Location

2013/02/12 18:12:43 46.311 12.567 8.7 3.8 Italy

Arrival Times (from USGS)

Felt Map

Focal Mechanism

SLU Moment Tensor Solution ENS 2013/02/12 18:12:43:0 46.31 12.57 8.7 3.8 Italy Stations used: CH.BERNI CH.DAVOX CH.FUORN CH.VDL IV.MABI IV.PTCC MN.TRI MN.TUE OE.ARSA OE.DAVA OE.KBA OE.MOA OE.WTTA SL.BOJS SL.CADS SL.CEY SL.CRES SL.CRNS SL.GBAS SL.GORS SL.GROS SL.JAVS SL.KNDS SL.LJU SL.MOZS SL.PERS SL.ROBS SL.SKDS SL.VISS SL.VNDS SL.VOJS Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.88e+21 dyne-cm Mw = 3.45 Z = 13 km Plane Strike Dip Rake NP1 245 50 85 NP2 73 40 96 Principal Axes: Axis Value Plunge Azimuth T 1.88e+21 84 120 N 0.00e+00 4 248 P -1.88e+21 5 339 Moment Tensor: (dyne-cm) Component Value Mxx -1.61e+21 Mxy 6.27e+20 Mxz -2.51e+20 Myy -2.34e+20 Myz 2.33e+20 Mzz 1.85e+21 ------------- -- P ----------------- ----- -------------------- ------------------------------ ---------------------------------- ----------------##################-- -------------######################### -----------############################# ---------############################### --------################################-- ------############### ###############--- -----################ T ###############--- ----################# #############----- --#################################----- --###############################------- -#############################-------- ---#######################---------- ------##############-------------- ------------------------------ ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 1.85e+21 -2.51e+20 -2.33e+20 -2.51e+20 -1.61e+21 -6.27e+20 -2.33e+20 -6.27e+20 -2.34e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20130212181243/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 = 245
      DIP = 50
     RAKE = 85
       MW = 3.45
       HS = 13.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

SLU Moment Tensor Solution ENS 2013/02/12 18:12:43:0 46.31 12.57 8.7 3.8 Italy Stations used: CH.BERNI CH.DAVOX CH.FUORN CH.VDL IV.MABI IV.PTCC MN.TRI MN.TUE OE.ARSA OE.DAVA OE.KBA OE.MOA OE.WTTA SL.BOJS SL.CADS SL.CEY SL.CRES SL.CRNS SL.GBAS SL.GORS SL.GROS SL.JAVS SL.KNDS SL.LJU SL.MOZS SL.PERS SL.ROBS SL.SKDS SL.VISS SL.VNDS SL.VOJS Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 br c 0.12 0.25 n 4 p 2 Best Fitting Double Couple Mo = 1.88e+21 dyne-cm Mw = 3.45 Z = 13 km Plane Strike Dip Rake NP1 245 50 85 NP2 73 40 96 Principal Axes: Axis Value Plunge Azimuth T 1.88e+21 84 120 N 0.00e+00 4 248 P -1.88e+21 5 339 Moment Tensor: (dyne-cm) Component Value Mxx -1.61e+21 Mxy 6.27e+20 Mxz -2.51e+20 Myy -2.34e+20 Myz 2.33e+20 Mzz 1.85e+21 ------------- -- P ----------------- ----- -------------------- ------------------------------ ---------------------------------- ----------------##################-- -------------######################### -----------############################# ---------############################### --------################################-- ------############### ###############--- -----################ T ###############--- ----################# #############----- --#################################----- --###############################------- -#############################-------- ---#######################---------- ------##############-------------- ------------------------------ ---------------------------- ---------------------- -------------- Global CMT Convention Moment Tensor: R T P 1.85e+21 -2.51e+20 -2.33e+20 -2.51e+20 -1.61e+21 -6.27e+20 -2.33e+20 -6.27e+20 -2.34e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20130212181243/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
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    1.0   165    45  -100   3.20 0.4867
WVFGRD96    2.0    -5    45   -85   3.27 0.4674
WVFGRD96    3.0    25    85   -60   3.31 0.4522
WVFGRD96    4.0    20    85   -60   3.31 0.5241
WVFGRD96    5.0    20    85   -65   3.40 0.5707
WVFGRD96    6.0    15    80   -65   3.39 0.6035
WVFGRD96    7.0    20    85   -60   3.38 0.6214
WVFGRD96    8.0    15    75   -55   3.35 0.6321
WVFGRD96    9.0   245    55    80   3.44 0.6416
WVFGRD96   10.0   245    50    80   3.44 0.6577
WVFGRD96   11.0    75    40    95   3.45 0.6685
WVFGRD96   12.0    75    40    95   3.45 0.6733
WVFGRD96   13.0   245    50    85   3.45 0.6749
WVFGRD96   14.0   245    50    85   3.46 0.6727
WVFGRD96   15.0   240    50    75   3.49 0.6730
WVFGRD96   16.0   240    50    75   3.49 0.6684
WVFGRD96   17.0   235    50    70   3.50 0.6624
WVFGRD96   18.0   235    50    70   3.50 0.6547
WVFGRD96   19.0   230    55    65   3.50 0.6454
WVFGRD96   20.0   230    55    60   3.52 0.6352
WVFGRD96   21.0   230    55    60   3.53 0.6237
WVFGRD96   22.0   230    55    60   3.54 0.6106
WVFGRD96   23.0   230    55    60   3.55 0.5959
WVFGRD96   24.0   230    55    60   3.56 0.5794
WVFGRD96   25.0   225    60    55   3.56 0.5615
WVFGRD96   26.0   225    60    55   3.57 0.5426
WVFGRD96   27.0   225    60    55   3.58 0.5224
WVFGRD96   28.0   225    55    50   3.60 0.5039
WVFGRD96   29.0   225    55    50   3.61 0.4866

The best solution is

WVFGRD96   13.0   245    50    85   3.45 0.6749

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
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:

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=Tue Feb 12 18:54:16 CST 2013

Last Changed 2013/02/12