Location

2006/06/11 10:01:50 40.25N 111.07W 10 3.4 Utah

Arrival Times (from USGS)

Arrival time list

Felt Map

USGS Felt map for this earthquake

USGS Felt reports page for Intermountain Western US

Focal Mechanism

 SLU Moment Tensor Solution
 2006/06/11 10:01:50 40.25N 111.07W 10 3.4 Utah
 
 Best Fitting Double Couple
    Mo = 2.00e+21 dyne-cm
    Mw = 3.50 
    Z  = 14 km
     Plane   Strike  Dip  Rake
      NP1      357    76   -111
      NP2      235    25   -35
 Principal Axes:
   Axis    Value   Plunge  Azimuth
     T   2.00e+21     28     104
     N   0.00e+00     20       3
     P  -2.00e+21     54     242



 Moment Tensor: (dyne-cm)
    Component  Value
       Mxx    -6.08e+19
       Mxy    -6.48e+20
       Mxz     2.47e+20
       Myy     9.38e+20
       Myz     1.64e+21
       Mzz    -8.77e+20
                                                     
                                                     
                                                     
                                                     
                     #######-------                  
                 ###########-----------              
              ##########-----##########---           
             #######----------############-          
           #######------------###############        
          ######--------------################       
         #####-----------------################      
        #####------------------#################     
        ####-------------------#################     
       ####--------------------##################    
       ###----------------------#################    
       ###----------------------#################    
       ###--------   -----------#########   #####    
        ##-------- P -----------######### T ####     
        ##--------   -----------#########   ####     
         #----------------------###############      
          ---------------------###############       
           --------------------##############        
             ------------------############          
              -----------------###########           
                 -------------#########              
                     --------######                  
                                                     
                                                     
                                                     

 Harvard Convention
 Moment Tensor:
      R          T          F
 -8.77e+20   2.47e+20  -1.64e+21 
  2.47e+20  -6.08e+19   6.48e+20 
 -1.64e+21   6.48e+20   9.38e+20 


Details of the solution is found at

http://www.eas.slu.edu/eqc/eqc_mt/NEW/20060611100150/index.html
        

The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.
Figure 1. Location of broadband stations used to obtain focal mechanism

Preferred Solution

The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is

      STK = 235
      DIP = 25
     RAKE = -35
       MW = 3.50
       HS = 14

The surface-wave solution technique was not used because of the small size of the event.

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 0.03 3
lp c 0.15 3
br c 0.12 0.2 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   185    50    90   2.93 0.1718
WVFGRD96    1.0   205    50    80   2.86 0.1428
WVFGRD96    2.0    15    45    85   3.07 0.2091
WVFGRD96    3.0   160    65    35   3.07 0.1822
WVFGRD96    4.0   150    80     5   3.13 0.1859
WVFGRD96    5.0   165    75   -30   3.16 0.1977
WVFGRD96    6.0   165    75   -35   3.23 0.2310
WVFGRD96    7.0   150    90    75   3.38 0.2844
WVFGRD96    8.0   270    15    30   3.46 0.3332
WVFGRD96    9.0   275    10    35   3.51 0.3780
WVFGRD96   10.0   270    15    30   3.53 0.4060
WVFGRD96   11.0   275    15    35   3.54 0.4198
WVFGRD96   12.0   270    15    30   3.56 0.4241
WVFGRD96   13.0   255    15    15   3.57 0.4228
WVFGRD96   14.0   235    25   -35   3.50 0.4247
WVFGRD96   15.0   230    20   -40   3.50 0.4238
WVFGRD96   16.0   230    20   -40   3.51 0.4209
WVFGRD96   17.0   235    20   -35   3.51 0.4137
WVFGRD96   18.0   260    25   -15   3.50 0.4051
WVFGRD96   18.0   260    25   -15   3.50 0.4051

The best solution is

WVFGRD96   14.0   235    25   -35   3.50 0.4247

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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was

hp c 0.03 3
lp c 0.15 3
br c 0.12 0.2 n 4 p 2
Figure 3. Waveform comparison for depth of 8 km
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.

First motion data

The P-wave first motion data for focal mechanism studies are as follow:

Sta Az(deg)    Dist(km)   First motion
CTU       311   77 eP_+
NOQ       298  100 eP_X
TCU       344  102 eP_X
BGU       295  182 iP_D
N13A      285  274 iP_D
M13A      296  289 iP_D
P12A      257  339 eP_X
N12A      283  343 eP_X
M12A      293  350 eP_X
N11A      281  401 eP_X
M11A      290  420 eP_X
ISCO       94  468 eP_X

University of Utah Seismograph Stations Focal Mechanism

This mechansim was generated
using HASH.  The nodal planes are:
        STR     DIP     Rake
1       175.39  89.73   116.74
2       265.93  26.74   0.60

The quality info from HASH is
cid =   20060611   100149.9  mech =     175.391    89.7268    116.736
      prob      var_avg       mfrac        stdr   Quality
    0.833333    25.7756   0.113020   0.615004   B

Last Changed 2006/06/11