2009/04/21 16:20:56 42.516 13.313 12.0 3.2 Italy
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/04/21 16:20:56:0 42.52 13.31 12.0 3.2 Italy
Stations used:
IV.CERT IV.CESX IV.FDMO IV.FIAM IV.MNS MN.AQU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 3.72e+20 dyne-cm
Mw = 2.98
Z = 8 km
Plane Strike Dip Rake
NP1 314 71 -95
NP2 150 20 -75
Principal Axes:
Axis Value Plunge Azimuth
T 3.72e+20 26 48
N 0.00e+00 5 316
P -3.72e+20 64 215
Moment Tensor: (dyne-cm)
Component Value
Mxx 8.62e+19
Mxy 1.16e+20
Mxz 2.16e+20
Myy 1.45e+20
Myz 1.93e+20
Mzz -2.31e+20
##############
######################
-###########################
#--###########################
##-------################## ####
##-----------############### T #####
##---------------############ ######
###-----------------####################
###-------------------##################
####---------------------#################
####-----------------------###############
####-------------------------#############
####------------ -----------############
####----------- P ------------##########
####----------- --------------########
####----------------------------######
#####---------------------------####
#####--------------------------###
#####-------------------------
######----------------------
#######---------------
##############
Global CMT Convention Moment Tensor:
R T P
-2.31e+20 2.16e+20 -1.93e+20
2.16e+20 8.62e+19 -1.16e+20
-1.93e+20 -1.16e+20 1.45e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090421162056/index.html
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STK = 150
DIP = 20
RAKE = -75
MW = 2.98
HS = 8.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/04/21 16:20:56:0 42.52 13.31 12.0 3.2 Italy
Stations used:
IV.CERT IV.CESX IV.FDMO IV.FIAM IV.MNS MN.AQU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 3.72e+20 dyne-cm
Mw = 2.98
Z = 8 km
Plane Strike Dip Rake
NP1 314 71 -95
NP2 150 20 -75
Principal Axes:
Axis Value Plunge Azimuth
T 3.72e+20 26 48
N 0.00e+00 5 316
P -3.72e+20 64 215
Moment Tensor: (dyne-cm)
Component Value
Mxx 8.62e+19
Mxy 1.16e+20
Mxz 2.16e+20
Myy 1.45e+20
Myz 1.93e+20
Mzz -2.31e+20
##############
######################
-###########################
#--###########################
##-------################## ####
##-----------############### T #####
##---------------############ ######
###-----------------####################
###-------------------##################
####---------------------#################
####-----------------------###############
####-------------------------#############
####------------ -----------############
####----------- P ------------##########
####----------- --------------########
####----------------------------######
#####---------------------------####
#####--------------------------###
#####-------------------------
######----------------------
#######---------------
##############
Global CMT Convention Moment Tensor:
R T P
-2.31e+20 2.16e+20 -1.93e+20
2.16e+20 8.62e+19 -1.16e+20
-1.93e+20 -1.16e+20 1.45e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090421162056/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 0.5 135 55 -95 2.78 0.3767
WVFGRD96 1.0 325 35 -80 2.80 0.3168
WVFGRD96 2.0 185 15 -40 2.92 0.3125
WVFGRD96 3.0 185 15 -35 2.91 0.4132
WVFGRD96 4.0 190 20 -35 2.90 0.4698
WVFGRD96 5.0 190 15 -30 3.01 0.5057
WVFGRD96 6.0 160 15 -65 3.01 0.5313
WVFGRD96 7.0 150 20 -75 3.02 0.5426
WVFGRD96 8.0 150 20 -75 2.98 0.5442
WVFGRD96 9.0 140 25 -85 3.00 0.5403
WVFGRD96 10.0 315 70 -95 3.00 0.5304
WVFGRD96 11.0 315 70 -95 3.00 0.5158
WVFGRD96 12.0 140 20 -85 3.01 0.4974
WVFGRD96 13.0 145 20 -80 3.02 0.4757
WVFGRD96 14.0 145 20 -80 3.02 0.4520
WVFGRD96 15.0 155 20 -70 3.06 0.4284
WVFGRD96 16.0 160 20 -65 3.06 0.4006
WVFGRD96 17.0 165 20 -60 3.07 0.3721
WVFGRD96 18.0 145 45 -50 3.11 0.3488
WVFGRD96 19.0 145 45 -50 3.11 0.3326
WVFGRD96 20.0 145 45 -60 3.11 0.3206
WVFGRD96 21.0 140 45 -65 3.11 0.3232
WVFGRD96 22.0 140 45 -65 3.12 0.3284
WVFGRD96 23.0 140 45 -65 3.12 0.3315
WVFGRD96 24.0 140 40 -70 3.12 0.3314
WVFGRD96 25.0 140 40 -70 3.12 0.3262
WVFGRD96 26.0 150 70 -20 3.20 0.3176
WVFGRD96 27.0 150 70 -20 3.21 0.3163
WVFGRD96 28.0 150 75 -15 3.24 0.3152
WVFGRD96 29.0 150 75 -15 3.26 0.3127
The best solution is
WVFGRD96 8.0 150 20 -75 2.98 0.5442
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 Sep 2 11:21:08 CDT 2009