2011/09/06 08:22:04 42.946 13.701 20.2 3.2 Italy
USGS Felt map for this earthquake
SLU Moment Tensor Solution ENS 2011/09/06 08:22:04:0 42.95 13.70 20.2 3.2 Italy Stations used: IV.ATPC IV.ATTE IV.ATVO IV.CING IV.FAGN IV.FDMO IV.FIAM IV.GUMA IV.MURB IV.NRCA IV.PIEI IV.POFI IV.PTQR IV.T0104 IV.TERO IV.TRTR MN.AQU Filtering commands used: hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 8.81e+20 dyne-cm Mw = 3.23 Z = 12 km Plane Strike Dip Rake NP1 245 55 -60 NP2 20 45 -126 Principal Axes: Axis Value Plunge Azimuth T 8.81e+20 6 314 N 0.00e+00 24 47 P -8.81e+20 65 212 Moment Tensor: (dyne-cm) Component Value Mxx 3.13e+20 Mxy -5.07e+20 Mxz 3.43e+20 Myy 4.04e+20 Myz 1.19e+20 Mzz -7.17e+20 ############## ####################-- #######################---- T ########################---- # ########################------ ####################----------####-- ################---------------####### #############-------------------######## ###########---------------------######## #########------------------------######### #######--------------------------######### ######--------------------------########## #####----------- -------------########## ###------------ P ------------########## ##------------- ------------########## ----------------------------########## -------------------------########### -----------------------########### -------------------########### ----------------############ ----------############ -############# Global CMT Convention Moment Tensor: R T P -7.17e+20 3.43e+20 -1.19e+20 3.43e+20 3.13e+20 5.07e+20 -1.19e+20 5.07e+20 4.04e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110906082204/index.html |
STK = 245 DIP = 55 RAKE = -60 MW = 3.23 HS = 12.0
The waveform inversion is preferred.
The following compares this source inversion to others
SLU Moment Tensor Solution ENS 2011/09/06 08:22:04:0 42.95 13.70 20.2 3.2 Italy Stations used: IV.ATPC IV.ATTE IV.ATVO IV.CING IV.FAGN IV.FDMO IV.FIAM IV.GUMA IV.MURB IV.NRCA IV.PIEI IV.POFI IV.PTQR IV.T0104 IV.TERO IV.TRTR MN.AQU Filtering commands used: hp c 0.03 n 3 lp c 0.10 n 3 Best Fitting Double Couple Mo = 8.81e+20 dyne-cm Mw = 3.23 Z = 12 km Plane Strike Dip Rake NP1 245 55 -60 NP2 20 45 -126 Principal Axes: Axis Value Plunge Azimuth T 8.81e+20 6 314 N 0.00e+00 24 47 P -8.81e+20 65 212 Moment Tensor: (dyne-cm) Component Value Mxx 3.13e+20 Mxy -5.07e+20 Mxz 3.43e+20 Myy 4.04e+20 Myz 1.19e+20 Mzz -7.17e+20 ############## ####################-- #######################---- T ########################---- # ########################------ ####################----------####-- ################---------------####### #############-------------------######## ###########---------------------######## #########------------------------######### #######--------------------------######### ######--------------------------########## #####----------- -------------########## ###------------ P ------------########## ##------------- ------------########## ----------------------------########## -------------------------########### -----------------------########### -------------------########### ----------------############ ----------############ -############# Global CMT Convention Moment Tensor: R T P -7.17e+20 3.43e+20 -1.19e+20 3.43e+20 3.13e+20 5.07e+20 -1.19e+20 5.07e+20 4.04e+20 Details of the solution is found at http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20110906082204/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 0.03 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 1.0 220 50 85 2.99 0.3117 WVFGRD96 2.0 345 85 -10 3.04 0.3098 WVFGRD96 3.0 80 80 10 3.07 0.3023 WVFGRD96 4.0 80 85 15 3.11 0.3087 WVFGRD96 5.0 135 25 -5 3.12 0.3394 WVFGRD96 6.0 125 25 -15 3.12 0.3680 WVFGRD96 7.0 55 45 -70 3.20 0.4194 WVFGRD96 8.0 225 45 -90 3.19 0.4632 WVFGRD96 9.0 235 50 -75 3.19 0.4925 WVFGRD96 10.0 235 50 -75 3.20 0.5110 WVFGRD96 11.0 235 50 -75 3.22 0.5187 WVFGRD96 12.0 245 55 -60 3.23 0.5192 WVFGRD96 13.0 250 60 -50 3.25 0.5133 WVFGRD96 14.0 250 60 -55 3.26 0.5058 WVFGRD96 15.0 250 60 -50 3.30 0.5057 WVFGRD96 16.0 255 65 -45 3.32 0.4980 WVFGRD96 17.0 255 65 -45 3.33 0.4870 WVFGRD96 18.0 255 70 -40 3.35 0.4737 WVFGRD96 19.0 255 70 -40 3.36 0.4580 WVFGRD96 20.0 150 40 60 3.31 0.4560 WVFGRD96 21.0 150 40 60 3.32 0.4557 WVFGRD96 22.0 150 40 60 3.33 0.4521 WVFGRD96 23.0 155 35 65 3.34 0.4472 WVFGRD96 24.0 160 35 70 3.35 0.4395 WVFGRD96 25.0 155 35 65 3.35 0.4277 WVFGRD96 26.0 170 30 80 3.36 0.4153 WVFGRD96 27.0 165 30 80 3.37 0.4011 WVFGRD96 28.0 175 30 85 3.37 0.3863 WVFGRD96 29.0 240 60 -50 3.43 0.3792
The best solution is
WVFGRD96 12.0 245 55 -60 3.23 0.5192
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 0.03 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=Thu Sep 8 09:30:40 CDT 2011