Location

2015/02/28 10:41:37 38.865 -115.381 0.0 4.2 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  2015/02/28 10:41:37:0  38.87 -115.38   0.0 4.2 Nevada
 
 Stations used:
   AE.W13A CI.GSC CI.ISA CI.OSI CI.PASC IM.NV31 IW.MFID LB.TPH 
   NN.BEK NN.KVN NN.LHV NN.PAH NN.PNT NN.PRN NN.REDF NN.RYN 
   NN.SHP NN.VCN NN.WAK NN.YER RE.PV12 RE.PV17 TA.R11A US.DUG 
   US.ELK US.HLID US.TPNV US.WUAZ US.WVOR UW.IRON 
 
 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 = 5.50e+21 dyne-cm
  Mw = 3.76 
  Z  = 9 km
  Plane   Strike  Dip  Rake
   NP1       80    65   -45
   NP2      193    50   -147
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.50e+21      9     140
    N   0.00e+00     40     237
    P  -5.50e+21     49      39

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.68e+21
       Mxy    -3.82e+21
       Mxz    -2.74e+21
       Myy     1.29e+21
       Myz    -1.18e+21
       Mzz    -2.98e+21
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 ###########-----------              
              ###########-----------------           
             ###########-------------------          
           ###########-----------------------        
          ###########------------   ----------       
         ###########------------- P -----------      
        ############-------------   ------------     
        ###########-----------------------------     
       ###########------------------------------#    
       ###########----------------------------###    
       ###########-------------------------######    
       ###########----------------------#########    
        -########-------------------############     
        -------###----------####################     
         ---------#############################      
          --------############################       
           --------####################   ###        
             ------#################### T #          
              ------###################              
                 ----##################              
                     --############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.98e+21  -2.74e+21   1.18e+21 
 -2.74e+21   1.68e+21   3.82e+21 
  1.18e+21   3.82e+21   1.29e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150228104137/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 = 80
      DIP = 65
     RAKE = -45
       MW = 3.76
       HS = 9.0

The NDK file is 20150228104137.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
UNR
 USGS/SLU Moment Tensor Solution
 ENS  2015/02/28 10:41:37:0  38.87 -115.38   0.0 4.2 Nevada
 
 Stations used:
   AE.W13A CI.GSC CI.ISA CI.OSI CI.PASC IM.NV31 IW.MFID LB.TPH 
   NN.BEK NN.KVN NN.LHV NN.PAH NN.PNT NN.PRN NN.REDF NN.RYN 
   NN.SHP NN.VCN NN.WAK NN.YER RE.PV12 RE.PV17 TA.R11A US.DUG 
   US.ELK US.HLID US.TPNV US.WUAZ US.WVOR UW.IRON 
 
 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 = 5.50e+21 dyne-cm
  Mw = 3.76 
  Z  = 9 km
  Plane   Strike  Dip  Rake
   NP1       80    65   -45
   NP2      193    50   -147
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   5.50e+21      9     140
    N   0.00e+00     40     237
    P  -5.50e+21     49      39

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     1.68e+21
       Mxy    -3.82e+21
       Mxz    -2.74e+21
       Myy     1.29e+21
       Myz    -1.18e+21
       Mzz    -2.98e+21
                                                     
                                                     
                                                     
                                                     
                     ##########----                  
                 ###########-----------              
              ###########-----------------           
             ###########-------------------          
           ###########-----------------------        
          ###########------------   ----------       
         ###########------------- P -----------      
        ############-------------   ------------     
        ###########-----------------------------     
       ###########------------------------------#    
       ###########----------------------------###    
       ###########-------------------------######    
       ###########----------------------#########    
        -########-------------------############     
        -------###----------####################     
         ---------#############################      
          --------############################       
           --------####################   ###        
             ------#################### T #          
              ------###################              
                 ----##################              
                     --############                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
 -2.98e+21  -2.74e+21   1.18e+21 
 -2.74e+21   1.68e+21   3.82e+21 
  1.18e+21   3.82e+21   1.29e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20150228104137/index.html
	
Regional Moment Tensor (Mwr)
Moment	6.140e+14 N-m
Magnitude	3.79
Depth	5.0 km
Percent DC	81%
Half Duration	–
Catalog	US (usc000ttyx)
Data Source	US2
Contributor	US2
Nodal Planes
Plane	Strike	Dip	Rake
NP1	58°	57°	-61°
NP2	193°	43°	-127°
Principal Axes
Axis	Value	Plunge	Azimuth
T	6.428	8°	128°
N	-0.624	24°	222°
P	-5.805	65°	21°

        
Mw
Moment	9.736e+14 N-m
Magnitude	3.93
Depth	8.0 km
Percent DC	98%
Half Duration	–
Catalog	NN (nn00485024)
Data Source	NN1
Contributor	NN1
Nodal Planes
Plane	Strike	Dip	Rake
NP1	52°	62°	-78°
NP2	209°	30°	-111°
Principal Axes
Axis	Value	Plunge	Azimuth
T	9.697	16°	134°
N	0.078	10°	227°
P	-9.775	71°	348°

        

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 0.03 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    45    45   -90   3.54 0.3660
WVFGRD96    2.0   225    45   -90   3.65 0.4766
WVFGRD96    3.0    70    65   -55   3.66 0.4936
WVFGRD96    4.0    70    65   -55   3.69 0.5432
WVFGRD96    5.0    75    65   -50   3.68 0.5740
WVFGRD96    6.0    80    65   -45   3.69 0.5957
WVFGRD96    7.0    80    65   -45   3.70 0.6137
WVFGRD96    8.0    75    60   -55   3.77 0.6380
WVFGRD96    9.0    80    65   -45   3.76 0.6421
WVFGRD96   10.0    80    65   -45   3.77 0.6403
WVFGRD96   11.0    85    70   -35   3.76 0.6356
WVFGRD96   12.0   275    80    30   3.76 0.6323
WVFGRD96   13.0   275    75    30   3.77 0.6288
WVFGRD96   14.0   275    75    30   3.78 0.6229
WVFGRD96   15.0   275    75    30   3.79 0.6147
WVFGRD96   16.0   280    70    30   3.80 0.6051
WVFGRD96   17.0   275    75    25   3.80 0.5946
WVFGRD96   18.0   275    75    25   3.81 0.5831
WVFGRD96   19.0   275    70    25   3.82 0.5709
WVFGRD96   20.0   275    70    25   3.83 0.5579
WVFGRD96   21.0   275    70    25   3.83 0.5438
WVFGRD96   22.0   275    70    25   3.84 0.5300
WVFGRD96   23.0   275    70    25   3.84 0.5160
WVFGRD96   24.0   275    70    25   3.85 0.5022
WVFGRD96   25.0   280    65    25   3.86 0.4893
WVFGRD96   26.0   280    65    25   3.87 0.4773
WVFGRD96   27.0   280    65    25   3.87 0.4656
WVFGRD96   28.0   280    65    25   3.88 0.4541
WVFGRD96   29.0   280    65    25   3.89 0.4433

The best solution is

WVFGRD96    9.0    80    65   -45   3.76 0.6421

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 Mon Dec 7 00:01:13 CST 2015