Location

2011/04/15 17:24:25 38.395 -118.742 16 4.00 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  2011/04/15 17:24:25:0  38.40 -118.74  16.0 4.0 Nevada
 
 Stations used:
   BK.BDM BK.BRIB BK.BRK BK.CMB BK.CVS BK.FARB BK.GASB BK.HAST 
   BK.HATC BK.HELL BK.HOPS BK.JRSC BK.MHC BK.MNRC BK.ORV 
   BK.PACP BK.SAO BK.SUTB BK.WENL CI.GSC CI.HEC CI.MLAC 
   CI.SPG2 CI.TIN II.PFO LB.DAC NC.AFD NC.GDXB NC.KHMB NC.KMR 
   NC.MDPB US.ELK 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
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 7.24e+21 dyne-cm
  Mw = 3.84 
  Z  = 4 km
  Plane   Strike  Dip  Rake
   NP1      200    55   -60
   NP2      335    45   -126
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.24e+21      6     269
    N   0.00e+00     24       2
    P  -7.24e+21     65     167

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.22e+21
       Mxy     3.78e+20
       Mxz     2.69e+21
       Myy     7.11e+21
       Myz    -1.31e+21
       Mzz    -5.90e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ########------########              
              ##############-#############           
             #############-----############          
           ##############--------############        
          #############------------###########       
         #############--------------###########      
        #############----------------###########     
        ############------------------##########     
       #############-------------------##########    
          #########---------------------#########    
        T #########---------------------#########    
          ########-----------------------########    
        ##########----------   ----------#######     
        ##########---------- P ----------#######     
         #########----------   ----------######      
          ########-----------------------#####       
           #######----------------------#####        
             #####----------------------###          
              #####--------------------###           
                 ###------------------#              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.90e+21   2.69e+21   1.31e+21 
  2.69e+21  -1.22e+21  -3.78e+20 
  1.31e+21  -3.78e+20   7.11e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110415172425/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 = 200
      DIP = 55
     RAKE = -60
       MW = 3.84
       HS = 4.0

The NDK file is 20110415172425.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  2011/04/15 17:24:25:0  38.40 -118.74  16.0 4.0 Nevada
 
 Stations used:
   BK.BDM BK.BRIB BK.BRK BK.CMB BK.CVS BK.FARB BK.GASB BK.HAST 
   BK.HATC BK.HELL BK.HOPS BK.JRSC BK.MHC BK.MNRC BK.ORV 
   BK.PACP BK.SAO BK.SUTB BK.WENL CI.GSC CI.HEC CI.MLAC 
   CI.SPG2 CI.TIN II.PFO LB.DAC NC.AFD NC.GDXB NC.KHMB NC.KMR 
   NC.MDPB US.ELK 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
   br c 0.12 0.25 n 4 p 2
 
 Best Fitting Double Couple
  Mo = 7.24e+21 dyne-cm
  Mw = 3.84 
  Z  = 4 km
  Plane   Strike  Dip  Rake
   NP1      200    55   -60
   NP2      335    45   -126
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.24e+21      6     269
    N   0.00e+00     24       2
    P  -7.24e+21     65     167

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.22e+21
       Mxy     3.78e+20
       Mxz     2.69e+21
       Myy     7.11e+21
       Myz    -1.31e+21
       Mzz    -5.90e+21
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ########------########              
              ##############-#############           
             #############-----############          
           ##############--------############        
          #############------------###########       
         #############--------------###########      
        #############----------------###########     
        ############------------------##########     
       #############-------------------##########    
          #########---------------------#########    
        T #########---------------------#########    
          ########-----------------------########    
        ##########----------   ----------#######     
        ##########---------- P ----------#######     
         #########----------   ----------######      
          ########-----------------------#####       
           #######----------------------#####        
             #####----------------------###          
              #####--------------------###           
                 ###------------------#              
                     --------------                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -5.90e+21   2.69e+21   1.31e+21 
  2.69e+21  -1.22e+21  -3.78e+20 
  1.31e+21  -3.78e+20   7.11e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20110415172425/index.html
	
REVIEWED BY NSL STAFF

Event ID:333213
Origin ID:788934
Algorithm: Ichinose (2003) Long Period, Regional-Distance Waves
Seismic Moment Tensor Solution

2011/04/15 (105) 17:24:26.00 38.3953 -118.7424 788934
	Depth =   2.0 (km)
	Mw    =  3.86
	Mo    =  7.77x10^21 (dyne x cm)

	Percent Double Couple =  87 %
	Percent CLVD          =  13 %
	no ISO calculated
	Epsilon=0.07
	 Percent Variance Reduction =  43.82 %
	 Total Fit                  =  3.12 
	Major Double Couple
		            strike dip   rake
		Nodal Plane 1: 345  32 -113
		Nodal Plane 2: 191  60  -76

	DEVIATORIC MOMENT TENSOR

	Moment Tensor Elements: Spherical Coordinates
		Mrr= -6.70 Mtt=  0.11 Mff=  6.59
		Mrt=  1.82 Mrf=  3.57 Mtf= -0.29 EXP=21


	Moment Tensor Elements: Cartesian Coordinates
		 0.11  0.29  1.82
		 0.29  6.59 -3.57
		 1.82 -3.57 -6.70

	Eigenvalues:
		T-axis eigenvalue=  7.49
		N-axis eigenvalue=  0.52
		P-axis eigenvalue= -8.02

	Eigenvalues and eigenvectors of the Major Double Couple:
		T-axis ev= 7.49 trend=271 plunge=14
		N-axis ev= 0.00 trend=4 plunge=12
		P-axis ev=-7.49 trend=133 plunge=71

	Maximum Azmuithal Gap=247 Distance to Nearest Station= 85.5 (km)

	Number of Stations (D=Displacement/V=Velocity) Used=4 (defining only)
		
	 MLAC.CI.D CMB.BK.D TIN.CI.D GRA.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)    
MLAC.CI (D) 	Y 	    85.5  	186  	  6  	0.020 	0.080 MLAC.CI.wus.glib
CMB.BK (D) 	Y 	   149.5  	255  	 74  	0.020 	0.080 CMB.BK.wus.glib
TIN.CI (D) 	Y 	   156.1  	163  	343  	0.020 	0.080 TIN.CI.wus.glib
GRA.CI (D) 	Y 	   196.4  	142  	323  	0.020 	0.080 GRA.CI.wus.glib

 (V)-velocity (D)-Displacement

Author: www-data
Date: 2011/04/15 20:07:00

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    0.5    35    65   -35   3.64 0.4818
WVFGRD96    1.0    35    65   -35   3.66 0.4870
WVFGRD96    2.0    35    65   -35   3.73 0.5493
WVFGRD96    3.0    30    60   -40   3.78 0.5636
WVFGRD96    4.0   200    55   -60   3.84 0.5686
WVFGRD96    5.0   195    60   -70   3.88 0.5422
WVFGRD96    6.0   200    65   -65   3.87 0.5058
WVFGRD96    7.0    45    70    20   3.81 0.5131
WVFGRD96    8.0    45    65    20   3.84 0.5039
WVFGRD96    9.0    50    65    25   3.85 0.5106
WVFGRD96   10.0    50    65    25   3.86 0.5100
WVFGRD96   11.0    50    65    25   3.86 0.5054
WVFGRD96   12.0    50    65    25   3.86 0.5009
WVFGRD96   13.0    50    65    25   3.87 0.4973
WVFGRD96   14.0    50    65    25   3.87 0.4920
WVFGRD96   15.0    50    65    25   3.87 0.4872
WVFGRD96   16.0    50    65    25   3.88 0.4861
WVFGRD96   17.0    50    65    25   3.88 0.4839
WVFGRD96   18.0    50    70    30   3.89 0.4813
WVFGRD96   19.0    50    70    30   3.90 0.4825
WVFGRD96   20.0    50    70    30   3.91 0.4828
WVFGRD96   21.0    50    70    30   3.92 0.4792
WVFGRD96   22.0    50    70    30   3.92 0.4774
WVFGRD96   23.0    50    70    30   3.93 0.4745
WVFGRD96   24.0    50    70    30   3.94 0.4709
WVFGRD96   25.0    50    70    30   3.94 0.4666
WVFGRD96   26.0    50    70    30   3.95 0.4616
WVFGRD96   27.0    50    65    25   3.96 0.4562
WVFGRD96   28.0    50    65    25   3.96 0.4509
WVFGRD96   29.0   155    60    45   3.91 0.4452

The best solution is

WVFGRD96    4.0   200    55   -60   3.84 0.5686

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 19:51:18 CST 2015