Location

2013/09/16 14:12:31 37.510 -115.481 8.0 3.8 Nevada

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  2013/09/16 14:12:31:0  37.51 -115.48   8.0 3.8 Nevada
 
 Stations used:
   AE.U15A AE.W13A BK.CMB CI.ADO CI.BEL CI.BFS CI.CHF CI.CWC 
   CI.DGR CI.EDW2 CI.FUR CI.GMR CI.GRA CI.GSC CI.HEC CI.IRM 
   CI.ISA CI.MLAC CI.MPM CI.NEE2 CI.SHO CI.SLA CI.TIN CI.TUQ 
   CI.VCS CI.VES II.PFO IM.NV31 LB.BMN NN.KVN NN.OMMB NN.PRN 
   NN.RYN NN.SHP NN.UNVG NN.WTNK PB.B086A TA.R11A TA.Y12C 
   US.TPNV UU.CCUT UU.KNB UU.LCMT UU.PKCU UU.PSUT UU.SZCU 
   UU.VRUT UU.ZNPU 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 2.02e+21 dyne-cm
  Mw = 3.47 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1        5    90   -150
   NP2      275    60     0
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.02e+21     21     136
    N   0.00e+00     60       5
    P  -2.02e+21     21     234

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.04e+20
       Mxy    -1.72e+21
       Mxz    -8.80e+19
       Myy    -3.04e+20
       Myz     1.01e+21
       Mzz     0.00e+00
                                                     
                                                     
                                                     
                                                     
                     #########-----                  
                 #############---------              
              ###############-------------           
             ################--------------          
           ##################----------------        
          ###################-----------------       
         ####################------------------      
        ########-------------######-------------     
        ###-----------------############--------     
       #--------------------################-----    
       ---------------------##################---    
       ---------------------####################-    
       ---------------------#####################    
        --------------------####################     
        -------------------#####################     
         ----   -----------####################      
          --- P -----------###########   #####       
           --   -----------########### T ####        
             --------------###########   ##          
              -------------###############           
                 ---------#############              
                     -----#########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  0.00e+00  -8.80e+19  -1.01e+21 
 -8.80e+19   3.04e+20   1.72e+21 
 -1.01e+21   1.72e+21  -3.04e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130916141231/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 = 60
     RAKE = 0
       MW = 3.47
       HS = 10.0

The NDK file is 20130916141231.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

        
SLU
UNR
 USGS/SLU Moment Tensor Solution
 ENS  2013/09/16 14:12:31:0  37.51 -115.48   8.0 3.8 Nevada
 
 Stations used:
   AE.U15A AE.W13A BK.CMB CI.ADO CI.BEL CI.BFS CI.CHF CI.CWC 
   CI.DGR CI.EDW2 CI.FUR CI.GMR CI.GRA CI.GSC CI.HEC CI.IRM 
   CI.ISA CI.MLAC CI.MPM CI.NEE2 CI.SHO CI.SLA CI.TIN CI.TUQ 
   CI.VCS CI.VES II.PFO IM.NV31 LB.BMN NN.KVN NN.OMMB NN.PRN 
   NN.RYN NN.SHP NN.UNVG NN.WTNK PB.B086A TA.R11A TA.Y12C 
   US.TPNV UU.CCUT UU.KNB UU.LCMT UU.PKCU UU.PSUT UU.SZCU 
   UU.VRUT UU.ZNPU 
 
 Filtering commands used:
   cut a -30 a 180
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.06 n 3 
 
 Best Fitting Double Couple
  Mo = 2.02e+21 dyne-cm
  Mw = 3.47 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1        5    90   -150
   NP2      275    60     0
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.02e+21     21     136
    N   0.00e+00     60       5
    P  -2.02e+21     21     234

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.04e+20
       Mxy    -1.72e+21
       Mxz    -8.80e+19
       Myy    -3.04e+20
       Myz     1.01e+21
       Mzz     0.00e+00
                                                     
                                                     
                                                     
                                                     
                     #########-----                  
                 #############---------              
              ###############-------------           
             ################--------------          
           ##################----------------        
          ###################-----------------       
         ####################------------------      
        ########-------------######-------------     
        ###-----------------############--------     
       #--------------------################-----    
       ---------------------##################---    
       ---------------------####################-    
       ---------------------#####################    
        --------------------####################     
        -------------------#####################     
         ----   -----------####################      
          --- P -----------###########   #####       
           --   -----------########### T ####        
             --------------###########   ##          
              -------------###############           
                 ---------#############              
                     -----#########                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  0.00e+00  -8.80e+19  -1.01e+21 
 -8.80e+19   3.04e+20   1.72e+21 
 -1.01e+21   1.72e+21  -3.04e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130916141231/index.html
	
REVIEWED BY NSL STAFF

Event ID:423851
Origin ID:1047662
Algorithm: Ichinose (2003) Long Period, Regional-Distance Waves
Seismic Moment Tensor Solution

2013/09/16 (259) 14:12:32.00 37.5096 -115.4806 1047662
	Depth =  10.0 (km)
	Mw    =  3.49
	Mo    =  2.16x10^21 (dyne x cm)

	Percent Double Couple =  99 %
	Percent CLVD          =   1 %
	no ISO calculated
	Epsilon=-0.00
	 Percent Variance Reduction =  52.35 %
	 Total Fit                  =  30.44 
	Major Double Couple
		            strike dip   rake
		Nodal Plane 1: 170  63  178
		Nodal Plane 2: 261  88   27

	DEVIATORIC MOMENT TENSOR

	Moment Tensor Elements: Spherical Coordinates
		Mrr=  0.06 Mtt= -0.63 Mff=  0.57
		Mrt= -0.95 Mrf= -0.21 Mtf=  1.83 EXP=21


	Moment Tensor Elements: Cartesian Coordinates
		-0.63 -1.83 -0.95
		-1.83  0.57  0.21
		-0.95  0.21  0.06

	Eigenvalues:
		T-axis eigenvalue=  2.16
		N-axis eigenvalue= -0.01
		P-axis eigenvalue= -2.15

	Eigenvalues and eigenvectors of the Major Double Couple:
		T-axis ev= 2.16 trend=129 plunge=20
		N-axis ev= 0.00 trend=265 plunge=63
		P-axis ev=-2.16 trend=33 plunge=17

	Maximum Azmuithal Gap=282 Distance to Nearest Station= 39.6 (km)

	Number of Stations (D=Displacement/V=Velocity) Used=3 (defining only)
		
	 PRN.NN.D SHP.NN.D CCUT.UU.D


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


All Stations defining and nondefining: 
Station.Net 	Def 	Distance 	Azi    	Bazi  	lo-f 	hi-f vmodel
            	    	(km)     	(deg)  	(deg) 	(Hz) 	(Hz)    
PRN.NN (D) 	Y 	    39.6  	106  	286  	0.020 	0.080 PRN.NN.wus.glib
SHP.NN (D) 	Y 	   115.7  	166  	346  	0.020 	0.080 SHP.NN.wus.glib
CCUT.UU (D) 	Y 	   186.9  	 88  	269  	0.020 	0.080 CCUT.UU.wus.glib

 (V)-velocity (D)-Displacement

Author: www-data
Date: 2013/09/16 14:46:54

mtinv Version 2.1_DEVEL OCT2008

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 0.06 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    0.5    90    70   -15   3.15 0.2906
WVFGRD96    1.0    95    90     5   3.16 0.3127
WVFGRD96    2.0   275    90     0   3.25 0.3882
WVFGRD96    3.0    95    90     0   3.29 0.4146
WVFGRD96    4.0   275    70     0   3.34 0.4308
WVFGRD96    5.0   275    70    -5   3.36 0.4428
WVFGRD96    6.0   275    70    -5   3.38 0.4512
WVFGRD96    7.0   275    65     5   3.41 0.4585
WVFGRD96    8.0   275    60     5   3.45 0.4659
WVFGRD96    9.0   275    60     5   3.46 0.4683
WVFGRD96   10.0   275    60     0   3.47 0.4692
WVFGRD96   11.0   275    60     0   3.49 0.4686
WVFGRD96   12.0   275    60     0   3.50 0.4664
WVFGRD96   13.0   275    65     0   3.50 0.4638
WVFGRD96   14.0   275    65     0   3.51 0.4600
WVFGRD96   15.0   275    65     0   3.52 0.4555
WVFGRD96   16.0   270    70   -15   3.53 0.4509
WVFGRD96   17.0   270    70   -20   3.54 0.4456
WVFGRD96   18.0   270    70   -15   3.54 0.4397
WVFGRD96   19.0   270    75   -20   3.55 0.4336
WVFGRD96   20.0   270    70   -15   3.56 0.4274
WVFGRD96   21.0   270    70   -15   3.57 0.4209
WVFGRD96   22.0   270    70   -15   3.57 0.4143
WVFGRD96   23.0   270    70   -15   3.58 0.4075
WVFGRD96   24.0   270    70   -15   3.59 0.4010
WVFGRD96   25.0   270    75   -15   3.59 0.3943
WVFGRD96   26.0   270    75   -15   3.60 0.3876
WVFGRD96   27.0   275    75   -15   3.61 0.3808
WVFGRD96   28.0   275    75   -15   3.61 0.3741
WVFGRD96   29.0   275    75   -15   3.62 0.3671

The best solution is

WVFGRD96   10.0   275    60     0   3.47 0.4692

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 0.06 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.
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 00:22:59 CST 2015