Location

2011/05/12 16:23:49 38.418 -118.737 4.5 4.21 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  2011/05/12 16:23:49:0  38.42 -118.74   4.5 4.2 Nevada
 
 Stations used:
   BK.CMB BK.HUMO BK.JCC BK.MOD BK.ORV BK.WDC BK.YBH CI.GSC 
   CI.ISA CI.LDF CI.MWC CI.OSI CI.PASC NN.TVH2 NN.TVH3 UU.BGU 
   UU.KNB UU.LCMT UU.PSUT UU.SZCU UU.TCRU UW.TREE 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 5.69e+21 dyne-cm
  Mw = 3.77 
  Z  = 4 km
  Plane   Strike  Dip  Rake
   NP1        6    57   -103
   NP2      210    35   -70
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.69e+21     11     106
    N   0.00e+00     11      13
    P  -5.69e+21     74     240

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.89e+20
       Mxy    -1.62e+21
       Mxz     4.66e+20
       Myy     4.73e+21
       Myz     2.38e+21
       Mzz    -5.02e+21
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 #############---######              
              ###########---------########           
             #########-------------########          
           #########---------------##########        
          #########-----------------##########       
         ########-------------------###########      
        ########--------------------############     
        #######---------------------############     
       #######----------------------#############    
       #######----------------------#############    
       ######---------   -----------#############    
       ######--------- P -----------########   ##    
        #####---------   -----------######## T #     
        #####----------------------#########   #     
         ####----------------------############      
          ####--------------------############       
           ###-------------------############        
             ##-----------------###########          
              ##---------------###########           
                 ------------##########              
                     -------#######                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.02e+21   4.66e+20  -2.38e+21 
  4.66e+20   2.89e+20   1.62e+21 
 -2.38e+21   1.62e+21   4.73e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110512162349/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 = 210
      DIP = 35
     RAKE = -70
       MW = 3.77
       HS = 4.0

The NDK file is 20110512162349.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  2011/05/12 16:23:49:0  38.42 -118.74   4.5 4.2 Nevada
 
 Stations used:
   BK.CMB BK.HUMO BK.JCC BK.MOD BK.ORV BK.WDC BK.YBH CI.GSC 
   CI.ISA CI.LDF CI.MWC CI.OSI CI.PASC NN.TVH2 NN.TVH3 UU.BGU 
   UU.KNB UU.LCMT UU.PSUT UU.SZCU UU.TCRU UW.TREE 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
 
 Best Fitting Double Couple
  Mo = 5.69e+21 dyne-cm
  Mw = 3.77 
  Z  = 4 km
  Plane   Strike  Dip  Rake
   NP1        6    57   -103
   NP2      210    35   -70
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.69e+21     11     106
    N   0.00e+00     11      13
    P  -5.69e+21     74     240

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.89e+20
       Mxy    -1.62e+21
       Mxz     4.66e+20
       Myy     4.73e+21
       Myz     2.38e+21
       Mzz    -5.02e+21
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 #############---######              
              ###########---------########           
             #########-------------########          
           #########---------------##########        
          #########-----------------##########       
         ########-------------------###########      
        ########--------------------############     
        #######---------------------############     
       #######----------------------#############    
       #######----------------------#############    
       ######---------   -----------#############    
       ######--------- P -----------########   ##    
        #####---------   -----------######## T #     
        #####----------------------#########   #     
         ####----------------------############      
          ####--------------------############       
           ###-------------------############        
             ##-----------------###########          
              ##---------------###########           
                 ------------##########              
                     -------#######                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.02e+21   4.66e+20  -2.38e+21 
  4.66e+20   2.89e+20   1.62e+21 
 -2.38e+21   1.62e+21   4.73e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110512162349/index.html
	
REVIEWED BY NSL STAFF

Event ID:336893
Origin ID:795904
Algorithm: Ichinose (2003) Long Period, Regional-Distance Waves
Seismic Moment Tensor Solution

2011/05/12 (132) 16:23:50.00 38.4176 -118.7369 795904
	Depth =   4.0 (km)
	Mw    =  4.03
	Mo    =  1.38x10^22 (dyne x cm)

	Percent Double Couple =  98 %
	Percent CLVD          =   2 %
	no ISO calculated
	Epsilon=0.01
	 Percent Variance Reduction =  70.50 %
	 Total Fit                  =  27.64 
	Major Double Couple
		            strike dip   rake
		Nodal Plane 1: 224  43  -77
		Nodal Plane 2:  27  49 -102

	DEVIATORIC MOMENT TENSOR

	Moment Tensor Elements: Spherical Coordinates
		Mrr= -1.35 Mtt=  0.44 Mff=  0.90
		Mrt=  0.09 Mrf= -0.24 Mtf=  0.66 EXP=22


	Moment Tensor Elements: Cartesian Coordinates
		 0.44 -0.66  0.09
		-0.66  0.90  0.24
		 0.09  0.24 -1.35

	Eigenvalues:
		T-axis eigenvalue=  1.37
		N-axis eigenvalue=  0.01
		P-axis eigenvalue= -1.39

	Eigenvalues and eigenvectors of the Major Double Couple:
		T-axis ev= 1.37 trend=125 plunge=3
		N-axis ev= 0.00 trend=34 plunge=9
		P-axis ev=-1.37 trend=234 plunge=81

	Maximum Azmuithal Gap=147 Distance to Nearest Station= 88.0 (km)

	Number of Stations (D=Displacement/V=Velocity) Used=10 (defining only)
		
	 MLAC.CI.D CMB.BK.D PAH.NN.D TIN.CI.D
	 GRA.CI.D DAC.LB.D FUR.CI.D TPNV.US.D
	 PACP.BK.D BDM.BK.D


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


All Stations defining and nondefining: 
Station.Net 	Def 	Distance 	Azi    	Bazi  	lo-f 	hi-f vmodel
            	    	(km)     	(deg)  	(deg) 	(Hz) 	(Hz)    
MLAC.CI (D) 	Y 	    88.0  	186  	  6  	0.020 	0.080 MLAC.CI.wus.glib
CMB.BK (D) 	Y 	   150.6  	254  	 73  	0.020 	0.080 CMB.BK.wus.glib
PAH.NN (D) 	Y 	   154.3  	339  	158  	0.020 	0.080 PAH.NN.wus.glib
TIN.CI (D) 	Y 	   158.3  	164  	344  	0.020 	0.080 TIN.CI.wus.glib
GRA.CI (D) 	Y 	   198.1  	142  	323  	0.020 	0.080 GRA.CI.wus.glib
DAC.LB (D) 	Y 	   258.2  	157  	337  	0.020 	0.080 DAC.LB.wus.glib
FUR.CI (D) 	Y 	   272.5  	142  	323  	0.020 	0.080 FUR.CI.wus.glib
TPNV.US (D) 	Y 	   272.8  	126  	307  	0.020 	0.080 TPNV.US.wus.glib
PACP.BK (D) 	Y 	   273.5  	236  	 54  	0.020 	0.080 PACP.BK.wus.glib
BDM.BK (D) 	Y 	   278.5  	260  	 78  	0.020 	0.080 BDM.BK.wus.glib

 (V)-velocity (D)-Displacement

Author: www-data
Date: 2011/05/12 17:03:16

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:

hp c 0.02 n 3
lp c 0.06 n 3

For the two stations at distacnes less than 20 km, the following were used: The results of this grid search from 0.5 to 19 km depth are as follow:
hp c 0.10 n 3
lp c 0.20 n 3
These stations, with distances of 4.73 and 10.0 km and azimuths of 200 and 225, rofr TVH2 and TVH3, respectively, were only used after carefully reading arrival times an locating with the WUS model. The inversion depth agreed with the UNR solutiongiven above for this event.

           DEPTH  STK   DIP  RAKE   MW    FIT
WVFGRD96    0.5   200    65    85   3.51 0.3790
WVFGRD96    1.0   260    60    10   3.29 0.3705
WVFGRD96    2.0    15    30   -80   3.62 0.4604
WVFGRD96    3.0   200    35   -80   3.72 0.5860
WVFGRD96    4.0   210    35   -70   3.77 0.6421
WVFGRD96    5.0   220    40   -60   3.83 0.6358
WVFGRD96    6.0   220    45   -55   3.87 0.6201
WVFGRD96    7.0   225    45   -50   3.91 0.5831
WVFGRD96    8.0   240    45   -40   4.04 0.5494
WVFGRD96    9.0    30    55   -30   3.78 0.5290
WVFGRD96   10.0    15    50   -50   3.81 0.5286
WVFGRD96   11.0    10    50   -80   3.87 0.5298
WVFGRD96   12.0   200    40   -75   3.96 0.5287
WVFGRD96   13.0   195    35   -85   3.95 0.5321
WVFGRD96   14.0   205    35   -80   3.97 0.5159
WVFGRD96   15.0   265    75    30   4.02 0.5237
WVFGRD96   16.0   270    75    35   4.03 0.5352
WVFGRD96   17.0   270    75    35   4.04 0.5413
WVFGRD96   18.0   265    80    25   4.09 0.5425
WVFGRD96   19.0   270    80    35   4.07 0.5411
WVFGRD96   20.0   275    60    75   3.99 0.5430
WVFGRD96   21.0   275    60    75   4.01 0.5430
WVFGRD96   22.0   275    60    75   4.02 0.5424
WVFGRD96   23.0   270    60    85   4.03 0.5379
WVFGRD96   24.0   270    85    40   4.11 0.5368
WVFGRD96   25.0   270    85    40   4.11 0.5297
WVFGRD96   26.0    60    75     0   4.28 0.5315
WVFGRD96   27.0   105    25   100   4.06 0.5307
WVFGRD96   28.0   275    65    80   4.07 0.5358
WVFGRD96   29.0   275    65    75   4.08 0.5376

The best solution is

WVFGRD96    4.0   210    35   -70   3.77 0.6421

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

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 Sun Dec 6 20:33:56 CST 2015