Location

2012/12/11 14:28:43 39.888 16.017 10.0 3.4 Italy

Arrival Times (from USGS)

Felt Map

Focal Mechanism

SLU Moment Tensor Solution ENS 2012/12/11 14:28:43:0 39.89 16.02 10.0 3.4 Italy Stations used: IV.CDRU IV.MGR IV.SALB IV.SERS IV.SLCN MN.CUC MN.TIP Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 8.51e+20 dyne-cm Mw = 3.22 Z = 7 km Plane Strike Dip Rake NP1 195 60 -50 NP2 316 48 -138 Principal Axes: Axis Value Plunge Azimuth T 8.51e+20 7 258 N 0.00e+00 34 352 P -8.51e+20 55 158 Moment Tensor: (dyne-cm) Component Value Mxx -1.99e+20 Mxy 2.69e+20 Mxz 3.49e+20 Myy 7.64e+20 Myz -2.44e+20 Mzz -5.65e+20 -----------### -------------######### --------------############## ############################## ##############----################ ##############--------############## ##############-----------############# ##############--------------############ #############-----------------########## ##############------------------########## #############--------------------######### #############---------------------######## ##########----------------------####### T #########-----------------------###### #########----------- ----------##### ##########----------- P ----------#### #########----------- ----------### #########-----------------------## #######----------------------- #######--------------------- ####------------------ #------------- Global CMT Convention Moment Tensor: R T P -5.65e+20 3.49e+20 2.44e+20 3.49e+20 -1.99e+20 -2.69e+20 2.44e+20 -2.69e+20 7.64e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20121211142843/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 = 195
      DIP = 60
     RAKE = -50
       MW = 3.22
       HS = 7.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

SLU Moment Tensor Solution ENS 2012/12/11 14:28:43:0 39.89 16.02 10.0 3.4 Italy Stations used: IV.CDRU IV.MGR IV.SALB IV.SERS IV.SLCN MN.CUC MN.TIP Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 8.51e+20 dyne-cm Mw = 3.22 Z = 7 km Plane Strike Dip Rake NP1 195 60 -50 NP2 316 48 -138 Principal Axes: Axis Value Plunge Azimuth T 8.51e+20 7 258 N 0.00e+00 34 352 P -8.51e+20 55 158 Moment Tensor: (dyne-cm) Component Value Mxx -1.99e+20 Mxy 2.69e+20 Mxz 3.49e+20 Myy 7.64e+20 Myz -2.44e+20 Mzz -5.65e+20 -----------### -------------######### --------------############## ############################## ##############----################ ##############--------############## ##############-----------############# ##############--------------############ #############-----------------########## ##############------------------########## #############--------------------######### #############---------------------######## ##########----------------------####### T #########-----------------------###### #########----------- ----------##### ##########----------- P ----------#### #########----------- ----------### #########-----------------------## #######----------------------- #######--------------------- ####------------------ #------------- Global CMT Convention Moment Tensor: R T P -5.65e+20 3.49e+20 2.44e+20 3.49e+20 -1.99e+20 -2.69e+20 2.44e+20 -2.69e+20 7.64e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20121211142843/index.html

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 0.10 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   190    75   -20   3.00 0.3074
WVFGRD96    2.0   190    70   -15   3.06 0.3239
WVFGRD96    3.0   205    80   -45   3.06 0.3511
WVFGRD96    4.0   205    75   -40   3.08 0.3853
WVFGRD96    5.0   215    85   -50   3.15 0.4035
WVFGRD96    6.0   195    65   -50   3.20 0.4170
WVFGRD96    7.0   195    60   -50   3.22 0.4234
WVFGRD96    8.0   200    60   -45   3.21 0.4215
WVFGRD96    9.0   215    45    35   3.26 0.4177
WVFGRD96   10.0   215    45    35   3.26 0.4129
WVFGRD96   11.0   210    45    25   3.27 0.4050
WVFGRD96   12.0   210    45    25   3.28 0.3963
WVFGRD96   13.0   205    50    20   3.28 0.3844
WVFGRD96   14.0   205    45    20   3.29 0.3745
WVFGRD96   15.0   205    45    20   3.31 0.3640
WVFGRD96   16.0   200    50    15   3.32 0.3550
WVFGRD96   17.0   200    50    15   3.33 0.3447
WVFGRD96   18.0   200    50    10   3.33 0.3353
WVFGRD96   19.0   195    60     5   3.34 0.3263
WVFGRD96   20.0   195    60     5   3.34 0.3169
WVFGRD96   21.0   195    55     5   3.35 0.3094
WVFGRD96   22.0   195    55     5   3.35 0.3027
WVFGRD96   23.0   195    55     5   3.36 0.2963
WVFGRD96   24.0   190    70    -5   3.38 0.2910
WVFGRD96   25.0   190    70    -5   3.39 0.2866
WVFGRD96   26.0   195    40    20   3.38 0.2875
WVFGRD96   27.0   195    40    20   3.39 0.2890
WVFGRD96   28.0   195    40    20   3.40 0.2905
WVFGRD96   29.0   180    55    15   3.46 0.2941

The best solution is

WVFGRD96    7.0   195    60   -50   3.22 0.4234

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

hp c 0.02 n 3
lp c 0.10 n 3

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:

The origin time and epicentral distance are incorrect
The velocity model used for the inversion is incorrect
The velocity model used to define the P-arrival time is not the same as the velocity model used for the waveform inversion (assuming that the initial trace alignment is based on the P arrival time)

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

Velocity Model

The nnCIA used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:

MODEL.01
C.It. A. Di Luzio et al Earth Plan Lettrs 280 (2009) 1-12 Fig 5. 7-8 MODEL/SURF3
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
     1.5000     3.7497     2.1436     2.2753  0.500E-02  0.100E-01   0.00       0.00       1.00       1.00    
     3.0000     4.9399     2.8210     2.4858  0.500E-02  0.100E-01   0.00       0.00       1.00       1.00    
     3.0000     6.0129     3.4336     2.7058  0.500E-02  0.100E-01   0.00       0.00       1.00       1.00    
     7.0000     5.5516     3.1475     2.6093  0.167E-02  0.333E-02   0.00       0.00       1.00       1.00    
    15.0000     5.8805     3.3583     2.6770  0.167E-02  0.333E-02   0.00       0.00       1.00       1.00    
     6.0000     7.1059     4.0081     3.0002  0.167E-02  0.333E-02   0.00       0.00       1.00       1.00    
     8.0000     7.1000     3.9864     3.0120  0.167E-02  0.333E-02   0.00       0.00       1.00       1.00    
     0.0000     7.9000     4.4036     3.2760  0.167E-02  0.333E-02   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:

DATE=Mon Dec 17 22:18:01 CST 2012

Last Changed 2012/12/11