2009/04/06 02:37:04 42.366 13.340 10.1 4.60 Italy
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/04/06 02:37:04:0 42.37 13.34 10.1 4.6 Italy
Stations used:
IV.CERA IV.CESI IV.FRES IV.GUAR IV.INTR IV.LATE IV.LPEL
IV.MA9 IV.MIDA IV.MTCE IV.MURB IV.NRCA IV.OFFI IV.RMP
IV.TOLF IV.TRTR IV.VVLD
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.37e+23 dyne-cm
Mw = 4.85
Z = 10 km
Plane Strike Dip Rake
NP1 312 80 -118
NP2 205 30 -20
Principal Axes:
Axis Value Plunge Azimuth
T 2.37e+23 29 65
N 0.00e+00 28 318
P -2.37e+23 47 193
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.28e+22
Mxy 4.47e+22
Mxz 1.58e+23
Myy 1.43e+23
Myz 1.18e+23
Mzz -7.02e+22
--------------
---------#############
---------###################
-------#######################
######--##########################
#######--###########################
#######------################## ####
#######---------################ T #####
######-------------############# #####
######----------------####################
######------------------##################
######--------------------################
######---------------------###############
#####-----------------------############
#####-------------------------##########
####----------- ------------########
####---------- P --------------#####
###---------- ---------------###
##----------------------------
##--------------------------
#---------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-7.02e+22 1.58e+23 -1.18e+23
1.58e+23 -7.28e+22 -4.47e+22
-1.18e+23 -4.47e+22 1.43e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406023704/index.html
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STK = 205
DIP = 30
RAKE = -20
MW = 4.85
HS = 10.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/04/06 02:37:04:0 42.37 13.34 10.1 4.6 Italy
Stations used:
IV.CERA IV.CESI IV.FRES IV.GUAR IV.INTR IV.LATE IV.LPEL
IV.MA9 IV.MIDA IV.MTCE IV.MURB IV.NRCA IV.OFFI IV.RMP
IV.TOLF IV.TRTR IV.VVLD
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.37e+23 dyne-cm
Mw = 4.85
Z = 10 km
Plane Strike Dip Rake
NP1 312 80 -118
NP2 205 30 -20
Principal Axes:
Axis Value Plunge Azimuth
T 2.37e+23 29 65
N 0.00e+00 28 318
P -2.37e+23 47 193
Moment Tensor: (dyne-cm)
Component Value
Mxx -7.28e+22
Mxy 4.47e+22
Mxz 1.58e+23
Myy 1.43e+23
Myz 1.18e+23
Mzz -7.02e+22
--------------
---------#############
---------###################
-------#######################
######--##########################
#######--###########################
#######------################## ####
#######---------################ T #####
######-------------############# #####
######----------------####################
######------------------##################
######--------------------################
######---------------------###############
#####-----------------------############
#####-------------------------##########
####----------- ------------########
####---------- P --------------#####
###---------- ---------------###
##----------------------------
##--------------------------
#---------------------
--------------
Global CMT Convention Moment Tensor:
R T P
-7.02e+22 1.58e+23 -1.18e+23
1.58e+23 -7.28e+22 -4.47e+22
-1.18e+23 -4.47e+22 1.43e+23
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406023704/index.html
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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 0.5 145 45 85 4.50 0.2817
WVFGRD96 1.0 335 45 100 4.49 0.2141
WVFGRD96 2.0 145 45 85 4.66 0.2832
WVFGRD96 3.0 130 80 70 4.67 0.2549
WVFGRD96 4.0 135 80 70 4.70 0.3287
WVFGRD96 5.0 220 25 5 4.71 0.3785
WVFGRD96 6.0 215 25 -5 4.73 0.4145
WVFGRD96 7.0 215 30 -5 4.74 0.4382
WVFGRD96 8.0 210 25 -10 4.82 0.4523
WVFGRD96 9.0 210 30 -10 4.83 0.4650
WVFGRD96 10.0 205 30 -20 4.85 0.4712
WVFGRD96 11.0 205 30 -20 4.87 0.4711
WVFGRD96 12.0 15 35 -30 4.89 0.4706
WVFGRD96 13.0 15 35 -30 4.90 0.4711
WVFGRD96 14.0 15 40 -25 4.92 0.4686
WVFGRD96 15.0 15 40 -25 4.93 0.4638
WVFGRD96 16.0 15 40 -25 4.94 0.4563
WVFGRD96 17.0 15 40 -25 4.95 0.4471
WVFGRD96 18.0 5 45 -35 4.97 0.4384
WVFGRD96 19.0 5 45 -35 4.98 0.4297
WVFGRD96 20.0 5 45 -35 4.98 0.4212
WVFGRD96 21.0 0 45 -45 5.00 0.4153
WVFGRD96 22.0 0 45 -45 5.01 0.4079
WVFGRD96 23.0 0 45 -45 5.02 0.4000
WVFGRD96 24.0 0 45 -45 5.02 0.3912
WVFGRD96 25.0 0 45 -45 5.03 0.3810
WVFGRD96 26.0 0 45 -45 5.03 0.3704
WVFGRD96 27.0 5 40 -40 5.03 0.3607
WVFGRD96 28.0 5 40 -40 5.04 0.3534
WVFGRD96 29.0 0 40 -45 5.05 0.3457
The best solution is
WVFGRD96 10.0 205 30 -20 4.85 0.4712
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 WUS used for the waveform synthetic seismograms and for the surface wave eigenfunctions and dispersion is as follows:
MODEL.01
Model after 8 iterations
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
1.9000 3.4065 2.0089 2.2150 0.302E-02 0.679E-02 0.00 0.00 1.00 1.00
6.1000 5.5445 3.2953 2.6089 0.349E-02 0.784E-02 0.00 0.00 1.00 1.00
13.0000 6.2708 3.7396 2.7812 0.212E-02 0.476E-02 0.00 0.00 1.00 1.00
19.0000 6.4075 3.7680 2.8223 0.111E-02 0.249E-02 0.00 0.00 1.00 1.00
0.0000 7.9000 4.6200 3.2760 0.164E-10 0.370E-10 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 Apr 15 20:47:41 CDT 2009