Location

2013/01/24 04:46:39 38.324 -108.989 2.5 3.90 Colorado

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  2013/01/24 04:46:39:0  38.32 -108.99   2.5 3.9 Colorado
 
 Stations used:
   AE.U15A AE.W13A AE.X16A IU.ANMO IW.PHWY IW.RWWY IW.SMCO 
   RE.PV02 RE.PV13 TA.N23A TA.O20A TA.Q24A TA.R11A TA.S22A 
   TA.W18A US.BW06 US.DUG US.ISCO US.MVCO US.SDCO US.WUAZ 
   UU.BGU UU.BRPU UU.CCUT UU.CTU UU.CVRU UU.HVU UU.JLU UU.KNB 
   UU.LCMT UU.MPU UU.MTPU UU.NLU UU.PKCU UU.PSUT UU.RDMU 
   UU.SPU UU.SRU UU.SZCU UU.TCRU UU.TCU UU.TMU 
 
 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 = 1.06e+22 dyne-cm
  Mw = 3.95 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      350    90   -10
   NP2       80    80   -180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.06e+22      7      35
    N   0.00e+00     80     170
    P  -1.06e+22      7     305

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.57e+21
       Mxy     9.80e+21
       Mxz     3.19e+20
       Myy    -3.57e+21
       Myz     1.81e+21
       Mzz     1.61e+14
                                                     
                                                     
                                                     
                                                     
                     ----##########                  
                 --------#############               
              -----------############# T #           
             -------------############   ##          
             -------------###################        
           P -------------####################       
         -   --------------####################      
        -------------------#####################     
        -------------------#####################     
       ---------------------###################--    
       ---------------------##############-------    
       ---------------------########-------------    
       --------------------#---------------------    
        #####################-------------------     
        #####################-------------------     
         ####################------------------      
          ####################----------------       
           ###################---------------        
             #################-------------          
              #################-----------           
                 ##############--------              
                     ##########----                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.61e+14   3.19e+20  -1.81e+21 
  3.19e+20   3.57e+21  -9.80e+21 
 -1.81e+21  -9.80e+21  -3.57e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130124044639/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 = 350
      DIP = 90
     RAKE = -10
       MW = 3.95
       HS = 5.0

The NDK file is 20130124044639.ndk The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others
SLU
USGSMT
SLUFM
 USGS/SLU Moment Tensor Solution
 ENS  2013/01/24 04:46:39:0  38.32 -108.99   2.5 3.9 Colorado
 
 Stations used:
   AE.U15A AE.W13A AE.X16A IU.ANMO IW.PHWY IW.RWWY IW.SMCO 
   RE.PV02 RE.PV13 TA.N23A TA.O20A TA.Q24A TA.R11A TA.S22A 
   TA.W18A US.BW06 US.DUG US.ISCO US.MVCO US.SDCO US.WUAZ 
   UU.BGU UU.BRPU UU.CCUT UU.CTU UU.CVRU UU.HVU UU.JLU UU.KNB 
   UU.LCMT UU.MPU UU.MTPU UU.NLU UU.PKCU UU.PSUT UU.RDMU 
   UU.SPU UU.SRU UU.SZCU UU.TCRU UU.TCU UU.TMU 
 
 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 = 1.06e+22 dyne-cm
  Mw = 3.95 
  Z  = 5 km
  Plane   Strike  Dip  Rake
   NP1      350    90   -10
   NP2       80    80   -180
  Principal Axes:
   Axis    Value   Plunge  Azimuth
    T   1.06e+22      7      35
    N   0.00e+00     80     170
    P  -1.06e+22      7     305

 Moment Tensor: (dyne-cm)
    Component   Value
       Mxx     3.57e+21
       Mxy     9.80e+21
       Mxz     3.19e+20
       Myy    -3.57e+21
       Myz     1.81e+21
       Mzz     1.61e+14
                                                     
                                                     
                                                     
                                                     
                     ----##########                  
                 --------#############               
              -----------############# T #           
             -------------############   ##          
             -------------###################        
           P -------------####################       
         -   --------------####################      
        -------------------#####################     
        -------------------#####################     
       ---------------------###################--    
       ---------------------##############-------    
       ---------------------########-------------    
       --------------------#---------------------    
        #####################-------------------     
        #####################-------------------     
         ####################------------------      
          ####################----------------       
           ###################---------------        
             #################-------------          
              #################-----------           
                 ##############--------              
                     ##########----                  
                                                     
                                                     
                                                     
 Global CMT Convention Moment Tensor:
      R          T          P
  1.61e+14   3.19e+20  -1.81e+21 
  3.19e+20   3.57e+21  -9.80e+21 
 -1.81e+21  -9.80e+21  -3.57e+21 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/MECH.NA/20130124044639/index.html
	

USGS/SLU Regional Moment Solution

13/01/24 04:46:40.22

Epicenter:  38.351 -109.003
MW 3.9

USGS/SLU REGIONAL MOMENT TENSOR
Depth   5         No. of sta: 86
Moment Tensor;   Scale 10**15 Nm
  Mrr= 0.01       Mtt= 0.30
  Mpp=-0.32       Mrt=-0.05
  Mrp= 0.25       Mtp=-0.94
 Principal axes:
  T  Val=  1.02  Plg=11  Azm=217
  N        0.01      75      355
  P       -1.03      10      125

Best Double Couple:Mo=1.0*10**15
 NP1:Strike=351 Dip=89 Slip=  15
 NP2:       261     75       179


        


First motions and takeoff angles from an elocate run.

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   350    90   -20   3.82 0.5306
WVFGRD96    1.0   170    90    10   3.83 0.5620
WVFGRD96    2.0   350    90   -20   3.90 0.6280
WVFGRD96    3.0   170    90    20   3.92 0.6574
WVFGRD96    4.0   175    80    20   3.94 0.6709
WVFGRD96    5.0   350    90   -10   3.95 0.6729
WVFGRD96    6.0   175    80    20   3.97 0.6706
WVFGRD96    7.0   175    80    15   3.98 0.6658
WVFGRD96    8.0   175    80    20   4.00 0.6626
WVFGRD96    9.0   350    60   -10   4.01 0.6527
WVFGRD96   10.0   350    80   -25   4.00 0.6480
WVFGRD96   11.0   350    85   -25   4.01 0.6465
WVFGRD96   12.0   175    85    25   4.02 0.6448
WVFGRD96   13.0   175    85    25   4.03 0.6423
WVFGRD96   14.0   175    85    25   4.04 0.6393
WVFGRD96   15.0   170    90    20   4.05 0.6355
WVFGRD96   16.0   350    90   -20   4.06 0.6324
WVFGRD96   17.0   170    90    20   4.07 0.6287
WVFGRD96   18.0   350    90   -20   4.08 0.6240
WVFGRD96   19.0   350    90   -20   4.09 0.6188
WVFGRD96   20.0   350    90   -20   4.10 0.6130
WVFGRD96   21.0   170    90    20   4.11 0.6063
WVFGRD96   22.0   170    90    20   4.12 0.5992
WVFGRD96   23.0   170    90    25   4.13 0.5915
WVFGRD96   24.0   170    90    25   4.14 0.5822
WVFGRD96   25.0   350    90   -25   4.15 0.5737
WVFGRD96   26.0   170    90    25   4.16 0.5651
WVFGRD96   27.0   170    90    25   4.16 0.5547
WVFGRD96   28.0   350    85   -20   4.17 0.5461
WVFGRD96   29.0   350    85   -20   4.18 0.5367

The best solution is

WVFGRD96    5.0   350    90   -10   3.95 0.6729

The mechanism corresponding 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 Mon Dec 7 00:20:12 CST 2015