2011/09/08 20:36:42 44.625 10.239 19.8 3.1 Italy
USGS Felt map for this earthquake
SLU Moment Tensor Solution
ENS 2011/09/08 20:36:42:0 44.62 10.24 19.8 3.1 Italy
Stations used:
GU.SC2M IV.ASQU IV.BDI IV.CRE IV.FNVD IV.FROS IV.MSSA
IV.PARC MN.VLC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.48e+21 dyne-cm
Mw = 3.38
Z = 20 km
Plane Strike Dip Rake
NP1 105 80 91
NP2 280 10 85
Principal Axes:
Axis Value Plunge Azimuth
T 1.48e+21 55 16
N 0.00e+00 1 285
P -1.48e+21 35 194
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.81e+20
Mxy -1.07e+20
Mxz 1.34e+21
Myy -2.29e+19
Myz 3.65e+20
Mzz 5.04e+20
--------------
---###############----
---######################---
-###########################--
-###############################--
-################## #############-
#################### T ##############-
-#################### ###############-
-######################################-
------###################################-
----------###############################-
---------------###########################
----------------------####################
-----------------------------###########
----------------------------------------
--------------------------------------
------------------------------------
------------ -------------------
---------- P -----------------
--------- ----------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
5.04e+20 1.34e+21 -3.65e+20
1.34e+21 -4.81e+20 1.07e+20
-3.65e+20 1.07e+20 -2.29e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110908203642/index.html
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STK = 280
DIP = 10
RAKE = 85
MW = 3.38
HS = 20.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution
ENS 2011/09/08 20:36:42:0 44.62 10.24 19.8 3.1 Italy
Stations used:
GU.SC2M IV.ASQU IV.BDI IV.CRE IV.FNVD IV.FROS IV.MSSA
IV.PARC MN.VLC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.48e+21 dyne-cm
Mw = 3.38
Z = 20 km
Plane Strike Dip Rake
NP1 105 80 91
NP2 280 10 85
Principal Axes:
Axis Value Plunge Azimuth
T 1.48e+21 55 16
N 0.00e+00 1 285
P -1.48e+21 35 194
Moment Tensor: (dyne-cm)
Component Value
Mxx -4.81e+20
Mxy -1.07e+20
Mxz 1.34e+21
Myy -2.29e+19
Myz 3.65e+20
Mzz 5.04e+20
--------------
---###############----
---######################---
-###########################--
-###############################--
-################## #############-
#################### T ##############-
-#################### ###############-
-######################################-
------###################################-
----------###############################-
---------------###########################
----------------------####################
-----------------------------###########
----------------------------------------
--------------------------------------
------------------------------------
------------ -------------------
---------- P -----------------
--------- ----------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
5.04e+20 1.34e+21 -3.65e+20
1.34e+21 -4.81e+20 1.07e+20
-3.65e+20 1.07e+20 -2.29e+19
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110908203642/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 80 40 85 2.99 0.2629
WVFGRD96 2.0 255 45 95 3.09 0.2918
WVFGRD96 3.0 205 90 0 3.18 0.2972
WVFGRD96 4.0 295 85 5 3.23 0.2809
WVFGRD96 5.0 300 80 10 3.28 0.2616
WVFGRD96 6.0 125 55 15 3.16 0.2312
WVFGRD96 7.0 130 45 15 3.13 0.2474
WVFGRD96 8.0 175 15 -15 3.07 0.2750
WVFGRD96 9.0 185 15 -5 3.10 0.3071
WVFGRD96 10.0 250 5 60 3.13 0.3397
WVFGRD96 11.0 260 5 70 3.15 0.3721
WVFGRD96 12.0 255 10 60 3.19 0.4029
WVFGRD96 13.0 270 10 75 3.21 0.4320
WVFGRD96 14.0 290 10 95 3.23 0.4586
WVFGRD96 15.0 280 10 85 3.29 0.4825
WVFGRD96 16.0 275 10 80 3.32 0.5066
WVFGRD96 17.0 275 10 80 3.34 0.5259
WVFGRD96 18.0 280 10 85 3.35 0.5399
WVFGRD96 19.0 280 10 85 3.37 0.5481
WVFGRD96 20.0 280 10 85 3.38 0.5504
WVFGRD96 21.0 280 10 85 3.39 0.5468
WVFGRD96 22.0 265 15 70 3.40 0.5399
WVFGRD96 23.0 260 15 65 3.41 0.5284
WVFGRD96 24.0 260 15 70 3.41 0.5134
WVFGRD96 25.0 240 20 50 3.42 0.4952
WVFGRD96 26.0 260 20 70 3.41 0.4773
WVFGRD96 27.0 155 5 -40 3.41 0.4600
WVFGRD96 28.0 135 5 -60 3.41 0.4482
WVFGRD96 29.0 145 5 -50 3.40 0.4345
The best solution is
WVFGRD96 20.0 280 10 85 3.38 0.5504
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 07:58:58 CDT 2011