Location

2009/04/13 13:36:04 42.444 13.440 9.0 3.40 Italy

Arrival Times (from USGS)

Felt Map

Focal Mechanism

Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090413360400/index.html Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090413360400/index.html Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090413360400/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 = 15
      DIP = 60
     RAKE = -30
       MW = 3.65
       HS = 7.0

The waveform inversion is preferred.

Moment Tensor Comparison

The following compares this source inversion to others

SLU

USGS/SLU Moment Tensor Solution ENS 2009/04/13 13:36:04:0 42.44 13.44 9.0 3.4 Italy Stations used: IV.ARVD IV.CERA IV.CERT IV.CING IV.FDMO IV.FIAM IV.INTR IV.LNSS IV.MIDA IV.MTCE IV.MURB IV.OFFI IV.PARC IV.PIEI IV.RMP IV.TERO Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 3.76e+21 dyne-cm Mw = 3.65 Z = 7 km Plane Strike Dip Rake NP1 121 64 -146 NP2 15 60 -30 Principal Axes: Axis Value Plunge Azimuth T 3.76e+21 3 247 N 0.00e+00 49 154 P -3.76e+21 41 340 Moment Tensor: (dyne-cm) Component Value Mxx -1.30e+21 Mxy 2.03e+21 Mxz -1.82e+21 Myy 2.93e+21 Myz 4.86e+20 Mzz -1.63e+21 -------------# ------------------#### ---------------------####### --------- -----------####### ----------- P -----------######### ------------ ------------######### ##--------------------------########## ####-------------------------########### #####------------------------########### ########---------------------############# #########--------------------############# ###########------------------############# ##############--------------############## ###############------------############# ###############--------############## T ###################---############## #####################---########### ####################-------------- #################------------- ##############-------------- #########------------- ###----------- Global CMT Convention Moment Tensor: R T P -1.63e+21 -1.82e+21 -4.86e+20 -1.82e+21 -1.30e+21 -2.03e+21 -4.86e+20 -2.03e+21 2.93e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090413360400/index.html Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090413360400/index.html Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090413360400/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    0.5    15    55   -25   3.39 0.3450
WVFGRD96    1.0    15    55   -25   3.41 0.3544
WVFGRD96    2.0    15    45   -20   3.50 0.4028
WVFGRD96    3.0    20    50   -10   3.51 0.4525
WVFGRD96    4.0    20    60   -15   3.54 0.4979
WVFGRD96    5.0    15    55   -25   3.62 0.5385
WVFGRD96    6.0    10    55   -40   3.65 0.5671
WVFGRD96    7.0    15    60   -30   3.65 0.5765
WVFGRD96    8.0    20    65   -20   3.63 0.5621
WVFGRD96    9.0    20    65   -20   3.64 0.5531
WVFGRD96   10.0    20    70   -20   3.66 0.5407
WVFGRD96   11.0    20    70   -20   3.67 0.5266
WVFGRD96   12.0    20    70   -20   3.68 0.5110
WVFGRD96   13.0    20    70   -20   3.68 0.4955
WVFGRD96   14.0    20    70   -20   3.69 0.4806
WVFGRD96   15.0    20    70   -20   3.72 0.4717
WVFGRD96   16.0    20    70   -20   3.73 0.4589
WVFGRD96   17.0    20    70   -20   3.73 0.4463
WVFGRD96   18.0    20    75     5   3.74 0.4365
WVFGRD96   19.0    20    75     5   3.75 0.4273
WVFGRD96   20.0    20    75     5   3.75 0.4176
WVFGRD96   21.0    15    80     5   3.77 0.4094
WVFGRD96   22.0    15    80     5   3.77 0.4006
WVFGRD96   23.0    15    80     5   3.78 0.3914
WVFGRD96   24.0    15    80     5   3.79 0.3825
WVFGRD96   25.0    15    85     5   3.80 0.3738
WVFGRD96   26.0    15    80     5   3.81 0.3663
WVFGRD96   27.0    20    75    10   3.81 0.3627
WVFGRD96   28.0    20    75    10   3.82 0.3615
WVFGRD96   29.0    20    75     5   3.84 0.3626

The best solution is

WVFGRD96    7.0    15    60   -30   3.65 0.5765

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 0.02 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.

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=Thu May 6 04:05:40 CDT 2010

Last Changed 2009/04/13