2009/04/07 22:29:50 42.284 13.489 9.6 3.1 Italy
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2009/04/07 22:29:50:0 42.28 13.49 9.6 3.1 Italy
Stations used:
IV.ARVD IV.ASSB IV.BSSO IV.INTR IV.MNS IV.OFFI IV.PIEI
IV.PTRJ IV.RDP IV.RMP IV.TERO IV.VAGA MN.AQU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.08e+21 dyne-cm
Mw = 3.29
Z = 7 km
Plane Strike Dip Rake
NP1 172 76 -111
NP2 50 25 -35
Principal Axes:
Axis Value Plunge Azimuth
T 1.08e+21 28 279
N 0.00e+00 20 178
P -1.08e+21 54 57
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.01e+19
Mxy -3.00e+20
Mxz -2.11e+20
Myy 5.66e+20
Myz -8.73e+20
Mzz -4.76e+20
####----------
#######---------------
##########------------------
###########-------------------
#############---------------------
##############---------------------#
###############----------------------#
################---------- ---------##
#### #########---------- P ---------##
##### T #########---------- ---------###
##### #########----------------------###
##################--------------------####
##################--------------------####
#################-------------------####
#################------------------#####
#################----------------#####
################--------------######
################-----------#######
###############--------#######
--############----##########
------------##########
---------#####
Global CMT Convention Moment Tensor:
R T P
-4.76e+20 -2.11e+20 8.73e+20
-2.11e+20 -9.01e+19 3.00e+20
8.73e+20 3.00e+20 5.66e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090407222950/index.html
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STK = 50
DIP = 25
RAKE = -35
MW = 3.29
HS = 7.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2009/04/07 22:29:50:0 42.28 13.49 9.6 3.1 Italy
Stations used:
IV.ARVD IV.ASSB IV.BSSO IV.INTR IV.MNS IV.OFFI IV.PIEI
IV.PTRJ IV.RDP IV.RMP IV.TERO IV.VAGA MN.AQU
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.08e+21 dyne-cm
Mw = 3.29
Z = 7 km
Plane Strike Dip Rake
NP1 172 76 -111
NP2 50 25 -35
Principal Axes:
Axis Value Plunge Azimuth
T 1.08e+21 28 279
N 0.00e+00 20 178
P -1.08e+21 54 57
Moment Tensor: (dyne-cm)
Component Value
Mxx -9.01e+19
Mxy -3.00e+20
Mxz -2.11e+20
Myy 5.66e+20
Myz -8.73e+20
Mzz -4.76e+20
####----------
#######---------------
##########------------------
###########-------------------
#############---------------------
##############---------------------#
###############----------------------#
################---------- ---------##
#### #########---------- P ---------##
##### T #########---------- ---------###
##### #########----------------------###
##################--------------------####
##################--------------------####
#################-------------------####
#################------------------#####
#################----------------#####
################--------------######
################-----------#######
###############--------#######
--############----##########
------------##########
---------#####
Global CMT Convention Moment Tensor:
R T P
-4.76e+20 -2.11e+20 8.73e+20
-2.11e+20 -9.01e+19 3.00e+20
8.73e+20 3.00e+20 5.66e+20
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20090407222950/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 80 70 25 3.02 0.4186
WVFGRD96 1.0 80 75 30 3.05 0.4095
WVFGRD96 2.0 75 85 60 3.18 0.4033
WVFGRD96 3.0 70 35 -5 3.18 0.4366
WVFGRD96 4.0 70 35 -10 3.18 0.4586
WVFGRD96 5.0 55 20 -25 3.28 0.4767
WVFGRD96 6.0 55 25 -25 3.29 0.4898
WVFGRD96 7.0 50 25 -35 3.29 0.4974
WVFGRD96 8.0 50 30 -35 3.26 0.4956
WVFGRD96 9.0 50 35 -35 3.27 0.4905
WVFGRD96 10.0 55 35 -30 3.28 0.4795
WVFGRD96 11.0 50 40 -40 3.29 0.4664
WVFGRD96 12.0 25 40 -50 3.29 0.4549
WVFGRD96 13.0 25 40 -50 3.30 0.4408
WVFGRD96 14.0 25 35 -50 3.30 0.4249
WVFGRD96 15.0 20 30 -50 3.34 0.4112
WVFGRD96 16.0 20 30 -50 3.34 0.3969
WVFGRD96 17.0 20 30 -50 3.35 0.3825
WVFGRD96 18.0 20 30 -50 3.36 0.3664
WVFGRD96 19.0 20 30 -50 3.36 0.3497
WVFGRD96 20.0 15 30 -55 3.36 0.3327
WVFGRD96 21.0 15 30 -55 3.37 0.3155
WVFGRD96 22.0 20 35 -50 3.37 0.2984
WVFGRD96 23.0 150 60 -30 3.38 0.2947
WVFGRD96 24.0 155 65 -20 3.40 0.2931
WVFGRD96 25.0 155 65 -20 3.41 0.2932
WVFGRD96 26.0 155 60 -15 3.42 0.2963
WVFGRD96 27.0 155 60 -15 3.43 0.3029
WVFGRD96 28.0 155 60 -15 3.44 0.3050
WVFGRD96 29.0 155 60 -15 3.46 0.3020
The best solution is
WVFGRD96 7.0 50 25 -35 3.29 0.4974
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=Sun Aug 23 15:29:37 CDT 2009