2011/09/08 15:43:52 44.629 10.231 24.1 3.0 Italy
USGS Felt map for this earthquake
SLU Moment Tensor Solution
ENS 2011/09/08 15:43:52:0 44.63 10.23 24.1 3.0 Italy
Stations used:
IV.BDI IV.MSSA IV.PRMA IV.ROVR MN.VLC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 8.81e+20 dyne-cm
Mw = 3.23
Z = 18 km
Plane Strike Dip Rake
NP1 95 71 120
NP2 215 35 35
Principal Axes:
Axis Value Plunge Azimuth
T 8.81e+20 54 42
N 0.00e+00 28 264
P -8.81e+20 20 163
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.45e+20
Mxy 3.65e+20
Mxz 5.83e+20
Myy 7.03e+19
Myz 1.98e+20
Mzz 4.75e+20
--------------
----------------####--
------------################
----------####################
----------########################
---------###########################
--------################ ###########
--------################# T ############
-------################## ############
-------###################################
##-----###################################
#####-####################################
######----##############################--
#####------------###############--------
#####-----------------------------------
####----------------------------------
###---------------------------------
###-------------------------------
#----------------- ---------
#---------------- P --------
-------------- -----
--------------
Global CMT Convention Moment Tensor:
R T P
4.75e+20 5.83e+20 -1.98e+20
5.83e+20 -5.45e+20 -3.65e+20
-1.98e+20 -3.65e+20 7.03e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110908154352/index.html
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STK = 215
DIP = 35
RAKE = 35
MW = 3.23
HS = 18.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution
ENS 2011/09/08 15:43:52:0 44.63 10.23 24.1 3.0 Italy
Stations used:
IV.BDI IV.MSSA IV.PRMA IV.ROVR MN.VLC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 8.81e+20 dyne-cm
Mw = 3.23
Z = 18 km
Plane Strike Dip Rake
NP1 95 71 120
NP2 215 35 35
Principal Axes:
Axis Value Plunge Azimuth
T 8.81e+20 54 42
N 0.00e+00 28 264
P -8.81e+20 20 163
Moment Tensor: (dyne-cm)
Component Value
Mxx -5.45e+20
Mxy 3.65e+20
Mxz 5.83e+20
Myy 7.03e+19
Myz 1.98e+20
Mzz 4.75e+20
--------------
----------------####--
------------################
----------####################
----------########################
---------###########################
--------################ ###########
--------################# T ############
-------################## ############
-------###################################
##-----###################################
#####-####################################
######----##############################--
#####------------###############--------
#####-----------------------------------
####----------------------------------
###---------------------------------
###-------------------------------
#----------------- ---------
#---------------- P --------
-------------- -----
--------------
Global CMT Convention Moment Tensor:
R T P
4.75e+20 5.83e+20 -1.98e+20
5.83e+20 -5.45e+20 -3.65e+20
-1.98e+20 -3.65e+20 7.03e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110908154352/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 1.0 40 85 10 2.81 0.3215
WVFGRD96 2.0 165 45 -75 2.95 0.3443
WVFGRD96 3.0 200 55 -10 2.92 0.3533
WVFGRD96 4.0 200 60 -5 2.94 0.3605
WVFGRD96 5.0 200 50 -10 3.00 0.3576
WVFGRD96 6.0 200 50 -5 3.00 0.3484
WVFGRD96 7.0 195 45 -5 3.01 0.3423
WVFGRD96 8.0 195 50 0 2.99 0.3460
WVFGRD96 9.0 195 50 5 3.01 0.3535
WVFGRD96 10.0 200 50 15 3.03 0.3664
WVFGRD96 11.0 200 45 20 3.05 0.3805
WVFGRD96 12.0 205 45 25 3.07 0.3959
WVFGRD96 13.0 210 40 35 3.10 0.4115
WVFGRD96 14.0 215 40 40 3.13 0.4291
WVFGRD96 15.0 220 35 45 3.18 0.4509
WVFGRD96 16.0 220 35 45 3.20 0.4625
WVFGRD96 17.0 215 35 40 3.22 0.4719
WVFGRD96 18.0 215 35 35 3.23 0.4749
WVFGRD96 19.0 215 35 35 3.24 0.4728
WVFGRD96 20.0 210 40 25 3.25 0.4693
WVFGRD96 21.0 210 50 15 3.26 0.4673
WVFGRD96 22.0 210 55 10 3.28 0.4675
WVFGRD96 23.0 210 60 5 3.29 0.4672
WVFGRD96 24.0 210 60 5 3.31 0.4686
WVFGRD96 25.0 215 70 -5 3.33 0.4699
WVFGRD96 26.0 215 70 -5 3.35 0.4670
WVFGRD96 27.0 215 70 -15 3.34 0.4630
WVFGRD96 28.0 215 70 -15 3.36 0.4608
WVFGRD96 29.0 215 70 -15 3.38 0.4593
The best solution is
WVFGRD96 18.0 215 35 35 3.23 0.4749
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. A pair of numbers is given in black at the right of each predicted traces. The upper number 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 lower number gives the percentage of variance reduction to characterize the individual goodness of fit (100% indicates a perfect fit).
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. |
A check on the assumed source location is possible by looking at the time shifts between the observed and predicted traces. The time shifts for waveform matching arise for several reasons:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifts for this inversion lead to the next figure:
The derived shift in origin time and epicentral coordinates are given at the bottom of 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=Fri Sep 9 07:45:40 CDT 2011