Location

2010/09/30 10:17:01 37.164 -117.379 11.0 3.80 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  2010/09/30 10:17:01:5  37.16 -117.38  11.0 3.8 Nevada
 
 Stations used:
   CI.FUR CI.GLA CI.GSC CI.LDF CI.TIN LB.DAC TA.R11A US.DUG 
   US.TPNV UU.CCUT UU.NLU UU.SZCU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 6.31e+21 dyne-cm
  Mw = 3.80 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1      240    75   -25
   NP2      337    66   -164
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.31e+21      6     290
    N   0.00e+00     61      31
    P  -6.31e+21     28     197

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.78e+21
       Mxy    -3.34e+21
       Mxz     2.74e+21
       Myy     5.12e+21
       Myz     1.27e+20
       Mzz    -1.33e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 #####-----------------              
              ###########-----------------           
             ##############----------------          
           #################-----------------        
          ###################---------------##       
           ####################------##########      
         T #####################################     
           #################-----###############     
       ##################--------################    
       ###############------------###############    
       #############---------------##############    
       ##########-------------------#############    
        #######---------------------############     
        #####-----------------------############     
         ##--------------------------##########      
          ---------------------------#########       
           -----------   ------------########        
             --------- P ------------######          
              --------   ------------#####           
                 --------------------##              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.33e+21   2.74e+21  -1.27e+20 
  2.74e+21  -3.78e+21   3.34e+21 
 -1.27e+20   3.34e+21   5.12e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100930101701/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 = 75
     RAKE = -25
       MW = 3.80
       HS = 10.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
UNR
 USGS/SLU Moment Tensor Solution
 ENS  2010/09/30 10:17:01:5  37.16 -117.38  11.0 3.8 Nevada
 
 Stations used:
   CI.FUR CI.GLA CI.GSC CI.LDF CI.TIN LB.DAC TA.R11A US.DUG 
   US.TPNV UU.CCUT UU.NLU UU.SZCU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.10 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 6.31e+21 dyne-cm
  Mw = 3.80 
  Z  = 10 km
  Plane   Strike  Dip  Rake
   NP1      240    75   -25
   NP2      337    66   -164
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.31e+21      6     290
    N   0.00e+00     61      31
    P  -6.31e+21     28     197

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -3.78e+21
       Mxy    -3.34e+21
       Mxz     2.74e+21
       Myy     5.12e+21
       Myz     1.27e+20
       Mzz    -1.33e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 #####-----------------              
              ###########-----------------           
             ##############----------------          
           #################-----------------        
          ###################---------------##       
           ####################------##########      
         T #####################################     
           #################-----###############     
       ##################--------################    
       ###############------------###############    
       #############---------------##############    
       ##########-------------------#############    
        #######---------------------############     
        #####-----------------------############     
         ##--------------------------##########      
          ---------------------------#########       
           -----------   ------------########        
             --------- P ------------######          
              --------   ------------#####           
                 --------------------##              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.33e+21   2.74e+21  -1.27e+20 
  2.74e+21  -3.78e+21   3.34e+21 
 -1.27e+20   3.34e+21   5.12e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20100930101701/index.html
	
REVIEWED BY NSL STAFF

Event ID:317403
Origin ID:755087
Seismic Moment Tensor Solution

2010/09/30 (273) 10:17:00.00 37.1636 -117.3788 755087
	Depth =  14.0 (km)
	Mw    =  3.77
	Mo    =  5.70x10^21 (dyne x cm)

	Percent Double Couple =  99 %
	Percent CLVD          =   1 %
	no ISO calculated
	Epsilon=-0.00
	 Percent Variance Reduction =  52.70 %
	 Total Fit                  =  32.74 
	Major Double Couple
		            strike dip   rake
		Nodal Plane 1:  68  80    7
		Nodal Plane 2: 337  83  170

	DEVIATORIC MOMENT TENSOR

	Moment Tensor Elements: Spherical Coordinates
		Mrr=  0.23 Mtt= -4.05 Mff=  3.82
		Mrt=  0.28 Mrf=  1.15 Mtf=  3.95 EXP=21


	Moment Tensor Elements: Cartesian Coordinates
		-4.05 -3.95  0.28
		-3.95  3.82 -1.15
		 0.28 -1.15  0.23

	Eigenvalues:
		T-axis eigenvalue=  5.71
		N-axis eigenvalue= -0.02
		P-axis eigenvalue= -5.69

	Eigenvalues and eigenvectors of the Major Double Couple:
		T-axis ev= 5.71 trend=292 plunge=12
		N-axis ev= 0.00 trend=121 plunge=78
		P-axis ev=-5.71 trend=23 plunge=2

	Maximum Azmuithal Gap=248 Distance to Nearest Station= 76.5 (km)

	Number of Stations (D=Displacement/V=Velocity) Used=3 (defining only)
		
	 TIN.CI.D FUR.CI.D DAC.LB.D


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


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 	    76.5  	261  	 80  	0.020 	0.080 TIN.CI.wus.glib
FUR.CI (D) 	Y 	    89.8  	149  	329  	0.020 	0.080 FUR.CI.wus.glib
DAC.LB (D) 	Y 	   100.0  	191  	 11  	0.020 	0.080 DAC.LB.wus.glib

 (V)-velocity (D)-Displacement

Author: www-data
Date: 2010/10/03 21:42:59

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 0.10 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   245    80     5   3.27 0.1813
WVFGRD96    1.0    65    90     0   3.32 0.2122
WVFGRD96    2.0    65    90     0   3.52 0.3656
WVFGRD96    3.0   245    85     0   3.58 0.4168
WVFGRD96    4.0   250    75    25   3.65 0.4530
WVFGRD96    5.0    70    75    30   3.69 0.4893
WVFGRD96    6.0   240    75   -30   3.72 0.5224
WVFGRD96    7.0   240    75   -25   3.74 0.5424
WVFGRD96    8.0   240    75   -30   3.77 0.5606
WVFGRD96    9.0   240    75   -25   3.78 0.5708
WVFGRD96   10.0   240    75   -25   3.80 0.5736
WVFGRD96   11.0   245    80   -20   3.80 0.5715
WVFGRD96   12.0   245    85   -15   3.81 0.5704
WVFGRD96   13.0    65    90    15   3.82 0.5691
WVFGRD96   14.0    65    90    15   3.83 0.5674
WVFGRD96   15.0    65    90    15   3.83 0.5649
WVFGRD96   16.0    65    90    15   3.84 0.5616
WVFGRD96   17.0    65    90    15   3.85 0.5576
WVFGRD96   18.0    65    90    15   3.86 0.5530
WVFGRD96   19.0    65    90    15   3.87 0.5481
WVFGRD96   20.0    65    90    15   3.88 0.5429
WVFGRD96   21.0    65    90    15   3.89 0.5373
WVFGRD96   22.0    65    85    15   3.90 0.5319
WVFGRD96   23.0    65    85    15   3.90 0.5264
WVFGRD96   24.0    65    85    15   3.91 0.5204
WVFGRD96   25.0    65    85    15   3.92 0.5149
WVFGRD96   26.0    65    85    15   3.92 0.5094
WVFGRD96   27.0    65    85    15   3.93 0.5041
WVFGRD96   28.0    65    85    15   3.94 0.4989
WVFGRD96   29.0    65    85    10   3.94 0.4941

The best solution is

WVFGRD96   10.0   240    75   -25   3.80 0.5736

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 0.10 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

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=Mon Oct 4 07:49:22 CDT 2010

Last Changed 2010/09/30