Location
2010/09/17 12:20:18 41.4900 15.6300 30.1 4.40 Italy
Arrival Times (from USGS)
Arrival time list
Felt Map
USGS Felt map for this earthquake
USGS Felt reports page for
Focal Mechanism
USGS/SLU Moment Tensor Solution
ENS 2010/09/17 12:20:18:0 41.49 15.63 30.1 4.4 Italy
Stations used:
GE.MATE IV.ACER IV.AMUR IV.BULG IV.CAFE IV.CDRU IV.CERA
IV.CIGN IV.CMPR IV.FRES IV.GUAR IV.INTR IV.MCEL IV.MCRV
IV.MESG IV.MGR IV.MMN IV.MOCO IV.MRLC IV.MRVN IV.MSAG
IV.NOCI IV.PALZ IV.PAOL IV.POFI IV.RNI2 IV.SALB IV.SGRT
IV.SGTA IV.TRIV IV.VULT MN.AQU MN.CUC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.66e+22 dyne-cm
Mw = 4.08
Z = 24 km
Plane Strike Dip Rake
NP1 259 87 -130
NP2 165 40 -5
Principal Axes:
Axis Value Plunge Azimuth
T 1.66e+22 30 20
N 0.00e+00 40 262
P -1.66e+22 36 135
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.41e+21
Mxy 9.56e+21
Mxz 1.23e+22
Myy -3.98e+21
Myz -3.04e+21
Mzz -1.42e+21
-#############
---###################
-----############# #######
-----############## T ########
------############### ##########
------##############################
-------###############################
-------#################################
-------#################################
--------########################----------
--------#############---------------------
---------####-----------------------------
-----####---------------------------------
########--------------------------------
#########-------------------------------
#########------------------ --------
#########----------------- P -------
#########---------------- ------
#########---------------------
##########------------------
#########-------------
##########----
Global CMT Convention Moment Tensor:
R T P
-1.42e+21 1.23e+22 3.04e+21
1.23e+22 5.41e+21 -9.56e+21
3.04e+21 -9.56e+21 -3.98e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20100917122018/index.html
|
Preferred Solution
The preferred solution from an analysis of the surface-wave spectral amplitude radiation pattern, waveform inversion and first motion observations is
STK = 165
DIP = 40
RAKE = -5
MW = 4.08
HS = 24.0
The waveform inversion is preferred.
Moment Tensor Comparison
The following compares this source inversion to others
| SLU |
DMT |
QRCMT |
USGS/SLU Moment Tensor Solution
ENS 2010/09/17 12:20:18:0 41.49 15.63 30.1 4.4 Italy
Stations used:
GE.MATE IV.ACER IV.AMUR IV.BULG IV.CAFE IV.CDRU IV.CERA
IV.CIGN IV.CMPR IV.FRES IV.GUAR IV.INTR IV.MCEL IV.MCRV
IV.MESG IV.MGR IV.MMN IV.MOCO IV.MRLC IV.MRVN IV.MSAG
IV.NOCI IV.PALZ IV.PAOL IV.POFI IV.RNI2 IV.SALB IV.SGRT
IV.SGTA IV.TRIV IV.VULT MN.AQU MN.CUC
Filtering commands used:
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 1.66e+22 dyne-cm
Mw = 4.08
Z = 24 km
Plane Strike Dip Rake
NP1 259 87 -130
NP2 165 40 -5
Principal Axes:
Axis Value Plunge Azimuth
T 1.66e+22 30 20
N 0.00e+00 40 262
P -1.66e+22 36 135
Moment Tensor: (dyne-cm)
Component Value
Mxx 5.41e+21
Mxy 9.56e+21
Mxz 1.23e+22
Myy -3.98e+21
Myz -3.04e+21
Mzz -1.42e+21
-#############
---###################
-----############# #######
-----############## T ########
------############### ##########
------##############################
-------###############################
-------#################################
-------#################################
--------########################----------
--------#############---------------------
---------####-----------------------------
-----####---------------------------------
########--------------------------------
#########-------------------------------
#########------------------ --------
#########----------------- P -------
#########---------------- ------
#########---------------------
##########------------------
#########-------------
##########----
Global CMT Convention Moment Tensor:
R T P
-1.42e+21 1.23e+22 3.04e+21
1.23e+22 5.41e+21 -9.56e+21
3.04e+21 -9.56e+21 -3.98e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20100917122018/index.html
|
INGV Tim Domain Moment Tensor
http://earthquake.rm.ingv.it/tdmt.php
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Regional Centroid Moment Tensor
http://www.bo.ingv.it/RCMT/
|
Waveform Inversion
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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Location of broadband stations used for waveform inversion
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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 3
The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 1.0 295 50 85 3.65 0.2318
WVFGRD96 2.0 290 55 85 3.73 0.2284
WVFGRD96 3.0 75 80 40 3.67 0.2011
WVFGRD96 4.0 255 90 -40 3.68 0.2085
WVFGRD96 5.0 180 35 20 3.77 0.2223
WVFGRD96 6.0 175 35 10 3.78 0.2457
WVFGRD96 7.0 170 40 0 3.80 0.2726
WVFGRD96 8.0 170 45 5 3.79 0.2998
WVFGRD96 9.0 165 45 -10 3.81 0.3241
WVFGRD96 10.0 165 45 -10 3.83 0.3482
WVFGRD96 11.0 165 45 -10 3.86 0.3708
WVFGRD96 12.0 165 45 -10 3.87 0.3916
WVFGRD96 13.0 165 45 -10 3.89 0.4103
WVFGRD96 14.0 165 45 -10 3.91 0.4270
WVFGRD96 15.0 165 45 -10 3.96 0.4434
WVFGRD96 16.0 165 45 -5 3.97 0.4576
WVFGRD96 17.0 165 45 -5 3.99 0.4700
WVFGRD96 18.0 165 40 -5 4.00 0.4812
WVFGRD96 19.0 165 40 -5 4.02 0.4910
WVFGRD96 20.0 165 40 -5 4.03 0.4991
WVFGRD96 21.0 165 40 -5 4.05 0.5060
WVFGRD96 22.0 165 40 -5 4.06 0.5115
WVFGRD96 23.0 165 40 -5 4.07 0.5149
WVFGRD96 24.0 165 40 -5 4.08 0.5162
WVFGRD96 25.0 165 40 -5 4.09 0.5155
WVFGRD96 26.0 165 40 -5 4.10 0.5121
WVFGRD96 27.0 165 40 -5 4.11 0.5072
WVFGRD96 28.0 165 40 -5 4.11 0.5005
WVFGRD96 29.0 165 45 -5 4.12 0.4931
The best solution is
WVFGRD96 24.0 165 40 -5 4.08 0.5162
The mechanism correspond to the best fit is
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Figure 1. Waveform inversion focal mechanism
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The best fit as a function of depth is given in the following figure:
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Figure 2. Depth sensitivity for waveform mechanism
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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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Figure 3. Waveform comparison for selected depth
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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.
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A check on the asusmed 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:
- The origin time and epicentral distance are incorrect
- The velocity model used for hte inversion is incorrect
- The velocity model used to define the P-arrival time is not the
same as the velocity model used for the waveform inversion
(assuming that the initial trace alignment is based on the
P arrival time)
Assuming only a mislocation, the time shifts are fit to a functional form:
Time_shift = A + B cos Azimuth + C Sin Azimuth
The time shifst 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.
Discussion
Velocity Model
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
Quality Control
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 17 11:06:45 CDT 2010
Last Changed 2010/09/17