Location

2011/05/27 19:45:48 38.437 -118.730 2.8 4.20 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  2011/05/27 19:45:48:0  38.44 -118.73   2.8 4.2 Nevada
 
 Stations used:
   BK.CMB BK.HUMO BK.MOD BK.ORV BK.WDC BK.YBH CI.GSC CI.LDF 
   CI.PASC LB.DAC NC.AFD NN.PAH NN.SHP UU.KNB UU.LCMT 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 = 6.31e+21 dyne-cm
  Mw = 3.80 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1       25    45   -90
   NP2      205    45   -90
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.31e+21     -0     115
    N   0.00e+00     -0      25
    P  -6.31e+21     90     240

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.13e+21
       Mxy    -2.42e+21
       Mxz    -6.02e+13
       Myy     5.18e+21
       Myz    -3.32e+14
       Mzz    -6.31e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ##############-------#              
              #############------------###           
             ############---------------###          
           ############-----------------#####        
          ###########-------------------######       
         ###########---------------------######      
        ###########----------------------#######     
        ##########-----------------------#######     
       ##########-----------------------#########    
       #########---------   ------------#########    
       #########--------- P ------------#########    
       #########---------   -----------##########    
        #######-----------------------##########     
        #######----------------------########        
         ######---------------------######### T      
          ######-------------------##########        
           #####-----------------############        
             ###---------------############          
              ###------------#############           
                 #-------##############              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -6.31e+21  -6.02e+13   3.32e+14 
 -6.02e+13   1.13e+21   2.42e+21 
  3.32e+14   2.42e+21   5.18e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110527194548/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 = -90
       MW = 3.80
       HS = 3.0

The NDK file is 20110527194548.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  2011/05/27 19:45:48:0  38.44 -118.73   2.8 4.2 Nevada
 
 Stations used:
   BK.CMB BK.HUMO BK.MOD BK.ORV BK.WDC BK.YBH CI.GSC CI.LDF 
   CI.PASC LB.DAC NC.AFD NN.PAH NN.SHP UU.KNB UU.LCMT 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 = 6.31e+21 dyne-cm
  Mw = 3.80 
  Z  = 3 km
  Plane   Strike  Dip  Rake
   NP1       25    45   -90
   NP2      205    45   -90
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   6.31e+21     -0     115
    N   0.00e+00     -0      25
    P  -6.31e+21     90     240

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.13e+21
       Mxy    -2.42e+21
       Mxz    -6.02e+13
       Myy     5.18e+21
       Myz    -3.32e+14
       Mzz    -6.31e+21
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ##############-------#              
              #############------------###           
             ############---------------###          
           ############-----------------#####        
          ###########-------------------######       
         ###########---------------------######      
        ###########----------------------#######     
        ##########-----------------------#######     
       ##########-----------------------#########    
       #########---------   ------------#########    
       #########--------- P ------------#########    
       #########---------   -----------##########    
        #######-----------------------##########     
        #######----------------------########        
         ######---------------------######### T      
          ######-------------------##########        
           #####-----------------############        
             ###---------------############          
              ###------------#############           
                 #-------##############              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -6.31e+21  -6.02e+13   3.32e+14 
 -6.02e+13   1.13e+21   2.42e+21 
  3.32e+14   2.42e+21   5.18e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110527194548/index.html
	
REVIEWED BY NSL STAFF

Event ID:338685
Origin ID:799891
Algorithm: Ichinose (2003) Long Period, Regional-Distance Waves
Seismic Moment Tensor Solution

2011/05/27 (147) 19:45:48.00 38.4379 -118.6947 799876
	Depth =   6.0 (km)
	Mw    =  3.95
	Mo    =  1.05x10^22 (dyne x cm)

	Percent Double Couple =  99 %
	Percent CLVD          =   1 %
	no ISO calculated
	Epsilon=0.00
	 Percent Variance Reduction =  39.79 %
	 Total Fit                  =  25.54 
	Major Double Couple
		            strike dip   rake
		Nodal Plane 1: 214  38 -105
		Nodal Plane 2:  54  53  -78

	DEVIATORIC MOMENT TENSOR

	Moment Tensor Elements: Spherical Coordinates
		Mrr= -0.98 Mtt=  0.47 Mff=  0.51
		Mrt= -0.31 Mrf= -0.07 Mtf=  0.52 EXP=22


	Moment Tensor Elements: Cartesian Coordinates
		 0.47 -0.52 -0.31
		-0.52  0.51  0.07
		-0.31  0.07 -0.98

	Eigenvalues:
		T-axis eigenvalue=  1.04
		N-axis eigenvalue=  0.00
		P-axis eigenvalue= -1.05

	Eigenvalues and eigenvectors of the Major Double Couple:
		T-axis ev= 1.04 trend=135 plunge=8
		N-axis ev= 0.00 trend=226 plunge=9
		P-axis ev=-1.04 trend=7 plunge=78

	Maximum Azmuithal Gap=150 Distance to Nearest Station= 90.7 (km)

	Number of Stations (D=Displacement/V=Velocity) Used=9 (defining only)
		
	 MLAC.CI.D PAH.NN.D CMB.BK.D TIN.CI.D
	 GRA.CI.D CWC.CI.D DAC.LB.D TPNV.US.D
	 FUR.CI.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 	    90.7  	188  	  8  	0.020 	0.080 MLAC.CI.wus.glib
PAH.NN (D) 	Y 	   153.5  	337  	157  	0.020 	0.080 PAH.NN.wus.glib
CMB.BK (D) 	Y 	   154.7  	253  	 72  	0.020 	0.080 CMB.BK.wus.glib
TIN.CI (D) 	Y 	   159.5  	165  	345  	0.020 	0.080 TIN.CI.wus.glib
GRA.CI (D) 	Y 	   197.7  	144  	324  	0.020 	0.080 GRA.CI.wus.glib
CWC.CI (D) 	Y 	   228.5  	166  	346  	0.020 	0.080 CWC.CI.wus.glib
DAC.LB (D) 	Y 	   258.8  	158  	338  	0.020 	0.080 DAC.LB.wus.glib
TPNV.US (D) 	Y 	   271.1  	127  	308  	0.020 	0.080 TPNV.US.wus.glib
FUR.CI (D) 	Y 	   272.0  	143  	324  	0.020 	0.080 FUR.CI.wus.glib

 (V)-velocity (D)-Displacement

Author: www-data
Date: 2011/05/27 20:21:40

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
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   230    50   -55   3.58 0.4330
WVFGRD96    1.0   215    45   -75   3.64 0.4681
WVFGRD96    2.0   225    45   -60   3.72 0.5678
WVFGRD96    3.0   205    45   -90   3.80 0.6066
WVFGRD96    4.0   220    45   -70   3.82 0.5774
WVFGRD96    5.0   235    55   -45   3.78 0.5404
WVFGRD96    6.0    60    85   -35   3.76 0.5356
WVFGRD96    7.0   245    85    35   3.77 0.5411
WVFGRD96    8.0    65    90   -40   3.81 0.5441
WVFGRD96    9.0    75    70    35   3.82 0.5496
WVFGRD96   10.0    80    65    35   3.84 0.5597
WVFGRD96   11.0    80    60    35   3.86 0.5673
WVFGRD96   12.0    80    60    35   3.87 0.5722
WVFGRD96   13.0    80    60    35   3.88 0.5741
WVFGRD96   14.0    80    60    35   3.89 0.5737
WVFGRD96   15.0    80    60    35   3.89 0.5713
WVFGRD96   16.0    80    60    35   3.90 0.5667
WVFGRD96   17.0    80    60    35   3.91 0.5614
WVFGRD96   18.0    80    60    35   3.92 0.5549
WVFGRD96   19.0    80    60    40   3.93 0.5471
WVFGRD96   20.0    80    55    35   3.94 0.5389
WVFGRD96   21.0    80    55    35   3.95 0.5278
WVFGRD96   22.0    80    55    35   3.95 0.5185
WVFGRD96   23.0    80    55    40   3.96 0.5094
WVFGRD96   24.0    85    50    35   3.97 0.5000
WVFGRD96   25.0    85    50    35   3.97 0.4904
WVFGRD96   26.0    85    50    35   3.98 0.4816
WVFGRD96   27.0    70    40   -25   3.97 0.4737
WVFGRD96   28.0    70    40   -25   3.98 0.4680
WVFGRD96   29.0    70    40   -25   3.98 0.4626

The best solution is

WVFGRD96    3.0   205    45   -90   3.80 0.6066

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 20:36:28 CST 2015