Location

Location ANSS

2016/12/28 09:13:47 38.377 -118.896 8.6 5.5 Nevada

Focal Mechanism

 USGS/SLU Moment Tensor Solution
 ENS  2016/12/28 09:13:47:0  38.38 -118.90   8.6 5.5 Nevada
 
 Stations used:
   CI.CCA CI.GSC LB.BMN NC.AFD NC.BBGB NC.MDPB NN.BEK NN.CMK6 
   NN.COLR NN.DSP NN.EMB NN.GWY NN.KVN NN.LCH NN.MPK NN.MZPB 
   NN.OMMB NN.PIO NN.PLTX NN.PNT NN.PRN NN.Q09A NN.S11A 
   NN.SPR3 NN.VCN NN.WLDB NN.WTNK NN.YER SN.HEL TA.R11A US.ELK 
   US.TPNV UU.PSUT 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 2.48e+24 dyne-cm
  Mw = 5.53 
  Z  = 14 km
  Plane   Strike  Dip  Rake
   NP1       30    90     5
   NP2      300    85   180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.48e+24      4     255
    N   0.00e+00     85      30
    P  -2.48e+24      4     165

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.14e+24
       Mxy     1.24e+24
       Mxz     1.08e+23
       Myy     2.14e+24
       Myz    -1.87e+23
       Mzz    -1.89e+16
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------------------#              
              -----------------------#####           
             -----------------------#######          
           ------------------------##########        
          #-----------------------############       
         ######------------------##############      
        ###########-------------################     
        ##############---------#################     
       ###################----###################    
       ##########################################    
       ####################-----#################    
          ################---------##############    
        T ###############-------------##########     
          ##############-----------------#######     
         ##############--------------------####      
          ############------------------------       
           ##########------------------------        
             #######-----------------------          
              #####-----------------------           
                 #--------------   ----              
                     ----------- P                   
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.89e+16   1.08e+23   1.87e+23 
  1.08e+23  -2.14e+24  -1.24e+24 
  1.87e+23  -1.24e+24   2.14e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20161228091347/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 = 30
      DIP = 90
     RAKE = 5
       MW = 5.53
       HS = 14.0

The NDK file is 20161228091347.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
GCMT
 USGS/SLU Moment Tensor Solution
 ENS  2016/12/28 09:13:47:0  38.38 -118.90   8.6 5.5 Nevada
 
 Stations used:
   CI.CCA CI.GSC LB.BMN NC.AFD NC.BBGB NC.MDPB NN.BEK NN.CMK6 
   NN.COLR NN.DSP NN.EMB NN.GWY NN.KVN NN.LCH NN.MPK NN.MZPB 
   NN.OMMB NN.PIO NN.PLTX NN.PNT NN.PRN NN.Q09A NN.S11A 
   NN.SPR3 NN.VCN NN.WLDB NN.WTNK NN.YER SN.HEL TA.R11A US.ELK 
   US.TPNV UU.PSUT 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.03 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 2.48e+24 dyne-cm
  Mw = 5.53 
  Z  = 14 km
  Plane   Strike  Dip  Rake
   NP1       30    90     5
   NP2      300    85   180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   2.48e+24      4     255
    N   0.00e+00     85      30
    P  -2.48e+24      4     165

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx    -2.14e+24
       Mxy     1.24e+24
       Mxz     1.08e+23
       Myy     2.14e+24
       Myz    -1.87e+23
       Mzz    -1.89e+16
                                                     
                                                     
                                                     
                                                     
                     --------------                  
                 ---------------------#              
              -----------------------#####           
             -----------------------#######          
           ------------------------##########        
          #-----------------------############       
         ######------------------##############      
        ###########-------------################     
        ##############---------#################     
       ###################----###################    
       ##########################################    
       ####################-----#################    
          ################---------##############    
        T ###############-------------##########     
          ##############-----------------#######     
         ##############--------------------####      
          ############------------------------       
           ##########------------------------        
             #######-----------------------          
              #####-----------------------           
                 #--------------   ----              
                     ----------- P                   
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.89e+16   1.08e+23   1.87e+23 
  1.08e+23  -2.14e+24  -1.24e+24 
  1.87e+23  -1.24e+24   2.14e+24 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20161228091347/index.html
	
Regional Moment Tensor (Mwr)
Moment	2.630e+17 N-m
Magnitude	5.5 Mwr
Depth	12.0 km
Percent DC	99 %
Half Duration	–
Catalog	NN
Data Source	NN2
Contributor	NN2
Nodal Planes
Plane	Strike	Dip	Rake
NP1	210	89	4
NP2	120	86	179
Principal Axes
Axis	Value	Plunge	Azimuth
T	2.618e+17 N-m	3	75
N	0.014e+17 N-m	86	225
P	-2.642e+17 N-m	2	345

        
December 28, 2016, CALIFORNIA-NEVADA BORDER REGION, MW=5.7

Goran Ekstrom

CENTROID-MOMENT-TENSOR  SOLUTION
GCMT EVENT:     C201612280913A
DATA: II IU CU MN LD G  IC DK GE
L.P.BODY WAVES:106S, 166C, T= 40
SURFACE WAVES: 150S, 313C, T= 50
TIMESTAMP:      Q-20161228123501
CENTROID LOCATION:
ORIGIN TIME:      09:13:51.9 0.1
LAT:38.38N 0.01;LON:118.92W 0.01
DEP: 24.9  0.5;TRIANG HDUR:  1.7
MOMENT TENSOR: SCALE 10**24 D-CM
RR=-0.817 0.068; TT=-3.580 0.060
PP= 4.400 0.064; RT=-0.622 0.146
RP= 1.100 0.134; TP=-2.440 0.051
PRINCIPAL AXES:
1.(T) VAL=  5.332;PLG=11;AZM=254
2.(N)      -1.035;    78;     99
3.(P)      -4.294;     5;    345
BEST DBLE.COUPLE:M0= 4.81*10**24
NP1: STRIKE= 30;DIP=78;SLIP=   4
NP2: STRIKE=299;DIP=86;SLIP= 168

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

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 using wvfgrd96

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 +70
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.07 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    35    90     0   5.06 0.3508
WVFGRD96    2.0    30    70   -20   5.22 0.4814
WVFGRD96    3.0   215    90     0   5.23 0.5362
WVFGRD96    4.0   210    75   -20   5.30 0.5834
WVFGRD96    5.0   215    85   -15   5.32 0.6270
WVFGRD96    6.0   215    90   -15   5.35 0.6693
WVFGRD96    7.0    35    85    15   5.38 0.7126
WVFGRD96    8.0    35    80    15   5.42 0.7536
WVFGRD96    9.0    35    80    15   5.45 0.7829
WVFGRD96   10.0   210    90   -10   5.47 0.8043
WVFGRD96   11.0    35    85    10   5.48 0.8210
WVFGRD96   12.0    30    90     5   5.50 0.8322
WVFGRD96   13.0    30    90     5   5.52 0.8379
WVFGRD96   14.0    30    90     5   5.53 0.8393
WVFGRD96   15.0    30    90    -5   5.54 0.8377
WVFGRD96   16.0    30    90    -5   5.55 0.8330
WVFGRD96   17.0   210    90     5   5.56 0.8254
WVFGRD96   18.0   210    90     5   5.57 0.8156
WVFGRD96   19.0   210    90     5   5.58 0.8041
WVFGRD96   20.0    30    90    -5   5.58 0.7911
WVFGRD96   21.0    30    90    -5   5.59 0.7772
WVFGRD96   22.0   210    90     5   5.60 0.7620
WVFGRD96   23.0   210    90     5   5.60 0.7464
WVFGRD96   24.0    30    90    -5   5.61 0.7301
WVFGRD96   25.0   210    90     5   5.61 0.7134
WVFGRD96   26.0   210    90     5   5.61 0.6968
WVFGRD96   27.0    30    90    -5   5.62 0.6798
WVFGRD96   28.0    30    90    -5   5.62 0.6631
WVFGRD96   29.0    30    90    -5   5.63 0.6465

The best solution is

WVFGRD96   14.0    30    90     5   5.53 0.8393

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 +70
rtr
taper w 0.1
hp c 0.03 n 3 
lp c 0.07 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 Wed Dec 28 15:54:03 CST 2016