2009/04/06 04:47:53 42.352 13.347 9.4 3.70 Italy
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/04/06 04:47:53:0 42.35 13.35 9.4 3.7 Italy
Stations used:
IV.ASSB IV.GUAR IV.INTR IV.MTCE IV.OFFI IV.TRTR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 8.32e+21 dyne-cm
Mw = 3.88
Z = 8 km
Plane Strike Dip Rake
NP1 131 79 100
NP2 270 15 50
Principal Axes:
Axis Value Plunge Azimuth
T 8.32e+21 55 53
N 0.00e+00 10 309
P -8.32e+21 33 213
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.19e+21
Mxy -1.38e+21
Mxz 5.52e+21
Myy -3.30e+13
Myz 5.16e+21
Mzz 3.19e+21
--------------
-------########-------
-----##################-----
---########################---
################################--
##--##############################--
#------##############################-
#--------################ ###########-
-----------############## T ############
#-------------############ ############-
----------------##########################
------------------########################
--------------------######################
---------------------###################
-----------------------#################
-------------------------#############
--------- ---------------#########
-------- P ------------------#####
------ ---------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
3.19e+21 5.52e+21 -5.16e+21
5.52e+21 -3.19e+21 1.38e+21
-5.16e+21 1.38e+21 -3.30e+13
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406044753/index.html
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STK = 270
DIP = 15
RAKE = 50
MW = 3.88
HS = 8.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/04/06 04:47:53:0 42.35 13.35 9.4 3.7 Italy
Stations used:
IV.ASSB IV.GUAR IV.INTR IV.MTCE IV.OFFI IV.TRTR
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 8.32e+21 dyne-cm
Mw = 3.88
Z = 8 km
Plane Strike Dip Rake
NP1 131 79 100
NP2 270 15 50
Principal Axes:
Axis Value Plunge Azimuth
T 8.32e+21 55 53
N 0.00e+00 10 309
P -8.32e+21 33 213
Moment Tensor: (dyne-cm)
Component Value
Mxx -3.19e+21
Mxy -1.38e+21
Mxz 5.52e+21
Myy -3.30e+13
Myz 5.16e+21
Mzz 3.19e+21
--------------
-------########-------
-----##################-----
---########################---
################################--
##--##############################--
#------##############################-
#--------################ ###########-
-----------############## T ############
#-------------############ ############-
----------------##########################
------------------########################
--------------------######################
---------------------###################
-----------------------#################
-------------------------#############
--------- ---------------#########
-------- P ------------------#####
------ ---------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
3.19e+21 5.52e+21 -5.16e+21
5.52e+21 -3.19e+21 1.38e+21
-5.16e+21 1.38e+21 -3.30e+13
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090406044753/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 0.5 265 60 25 3.65 0.4116
WVFGRD96 1.0 260 80 5 3.72 0.3892
WVFGRD96 2.0 265 60 20 3.83 0.4148
WVFGRD96 3.0 260 50 5 3.89 0.3957
WVFGRD96 4.0 255 50 -5 3.90 0.4342
WVFGRD96 5.0 275 15 55 3.79 0.4848
WVFGRD96 6.0 265 15 45 3.79 0.5097
WVFGRD96 7.0 275 15 55 3.79 0.5198
WVFGRD96 8.0 270 15 50 3.88 0.5267
WVFGRD96 9.0 260 15 40 3.88 0.5218
WVFGRD96 10.0 255 15 35 3.88 0.5085
WVFGRD96 11.0 220 15 0 3.88 0.4896
WVFGRD96 12.0 175 25 -55 3.90 0.4739
WVFGRD96 13.0 165 30 -65 3.92 0.4621
WVFGRD96 14.0 165 30 -65 3.93 0.4472
WVFGRD96 15.0 155 35 -75 3.94 0.4301
WVFGRD96 16.0 25 25 -5 3.94 0.4111
WVFGRD96 17.0 30 25 0 3.95 0.3977
WVFGRD96 18.0 40 20 10 3.95 0.3841
WVFGRD96 19.0 40 20 10 3.96 0.3695
WVFGRD96 20.0 145 45 -85 3.99 0.3612
WVFGRD96 21.0 320 40 -95 4.01 0.3535
WVFGRD96 22.0 145 50 -85 4.01 0.3466
WVFGRD96 23.0 160 55 -65 4.03 0.3381
WVFGRD96 24.0 160 55 -65 4.04 0.3298
WVFGRD96 25.0 355 50 -30 4.05 0.3216
WVFGRD96 26.0 355 55 -25 4.07 0.3184
WVFGRD96 27.0 355 55 -25 4.08 0.3169
WVFGRD96 28.0 355 45 -25 4.07 0.3185
WVFGRD96 29.0 355 45 -25 4.08 0.3214
The best solution is
WVFGRD96 8.0 270 15 50 3.88 0.5267
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=Thu Apr 16 08:09:58 CDT 2009