2009/04/06 07:17:10 42.355 13.367 9.2 3.90 Italy
USGS Felt map for this earthquake
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406071710/index.html
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406071710/index.html
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STK = 335
DIP = 35
RAKE = -75
MW = 4.03
HS = 6.0
The waveform inversion is preferred.
The following compares this source inversion to others
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406071710/index.html
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406071710/index.html
USGS/SLU Moment Tensor Solution
ENS 2009/04/09 07:17:10:0 42.35 13.37 9.2 3.9 Italy
Stations used:
IV.ASSB IV.CAFR IV.CERA IV.CERT IV.CESI IV.CING IV.FAGN
IV.FDMO IV.FRES IV.INTR IV.MIDA IV.MNS IV.MTCE IV.NRCA
IV.POFI IV.RMP IV.TERO IV.TOLF IV.TRTR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.40e+22 dyne-cm
Mw = 4.03
Z = 6 km
Plane Strike Dip Rake
NP1 137 56 -100
NP2 335 35 -75
Principal Axes:
Axis Value Plunge Azimuth
T 1.40e+22 11 234
N 0.00e+00 9 143
P -1.40e+22 76 15
Moment Tensor: (dyne-cm)
Component Value
Mxx 3.85e+21
Mxy 6.19e+21
Mxz -4.63e+21
Myy 8.82e+21
Myz -2.93e+21
Mzz -1.27e+22
##############
-----------###########
------------------##########
#--------------------#########
###----------------------#########
####------------------------########
#####-------------------------########
######--------------------------########
#######------------ -----------#######
#########----------- P -----------########
##########---------- ------------#######
###########------------------------#######
############------------------------######
#############----------------------#####
##############--------------------######
## ##########------------------#####
# T #############---------------####
################-----------####
####################-------###
#########################---
#####################-
##############
Global CMT Convention Moment Tensor:
R T P
-1.27e+22 -4.63e+21 2.93e+21
-4.63e+21 3.85e+21 -6.19e+21
2.93e+21 -6.19e+21 8.82e+21
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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.
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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 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 345 25 -60 3.83 0.2234
WVFGRD96 1.0 345 30 -60 3.81 0.2196
WVFGRD96 2.0 350 30 -50 3.89 0.2596
WVFGRD96 3.0 335 30 -75 3.93 0.2940
WVFGRD96 4.0 330 35 -80 3.96 0.3169
WVFGRD96 5.0 335 35 -75 4.04 0.3416
WVFGRD96 6.0 335 35 -75 4.03 0.3428
WVFGRD96 7.0 335 35 -75 4.02 0.3313
WVFGRD96 8.0 340 35 -70 3.97 0.3022
WVFGRD96 9.0 10 80 25 3.96 0.2902
WVFGRD96 10.0 10 75 20 3.97 0.2843
WVFGRD96 11.0 10 75 20 3.98 0.2773
WVFGRD96 12.0 10 75 20 3.99 0.2693
WVFGRD96 13.0 10 70 20 3.99 0.2611
WVFGRD96 14.0 10 70 20 4.00 0.2536
WVFGRD96 15.0 180 65 -30 4.03 0.2513
WVFGRD96 16.0 180 65 -30 4.04 0.2467
WVFGRD96 17.0 180 65 -30 4.05 0.2417
WVFGRD96 18.0 180 65 -30 4.05 0.2367
WVFGRD96 19.0 180 65 -30 4.06 0.2313
WVFGRD96 20.0 180 65 -30 4.07 0.2252
WVFGRD96 21.0 180 70 -30 4.07 0.2193
WVFGRD96 22.0 180 70 -30 4.08 0.2134
WVFGRD96 23.0 10 85 15 4.07 0.2076
WVFGRD96 24.0 10 85 15 4.08 0.2044
WVFGRD96 25.0 305 65 60 4.10 0.2045
WVFGRD96 26.0 305 65 60 4.11 0.2104
WVFGRD96 27.0 315 65 60 4.12 0.2142
WVFGRD96 28.0 315 65 60 4.13 0.2159
WVFGRD96 29.0 305 60 60 4.15 0.2159
The best solution is
WVFGRD96 6.0 335 35 -75 4.03 0.3428
The mechanism correspond to the best fit is
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The best fit as a function of depth is given in the following figure:
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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
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| 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. |
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
Here we tabulate the reasons for not using certain digital data sets
The following stations did not have a valid response files:
DATE=Fri Apr 17 12:41:18 CDT 2009