2011/09/18 20:25:23 44.568 10.250 4 3.1 Italy
USGS Felt map for this earthquake
SLU Moment Tensor Solution
ENS 2011/09/18 20:25:23:0 44.57 10.25 4.0 3.1 Italy
Stations used:
GU.MAIM IV.BDI IV.CRMI IV.MSSA IV.PRMA MN.VLC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.32e+21 dyne-cm
Mw = 3.51
Z = 17 km
Plane Strike Dip Rake
NP1 120 82 96
NP2 265 10 55
Principal Axes:
Axis Value Plunge Azimuth
T 2.32e+21 53 37
N 0.00e+00 6 300
P -2.32e+21 37 205
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.84e+20
Mxy -1.71e+20
Mxz 1.89e+21
Myy 3.51e+19
Myz 1.15e+21
Mzz 6.49e+20
--------------
----##############----
---######################---
--###########################-
--###############################-
-###################### #########-
#--##################### T ##########-
#------################## ###########-
---------###############################
#------------############################-
---------------###########################
------------------########################
----------------------####################
------------------------################
----------------------------############
-------------------------------#######
----------- ---------------------#
---------- P ---------------------
-------- -------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
6.49e+20 1.89e+21 -1.15e+21
1.89e+21 -6.84e+20 1.71e+20
-1.15e+21 1.71e+20 3.51e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110918202523/index.html
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STK = 265
DIP = 10
RAKE = 55
MW = 3.51
HS = 17.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution
ENS 2011/09/18 20:25:23:0 44.57 10.25 4.0 3.1 Italy
Stations used:
GU.MAIM IV.BDI IV.CRMI IV.MSSA IV.PRMA MN.VLC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.32e+21 dyne-cm
Mw = 3.51
Z = 17 km
Plane Strike Dip Rake
NP1 120 82 96
NP2 265 10 55
Principal Axes:
Axis Value Plunge Azimuth
T 2.32e+21 53 37
N 0.00e+00 6 300
P -2.32e+21 37 205
Moment Tensor: (dyne-cm)
Component Value
Mxx -6.84e+20
Mxy -1.71e+20
Mxz 1.89e+21
Myy 3.51e+19
Myz 1.15e+21
Mzz 6.49e+20
--------------
----##############----
---######################---
--###########################-
--###############################-
-###################### #########-
#--##################### T ##########-
#------################## ###########-
---------###############################
#------------############################-
---------------###########################
------------------########################
----------------------####################
------------------------################
----------------------------############
-------------------------------#######
----------- ---------------------#
---------- P ---------------------
-------- -------------------
----------------------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
6.49e+20 1.89e+21 -1.15e+21
1.89e+21 -6.84e+20 1.71e+20
-1.15e+21 1.71e+20 3.51e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110918202523/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 1.0 265 25 70 3.18 0.2718
WVFGRD96 2.0 255 25 60 3.26 0.3205
WVFGRD96 3.0 235 35 30 3.25 0.3428
WVFGRD96 4.0 225 40 15 3.25 0.3665
WVFGRD96 5.0 235 30 30 3.34 0.4117
WVFGRD96 6.0 230 25 20 3.35 0.4495
WVFGRD96 7.0 235 20 25 3.36 0.4906
WVFGRD96 8.0 235 25 25 3.33 0.5320
WVFGRD96 9.0 235 25 25 3.35 0.5667
WVFGRD96 10.0 280 15 70 3.36 0.5946
WVFGRD96 11.0 230 25 20 3.38 0.6185
WVFGRD96 12.0 260 15 50 3.39 0.6430
WVFGRD96 13.0 270 15 60 3.41 0.6602
WVFGRD96 14.0 260 15 50 3.42 0.6730
WVFGRD96 15.0 275 10 65 3.47 0.6816
WVFGRD96 16.0 270 10 60 3.49 0.6881
WVFGRD96 17.0 265 10 55 3.51 0.6892
WVFGRD96 18.0 260 10 50 3.52 0.6846
WVFGRD96 19.0 245 10 35 3.53 0.6728
WVFGRD96 20.0 235 10 25 3.54 0.6614
WVFGRD96 21.0 205 25 -5 3.56 0.6485
WVFGRD96 22.0 190 25 -25 3.57 0.6446
WVFGRD96 23.0 180 25 -40 3.59 0.6407
WVFGRD96 24.0 175 25 -45 3.60 0.6415
WVFGRD96 25.0 175 30 -50 3.62 0.6426
WVFGRD96 26.0 170 30 -60 3.64 0.6465
WVFGRD96 27.0 165 30 -65 3.66 0.6495
WVFGRD96 28.0 165 30 -65 3.67 0.6493
WVFGRD96 29.0 155 30 -75 3.69 0.6473
The best solution is
WVFGRD96 17.0 265 10 55 3.51 0.6892
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=Sun Sep 18 16:41:03 CDT 2011