Location

2010/11/24 22:48:30 35.627 -97.246 7.8 4.20 Oklahoma

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports main page

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2010/11/24 22:48:30:0 35.63 -97.25 7.8 4.2 Oklahoma Stations used: AG.HHAR AG.WHAR NM.MGMO NM.UALR TA.133A TA.134A TA.135A TA.336A TA.ABTX TA.P31A TA.P32A TA.P33A TA.P36A TA.Q31A TA.Q32A TA.Q33A TA.Q35A TA.Q36A TA.Q37A TA.R29A TA.R30A TA.R31A TA.R32A TA.R33A TA.R34A TA.R36A TA.R37A TA.S28A TA.S30A TA.S31A TA.S32A TA.S33A TA.S34A TA.S35A TA.S36A TA.S37A TA.T29A TA.T30A TA.T31A TA.T32A TA.T33A TA.T34A TA.T35A TA.T36A TA.T37A TA.TUL1 TA.U29A TA.U30A TA.U31A TA.U32A TA.U33A TA.U34A TA.U35A TA.U36A TA.U37A TA.U38A TA.V30A TA.V31A TA.V32A TA.V33A TA.V34A TA.V35A TA.V36A TA.V37A TA.V38A TA.W30A TA.W31A TA.W33A TA.W34A TA.W35A TA.W36A TA.W38A TA.X30A TA.X31A TA.X32A TA.X34A TA.X35A TA.X36A TA.X38A TA.Y31A TA.Y32A TA.Y33A TA.Y34A TA.Y35A TA.Y36A TA.Y38A TA.Y39A TA.Z31A TA.Z32A TA.Z33A TA.Z34A TA.Z35A TA.Z37A TA.Z39A US.AMTX US.CBKS US.KSU1 US.MIAR US.WMOK Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 9.89e+21 dyne-cm Mw = 3.93 Z = 3 km Plane Strike Dip Rake NP1 190 90 180 NP2 280 90 -0 Principal Axes: Axis Value Plunge Azimuth T 9.89e+21 -0 325 N 0.00e+00 90 190 P -9.89e+21 -0 55 Moment Tensor: (dyne-cm) Component Value Mxx 3.38e+21 Mxy -9.29e+21 Mxz -7.50e+13 Myy -3.38e+21 Myz 4.26e+14 Mzz -0.00e+00 ##########---- T ############-------- ## ############----------- #################------------- ###################------------- P ####################------------- ####################------------------ #####################------------------- #####################------------------- -----################--------------------- ----------------#####--------------------- ---------------------#####---------------- ---------------------################----- -------------------##################### -------------------##################### ------------------#################### ----------------#################### ---------------################### -------------################# -----------################# --------############## ----########## Global CMT Convention Moment Tensor: R T P -0.00e+00 -7.50e+13 -4.26e+14 -7.50e+13 3.38e+21 9.29e+21 -4.26e+14 9.29e+21 -3.38e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101124224830/index.html

Preferred Solution

      STK = 100
      DIP = 90
     RAKE = 0
       MW = 3.93
       HS = 3.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGS/SLU Moment Tensor Solution ENS 2010/11/24 22:48:30:0 35.63 -97.25 7.8 4.2 Oklahoma Stations used: AG.HHAR AG.WHAR NM.MGMO NM.UALR TA.133A TA.134A TA.135A TA.336A TA.ABTX TA.P31A TA.P32A TA.P33A TA.P36A TA.Q31A TA.Q32A TA.Q33A TA.Q35A TA.Q36A TA.Q37A TA.R29A TA.R30A TA.R31A TA.R32A TA.R33A TA.R34A TA.R36A TA.R37A TA.S28A TA.S30A TA.S31A TA.S32A TA.S33A TA.S34A TA.S35A TA.S36A TA.S37A TA.T29A TA.T30A TA.T31A TA.T32A TA.T33A TA.T34A TA.T35A TA.T36A TA.T37A TA.TUL1 TA.U29A TA.U30A TA.U31A TA.U32A TA.U33A TA.U34A TA.U35A TA.U36A TA.U37A TA.U38A TA.V30A TA.V31A TA.V32A TA.V33A TA.V34A TA.V35A TA.V36A TA.V37A TA.V38A TA.W30A TA.W31A TA.W33A TA.W34A TA.W35A TA.W36A TA.W38A TA.X30A TA.X31A TA.X32A TA.X34A TA.X35A TA.X36A TA.X38A TA.Y31A TA.Y32A TA.Y33A TA.Y34A TA.Y35A TA.Y36A TA.Y38A TA.Y39A TA.Z31A TA.Z32A TA.Z33A TA.Z34A TA.Z35A TA.Z37A TA.Z39A US.AMTX US.CBKS US.KSU1 US.MIAR US.WMOK Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 9.89e+21 dyne-cm Mw = 3.93 Z = 3 km Plane Strike Dip Rake NP1 190 90 180 NP2 280 90 -0 Principal Axes: Axis Value Plunge Azimuth T 9.89e+21 -0 325 N 0.00e+00 90 190 P -9.89e+21 -0 55 Moment Tensor: (dyne-cm) Component Value Mxx 3.38e+21 Mxy -9.29e+21 Mxz -7.50e+13 Myy -3.38e+21 Myz 4.26e+14 Mzz -0.00e+00 ##########---- T ############-------- ## ############----------- #################------------- ###################------------- P ####################------------- ####################------------------ #####################------------------- #####################------------------- -----################--------------------- ----------------#####--------------------- ---------------------#####---------------- ---------------------################----- -------------------##################### -------------------##################### ------------------#################### ----------------#################### ---------------################### -------------################# -----------################# --------############## ----########## Global CMT Convention Moment Tensor: R T P -0.00e+00 -7.50e+13 -4.26e+14 -7.50e+13 3.38e+21 9.29e+21 -4.26e+14 9.29e+21 -3.38e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101124224830/index.html

Waveform Inversion

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.

Location of broadband stations used for waveform 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 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    0.5   280    80    -5   3.83 0.4760
WVFGRD96    1.0   280    80    -5   3.86 0.5038
WVFGRD96    2.0   100    90     0   3.90 0.5359
WVFGRD96    3.0   100    90     0   3.93 0.5410
WVFGRD96    4.0   100    80    10   3.95 0.5331
WVFGRD96    5.0   100    85    20   3.97 0.5270
WVFGRD96    6.0   100    85    20   3.98 0.5229
WVFGRD96    7.0   100    85    20   3.98 0.5199
WVFGRD96    8.0   280    90   -20   3.99 0.5180
WVFGRD96    9.0   100    70     5   4.00 0.5210
WVFGRD96   10.0   100    70    10   4.01 0.5226
WVFGRD96   11.0   100    70    10   4.02 0.5240
WVFGRD96   12.0   100    70    10   4.03 0.5237
WVFGRD96   13.0   100    75    10   4.03 0.5231
WVFGRD96   14.0   100    80    15   4.04 0.5219
WVFGRD96   15.0   100    80    15   4.05 0.5206
WVFGRD96   16.0   100    80    15   4.05 0.5182
WVFGRD96   17.0   100    80    15   4.06 0.5151
WVFGRD96   18.0   100    80    15   4.07 0.5116
WVFGRD96   19.0   100    85    15   4.08 0.5072
WVFGRD96   20.0   100    85    15   4.09 0.5020
WVFGRD96   21.0   100    85    15   4.10 0.4979
WVFGRD96   22.0   280    90   -15   4.10 0.4935
WVFGRD96   23.0   100    90    15   4.11 0.4889
WVFGRD96   24.0   100    90    15   4.12 0.4833
WVFGRD96   25.0   100    90    15   4.12 0.4772
WVFGRD96   26.0   100    90    15   4.13 0.4701
WVFGRD96   27.0   100    90    15   4.14 0.4623
WVFGRD96   28.0    10    75     5   4.14 0.4532
WVFGRD96   29.0    10    75     5   4.15 0.4490

The best solution is

WVFGRD96    3.0   100    90     0   3.93 0.5410

The mechanism correspond to the best fit is

Figure 1. Waveform inversion focal mechanism

The best fit as a function of depth is given in the following figure:

Figure 2. Depth sensitivity for waveform mechanism

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 0.02 n 3
lp c 0.10 n 3
br c 0.12 0.25 n 4 p 2

Figure 3. Waveform comparison for selected depth

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:

• The origin time and epicentral distance are incorrect
• The velocity model used for the inversion is incorrect
• The velocity model used to define the P-arrival time is not the same as the velocity model used for the waveform inversion (assuming that the initial trace alignment is based on the P arrival time)

 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.

Discussion

The Future

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.

Acknowledgements

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.

Velocity Model

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 

Quality Control

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 24 17:16:36 MST 2010