Location

Location ANSS

The ANSS event ID is usp000jadn and the event page is at https://earthquake.usgs.gov/earthquakes/eventpage/usp000jadn/executive.

2011/11/06 03:53:10 35.532 -96.765 5.2 5.7 Oklahoma

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2011/11/06 03:53:10:0  35.53  -96.76   5.2 5.7 Oklahoma
 
 Stations used:
   AG.CCAR AG.FCAR AG.HHAR AG.LCAR AG.WHAR AG.WLAR IU.CCM 
   NM.HBAR NM.MGMO NM.PBMO NM.UALR TA.136A TA.137A TA.236A 
   TA.237A TA.238A TA.ABTX TA.N33A TA.N34A TA.O33A TA.O34A 
   TA.O35A TA.O36A TA.O37A TA.O38A TA.P34A TA.P35A TA.P36A 
   TA.P37A TA.P38A TA.P39B TA.Q34A TA.Q35A TA.Q36A TA.Q37A 
   TA.Q38A TA.Q39A TA.Q40A TA.R34A TA.R35A TA.R36A TA.R37A 
   TA.R38A TA.R39A TA.R40A TA.R41A TA.S34A TA.S35A TA.S36A 
   TA.S37A TA.S38A TA.S39A TA.S40A TA.S42A TA.T34A TA.T35A 
   TA.T36A TA.T37A TA.T38A TA.T39A TA.T40A TA.T41A TA.TUL1 
   TA.U32A TA.U35A TA.U36A TA.U37A TA.U38A TA.U39A TA.U40A 
   TA.U41A TA.U42A TA.U43A TA.V35A TA.V36A TA.V37A TA.V38A 
   TA.V39A TA.V40A TA.V41A TA.V42A TA.V43A TA.W35A TA.W36A 
   TA.W37B TA.W38A TA.W39A TA.W40A TA.W41B TA.W42A TA.W43A 
   TA.WHTX TA.X35A TA.X36A TA.X37A TA.X38A TA.X39A TA.X40A 
   TA.X41A TA.X42A TA.X43A TA.Y35A TA.Y36A TA.Y37A TA.Y38A 
   TA.Y39A TA.Y40A TA.Y41A TA.Y42A TA.Z37A TA.Z38A TA.Z40A 
   US.KSU1 US.MIAR US.WMOK 
 
 Filtering commands used:
   hp c 0.01 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 3.05e+24 dyne-cm
  Mw = 5.59 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1      235    85   -175
   NP2      145    85    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.05e+24      0      10
    N   0.00e+00     83     280
    P  -3.05e+24      7     100

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.86e+24
       Mxy     1.06e+24
       Mxz     6.69e+22
       Myy    -2.82e+24
       Myz    -3.67e+23
       Mzz    -4.62e+22
                                                     
                                                     
                                                     
                                                     
                     ######### T ##                  
                 #############   ######              
              ---#########################           
             -----#########################          
           --------##########################        
          ----------######################----       
         ------------##################--------      
        --------------##############------------     
        ---------------##########---------------     
       ------------------#####-------------------    
       -------------------#----------------------    
       -----------------###-------------------       
       ---------------######------------------ P     
        -----------###########----------------       
        ---------##############-----------------     
         ------##################--------------      
          ---#####################------------       
           ########################----------        
             ########################------          
              #########################---           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.62e+22   6.69e+22   3.67e+23 
  6.69e+22   2.86e+24  -1.06e+24 
  3.67e+23  -1.06e+24  -2.82e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111106035310/index.html
        

Preferred Solution

The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion or first motion observations is

      STK = 145
      DIP = 85
     RAKE = -5
       MW = 5.59
       HS = 8.0

The NDK file is 20111106035310.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to those provided by others. The purpose is to look for major differences and also to note slight differences that might be inherent to the processing procedure. For completeness the USGS/SLU solution is repeated from above.
SLU
USGSMT
GCMT
 USGS/SLU Moment Tensor Solution
 ENS  2011/11/06 03:53:10:0  35.53  -96.76   5.2 5.7 Oklahoma
 
 Stations used:
   AG.CCAR AG.FCAR AG.HHAR AG.LCAR AG.WHAR AG.WLAR IU.CCM 
   NM.HBAR NM.MGMO NM.PBMO NM.UALR TA.136A TA.137A TA.236A 
   TA.237A TA.238A TA.ABTX TA.N33A TA.N34A TA.O33A TA.O34A 
   TA.O35A TA.O36A TA.O37A TA.O38A TA.P34A TA.P35A TA.P36A 
   TA.P37A TA.P38A TA.P39B TA.Q34A TA.Q35A TA.Q36A TA.Q37A 
   TA.Q38A TA.Q39A TA.Q40A TA.R34A TA.R35A TA.R36A TA.R37A 
   TA.R38A TA.R39A TA.R40A TA.R41A TA.S34A TA.S35A TA.S36A 
   TA.S37A TA.S38A TA.S39A TA.S40A TA.S42A TA.T34A TA.T35A 
   TA.T36A TA.T37A TA.T38A TA.T39A TA.T40A TA.T41A TA.TUL1 
   TA.U32A TA.U35A TA.U36A TA.U37A TA.U38A TA.U39A TA.U40A 
   TA.U41A TA.U42A TA.U43A TA.V35A TA.V36A TA.V37A TA.V38A 
   TA.V39A TA.V40A TA.V41A TA.V42A TA.V43A TA.W35A TA.W36A 
   TA.W37B TA.W38A TA.W39A TA.W40A TA.W41B TA.W42A TA.W43A 
   TA.WHTX TA.X35A TA.X36A TA.X37A TA.X38A TA.X39A TA.X40A 
   TA.X41A TA.X42A TA.X43A TA.Y35A TA.Y36A TA.Y37A TA.Y38A 
   TA.Y39A TA.Y40A TA.Y41A TA.Y42A TA.Z37A TA.Z38A TA.Z40A 
   US.KSU1 US.MIAR US.WMOK 
 
 Filtering commands used:
   hp c 0.01 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 3.05e+24 dyne-cm
  Mw = 5.59 
  Z  = 8 km
  Plane   Strike  Dip  Rake
   NP1      235    85   -175
   NP2      145    85    -5
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   3.05e+24      0      10
    N   0.00e+00     83     280
    P  -3.05e+24      7     100

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.86e+24
       Mxy     1.06e+24
       Mxz     6.69e+22
       Myy    -2.82e+24
       Myz    -3.67e+23
       Mzz    -4.62e+22
                                                     
                                                     
                                                     
                                                     
                     ######### T ##                  
                 #############   ######              
              ---#########################           
             -----#########################          
           --------##########################        
          ----------######################----       
         ------------##################--------      
        --------------##############------------     
        ---------------##########---------------     
       ------------------#####-------------------    
       -------------------#----------------------    
       -----------------###-------------------       
       ---------------######------------------ P     
        -----------###########----------------       
        ---------##############-----------------     
         ------##################--------------      
          ---#####################------------       
           ########################----------        
             ########################------          
              #########################---           
                 ######################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -4.62e+22   6.69e+22   3.67e+23 
  6.69e+22   2.86e+24  -1.06e+24 
  3.67e+23  -1.06e+24  -2.82e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20111106035310/index.html
	
USGS/SLU Regional Moment Solution
OKLAHOMA

11/11/06 03:53:10.53

Epicenter:  35.537  -96.747
MW 5.6

USGS/SLU REGIONAL MOMENT TENSOR
Depth   7         No. of sta: 32
Moment Tensor;   Scale 10**17 Nm
  Mrr=-0.17       Mtt= 3.22
  Mpp=-3.05       Mrt=-0.07
  Mrp=-0.28       Mtp=-1.09
 Principal axes:
  T  Val=  3.40  Plg= 0  Azm=190
  N       -0.14      85       95
  P       -3.26       5      280

Best Double Couple:Mo=3.3*10**17
 NP1:Strike= 55 Dip=87 Slip=-176
 NP2:       324     86        -3



November 6, 2011, OKLAHOMA, MW=5.7

Meredith Nettles
Goran Ekstrom

CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     C201111060353A
DATA: II IU DK CU MN G  IC GE LD
L.P.BODY WAVES:108S, 197C, T= 40
MANTLE WAVES:   67S,  77C, T=125
SURFACE WAVES: 146S, 319C, T= 50
TIMESTAMP:      Q-20111106092416
CENTROID LOCATION:
ORIGIN TIME:      03:53:13.4 0.1
LAT:35.64N 0.01;LON: 96.73W 0.01
DEP: 12.1  0.6;TRIANG HDUR:  1.8
MOMENT TENSOR: SCALE 10**24 D-CM
RR=-0.360 0.035; TT= 4.580 0.041
PP=-4.220 0.042; RT=-1.550 0.133
RP=-0.320 0.095; TP=-1.640 0.034
PRINCIPAL AXES:
1.(T) VAL=  5.262;PLG=15;AZM=189
2.(N)      -0.659;    73;     40
3.(P)      -4.602;     8;    282
BEST DBLE.COUPLE:M0= 4.93*10**24
NP1: STRIKE=326;DIP=74;SLIP=   5
NP2: STRIKE=235;DIP=86;SLIP= 164

           ###########
       ###################
     -----##################
   ---------##################
  ------------##############---
 ---------------#########-------
   --------------#####----------
 P ------------------------------
   -------------####-------------
 --------------#######------------
 -----------###########-----------
 --------##############---------
 ------#################--------
  --####################-------
   ######################-----
     ########   #########---
       ###### T ##########
           ##   ######
        

Magnitudes

Given the availability of digital waveforms for determination of the moment tensor, this section documents the added processing leading to mLg, if appropriate to the region, and ML by application of the respective IASPEI formulae. As a research study, the linear distance term of the IASPEI formula for ML is adjusted to remove a linear distance trend in residuals to give a regionally defined ML. The defined ML uses horizontal component recordings, but the same procedure is applied to the vertical components since there may be some interest in vertical component ground motions. Residual plots versus distance may indicate interesting features of ground motion scaling in some distance ranges. A residual plot of the regionalized magnitude is given as a function of distance and azimuth, since data sets may transcend different wave propagation provinces.

mLg Magnitude


Left: mLg computed using the IASPEI formula. Center: mLg residuals versus epicentral distance ; the values used for the trimmed mean magnitude estimate are indicated. Right: residuals as a function of distance and azimuth.

ML Magnitude


Left: ML computed using the IASPEI formula for Horizontal components. Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot. Right: Residuals from new relation as a function of distance and azimuth.


Left: ML computed using the IASPEI formula for Vertical components (research). Center: ML residuals computed using a modified IASPEI formula that accounts for path specific attenuation; the values used for the trimmed mean are indicated. The ML relation used for each figure is given at the bottom of each plot. Right: Residuals from new relation as a function of distance and azimuth.

Context

The left panel of the next figure presents the focal mechanism for this earthquake (red) in the context of other nearby events (blue) in the SLU Moment Tensor Catalog. The right panel shows the inferred direction of maximum compressive stress and the type of faulting (green is strike-slip, red is normal, blue is thrust; oblique is shown by a combination of colors). Thus context plot is useful for assessing the appropriateness of the moment tensor of this event.

Waveform Inversion using wvfgrd96

The focal mechanism was determined using broadband seismic waveforms. The location of the event (star) and the stations used for (red) 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's 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 0.01 n 3
lp c 0.06 n 3
The results of this grid search are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    0.5   325    85   -10   5.26 0.3693
WVFGRD96    1.0   325    85    -5   5.29 0.4045
WVFGRD96    2.0   325    85    -5   5.40 0.5247
WVFGRD96    3.0   325    90     0   5.45 0.5795
WVFGRD96    4.0   145    90     0   5.49 0.6132
WVFGRD96    5.0   145    90     0   5.51 0.6285
WVFGRD96    6.0   325    90     5   5.54 0.6352
WVFGRD96    7.0   145    85    -5   5.56 0.6400
WVFGRD96    8.0   145    85    -5   5.59 0.6425
WVFGRD96    9.0   145    85   -10   5.60 0.6298
WVFGRD96   10.0   145    90   -15   5.61 0.6187
WVFGRD96   11.0   325    90    15   5.62 0.6105
WVFGRD96   12.0   325    85    15   5.63 0.6055
WVFGRD96   13.0   325    85    15   5.64 0.6013
WVFGRD96   14.0   325    85    15   5.65 0.5960
WVFGRD96   15.0   325    80    10   5.66 0.5919
WVFGRD96   16.0   325    80    10   5.66 0.5870
WVFGRD96   17.0   325    80    10   5.67 0.5821
WVFGRD96   18.0   325    80    10   5.68 0.5778
WVFGRD96   19.0   325    80    10   5.68 0.5689
WVFGRD96   20.0   325    80    10   5.69 0.5632
WVFGRD96   21.0   325    80    10   5.70 0.5572
WVFGRD96   22.0   325    80    10   5.71 0.5482
WVFGRD96   23.0   325    80    10   5.71 0.5405
WVFGRD96   24.0   325    80    10   5.72 0.5326
WVFGRD96   25.0   325    80    10   5.72 0.5241
WVFGRD96   26.0   325    80    10   5.73 0.5144
WVFGRD96   27.0   325    80    10   5.73 0.5044
WVFGRD96   28.0   325    80    10   5.74 0.4941
WVFGRD96   29.0   325    80    10   5.75 0.4857

The best solution is

WVFGRD96    8.0   145    85    -5   5.59 0.6425

The mechanism corresponding 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, the velocity model used in the predictions may not be perfect and the epicentral parameters may be be off. 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 0.01 n 3
lp c 0.06 n 3
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated. The time scale is relative to the first trace sample.

Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the waveforms. 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:

Assuming only a mislocation, the time shifts are fit to a functional form:

 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.

Surface-Wave Focal Mechanism

The following figure shows the stations used in the grid search for the best focal mechanism to fit the surface-wave spectral amplitudes of the Love and Rayleigh waves.
Location of broadband stations used to obtain focal mechanism from surface-wave spectral amplitudes

The surface-wave determined focal mechanism is shown here.


  NODAL PLANES 

  
  STK=      53.70
  DIP=      85.17
 RAKE=     164.95
  
             OR
  
  STK=     144.99
  DIP=      75.00
 RAKE=       5.00
 
 
DEPTH = 9.0 km
 
Mw = 5.76
Best Fit 0.7820 - P-T axis plot gives solutions with FIT greater than FIT90

Surface-wave analysis

Surface wave analysis was performed using codes from Computer Programs in Seismology, specifically the multiple filter analysis program do_mft and the surface-wave radiation pattern search program srfgrd96.

Data preparation

Digital data were collected, instrument response removed and traces converted to Z, R an T components. Multiple filter analysis was applied to the Z and T traces to obtain the Rayleigh- and Love-wave spectral amplitudes, respectively. These were input to the search program which examined all depths between 1 and 25 km and all possible mechanisms.
Best mechanism fit as a function of depth. The preferred depth is given above. Lower hemisphere projection

Pressure-tension axis trends. Since the surface-wave spectra search does not distinguish between P and T axes and since there is a 180 ambiguity in strike, all possible P and T axes are plotted. First motion data and waveforms will be used to select the preferred mechanism. The purpose of this plot is to provide an idea of the possible range of solutions. The P and T-axes for all mechanisms with goodness of fit greater than 0.9 FITMAX (above) are plotted here.


Focal mechanism sensitivity at the preferred depth. The red color indicates a very good fit to the Love and Rayleigh wave radiation patterns. 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. Because of the symmetry of the spectral amplitude rediation patterns, only strikes from 0-180 degrees are sampled.

Love-wave radiation patterns

Rayleigh-wave radiation patterns