2008/11/04 15:46:34 66.4630 -157.9640 5.0 4.00 Alaska
USGS Felt map for this earthquake
SLU Moment Tensor Solution
2008/11/04 15:46:34 66.4630 -157.9640 5.0 4.00 Alaska
Best Fitting Double Couple
Mo = 2.11e+22 dyne-cm
Mw = 4.15
Z = 10 km
Plane Strike Dip Rake
NP1 345 80 30
NP2 249 61 168
Principal Axes:
Axis Value Plunge Azimuth
T 2.11e+22 28 211
N 0.00e+00 59 2
P -2.11e+22 13 114
Moment Tensor: (dyne-cm)
Component Value
Mxx 8.77e+21
Mxy 1.47e+22
Mxz -5.64e+21
Myy -1.24e+22
Myz -8.77e+21
Mzz 3.61e+21
--############
-------###############
-----------#################
-------------#################
----------------##################
-----------------###################
-------------------##---------------##
----------------#####-------------------
------------#########-------------------
----------#############-------------------
--------###############-------------------
------##################------------------
----####################------------------
--######################----------------
-#######################----------- --
#######################----------- P -
######### ###########----------
######## T ###########------------
###### ###########----------
###################---------
################------
############--
Harvard Convention
Moment Tensor:
R T F
3.61e+21 -5.64e+21 8.77e+21
-5.64e+21 8.77e+21 -1.47e+22
8.77e+21 -1.47e+22 -1.24e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081104154634/index.html
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STK = 345
DIP = 80
RAKE = 30
MW = 4.15
HS = 10.0
The waveform inversion is preferred. The WUS model is used since it provides a better fit, especially to the PnL and surfwave-wave at the same station at some stations. Obviously no one model fits alld ata well.
The following compares this source inversion to others
SLU Moment Tensor Solution
2008/11/04 15:46:34 66.4630 -157.9640 5.0 4.00 Alaska
Best Fitting Double Couple
Mo = 2.11e+22 dyne-cm
Mw = 4.15
Z = 10 km
Plane Strike Dip Rake
NP1 345 80 30
NP2 249 61 168
Principal Axes:
Axis Value Plunge Azimuth
T 2.11e+22 28 211
N 0.00e+00 59 2
P -2.11e+22 13 114
Moment Tensor: (dyne-cm)
Component Value
Mxx 8.77e+21
Mxy 1.47e+22
Mxz -5.64e+21
Myy -1.24e+22
Myz -8.77e+21
Mzz 3.61e+21
--############
-------###############
-----------#################
-------------#################
----------------##################
-----------------###################
-------------------##---------------##
----------------#####-------------------
------------#########-------------------
----------#############-------------------
--------###############-------------------
------##################------------------
----####################------------------
--######################----------------
-#######################----------- --
#######################----------- P -
######### ###########----------
######## T ###########------------
###### ###########----------
###################---------
################------
############--
Harvard Convention
Moment Tensor:
R T F
3.61e+21 -5.64e+21 8.77e+21
-5.64e+21 8.77e+21 -1.47e+22
8.77e+21 -1.47e+22 -1.24e+22
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20081104154634/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 0.5 155 65 -40 4.00 0.6103
WVFGRD96 1.0 150 60 -45 4.03 0.6127
WVFGRD96 2.0 150 60 -45 4.09 0.6686
WVFGRD96 3.0 150 65 -50 4.11 0.6713
WVFGRD96 4.0 160 90 -45 4.08 0.6955
WVFGRD96 5.0 160 90 -40 4.07 0.7209
WVFGRD96 6.0 345 80 35 4.08 0.7437
WVFGRD96 7.0 345 80 35 4.10 0.7565
WVFGRD96 8.0 350 75 40 4.14 0.7662
WVFGRD96 9.0 345 85 30 4.13 0.7727
WVFGRD96 10.0 345 80 30 4.15 0.7759
WVFGRD96 11.0 345 85 25 4.15 0.7751
WVFGRD96 12.0 345 85 25 4.16 0.7713
WVFGRD96 13.0 345 85 25 4.17 0.7665
WVFGRD96 14.0 160 90 -25 4.17 0.7585
WVFGRD96 15.0 160 85 -20 4.18 0.7521
WVFGRD96 16.0 160 85 -20 4.19 0.7454
WVFGRD96 17.0 160 85 -20 4.20 0.7376
WVFGRD96 18.0 345 75 20 4.22 0.7377
WVFGRD96 19.0 345 80 20 4.23 0.7286
WVFGRD96 20.0 345 80 20 4.23 0.7171
WVFGRD96 21.0 345 80 20 4.24 0.7034
WVFGRD96 22.0 345 80 20 4.25 0.6885
WVFGRD96 23.0 345 80 20 4.26 0.6719
WVFGRD96 24.0 160 90 -20 4.26 0.6520
WVFGRD96 25.0 160 90 -20 4.27 0.6341
WVFGRD96 26.0 160 90 -20 4.27 0.6156
WVFGRD96 27.0 340 90 20 4.28 0.5972
WVFGRD96 28.0 340 90 20 4.29 0.5784
WVFGRD96 29.0 340 90 20 4.29 0.5595
WVFGRD96 30.0 340 90 20 4.30 0.5416
WVFGRD96 31.0 160 85 -20 4.31 0.5249
WVFGRD96 32.0 160 85 -20 4.31 0.5093
WVFGRD96 33.0 340 90 20 4.32 0.4946
WVFGRD96 34.0 160 90 -20 4.33 0.4818
WVFGRD96 35.0 70 75 -15 4.34 0.4740
WVFGRD96 36.0 70 75 -15 4.35 0.4735
WVFGRD96 37.0 70 75 -15 4.37 0.4731
WVFGRD96 38.0 70 75 -15 4.39 0.4720
WVFGRD96 39.0 70 75 -15 4.41 0.4695
WVFGRD96 40.0 70 70 -20 4.45 0.4565
WVFGRD96 41.0 70 70 -20 4.46 0.4504
WVFGRD96 42.0 70 70 -20 4.47 0.4431
WVFGRD96 43.0 70 70 -20 4.48 0.4353
WVFGRD96 44.0 70 70 -20 4.49 0.4272
WVFGRD96 45.0 70 75 -20 4.49 0.4192
WVFGRD96 46.0 70 75 -20 4.50 0.4109
WVFGRD96 47.0 70 75 -20 4.51 0.4023
WVFGRD96 48.0 70 75 -20 4.52 0.3935
WVFGRD96 49.0 70 75 -15 4.52 0.3844
WVFGRD96 50.0 70 75 -15 4.53 0.3761
The best solution is
WVFGRD96 10.0 345 80 30 4.15 0.7759
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 WUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01
Model after 8 iterations
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
1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00
6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00
13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00
19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00
0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 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 Nov 5 11:50:07 CST 2008