2008/11/14 13:26:05 42.5000 18.5000 10.0 4.20
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
2008/11/14 13:26:05 42.5000 18.5000 10.0 4.20
Best Fitting Double Couple
Mo = 2.16e+22 dyne-cm
Mw = 4.19
Z = 16 km
Plane Strike Dip Rake
NP1 117 61 99
NP2 280 30 75
Principal Axes:
Axis Value Plunge Azimuth
T 2.16e+22 73 48
N 0.00e+00 7 293
P -2.16e+22 16 201
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.66e+22
Mxy -5.72e+21
Mxz 9.44e+21
Myy -1.50e+21
Myz 6.59e+21
Mzz 1.81e+22
--------------
----------------------
----------------------------
-------#############----------
-----######################-------
---###########################------
#-################################----
#--#################################----
----################## #############--
------################# T ##############--
--------############### ##############--
---------################################-
------------#############################-
-------------###########################
-----------------#######################
--------------------##################
-------------------------#########--
----------------------------------
------- --------------------
------ P -------------------
--- ----------------
--------------
Harvard Convention
Moment Tensor:
R T F
1.81e+22 9.44e+21 -6.59e+21
9.44e+21 -1.66e+22 5.72e+21
-6.59e+21 5.72e+21 -1.50e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20081114132605/index.html
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STK = 280
DIP = 30
RAKE = 75
MW = 4.19
HS = 16.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
2008/11/14 13:26:05 42.5000 18.5000 10.0 4.20
Best Fitting Double Couple
Mo = 2.16e+22 dyne-cm
Mw = 4.19
Z = 16 km
Plane Strike Dip Rake
NP1 117 61 99
NP2 280 30 75
Principal Axes:
Axis Value Plunge Azimuth
T 2.16e+22 73 48
N 0.00e+00 7 293
P -2.16e+22 16 201
Moment Tensor: (dyne-cm)
Component Value
Mxx -1.66e+22
Mxy -5.72e+21
Mxz 9.44e+21
Myy -1.50e+21
Myz 6.59e+21
Mzz 1.81e+22
--------------
----------------------
----------------------------
-------#############----------
-----######################-------
---###########################------
#-################################----
#--#################################----
----################## #############--
------################# T ##############--
--------############### ##############--
---------################################-
------------#############################-
-------------###########################
-----------------#######################
--------------------##################
-------------------------#########--
----------------------------------
------- --------------------
------ P -------------------
--- ----------------
--------------
Harvard Convention
Moment Tensor:
R T F
1.81e+22 9.44e+21 -6.59e+21
9.44e+21 -1.66e+22 5.72e+21
-6.59e+21 5.72e+21 -1.50e+21
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/MECH.NA/20081114132605/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 0.05 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 110 45 90 3.86 0.2463
WVFGRD96 1.0 65 75 15 3.76 0.2344
WVFGRD96 2.0 70 65 20 3.87 0.2814
WVFGRD96 3.0 70 65 20 3.90 0.2919
WVFGRD96 4.0 70 60 15 3.92 0.2988
WVFGRD96 5.0 70 60 15 3.93 0.3072
WVFGRD96 6.0 70 60 10 3.94 0.3173
WVFGRD96 7.0 275 20 70 4.08 0.3333
WVFGRD96 8.0 280 20 75 4.16 0.3628
WVFGRD96 9.0 285 20 80 4.17 0.3950
WVFGRD96 10.0 115 70 95 4.18 0.4188
WVFGRD96 11.0 285 25 80 4.18 0.4420
WVFGRD96 12.0 285 25 80 4.19 0.4584
WVFGRD96 13.0 285 25 80 4.19 0.4698
WVFGRD96 14.0 285 30 80 4.19 0.4761
WVFGRD96 15.0 285 30 80 4.19 0.4791
WVFGRD96 16.0 280 30 75 4.19 0.4800
WVFGRD96 17.0 280 30 75 4.19 0.4784
WVFGRD96 18.0 280 30 75 4.19 0.4750
WVFGRD96 19.0 275 35 65 4.18 0.4725
WVFGRD96 20.0 275 35 65 4.18 0.4679
WVFGRD96 21.0 270 35 60 4.20 0.4694
WVFGRD96 22.0 265 45 50 4.19 0.4647
WVFGRD96 23.0 265 45 50 4.19 0.4612
WVFGRD96 24.0 265 45 50 4.20 0.4583
WVFGRD96 25.0 265 45 50 4.20 0.4538
WVFGRD96 26.0 265 45 50 4.21 0.4483
WVFGRD96 27.0 260 50 40 4.21 0.4436
WVFGRD96 28.0 260 50 40 4.21 0.4381
WVFGRD96 29.0 260 50 40 4.22 0.4324
WVFGRD96 30.0 260 55 40 4.23 0.4248
WVFGRD96 31.0 260 55 40 4.23 0.4170
WVFGRD96 32.0 260 55 40 4.24 0.4088
WVFGRD96 33.0 260 55 40 4.24 0.3990
WVFGRD96 34.0 260 55 40 4.24 0.3884
WVFGRD96 35.0 110 65 90 4.24 0.3816
WVFGRD96 36.0 285 25 85 4.24 0.3760
WVFGRD96 37.0 115 75 105 4.26 0.3709
WVFGRD96 38.0 250 25 45 4.25 0.3653
WVFGRD96 39.0 240 25 40 4.27 0.3622
WVFGRD96 40.0 265 45 50 4.40 0.3834
WVFGRD96 41.0 260 45 45 4.40 0.3786
WVFGRD96 42.0 260 45 45 4.41 0.3735
WVFGRD96 43.0 260 45 45 4.41 0.3680
WVFGRD96 44.0 260 50 40 4.41 0.3627
WVFGRD96 45.0 260 50 40 4.41 0.3576
WVFGRD96 46.0 260 50 40 4.42 0.3528
WVFGRD96 47.0 260 50 40 4.43 0.3477
WVFGRD96 48.0 260 50 40 4.43 0.3423
WVFGRD96 49.0 260 50 40 4.44 0.3371
WVFGRD96 50.0 260 50 40 4.44 0.3317
The best solution is
WVFGRD96 16.0 280 30 75 4.19 0.4800
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 0.05 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. |
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=Fri Nov 14 08:47:00 MST 2008