266
WVFGRD96 19.0 235 55 15 4.13 0.5178
WVFGRD96 20.0 240 50 15 4.15 0.5081
WVFGRD96 21.0 240 50 15 4.16 0.4966
WVFGRD96 22.0 240 50 15 4.17 0.4855
WVFGRD96 23.0 240 50 15 4.18 0.4733
WVFGRD96 24.0 240 45 15 4.19 0.4607
WVFGRD96 25.0 240 45 15 4.20 0.4476
WVFGRD96 26.0 240 40 10 4.21 0.4355
WVFGRD96 27.0 240 35 10 4.22 0.4234
WVFGRD96 28.0 240 35 10 4.22 0.4122
WVFGRD96 29.0 240 30 10 4.23 0.4008
WVFGRD96 30.0 235 30 5 4.24 0.3898
WVFGRD96 31.0 235 30 5 4.25 0.3785
WVFGRD96 32.0 235 30 5 4.25 0.3670
WVFGRD96 33.0 235 30 5 4.26 0.3552
WVFGRD96 34.0 235 30 5 4.26 0.3440
WVFGRD96 35.0 235 30 5 4.27 0.3324
WVFGRD96 36.0 245 40 0 4.25 0.3220
WVFGRD96 37.0 245 40 0 4.25 0.3131
WVFGRD96 38.0 245 40 0 4.26 0.3057
WVFGRD96 39.0 245 45 -5 4.27 0.3000
The best solution is
WVFGRD96 6.0 270 35 60 4.15 0.5960
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 0.08 n 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. |
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=Wed Dec 3 06:07:52 CST 2008