Location

Location ANSS

2016/03/22 10:00:45 38.656 -118.784 10.9 4.1 Nevada

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2016/03/22 10:00:45:0  38.66 -118.78  10.9 4.1 Nevada
 
 Stations used:
   CI.ISA IM.NV31 LB.BMN NN.BEK NN.COLR NN.CTC NN.EMB NN.KVN 
   NN.LCH NN.LHV NN.MPK NN.OMMB NN.PAH NN.PNT NN.PRN NN.Q09A 
   NN.REDF NN.RUB NN.S11A NN.VCN NN.YER TA.O03E TA.R11A US.ELK 
   US.WVOR 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 7.50e+21 dyne-cm
  Mw = 3.85 
  Z  = 9 km
  Plane   Strike  Dip  Rake
   NP1      350    79   -139
   NP2      250    50   -15
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.50e+21     18     114
    N   0.00e+00     48       3
    P  -7.50e+21     36     218

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.88e+21
       Mxy    -4.86e+21
       Mxz     1.91e+21
       Myy     3.79e+21
       Myz     4.26e+21
       Mzz    -1.91e+21
                                                     
                                                     
                                                     
                                                     
                     ####----------                  
                 #########-------------              
              #############---------------           
             ##############----------------          
           #################-----------------        
          #################--#############----       
         #############-------#################-      
        ###########-----------##################     
        ########--------------##################     
       #######----------------###################    
       #####-------------------##################    
       ####--------------------##################    
       ###---------------------##################    
        #-----------------------##########   ###     
        #-----------------------########## T ###     
         ---------   -----------##########   ##      
          -------- P -----------##############       
           -------   -----------#############        
             -------------------###########          
              ------------------##########           
                 ---------------#######              
                     -----------###                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.91e+21   1.91e+21  -4.26e+21 
  1.91e+21  -1.88e+21   4.86e+21 
 -4.26e+21   4.86e+21   3.79e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160322100045/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 = 250
      DIP = 50
     RAKE = -15
       MW = 3.85
       HS = 9.0

The NDK file is 20160322100045.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  2016/03/22 10:00:45:0  38.66 -118.78  10.9 4.1 Nevada
 
 Stations used:
   CI.ISA IM.NV31 LB.BMN NN.BEK NN.COLR NN.CTC NN.EMB NN.KVN 
   NN.LCH NN.LHV NN.MPK NN.OMMB NN.PAH NN.PNT NN.PRN NN.Q09A 
   NN.REDF NN.RUB NN.S11A NN.VCN NN.YER TA.O03E TA.R11A US.ELK 
   US.WVOR 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +50
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.10 n 3 
 
 Best Fitting Double Couple
  Mo = 7.50e+21 dyne-cm
  Mw = 3.85 
  Z  = 9 km
  Plane   Strike  Dip  Rake
   NP1      350    79   -139
   NP2      250    50   -15
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   7.50e+21     18     114
    N   0.00e+00     48       3
    P  -7.50e+21     36     218

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -1.88e+21
       Mxy    -4.86e+21
       Mxz     1.91e+21
       Myy     3.79e+21
       Myz     4.26e+21
       Mzz    -1.91e+21
                                                     
                                                     
                                                     
                                                     
                     ####----------                  
                 #########-------------              
              #############---------------           
             ##############----------------          
           #################-----------------        
          #################--#############----       
         #############-------#################-      
        ###########-----------##################     
        ########--------------##################     
       #######----------------###################    
       #####-------------------##################    
       ####--------------------##################    
       ###---------------------##################    
        #-----------------------##########   ###     
        #-----------------------########## T ###     
         ---------   -----------##########   ##      
          -------- P -----------##############       
           -------   -----------#############        
             -------------------###########          
              ------------------##########           
                 ---------------#######              
                     -----------###                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.91e+21   1.91e+21  -4.26e+21 
  1.91e+21  -1.88e+21   4.86e+21 
 -4.26e+21   4.86e+21   3.79e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20160322100045/index.html
	
Mw
Moment	6.561e+14 N-m
Magnitude	3.81
Depth	10.0 km
Percent DC	93%
Half Duration	–
Catalog	NN (nn00536804)
Data Source	NN2
Contributor	NN2
Nodal Planes
Plane	Strike	Dip	Rake
NP1	252	61	-6
NP2	345	85	-151
Principal Axes
Axis	Value	Plunge	Azimuth
T	6.671	16	115
N	-0.227	60	355
P	-6.444	24	213

        

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:

cut o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 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    1.0   255    80   -15   3.39 0.3273
WVFGRD96    2.0    75    90    10   3.52 0.3972
WVFGRD96    3.0   265    45    20   3.66 0.4378
WVFGRD96    4.0   265    45    20   3.70 0.5054
WVFGRD96    5.0   260    45     5   3.72 0.5580
WVFGRD96    6.0   260    50     5   3.74 0.5950
WVFGRD96    7.0   255    50   -10   3.76 0.6207
WVFGRD96    8.0   250    45   -20   3.83 0.6367
WVFGRD96    9.0   250    50   -15   3.85 0.6398
WVFGRD96   10.0   250    50   -15   3.86 0.6333
WVFGRD96   11.0   255    55    -5   3.88 0.6180
WVFGRD96   12.0   255    60    -5   3.89 0.5978
WVFGRD96   13.0   255    60    -5   3.90 0.5726
WVFGRD96   14.0   255    60     0   3.91 0.5439
WVFGRD96   15.0   255    60     0   3.92 0.5136
WVFGRD96   16.0   255    60    10   3.92 0.4843
WVFGRD96   17.0   255    60    10   3.93 0.4562
WVFGRD96   18.0   255    60    10   3.93 0.4291
WVFGRD96   19.0   255    60    15   3.93 0.4046
WVFGRD96   20.0   255    60    15   3.94 0.3815
WVFGRD96   21.0   255    60    20   3.94 0.3601
WVFGRD96   22.0   255    60    20   3.95 0.3425
WVFGRD96   23.0   255    60    20   3.95 0.3276
WVFGRD96   24.0   260    60    25   3.96 0.3142
WVFGRD96   25.0   165    90    35   3.94 0.3088
WVFGRD96   26.0   345    90   -35   3.94 0.3078
WVFGRD96   27.0   170    85    35   3.95 0.3061
WVFGRD96   28.0   170    85    35   3.96 0.3054
WVFGRD96   29.0   170    90    35   3.97 0.3040

The best solution is

WVFGRD96    9.0   250    50   -15   3.85 0.6398

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

cut o DIST/3.3 -30 o DIST/3.3 +50
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.10 n 3 
Figure 3. Waveform comparison for selected depth. Red: observed; Blue - predicted. The time shift with respect to the model prediction is indicated. The percent of fit is also indicated.
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 Tue Mar 22 06:21:47 CDT 2016