SLU Moment Tensor Solution
ENS 2013/08/26 22:09:48:0 43.37 12.54 8.6 3.7 Italy
Stations used:
GU.MAIM IV.AOI IV.ARVD IV.ASQU IV.ASSB IV.BDI IV.CAFI
IV.CASP IV.CELB IV.CESX IV.CING IV.CRMI IV.FSSB IV.GUMA
IV.INTR IV.LAV9 IV.MAON IV.MGAB IV.MTCE IV.MTRZ IV.NRCA
IV.OSSC IV.PARC IV.PESA IV.PLMA IV.PTQR IV.RNI2 IV.SACS
IV.SAMA IV.SNTG IV.SSFR IV.T0104 IV.TERO IV.TRTR MN.VLC
Filtering commands used:
cut a -10 a 60
rtr
taper w 0.1
hp c 0.02 n 3
lp c 0.10 n 3
Best Fitting Double Couple
Mo = 5.89e+21 dyne-cm
Mw = 3.78
Z = 5 km
Plane Strike Dip Rake
NP1 145 65 -90
NP2 325 25 -90
Principal Axes:
Axis Value Plunge Azimuth
T 5.89e+21 20 235
N 0.00e+00 -0 145
P -5.89e+21 70 55
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.48e+21
Mxy 2.12e+21
Mxz -2.17e+21
Myy 3.03e+21
Myz -3.10e+21
Mzz -4.51e+21
##############
#-----------##########
##------------------########
###--------------------#######
#####----------------------#######
######------------------------######
########------------------------######
##########------------------------######
##########------------- ---------#####
############------------ P ----------#####
#############----------- ----------#####
##############------------------------####
###############-----------------------####
###############----------------------###
#################--------------------###
#### ###########-----------------###
### T ############----------------##
## ##############-------------##
####################---------#
######################-----#
######################
##############
Global CMT Convention Moment Tensor:
R T P
-4.51e+21 -2.17e+21 3.10e+21
-2.17e+21 1.48e+21 -2.12e+21
3.10e+21 -2.12e+21 3.03e+21
Details of the solution is found at
http://www.eas.slu.edu/eqc/eqc_mt/MECH.IT/20130826220948/index.html
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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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:
cut a -10 a 60 rtr taper w 0.1 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 1.0 165 75 -75 3.62 0.3976
WVFGRD96 2.0 150 75 -85 3.71 0.4751
WVFGRD96 3.0 145 70 -90 3.69 0.5509
WVFGRD96 4.0 145 65 -90 3.69 0.5812
WVFGRD96 5.0 325 25 -90 3.78 0.5969
WVFGRD96 6.0 330 25 -85 3.76 0.5705
WVFGRD96 7.0 335 25 -80 3.75 0.5293
WVFGRD96 8.0 -10 25 -65 3.69 0.4846
WVFGRD96 9.0 5 30 -45 3.69 0.4576
WVFGRD96 10.0 15 30 -30 3.69 0.4350
WVFGRD96 11.0 15 30 -30 3.69 0.4154
WVFGRD96 12.0 20 30 -25 3.70 0.3969
WVFGRD96 13.0 25 30 -20 3.70 0.3796
WVFGRD96 14.0 35 45 20 3.71 0.3667
WVFGRD96 15.0 25 30 -15 3.74 0.3522
WVFGRD96 16.0 20 30 -20 3.75 0.3392
WVFGRD96 17.0 40 40 20 3.76 0.3278
WVFGRD96 18.0 60 30 20 3.77 0.3184
WVFGRD96 19.0 65 30 30 3.78 0.3099
WVFGRD96 20.0 65 30 30 3.79 0.3023
WVFGRD96 21.0 70 30 35 3.80 0.2944
WVFGRD96 22.0 315 70 75 3.81 0.2880
WVFGRD96 23.0 315 70 70 3.82 0.2821
WVFGRD96 24.0 325 55 85 3.82 0.2782
WVFGRD96 25.0 140 40 80 3.83 0.2809
WVFGRD96 26.0 145 40 85 3.84 0.2911
WVFGRD96 27.0 145 40 85 3.85 0.2993
WVFGRD96 28.0 145 40 85 3.87 0.3026
WVFGRD96 29.0 145 40 85 3.89 0.3023
The best solution is
WVFGRD96 5.0 325 25 -90 3.78 0.5969
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
cut a -10 a 60 rtr taper w 0.1 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:
- The origin time and epicentral distance are incorrect
- The velocity model used for the 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)
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.
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=Tue Aug 27 18:10:12 CDT 2013