Location

2010/10/05 21:22:47 37.153 -117.376 9.2 4.10 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  2010/10/05 21:22:47:0  37.15 -117.38   9.2 4.1 Nevada
 
 Stations used:
   BK.MOD BK.WDC CI.BAR CI.FUR CI.GSC CI.ISA CI.MLAC CI.PASC 
   CI.TIN II.PFO LB.BMN LB.DAC NC.AFD NC.MDPB US.DUG US.TPNV 
   US.WVOR UU.BGU UU.CCUT UU.CVRU UU.LCMT UU.PSUT UU.TCRU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 1.30e+22 dyne-cm
  Mw = 4.01 
  Z  = 11 km
  Plane   Strike  Dip  Rake
   NP1      240    80   -20
   NP2      334    70   -169
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.30e+22      7     288
    N   0.00e+00     68      34
    P  -1.30e+22     21     195

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -9.30e+21
       Mxy    -6.69e+21
       Mxz     4.69e+21
       Myy     1.08e+22
       Myz    -2.53e+20
       Mzz    -1.52e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ###-------------------              
              #########-------------------           
             ############------------------          
           ###############-------------------        
          ##################-----------------#       
           ##################----------########      
         T ###################-----#############     
           #####################################     
       #####################----#################    
       ##################--------################    
       ###############------------###############    
       ############----------------##############    
        ########-------------------#############     
        ######----------------------############     
         ###------------------------###########      
          ---------------------------#########       
           --------------------------########        
             ---------   ------------######          
              -------- P ------------#####           
                 -----   ------------##              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.52e+21   4.69e+21   2.53e+20 
  4.69e+21  -9.30e+21   6.69e+21 
  2.53e+20   6.69e+21   1.08e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101005212247/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 = 240
      DIP = 80
     RAKE = -20
       MW = 4.01
       HS = 11.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
        
SLU
UNR
 USGS/SLU Moment Tensor Solution
 ENS  2010/10/05 21:22:47:0  37.15 -117.38   9.2 4.1 Nevada
 
 Stations used:
   BK.MOD BK.WDC CI.BAR CI.FUR CI.GSC CI.ISA CI.MLAC CI.PASC 
   CI.TIN II.PFO LB.BMN LB.DAC NC.AFD NC.MDPB US.DUG US.TPNV 
   US.WVOR UU.BGU UU.CCUT UU.CVRU UU.LCMT UU.PSUT UU.TCRU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 1.30e+22 dyne-cm
  Mw = 4.01 
  Z  = 11 km
  Plane   Strike  Dip  Rake
   NP1      240    80   -20
   NP2      334    70   -169
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.30e+22      7     288
    N   0.00e+00     68      34
    P  -1.30e+22     21     195

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -9.30e+21
       Mxy    -6.69e+21
       Mxz     4.69e+21
       Myy     1.08e+22
       Myz    -2.53e+20
       Mzz    -1.52e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ###-------------------              
              #########-------------------           
             ############------------------          
           ###############-------------------        
          ##################-----------------#       
           ##################----------########      
         T ###################-----#############     
           #####################################     
       #####################----#################    
       ##################--------################    
       ###############------------###############    
       ############----------------##############    
        ########-------------------#############     
        ######----------------------############     
         ###------------------------###########      
          ---------------------------#########       
           --------------------------########        
             ---------   ------------######          
              -------- P ------------#####           
                 -----   ------------##              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.52e+21   4.69e+21   2.53e+20 
  4.69e+21  -9.30e+21   6.69e+21 
  2.53e+20   6.69e+21   1.08e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20101005212247/index.html
	
REVIEWED BY NSL STAFF

Event ID:318065
Origin ID:756357
Seismic Moment Tensor Solution

2010/10/05 (278) 21:22:49.00 37.1343 -117.3842 756357
	Depth =  10.0 (km)
	Mw    =  4.01
	Mo    =  1.27x10^22 (dyne x cm)

	Percent Double Couple = 100 %
	Percent CLVD          =   0 %
	no ISO calculated
	Epsilon=-0.00
	 Percent Variance Reduction =  60.03 %
	 Total Fit                  =  49.05 
	Major Double Couple
		            strike dip   rake
		Nodal Plane 1: 337  62 -161
		Nodal Plane 2: 238  74  -30

	DEVIATORIC MOMENT TENSOR

	Moment Tensor Elements: Spherical Coordinates
		Mrr= -0.34 Mtt= -0.71 Mff=  1.05
		Mrt=  0.61 Mrf=  0.02 Mtf=  0.62 EXP=22


	Moment Tensor Elements: Cartesian Coordinates
		-0.71 -0.62  0.61
		-0.62  1.05 -0.02
		 0.61 -0.02 -0.34

	Eigenvalues:
		T-axis eigenvalue=  1.27
		N-axis eigenvalue= -0.00
		P-axis eigenvalue= -1.27

	Eigenvalues and eigenvectors of the Major Double Couple:
		T-axis ev= 1.27 trend=290 plunge=8
		N-axis ev= 0.00 trend=32 plunge=57
		P-axis ev=-1.27 trend=195 plunge=32

	Maximum Azmuithal Gap=168 Distance to Nearest Station= 75.5 (km)

	Number of Stations (D=Displacement/V=Velocity) Used=6 (defining only)
		
	 TIN.CI.D FUR.CI.D DAC.LB.D TPNV.US.D
	 MLAC.CI.D LRL.CI.D


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


All Stations defining and nondefining: 
Station.Net 	Def 	Distance 	Azi    	Bazi  	lo-f 	hi-f vmodel
            	    	(km)     	(deg)  	(deg) 	(Hz) 	(Hz)    
TIN.CI (D) 	Y 	    75.5  	263  	 83  	0.020 	0.080 TIN.CI.wus.glib
FUR.CI (D) 	Y 	    87.3  	148  	328  	0.020 	0.080 FUR.CI.wus.glib
DAC.LB (D) 	Y 	    96.7  	191  	 11  	0.020 	0.080 DAC.LB.wus.glib
TPNV.US (D) 	Y 	   102.7  	101  	282  	0.020 	0.080 TPNV.US.wus.glib
MLAC.CI (D) 	Y 	   139.8  	294  	113  	0.020 	0.080 MLAC.CI.wus.glib
LRL.CI (D) 	Y 	   185.7  	188  	  8  	0.020 	0.080 LRL.CI.wus.glib

 (V)-velocity (D)-Displacement

Author: www-data
Date: 2010/10/05 21:45:05

mtinv Version 2.1_DEVEL OCT2008

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 0.06 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    65    85     5   3.57 0.2568
WVFGRD96    1.0    65    85     5   3.61 0.2822
WVFGRD96    2.0    65    85     5   3.72 0.3573
WVFGRD96    3.0    65    80    20   3.80 0.3946
WVFGRD96    4.0   245    90   -25   3.83 0.4186
WVFGRD96    5.0   240    80   -30   3.88 0.4466
WVFGRD96    6.0   240    80   -25   3.90 0.4791
WVFGRD96    7.0   240    80   -25   3.92 0.5034
WVFGRD96    8.0   240    75   -30   3.97 0.5279
WVFGRD96    9.0   240    75   -25   3.98 0.5446
WVFGRD96   10.0   240    80   -25   4.00 0.5543
WVFGRD96   11.0   240    80   -20   4.01 0.5578
WVFGRD96   12.0   240    80   -20   4.02 0.5561
WVFGRD96   13.0   240    80   -20   4.02 0.5514
WVFGRD96   14.0   245    85   -20   4.02 0.5446
WVFGRD96   15.0   245    85   -15   4.03 0.5368
WVFGRD96   16.0   245    85   -15   4.03 0.5280
WVFGRD96   17.0   245    85   -15   4.04 0.5186
WVFGRD96   18.0   245    85   -15   4.04 0.5082
WVFGRD96   19.0   245    85   -15   4.05 0.4975
WVFGRD96   20.0   245    85   -15   4.05 0.4878
WVFGRD96   21.0   245    85   -15   4.06 0.4783
WVFGRD96   22.0    65    90    15   4.06 0.4681
WVFGRD96   23.0    65    90    15   4.06 0.4588
WVFGRD96   24.0    65    90    15   4.07 0.4496
WVFGRD96   25.0    65    90    15   4.07 0.4407
WVFGRD96   26.0    65    90    15   4.08 0.4319
WVFGRD96   27.0   245    90   -15   4.08 0.4236
WVFGRD96   28.0    65    90    15   4.08 0.4156
WVFGRD96   29.0    65    90    15   4.09 0.4077

The best solution is

WVFGRD96   11.0   240    80   -20   4.01 0.5578

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 0.06 n 3
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

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 WUS 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:

DATE=Tue Oct 5 18:25:48 CDT 2010

Last Changed 2010/10/05