Location

2009/04/07 12:29:28 42.437 13.403 12 3.30 Italy

Arrival Times (from USGS)

Felt Map

Focal Mechanism

USGS/SLU Moment Tensor Solution ENS 2009/04/07 12:29:28:0 42.44 13.40 12.0 3.3 Italy Stations used: IV.AOI IV.ARVD IV.ASSB IV.BSSO IV.CERA IV.CERT IV.CING IV.FAGN IV.FDMO IV.FIAM IV.GUAR IV.INTR IV.MIDA IV.MNS IV.OFFI IV.PIEI IV.PTRJ IV.SACS IV.TERO IV.TOLF IV.TRIV IV.VAGA MN.AQU Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 3.05e+21 dyne-cm Mw = 3.59 Z = 7 km Plane Strike Dip Rake NP1 149 55 -93 NP2 335 35 -85 Principal Axes: Axis Value Plunge Azimuth T 3.05e+21 10 241 N 0.00e+00 3 151 P -3.05e+21 79 45 Moment Tensor: (dyne-cm) Component Value Mxx 6.28e+20 Mxy 1.19e+21 Mxz -6.38e+20 Myy 2.23e+21 Myz -8.51e+20 Mzz -2.86e+21 ############## -----------########### ###---------------########## ###------------------######### #####--------------------######### ######----------------------######## #######-----------------------######## ########------------------------######## #########------------ ---------####### ##########------------ P ---------######## ###########----------- ----------####### ############-----------------------####### ############------------------------###### #############----------------------##### ## #########--------------------###### # T ##########-------------------##### ############-----------------#### ################--------------#### ################-----------### ##################-------### ####################-# ############## Global CMT Convention Moment Tensor: R T P -2.86e+21 -6.38e+20 8.51e+20 -6.38e+20 6.28e+20 -1.19e+21 8.51e+20 -1.19e+21 2.23e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090407122928/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 = 335
      DIP = 35
     RAKE = -85
       MW = 3.59
       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 2009/04/07 12:29:00:0 42.46 13.41 8.3 3.3 Italy Stations used: IV.ARVD IV.ASSB IV.BSSO IV.CAFI IV.CERT IV.CESI IV.CING IV.FAGN IV.FDMO IV.FIAM IV.GUAR IV.INTR IV.MIDA IV.MNS IV.OFFI IV.PIEI IV.PTRJ IV.SACS IV.SGG IV.TERO IV.TOLF IV.VAGA MN.AQU Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 3.24e+20 dyne-cm Mw = 2.94 Z = 19 km Plane Strike Dip Rake NP1 330 75 -85 NP2 131 16 -108 Principal Axes: Axis Value Plunge Azimuth T 3.24e+20 30 56 N 0.00e+00 5 149 P -3.24e+20 60 247 Moment Tensor: (dyne-cm) Component Value Mxx 6.39e+19 Mxy 8.34e+19 Mxz 1.33e+20 Myy 9.73e+19 Myz 2.45e+20 Mzz -1.61e+20 ############## -##################### -------##################### ----------#################### -------------##################### #---------------############# #### #-----------------############ T ##### #-------------------########### ###### #---------------------################## ##----------------------################## ##-----------------------################# ##----------- ----------################ ###---------- P -----------############### ##---------- ------------############# ###------------------------############# ###------------------------########### ###------------------------######### ####----------------------######## ####---------------------##### ######------------------###- #######-------------#- ############## Global CMT Convention Moment Tensor: R T P -1.61e+20 1.33e+20 -2.45e+20 1.33e+20 6.39e+19 -8.34e+19 -2.45e+20 -8.34e+19 9.73e+19 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090407122900/index.html USGS/SLU Moment Tensor Solution ENS 2009/04/07 12:29:28:0 42.44 13.40 12.0 3.3 Italy Stations used: IV.AOI IV.ARVD IV.ASSB IV.BSSO IV.CERA IV.CERT IV.CING IV.FAGN IV.FDMO IV.FIAM IV.GUAR IV.INTR IV.MIDA IV.MNS IV.OFFI IV.PIEI IV.PTRJ IV.SACS IV.TERO IV.TOLF IV.TRIV IV.VAGA MN.AQU Filtering commands used: hp c 0.02 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 3.05e+21 dyne-cm Mw = 3.59 Z = 7 km Plane Strike Dip Rake NP1 149 55 -93 NP2 335 35 -85 Principal Axes: Axis Value Plunge Azimuth T 3.05e+21 10 241 N 0.00e+00 3 151 P -3.05e+21 79 45 Moment Tensor: (dyne-cm) Component Value Mxx 6.28e+20 Mxy 1.19e+21 Mxz -6.38e+20 Myy 2.23e+21 Myz -8.51e+20 Mzz -2.86e+21 ############## -----------########### ###---------------########## ###------------------######### #####--------------------######### ######----------------------######## #######-----------------------######## ########------------------------######## #########------------ ---------####### ##########------------ P ---------######## ###########----------- ----------####### ############-----------------------####### ############------------------------###### #############----------------------##### ## #########--------------------###### # T ##########-------------------##### ############-----------------#### ################--------------#### ################-----------### ##################-------### ####################-# ############## Global CMT Convention Moment Tensor: R T P -2.86e+21 -6.38e+20 8.51e+20 -6.38e+20 6.28e+20 -1.19e+21 8.51e+20 -1.19e+21 2.23e+21 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090407122928/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    10    30   -20   3.37 0.3144
WVFGRD96    1.0    10    35   -20   3.33 0.3240
WVFGRD96    2.0    10    25   -20   3.42 0.3961
WVFGRD96    3.0     0    25   -40   3.42 0.4699
WVFGRD96    4.0   350    30   -60   3.45 0.5255
WVFGRD96    5.0   345    30   -65   3.56 0.5803
WVFGRD96    6.0   340    35   -75   3.58 0.6235
WVFGRD96    7.0   335    35   -85   3.59 0.6330
WVFGRD96    8.0   335    35   -85   3.55 0.6051
WVFGRD96    9.0   340    35   -75   3.53 0.5824
WVFGRD96   10.0   340    35   -75   3.53 0.5577
WVFGRD96   11.0    15    45   -20   3.50 0.5339
WVFGRD96   12.0    20    45   -15   3.52 0.5181
WVFGRD96   13.0    20    45   -15   3.53 0.5010
WVFGRD96   14.0    20    45   -15   3.54 0.4817
WVFGRD96   15.0    25    40   -10   3.58 0.4682
WVFGRD96   16.0    25    35   -10   3.59 0.4520
WVFGRD96   17.0    30    40     0   3.60 0.4374
WVFGRD96   18.0    30    40     0   3.61 0.4244
WVFGRD96   19.0    30    40     0   3.62 0.4120
WVFGRD96   20.0    30    40     0   3.63 0.4005
WVFGRD96   21.0    30    40     0   3.64 0.3892
WVFGRD96   22.0    30    40     0   3.65 0.3788
WVFGRD96   23.0    30    40     0   3.66 0.3698
WVFGRD96   24.0    30    40     0   3.67 0.3615
WVFGRD96   25.0    30    40     0   3.68 0.3561
WVFGRD96   26.0    30    40     0   3.68 0.3522
WVFGRD96   27.0    30    45     0   3.70 0.3498
WVFGRD96   28.0    30    45     5   3.70 0.3483
WVFGRD96   29.0    30    50     5   3.72 0.3471

The best solution is

WVFGRD96    7.0   335    35   -85   3.59 0.6330

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. 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 04:05:08 CDT 2010

Last Changed 2009/04/07