2011/05/25 04:07:46 43.841 12.007 5.1 3.2 Italy
USGS Felt map for this earthquake
USGS/SLU Moment Tensor Solution
ENS 2011/05/25 04:07:46:0 43.84 12.01 5.1 3.2 Italy
Stations used:
IV.CASP IV.FROS IV.MCIV IV.TRIF IV.ZCCA
Filtering commands used:
hp c 0.04 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.57e+21 dyne-cm
Mw = 3.54
Z = 8 km
Plane Strike Dip Rake
NP1 215 50 90
NP2 35 40 90
Principal Axes:
Axis Value Plunge Azimuth
T 2.57e+21 85 125
N 0.00e+00 -0 35
P -2.57e+21 5 305
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.33e+20
Mxy 1.19e+21
Mxz -2.56e+20
Myy -1.70e+21
Myz 3.66e+20
Mzz 2.53e+21
--------------
----------------------
------------------#########-
--------------#############--
P ------------################---
- ----------##################----
-------------#####################----
------------#######################-----
-----------########################-----
-----------########################-------
----------########### ###########-------
---------############ T ##########--------
---------############ ##########--------
-------#########################--------
-------########################---------
------######################----------
-----#####################----------
----###################-----------
--################------------
--############--------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.53e+21 -2.56e+20 -3.66e+20
-2.56e+20 -8.33e+20 -1.19e+21
-3.66e+20 -1.19e+21 -1.70e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110525040746/index.html
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STK = 35
DIP = 40
RAKE = 90
MW = 3.54
HS = 8.0
The waveform inversion is preferred.
The following compares this source inversion to others
USGS/SLU Moment Tensor Solution
ENS 2011/05/25 04:07:46:0 43.84 12.01 5.1 3.2 Italy
Stations used:
IV.CASP IV.FROS IV.MCIV IV.TRIF IV.ZCCA
Filtering commands used:
hp c 0.04 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 2.57e+21 dyne-cm
Mw = 3.54
Z = 8 km
Plane Strike Dip Rake
NP1 215 50 90
NP2 35 40 90
Principal Axes:
Axis Value Plunge Azimuth
T 2.57e+21 85 125
N 0.00e+00 -0 35
P -2.57e+21 5 305
Moment Tensor: (dyne-cm)
Component Value
Mxx -8.33e+20
Mxy 1.19e+21
Mxz -2.56e+20
Myy -1.70e+21
Myz 3.66e+20
Mzz 2.53e+21
--------------
----------------------
------------------#########-
--------------#############--
P ------------################---
- ----------##################----
-------------#####################----
------------#######################-----
-----------########################-----
-----------########################-------
----------########### ###########-------
---------############ T ##########--------
---------############ ##########--------
-------#########################--------
-------########################---------
------######################----------
-----#####################----------
----###################-----------
--################------------
--############--------------
----------------------
--------------
Global CMT Convention Moment Tensor:
R T P
2.53e+21 -2.56e+20 -3.66e+20
-2.56e+20 -8.33e+20 -1.19e+21
-3.66e+20 -1.19e+21 -1.70e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110525040746/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 0.04 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 1.0 240 50 -55 3.39 0.3403
WVFGRD96 2.0 -5 40 0 3.40 0.3430
WVFGRD96 3.0 170 10 -100 3.38 0.3933
WVFGRD96 4.0 5 80 -95 3.36 0.4171
WVFGRD96 5.0 240 15 -55 3.51 0.4343
WVFGRD96 6.0 210 60 80 3.58 0.4578
WVFGRD96 7.0 210 40 85 3.59 0.4950
WVFGRD96 8.0 35 40 90 3.54 0.5024
WVFGRD96 9.0 35 35 90 3.52 0.4876
WVFGRD96 10.0 35 35 90 3.51 0.4680
WVFGRD96 11.0 30 35 85 3.51 0.4469
WVFGRD96 12.0 45 30 105 3.50 0.4282
WVFGRD96 13.0 205 60 85 3.50 0.4101
WVFGRD96 14.0 205 65 80 3.50 0.3940
WVFGRD96 15.0 200 65 75 3.54 0.3809
WVFGRD96 16.0 200 65 75 3.55 0.3684
WVFGRD96 17.0 200 70 80 3.55 0.3555
WVFGRD96 18.0 200 70 80 3.56 0.3427
WVFGRD96 19.0 200 70 80 3.57 0.3297
WVFGRD96 20.0 200 70 80 3.58 0.3155
WVFGRD96 21.0 200 70 75 3.60 0.3020
WVFGRD96 22.0 200 70 80 3.60 0.2881
WVFGRD96 23.0 200 70 80 3.61 0.2726
WVFGRD96 24.0 200 70 80 3.61 0.2560
WVFGRD96 25.0 200 70 75 3.62 0.2400
WVFGRD96 26.0 260 80 -40 3.67 0.2265
WVFGRD96 27.0 260 80 -40 3.68 0.2189
WVFGRD96 28.0 260 80 -35 3.69 0.2107
WVFGRD96 29.0 260 80 -35 3.70 0.2027
The best solution is
WVFGRD96 8.0 35 40 90 3.54 0.5024
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 0.04 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 May 27 03:37:14 CDT 2011