2010/12/12 01:07:56 35.392 -96.995 7.6 4.30 Oklahoma
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2010/12/12 01:07:56:7 35.39 -97.00 7.6 4.3 Oklahoma
Stations used:
TA.TUL1 TA.U34A TA.V34A TA.V35A TA.V36A TA.W34A TA.W35A
TA.W36A TA.X35A TA.X36A
Filtering commands used:
hp c 0.04 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 7.94e+20 dyne-cm
Mw = 3.20
Z = 4 km
Plane Strike Dip Rake
NP1 46 85 -170
NP2 315 80 -5
Principal Axes:
Axis Value Plunge Azimuth
T 7.94e+20 4 180
N 0.00e+00 79 72
P -7.94e+20 11 271
Moment Tensor: (dyne-cm)
Component Value
Mxx 7.91e+20
Mxy 1.18e+19
Mxz -5.12e+19
Myy -7.67e+20
Myz 1.43e+20
Mzz -2.37e+19
##############
######################
############################
--###########################-
-------#######################----
----------###################-------
--------------###############---------
-----------------###########------------
-------------------#######--------------
- ------------------####----------------
- P --------------------------------------
- ------------------###-----------------
--------------------#######---------------
-----------------###########------------
---------------##############-----------
------------##################--------
---------#####################------
-----#########################----
-############################-
############################
######### ##########
##### T ######
Global CMT Convention Moment Tensor:
R T P
-2.37e+19 -5.12e+19 -1.43e+20
-5.12e+19 7.91e+20 -1.18e+19
-1.43e+20 -1.18e+19 -7.67e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101212010756/index.html
|
STK = 315
DIP = 80
RAKE = -5
MW = 3.20
HS = 4.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2010/12/12 01:07:56:7 35.39 -97.00 7.6 4.3 Oklahoma
Stations used:
TA.TUL1 TA.U34A TA.V34A TA.V35A TA.V36A TA.W34A TA.W35A
TA.W36A TA.X35A TA.X36A
Filtering commands used:
hp c 0.04 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 7.94e+20 dyne-cm
Mw = 3.20
Z = 4 km
Plane Strike Dip Rake
NP1 46 85 -170
NP2 315 80 -5
Principal Axes:
Axis Value Plunge Azimuth
T 7.94e+20 4 180
N 0.00e+00 79 72
P -7.94e+20 11 271
Moment Tensor: (dyne-cm)
Component Value
Mxx 7.91e+20
Mxy 1.18e+19
Mxz -5.12e+19
Myy -7.67e+20
Myz 1.43e+20
Mzz -2.37e+19
##############
######################
############################
--###########################-
-------#######################----
----------###################-------
--------------###############---------
-----------------###########------------
-------------------#######--------------
- ------------------####----------------
- P --------------------------------------
- ------------------###-----------------
--------------------#######---------------
-----------------###########------------
---------------##############-----------
------------##################--------
---------#####################------
-----#########################----
-############################-
############################
######### ##########
##### T ######
Global CMT Convention Moment Tensor:
R T P
-2.37e+19 -5.12e+19 -1.43e+20
-5.12e+19 7.91e+20 -1.18e+19
-1.43e+20 -1.18e+19 -7.67e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101212010756/index.html
|
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.
|
|
|
|
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 0.04 n 3 lp c 0.10 n 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 135 85 -25 2.94 0.3235
WVFGRD96 1.0 135 80 -15 2.96 0.3480
WVFGRD96 2.0 135 80 0 3.10 0.4344
WVFGRD96 3.0 315 85 -5 3.15 0.4633
WVFGRD96 4.0 315 80 -5 3.20 0.4698
WVFGRD96 5.0 315 75 0 3.24 0.4668
WVFGRD96 6.0 315 70 0 3.28 0.4586
WVFGRD96 7.0 320 70 10 3.30 0.4465
WVFGRD96 8.0 320 85 25 3.34 0.4319
WVFGRD96 9.0 320 85 25 3.36 0.4162
WVFGRD96 10.0 320 85 25 3.38 0.3991
WVFGRD96 11.0 320 90 25 3.39 0.3816
WVFGRD96 12.0 320 90 25 3.40 0.3645
WVFGRD96 13.0 320 85 20 3.41 0.3489
WVFGRD96 14.0 320 85 20 3.42 0.3334
WVFGRD96 15.0 320 85 20 3.43 0.3185
WVFGRD96 16.0 140 90 -20 3.44 0.3054
WVFGRD96 17.0 320 85 20 3.45 0.2938
WVFGRD96 18.0 320 85 15 3.45 0.2827
WVFGRD96 19.0 320 80 15 3.46 0.2729
WVFGRD96 20.0 320 80 0 3.45 0.2642
WVFGRD96 21.0 320 80 0 3.46 0.2571
WVFGRD96 22.0 320 80 0 3.46 0.2514
WVFGRD96 23.0 320 75 -5 3.47 0.2454
WVFGRD96 24.0 320 85 -15 3.47 0.2410
WVFGRD96 25.0 230 80 -30 3.51 0.2462
WVFGRD96 26.0 55 75 20 3.50 0.2606
WVFGRD96 27.0 55 75 20 3.51 0.2706
WVFGRD96 28.0 55 75 20 3.51 0.2803
WVFGRD96 29.0 55 75 20 3.52 0.2879
The best solution is
WVFGRD96 4.0 315 80 -5 3.20 0.4698
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 component is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
The bandpass filter used in the processing and for the display was
hp c 0.04 n 3 lp c 0.10 n 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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of 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=Sat Dec 11 20:53:34 CST 2010