2009/08/04 16:22:18 41.738 14.224 20.2 3.10 Italy
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/08/04 16:22:18:0 41.74 14.22 20.2 3.1 Italy
Stations used:
IV.CAFR IV.CERA IV.GUAR IV.MIDA IV.POFI IV.PTRJ IV.SACR
IV.TERO IV.VAGA
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 7.94e+20 dyne-cm
Mw = 3.20
Z = 17 km
Plane Strike Dip Rake
NP1 25 80 -20
NP2 119 70 -169
Principal Axes:
Axis Value Plunge Azimuth
T 7.94e+20 7 73
N 0.00e+00 68 179
P -7.94e+20 21 340
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.47e+20
Mxy 4.37e+20
Mxz -2.25e+20
Myy 6.39e+20
Myz 1.77e+20
Mzz -9.29e+19
--------------
---- -------------##
------- P ------------######
-------- ------------#######
------------------------##########
-------------------------###########
##-----------------------###########
####----------------------########### T
######-------------------############
########-----------------#################
###########-------------##################
#############----------###################
################-------###################
##################---###################
####################--##################
##################--------############
################--------------------
#############---------------------
##########--------------------
########--------------------
###-------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-9.29e+19 -2.25e+20 -1.77e+20
-2.25e+20 -5.47e+20 -4.37e+20
-1.77e+20 -4.37e+20 6.39e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090804162218/index.html
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STK = 25
DIP = 80
RAKE = -20
MW = 3.20
HS = 17.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/08/04 16:22:18:0 41.74 14.22 20.2 3.1 Italy
Stations used:
IV.CAFR IV.CERA IV.GUAR IV.MIDA IV.POFI IV.PTRJ IV.SACR
IV.TERO IV.VAGA
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 7.94e+20 dyne-cm
Mw = 3.20
Z = 17 km
Plane Strike Dip Rake
NP1 25 80 -20
NP2 119 70 -169
Principal Axes:
Axis Value Plunge Azimuth
T 7.94e+20 7 73
N 0.00e+00 68 179
P -7.94e+20 21 340
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.47e+20
Mxy 4.37e+20
Mxz -2.25e+20
Myy 6.39e+20
Myz 1.77e+20
Mzz -9.29e+19
--------------
---- -------------##
------- P ------------######
-------- ------------#######
------------------------##########
-------------------------###########
##-----------------------###########
####----------------------########### T
######-------------------############
########-----------------#################
###########-------------##################
#############----------###################
################-------###################
##################---###################
####################--##################
##################--------############
################--------------------
#############---------------------
##########--------------------
########--------------------
###-------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-9.29e+19 -2.25e+20 -1.77e+20
-2.25e+20 -5.47e+20 -4.37e+20
-1.77e+20 -4.37e+20 6.39e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090804162218/index.html
|
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 45 45 -75 2.82 0.2385
WVFGRD96 1.0 40 45 -80 2.87 0.2332
WVFGRD96 2.0 195 50 65 2.93 0.2401
WVFGRD96 3.0 345 55 0 2.91 0.2618
WVFGRD96 4.0 340 55 -10 2.95 0.3006
WVFGRD96 5.0 335 50 -15 3.04 0.3335
WVFGRD96 6.0 335 55 -15 3.06 0.3576
WVFGRD96 7.0 340 50 -5 3.08 0.3774
WVFGRD96 8.0 340 55 -5 3.07 0.3924
WVFGRD96 9.0 345 60 5 3.10 0.4035
WVFGRD96 10.0 345 60 5 3.12 0.4128
WVFGRD96 11.0 210 85 20 3.11 0.4265
WVFGRD96 12.0 30 90 -15 3.13 0.4381
WVFGRD96 13.0 30 90 -15 3.15 0.4462
WVFGRD96 14.0 210 90 20 3.16 0.4514
WVFGRD96 15.0 25 80 -15 3.18 0.4547
WVFGRD96 16.0 210 90 20 3.19 0.4547
WVFGRD96 17.0 25 80 -20 3.20 0.4549
WVFGRD96 18.0 210 90 25 3.21 0.4487
WVFGRD96 19.0 25 80 -20 3.22 0.4455
WVFGRD96 20.0 210 90 25 3.23 0.4372
WVFGRD96 21.0 210 90 25 3.23 0.4293
WVFGRD96 22.0 210 90 25 3.24 0.4209
WVFGRD96 23.0 210 90 20 3.25 0.4120
WVFGRD96 24.0 210 90 20 3.26 0.4025
WVFGRD96 25.0 210 90 20 3.27 0.3931
WVFGRD96 26.0 25 60 -10 3.28 0.3910
WVFGRD96 27.0 25 60 -10 3.29 0.3846
WVFGRD96 28.0 25 60 -10 3.30 0.3790
WVFGRD96 29.0 25 60 -10 3.32 0.3768
The best solution is
WVFGRD96 17.0 25 80 -20 3.20 0.4549
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=Wed Aug 5 12:03:31 CDT 2009