Location

2015/02/14 02:28:56 37.145 -117.258 18.0 4.6 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  2015/02/14 02:28:56:0  37.15 -117.26  18.0 4.6 Nevada
 
 Stations used:
   AE.113A AE.U15A AE.W13A BC.CCX BC.RMX BC.SJX BC.TJX BC.TKX 
   BK.SAO BK.WDC CI.BAR CI.GLA CI.GSC CI.ISA CI.MWC CI.OSI 
   CI.PASC CI.SNCC IM.NV31 LB.MVU LB.TPH NC.AFD NC.MDPB NN.BEK 
   NN.LHV NN.OMMB NN.PAH NN.PNT NN.PRN NN.REDF NN.RUB NN.RYN 
   NN.SHP NN.VCN NN.WAK NN.WDEM NN.YER TA.109C TA.R11A US.DUG 
   US.ELK US.TPNV US.WUAZ US.WVOR UU.BGU UU.CCUT UU.KNB 
   UU.LCMT UU.MPU UU.MTPU UU.NLU UU.PKCU UU.PSUT UU.SZCU 
   UU.TCRU UU.TMU UU.VRUT 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 1.32e+23 dyne-cm
  Mw = 4.68 
  Z  = 12 km
  Plane   Strike  Dip  Rake
   NP1      203    56   -97
   NP2       35    35   -80
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.32e+23     10     298
    N   0.00e+00      6     207
    P  -1.32e+23     78      88

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.78e+22
       Mxy    -5.28e+22
       Mxz     1.01e+22
       Myy     9.42e+22
       Myz    -4.71e+22
       Mzz    -1.22e+23
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ###############-------              
              ###############------------#           
             ##############---------------#          
           ##############-----------------###        
             ###########-------------------###       
         # T ##########--------------------####      
        ##   ########----------------------#####     
        #############----------------------#####     
       #############----------   ----------######    
       ############----------- P ----------######    
       ############-----------   ---------#######    
       ###########------------------------#######    
        ##########-----------------------#######     
        #########-----------------------########     
         ########----------------------########      
          #######--------------------#########       
           #######-----------------##########        
             #####---------------##########          
              ####------------############           
                 ------################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.22e+23   1.01e+22   4.71e+22 
  1.01e+22   2.78e+22   5.28e+22 
  4.71e+22   5.28e+22   9.42e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150214022856/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 = 35
      DIP = 35
     RAKE = -80
       MW = 4.68
       HS = 12.0

The NDK file is 20150214022856.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  2015/02/14 02:28:56:0  37.15 -117.26  18.0 4.6 Nevada
 
 Stations used:
   AE.113A AE.U15A AE.W13A BC.CCX BC.RMX BC.SJX BC.TJX BC.TKX 
   BK.SAO BK.WDC CI.BAR CI.GLA CI.GSC CI.ISA CI.MWC CI.OSI 
   CI.PASC CI.SNCC IM.NV31 LB.MVU LB.TPH NC.AFD NC.MDPB NN.BEK 
   NN.LHV NN.OMMB NN.PAH NN.PNT NN.PRN NN.REDF NN.RUB NN.RYN 
   NN.SHP NN.VCN NN.WAK NN.WDEM NN.YER TA.109C TA.R11A US.DUG 
   US.ELK US.TPNV US.WUAZ US.WVOR UU.BGU UU.CCUT UU.KNB 
   UU.LCMT UU.MPU UU.MTPU UU.NLU UU.PKCU UU.PSUT UU.SZCU 
   UU.TCRU UU.TMU UU.VRUT 
 
 Filtering commands used:
   cut o DIST/3.3 -30 o DIST/3.3 +70
   rtr
   taper w 0.1
   hp c 0.02 n 3 
   lp c 0.07 n 3 
 
 Best Fitting Double Couple
  Mo = 1.32e+23 dyne-cm
  Mw = 4.68 
  Z  = 12 km
  Plane   Strike  Dip  Rake
   NP1      203    56   -97
   NP2       35    35   -80
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.32e+23     10     298
    N   0.00e+00      6     207
    P  -1.32e+23     78      88

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     2.78e+22
       Mxy    -5.28e+22
       Mxz     1.01e+22
       Myy     9.42e+22
       Myz    -4.71e+22
       Mzz    -1.22e+23
                                                     
                                                     
                                                     
                                                     
                     ##############                  
                 ###############-------              
              ###############------------#           
             ##############---------------#          
           ##############-----------------###        
             ###########-------------------###       
         # T ##########--------------------####      
        ##   ########----------------------#####     
        #############----------------------#####     
       #############----------   ----------######    
       ############----------- P ----------######    
       ############-----------   ---------#######    
       ###########------------------------#######    
        ##########-----------------------#######     
        #########-----------------------########     
         ########----------------------########      
          #######--------------------#########       
           #######-----------------##########        
             #####---------------##########          
              ####------------############           
                 ------################              
                     ##############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -1.22e+23   1.01e+22   4.71e+22 
  1.01e+22   2.78e+22   5.28e+22 
  4.71e+22   5.28e+22   9.42e+22 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150214022856/index.html
	
Moment	9.684e+15 N-m
Magnitude	4.59
Depth	1.5 km
Percent DC	74%
Half Duration	–
Catalog	CI (ci37316264)
Data Source	CI3
Contributor	CI3
Nodal Planes
Plane	Strike	Dip	Rake
NP1	2°	38°	-133°
NP2	232°	63°	-62°
Principal Axes
Axis	Value	Plunge	Azimuth
T	10.289	14°	302°
N	-1.354	25°	38°
P	-8.935	61°	185°

        

Magnitudes

mLg Magnitude


(a) mLg computed using the IASPEI formula; (b) mLg residuals ; the values used for the trimmed mean are indicated.

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 +70
rtr
taper w 0.1
hp c 0.02 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   245    75   -15   4.29 0.3839
WVFGRD96    2.0    65    70   -20   4.39 0.4391
WVFGRD96    3.0    60    65   -35   4.46 0.4290
WVFGRD96    4.0    70    35    -5   4.53 0.4535
WVFGRD96    5.0    75    35     5   4.54 0.4942
WVFGRD96    6.0    75    40    10   4.55 0.5278
WVFGRD96    7.0    40    30   -70   4.59 0.5634
WVFGRD96    8.0    30    25   -85   4.65 0.6065
WVFGRD96    9.0    20    30  -100   4.67 0.6451
WVFGRD96   10.0    20    35  -100   4.68 0.6677
WVFGRD96   11.0   210    55   -85   4.68 0.6803
WVFGRD96   12.0    35    35   -80   4.68 0.6811
WVFGRD96   13.0    35    35   -80   4.68 0.6721
WVFGRD96   14.0   220    55   -75   4.68 0.6572
WVFGRD96   15.0   230    60   -60   4.67 0.6406
WVFGRD96   16.0   230    60   -60   4.67 0.6229
WVFGRD96   17.0   235    60   -50   4.68 0.6043
WVFGRD96   18.0    80    60    30   4.69 0.5890
WVFGRD96   19.0    80    60    30   4.70 0.5744
WVFGRD96   20.0    80    60    30   4.70 0.5583
WVFGRD96   21.0    80    60    30   4.71 0.5393
WVFGRD96   22.0    80    60    30   4.71 0.5203
WVFGRD96   23.0    80    60    30   4.72 0.5004
WVFGRD96   24.0    80    60    30   4.72 0.4804
WVFGRD96   25.0    80    60    30   4.72 0.4601
WVFGRD96   26.0    80    60    30   4.72 0.4394
WVFGRD96   27.0    80    60    30   4.72 0.4189
WVFGRD96   28.0    80    60    25   4.73 0.3989
WVFGRD96   29.0    80    55    25   4.73 0.3797

The best solution is

WVFGRD96   12.0    35    35   -80   4.68 0.6811

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 0.02 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 Mon Dec 7 00:00:58 CST 2015