Location

2013/07/07 08:38:59 36.456 -112.576 5.2 4.0 Arizona

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  2013/07/07 08:38:59:0  36.46 -112.58   5.2 4.0 Arizona
 
 Stations used:
   AE.W13A AE.X18A AE.Y14A AZ.KNW AZ.SND AZ.TRO AZ.WMC CI.ADO 
   CI.BC3 CI.BEL CI.BFS CI.DAN CI.FUR CI.GLA CI.GMR CI.GSC 
   CI.HEC CI.IRM CI.MPM CI.MUR CI.PDM CI.PLM CI.RRX CI.SVD 
   CI.SWS CI.TIN CI.TUQ CI.VTV IU.TUC PB.B082A PB.B086A 
   PB.B088A TA.214A TA.R11A TA.S22A TA.W18A TA.Y12C US.DUG 
   US.HWUT US.MVCO US.TPNV US.WUAZ UU.BGU UU.BRPU UU.CCUT 
   UU.HVU UU.KNB UU.LCMT UU.MPU UU.MTPU UU.PKCU UU.PSUT UU.SRU 
   UU.SZCU UU.TCRU UU.TMU 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.08 n 3 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 2.24e+21 dyne-cm
  Mw = 3.50 
  Z  = 17 km
  Plane   Strike  Dip  Rake
   NP1      111    66   -129
   NP2      355    45   -35
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.24e+21     12     229
    N   0.00e+00     35     130
    P  -2.24e+21     52     335

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.35e+20
       Mxy     1.39e+21
       Mxz    -1.29e+21
       Myy     1.05e+21
       Myz     1.13e+20
       Mzz    -1.28e+21
                                                     
                                                     
                                                     
                                                     
                     --------######                  
                 --------------########              
              -------------------#########           
             ----------------------########          
           -------------------------#########        
          ------------   ------------#########       
         ------------- P -------------#########      
        #-------------   -------------##########     
        ###----------------------------#########     
       #####---------------------------##########    
       #######-------------------------##########    
       ##########----------------------##########    
       #############-------------------##########    
        ###############----------------#########     
        ####################-----------#########     
         ###########################--######---      
          ###   ######################--------       
           ## T #####################--------        
                ####################-------          
              #####################-------           
                 #################-----              
                     ###########---                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.28e+21  -1.29e+21  -1.13e+20 
 -1.29e+21   2.35e+20  -1.39e+21 
 -1.13e+20  -1.39e+21   1.05e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130707083859/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 = 355
      DIP = 45
     RAKE = -35
       MW = 3.50
       HS = 17.0

The NDK file is 20130707083859.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
 USGS/SLU Moment Tensor Solution
 ENS  2013/07/07 08:38:59:0  36.46 -112.58   5.2 4.0 Arizona
 
 Stations used:
   AE.W13A AE.X18A AE.Y14A AZ.KNW AZ.SND AZ.TRO AZ.WMC CI.ADO 
   CI.BC3 CI.BEL CI.BFS CI.DAN CI.FUR CI.GLA CI.GMR CI.GSC 
   CI.HEC CI.IRM CI.MPM CI.MUR CI.PDM CI.PLM CI.RRX CI.SVD 
   CI.SWS CI.TIN CI.TUQ CI.VTV IU.TUC PB.B082A PB.B086A 
   PB.B088A TA.214A TA.R11A TA.S22A TA.W18A TA.Y12C US.DUG 
   US.HWUT US.MVCO US.TPNV US.WUAZ UU.BGU UU.BRPU UU.CCUT 
   UU.HVU UU.KNB UU.LCMT UU.MPU UU.MTPU UU.PKCU UU.PSUT UU.SRU 
   UU.SZCU UU.TCRU UU.TMU 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.08 n 3 
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 2.24e+21 dyne-cm
  Mw = 3.50 
  Z  = 17 km
  Plane   Strike  Dip  Rake
   NP1      111    66   -129
   NP2      355    45   -35
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.24e+21     12     229
    N   0.00e+00     35     130
    P  -2.24e+21     52     335

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.35e+20
       Mxy     1.39e+21
       Mxz    -1.29e+21
       Myy     1.05e+21
       Myz     1.13e+20
       Mzz    -1.28e+21
                                                     
                                                     
                                                     
                                                     
                     --------######                  
                 --------------########              
              -------------------#########           
             ----------------------########          
           -------------------------#########        
          ------------   ------------#########       
         ------------- P -------------#########      
        #-------------   -------------##########     
        ###----------------------------#########     
       #####---------------------------##########    
       #######-------------------------##########    
       ##########----------------------##########    
       #############-------------------##########    
        ###############----------------#########     
        ####################-----------#########     
         ###########################--######---      
          ###   ######################--------       
           ## T #####################--------        
                ####################-------          
              #####################-------           
                 #################-----              
                     ###########---                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.28e+21  -1.29e+21  -1.13e+20 
 -1.29e+21   2.35e+20  -1.39e+21 
 -1.13e+20  -1.39e+21   1.05e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130707083859/index.html
	

Magnitudes

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 a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.08 n 3 
br c 0.12 0.25 n 4 p 2
The results of this grid search from 0.5 to 19 km depth are as follow:

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    0.5   305    50   -90   3.19 0.3116
WVFGRD96    1.0   165    90     5   3.22 0.3039
WVFGRD96    2.0   170    80   -10   3.29 0.3469
WVFGRD96    3.0   170    75    -5   3.34 0.3453
WVFGRD96    4.0    10    30   -10   3.41 0.3576
WVFGRD96    5.0    10    30   -10   3.41 0.4042
WVFGRD96    6.0     5    35   -15   3.40 0.4310
WVFGRD96    7.0     5    35   -20   3.40 0.4469
WVFGRD96    8.0     5    30   -15   3.45 0.4558
WVFGRD96    9.0     5    35   -15   3.45 0.4654
WVFGRD96   10.0     0    35   -25   3.45 0.4726
WVFGRD96   11.0     0    40   -25   3.45 0.4793
WVFGRD96   12.0    -5    40   -35   3.47 0.4854
WVFGRD96   13.0   355    40   -40   3.48 0.4909
WVFGRD96   14.0   355    45   -35   3.48 0.4959
WVFGRD96   15.0   355    45   -35   3.49 0.4997
WVFGRD96   16.0   355    45   -35   3.49 0.5019
WVFGRD96   17.0   355    45   -35   3.50 0.5026
WVFGRD96   18.0   355    45   -35   3.51 0.5025
WVFGRD96   19.0   355    50   -35   3.53 0.5015
WVFGRD96   20.0   355    50   -35   3.53 0.4994
WVFGRD96   21.0   350    50   -35   3.55 0.4970
WVFGRD96   22.0   350    50   -35   3.56 0.4929
WVFGRD96   23.0   350    50   -35   3.56 0.4876
WVFGRD96   24.0   350    50   -35   3.57 0.4811
WVFGRD96   25.0   350    50   -35   3.58 0.4737
WVFGRD96   26.0   350    50   -35   3.59 0.4652
WVFGRD96   27.0   350    50   -35   3.59 0.4565
WVFGRD96   28.0   350    50   -35   3.60 0.4470
WVFGRD96   29.0   350    50   -35   3.61 0.4377

The best solution is

WVFGRD96   17.0   355    45   -35   3.50 0.5026

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 a -30 a 180
rtr
taper w 0.1
hp c 0.02 n 3 
lp c 0.08 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:

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 WUS model 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    

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 00:21:50 CST 2015