Location

2011/04/17 00:45:37 38.394 -118.735 02 4.50 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  2011/04/17 00:45:37:0  38.39 -118.74   2.0 4.5 Nevada
 
 Stations used:
   BK.CMB BK.HOPS BK.MOD BK.ORV BK.SAO BK.WDC BK.YBH CI.GSC 
   CI.ISA CI.LDF CI.MWC CI.OSI CI.PASC LB.BMN NC.AFD NC.KMR 
   NC.MDPB UU.CCUT UU.LCMT UU.PSUT UU.SZCU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 6.84e+22 dyne-cm
  Mw = 4.49 
  Z  = 2 km
  Plane   Strike  Dip  Rake
   NP1      358    48   -109
   NP2      205    45   -70
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.84e+22      2     101
    N   0.00e+00     14      11
    P  -6.84e+22     76     198

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.19e+21
       Mxy    -1.40e+22
       Mxz     1.50e+22
       Myy     6.55e+22
       Myz     6.99e+21
       Mzz    -6.43e+22
                                                     
                                                     
                                                     
                                                     
                     ########------                  
                 ##############-#######              
              #############------#########           
             ############---------#########          
           ############------------##########        
          ###########---------------##########       
         ###########-----------------##########      
        ###########-------------------##########     
        ##########--------------------##########     
       ##########---------------------###########    
       #########----------------------###########    
       #########----------------------#########      
       #########---------   ----------######### T    
        #######---------- P ----------#########      
        #######----------   ----------##########     
         ######----------------------##########      
          ######---------------------#########       
           #####--------------------#########        
             ###-------------------########          
              ###-----------------########           
                 #---------------######              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -6.43e+22   1.50e+22  -6.99e+21 
  1.50e+22  -1.19e+21   1.40e+22 
 -6.99e+21   1.40e+22   6.55e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110417004537/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 = 205
      DIP = 45
     RAKE = -70
       MW = 4.49
       HS = 2.0

The NDK file is 20110417004537.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  2011/04/17 00:45:37:0  38.39 -118.74   2.0 4.5 Nevada
 
 Stations used:
   BK.CMB BK.HOPS BK.MOD BK.ORV BK.SAO BK.WDC BK.YBH CI.GSC 
   CI.ISA CI.LDF CI.MWC CI.OSI CI.PASC LB.BMN NC.AFD NC.KMR 
   NC.MDPB UU.CCUT UU.LCMT UU.PSUT UU.SZCU 
 
 Filtering commands used:
   hp c 0.02 n 3
   lp c 0.06 n 3
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 6.84e+22 dyne-cm
  Mw = 4.49 
  Z  = 2 km
  Plane   Strike  Dip  Rake
   NP1      358    48   -109
   NP2      205    45   -70
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.84e+22      2     101
    N   0.00e+00     14      11
    P  -6.84e+22     76     198

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.19e+21
       Mxy    -1.40e+22
       Mxz     1.50e+22
       Myy     6.55e+22
       Myz     6.99e+21
       Mzz    -6.43e+22
                                                     
                                                     
                                                     
                                                     
                     ########------                  
                 ##############-#######              
              #############------#########           
             ############---------#########          
           ############------------##########        
          ###########---------------##########       
         ###########-----------------##########      
        ###########-------------------##########     
        ##########--------------------##########     
       ##########---------------------###########    
       #########----------------------###########    
       #########----------------------#########      
       #########---------   ----------######### T    
        #######---------- P ----------#########      
        #######----------   ----------##########     
         ######----------------------##########      
          ######---------------------#########       
           #####--------------------#########        
             ###-------------------########          
              ###-----------------########           
                 #---------------######              
                     ----------####                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -6.43e+22   1.50e+22  -6.99e+21 
  1.50e+22  -1.19e+21   1.40e+22 
 -6.99e+21   1.40e+22   6.55e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110417004537/index.html
	
REVIEWED BY NSL STAFF

Event ID:333401
Origin ID:789346
Algorithm: Ichinose (2003) Long Period, Regional-Distance Waves
Seismic Moment Tensor Solution

2011/04/17 (107) 00:45:38.00 38.3943 -118.7348 789346
	Depth =   2.0 (km)
	Mw    =  4.60
	Mo    =  9.98x10^22 (dyne x cm)

	Percent Double Couple =  95 %
	Percent CLVD          =   5 %
	no ISO calculated
	Epsilon=0.02
	 Percent Variance Reduction =  79.76 %
	 Total Fit                  =  13.41 
	Major Double Couple
		            strike dip   rake
		Nodal Plane 1:  32  32  -60
		Nodal Plane 2: 178  63 -107

	DEVIATORIC MOMENT TENSOR

	Moment Tensor Elements: Spherical Coordinates
		Mrr= -7.82 Mtt=  0.01 Mff=  7.81
		Mrt= -1.67 Mrf=  5.54 Mtf=  2.25 EXP=22


	Moment Tensor Elements: Cartesian Coordinates
		 0.01 -2.25 -1.67
		-2.25  7.81 -5.54
		-1.67 -5.54 -7.82

	Eigenvalues:
		T-axis eigenvalue=  9.85
		N-axis eigenvalue=  0.25
		P-axis eigenvalue=-10.10

	Eigenvalues and eigenvectors of the Major Double Couple:
		T-axis ev= 9.85 trend=280 plunge=16
		N-axis ev= 0.00 trend=186 plunge=15
		P-axis ev=-9.85 trend=55 plunge=67

	Maximum Azmuithal Gap=203 Distance to Nearest Station= 85.4 (km)

	Number of Stations (D=Displacement/V=Velocity) Used=7 (defining only)
		
	 MLAC.CI.D CMB.BK.D TIN.CI.D HELL.BK.D
	 DAC.LB.D FUR.CI.D ORV.BK.D


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


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 	    85.4  	186  	  6  	0.020 	0.080 MLAC.CI.wus.glib
CMB.BK (D) 	Y 	   150.1  	255  	 74  	0.020 	0.080 CMB.BK.wus.glib
TIN.CI (D) 	Y 	   155.8  	163  	344  	0.020 	0.080 TIN.CI.wus.glib
HELL.BK (D) 	Y 	   192.1  	188  	  7  	0.020 	0.080 HELL.BK.wus.glib
DAC.LB (D) 	Y 	   255.8  	156  	337  	0.020 	0.080 DAC.LB.wus.glib
FUR.CI (D) 	Y 	   270.3  	142  	323  	0.020 	0.080 FUR.CI.wus.glib
ORV.BK (D) 	Y 	   271.2  	299  	117  	0.020 	0.080 ORV.BK.wus.glib

 (V)-velocity (D)-Displacement

Author: www-data
Date: 2011/04/17 01:38:04

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
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    1.0   220    55   -50   4.42 0.6597
WVFGRD96    2.0   205    45   -70   4.49 0.7309
WVFGRD96    3.0   215    55   -60   4.54 0.7131
WVFGRD96    4.0   210    70   -75   4.63 0.6719
WVFGRD96    5.0   210    75   -75   4.64 0.6744
WVFGRD96    6.0   200    70   -80   4.63 0.6760
WVFGRD96    7.0   200    70   -80   4.61 0.6744
WVFGRD96    8.0   200    70   -80   4.66 0.6878
WVFGRD96    9.0   200    70   -80   4.65 0.6835
WVFGRD96   10.0   205    70   -80   4.63 0.6759
WVFGRD96   11.0   205    70   -80   4.62 0.6683
WVFGRD96   12.0   205    70   -75   4.61 0.6612
WVFGRD96   13.0   205    70   -75   4.61 0.6537
WVFGRD96   14.0   210    75   -70   4.60 0.6475
WVFGRD96   15.0   210    75   -70   4.60 0.6418
WVFGRD96   16.0   210    75   -70   4.60 0.6368
WVFGRD96   17.0   210    75   -70   4.60 0.6308
WVFGRD96   18.0   210    75   -70   4.60 0.6245
WVFGRD96   19.0   210    75   -65   4.61 0.6203
WVFGRD96   20.0   215    80   -60   4.61 0.6142
WVFGRD96   21.0   215    80   -60   4.63 0.6122
WVFGRD96   22.0   215    80   -60   4.63 0.6057
WVFGRD96   23.0   215    80   -60   4.64 0.5985
WVFGRD96   24.0   215    80   -60   4.64 0.5928
WVFGRD96   25.0   215    80   -60   4.65 0.5850
WVFGRD96   26.0    85    30   -10   4.64 0.5735
WVFGRD96   27.0    85    30   -10   4.65 0.5666
WVFGRD96   28.0    85    30   -10   4.65 0.5581
WVFGRD96   29.0   190    55    80   4.64 0.5499

The best solution is

WVFGRD96    2.0   205    45   -70   4.49 0.7309

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
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 Sun Dec 6 19:53:19 CST 2015