Location

2014/06/04 21:19:24 35.571 -92.271 2.8 3.8 Arkansas

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  2014/06/04 21:19:24:0  35.57  -92.27   2.8 3.8 Arkansas
 
 Stations used:
   AG.FCAR AG.HHAR AG.LCAR AG.WHAR AG.WLAR GS.KAN12 GS.OK027 
   GS.OK028 GS.OK029 IU.CCM IU.WVT N4.N38B N4.N41A N4.P38B 
   N4.P40B N4.P43A N4.Q44B N4.R40B N4.S44A N4.T35B N4.T42B 
   N4.T47A N4.V48A N4.Y49A N4.Z38B NM.CLTN NM.GLAT NM.GNAR 
   NM.HALT NM.HENM NM.HICK NM.LNXT NM.MPH NM.OLIL NM.PEBM 
   NM.PENM NM.PLAL NM.PVMO NM.SLM NM.UALR NM.USIN NM.UTMT 
   OK.X37A TA.TUL1 TA.U40A TA.W39A TA.W41B TA.X40A TA.Z41A 
   US.KSU1 US.LRAL US.MIAR 
 
 Filtering commands used:
   cut o DIST/3.3 -50 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 6.53e+21 dyne-cm
  Mw = 3.81 
  Z  = 2 km
  Plane   Strike  Dip  Rake
   NP1      182    80   165
   NP2      275    75    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.53e+21     18     138
    N   0.00e+00     72     331
    P  -6.53e+21      4     229

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.16e+20
       Mxy    -6.17e+21
       Mxz    -1.12e+21
       Myy    -1.08e+21
       Myz     1.57e+21
       Mzz     5.67e+20
                                                     
                                                     
                                                     
                                                     
                     #######-------                  
                 ###########-----------              
              #############---------------           
             ##############----------------          
           ################------------------        
          ################--------------------       
         #################---------------------      
        ##################----------------------     
        ##################----------------------     
       ###----------------##########-------------    
       -------------------#################------    
       ------------------######################--    
       ------------------########################    
        -----------------#######################     
        -----------------#######################     
         ----------------######################      
          ----------------#############   ####       
           -   -----------############# T ###        
             P -----------#############   #          
               -----------################           
                 ---------#############              
                     ------########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.67e+20  -1.12e+21  -1.57e+21 
 -1.12e+21   5.16e+20   6.17e+21 
 -1.57e+21   6.17e+21  -1.08e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140604211924/index.html
        

Preferred Solution

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

      STK = 275
      DIP = 75
     RAKE = 10
       MW = 3.81
       HS = 2.0

The NDK file is 20140604211924.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
 USGS/SLU Moment Tensor Solution
 ENS  2014/06/04 21:19:24:0  35.57  -92.27   2.8 3.8 Arkansas
 
 Stations used:
   AG.FCAR AG.HHAR AG.LCAR AG.WHAR AG.WLAR GS.KAN12 GS.OK027 
   GS.OK028 GS.OK029 IU.CCM IU.WVT N4.N38B N4.N41A N4.P38B 
   N4.P40B N4.P43A N4.Q44B N4.R40B N4.S44A N4.T35B N4.T42B 
   N4.T47A N4.V48A N4.Y49A N4.Z38B NM.CLTN NM.GLAT NM.GNAR 
   NM.HALT NM.HENM NM.HICK NM.LNXT NM.MPH NM.OLIL NM.PEBM 
   NM.PENM NM.PLAL NM.PVMO NM.SLM NM.UALR NM.USIN NM.UTMT 
   OK.X37A TA.TUL1 TA.U40A TA.W39A TA.W41B TA.X40A TA.Z41A 
   US.KSU1 US.LRAL US.MIAR 
 
 Filtering commands used:
   cut o DIST/3.3 -50 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 6.53e+21 dyne-cm
  Mw = 3.81 
  Z  = 2 km
  Plane   Strike  Dip  Rake
   NP1      182    80   165
   NP2      275    75    10
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.53e+21     18     138
    N   0.00e+00     72     331
    P  -6.53e+21      4     229

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     5.16e+20
       Mxy    -6.17e+21
       Mxz    -1.12e+21
       Myy    -1.08e+21
       Myz     1.57e+21
       Mzz     5.67e+20
                                                     
                                                     
                                                     
                                                     
                     #######-------                  
                 ###########-----------              
              #############---------------           
             ##############----------------          
           ################------------------        
          ################--------------------       
         #################---------------------      
        ##################----------------------     
        ##################----------------------     
       ###----------------##########-------------    
       -------------------#################------    
       ------------------######################--    
       ------------------########################    
        -----------------#######################     
        -----------------#######################     
         ----------------######################      
          ----------------#############   ####       
           -   -----------############# T ###        
             P -----------#############   #          
               -----------################           
                 ---------#############              
                     ------########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  5.67e+20  -1.12e+21  -1.57e+21 
 -1.12e+21   5.16e+20   6.17e+21 
 -1.57e+21   6.17e+21  -1.08e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20140604211924/index.html
	
Regional Moment Tensor (Mwr)

Moment magnitude derived from a moment tensor 
inversion of complete waveforms at regional 
distances (less than ~8 degrees), generally used 
for the analysis of small to moderate size 
earthquakes (typically Mw 3.5-6.0) crust or 
upper mantle earthquakes.

Moment
    5.83e+14 N-m
Magnitude
    3.8
Percent DC
    75%
Depth
    8.0 km
Updated
    2014-06-04 21:51:27 UTC
Author
    us
Catalog
    us
Contributor
    us
Code
    us_c000rb2u_mwr

Principal Axes
Axis	Value	Plunge	Azimuth
T	5.470	15	313
N	0.662	65	187
P	-6.133	19	48
Nodal Planes
Plane	Strike	Dip	Rake
NP1	181	87	-156
NP2	90	66	-3



        

Magnitudes

mLg Magnitude


(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

ML Magnitude


(a) ML computed using the IASPEI formula for Horizontal components; (b) 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.


(a) ML computed using the IASPEI formula for Vertical components (research); (b) 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.

Context

The next figure presents the focal mechanism for this earthquake (red) in the context of other events (blue) in the SLU Moment Tensor Catalog which are within ± 0.5 degrees of the new event. This comparison is shown in the left panel of the figure. 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).

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:

cut o DIST/3.3 -50 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 n 3 
The results of this grid search from 0.5 to 19 km depth are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    1.0   270    80   -20   3.79 0.6038
WVFGRD96    2.0   275    75    10   3.81 0.6118
WVFGRD96    3.0   275    65    10   3.84 0.6001
WVFGRD96    4.0   275    65     5   3.85 0.5823
WVFGRD96    5.0    90    65    -5   3.85 0.5767
WVFGRD96    6.0    90    65    -5   3.86 0.5758
WVFGRD96    7.0    90    65    -5   3.87 0.5744
WVFGRD96    8.0    90    70    -5   3.88 0.5738
WVFGRD96    9.0    90    70    -5   3.89 0.5743
WVFGRD96   10.0    90    65    -5   3.90 0.5735
WVFGRD96   11.0    90    65    -5   3.91 0.5700
WVFGRD96   12.0    90    70    -5   3.92 0.5657
WVFGRD96   13.0    90    70    -5   3.93 0.5605
WVFGRD96   14.0    90    70    -5   3.93 0.5560
WVFGRD96   15.0    95    70     5   3.94 0.5519
WVFGRD96   16.0    95    70     5   3.95 0.5460
WVFGRD96   17.0    95    70     5   3.96 0.5400
WVFGRD96   18.0    95    70     5   3.96 0.5334
WVFGRD96   19.0    95    70    -5   3.97 0.5264
WVFGRD96   20.0    95    70    -5   3.98 0.5184
WVFGRD96   21.0    95    70    -5   3.99 0.5113
WVFGRD96   22.0    95    70    -5   3.99 0.5052
WVFGRD96   23.0    95    70    -5   4.00 0.4980
WVFGRD96   24.0   275    75     5   3.99 0.4864
WVFGRD96   25.0   275    75     5   4.00 0.4814
WVFGRD96   26.0   275    75    10   4.00 0.4756
WVFGRD96   27.0   275    75    10   4.01 0.4720
WVFGRD96   28.0    95    75     0   4.02 0.4710
WVFGRD96   29.0    95    75     0   4.02 0.4693

The best solution is

WVFGRD96    2.0   275    75    10   3.81 0.6118

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

cut o DIST/3.3 -50 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.10 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.
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:

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.

Discussion

Acknowledgements

Thanks also to the many seismic network operators whose dedication make this effort possible: University of Nevada Reno, University of Alaska, University of Washington, Oregon State University, University of Utah, Montana Bureas of Mines, UC Berkely, Caltech, UC San Diego, Saint Louis University, University of Memphis, Lamont Doherty Earth Observatory, the Iris stations and the Transportable Array of EarthScope.

Velocity Model

The CUS model 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:

Last Changed Mon Dec 7 00:12:16 CST 2015