2005/05/05 13:21:21 41.89N 13.71E 19 3.5 Italy
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
SLU Moment Tensor Solution
2005/05/05 13:21:21 41.89N 13.71E 19 3.5 Italy
Best Fitting Double Couple
Mo = 1.46e+21 dyne-cm
Mw = 3.41
Z = 15 km
Plane Strike Dip Rake
NP1 185 90 -35
NP2 275 55 -180
Principal Axes:
Axis Value Plunge Azimuth
T 1.46e+21 24 236
N 0.00e+00 55 5
P -1.46e+21 24 134
Moment Tensor: (dyne-cm)
Component Value
Mxx -2.08e+20
Mxy 1.18e+21
Mxz 7.31e+19
Myy 2.08e+20
Myz -8.35e+20
Mzz -2.04e+13
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#### T ###########--------------------
### ###########---------- ------
################---------- P -----
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Harvard Convention
Moment Tensor:
R T F
-2.04e+13 7.31e+19 8.35e+20
7.31e+19 -2.08e+20 -1.18e+21
8.35e+20 -1.18e+21 2.08e+20
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/NEW/20050505132121/index.html
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The focal mechanism was determined using broadband seismic waveforms. The location of the event and the station distribution are given in Figure 1.
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STK = 185
DIP = 90
RAKE = -35
MW = 3.41
HS = 15
The solution given here is from waveform inversion of regional vaeforms from the INGV digital seismic stations.
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 3 lp c 0.10 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 345 40 90 2.91 0.1937
WVFGRD96 1.0 185 50 -75 2.92 0.1649
WVFGRD96 2.0 170 45 -90 3.06 0.2093
WVFGRD96 3.0 10 90 -35 3.07 0.2163
WVFGRD96 4.0 190 90 35 3.12 0.2439
WVFGRD96 5.0 190 90 35 3.16 0.2625
WVFGRD96 6.0 195 75 35 3.20 0.2755
WVFGRD96 7.0 190 85 30 3.23 0.2927
WVFGRD96 8.0 190 85 30 3.28 0.3080
WVFGRD96 9.0 330 25 -90 3.38 0.3283
WVFGRD96 10.0 335 25 -85 3.40 0.3527
WVFGRD96 11.0 340 25 -75 3.42 0.3692
WVFGRD96 12.0 345 25 -70 3.43 0.3790
WVFGRD96 13.0 185 85 -35 3.39 0.3849
WVFGRD96 14.0 185 90 -35 3.40 0.3904
WVFGRD96 15.0 185 90 -35 3.41 0.3924
WVFGRD96 16.0 185 90 -35 3.42 0.3915
WVFGRD96 17.0 185 90 -35 3.42 0.3884
WVFGRD96 18.0 185 90 -30 3.43 0.3844
WVFGRD96 19.0 10 80 30 3.43 0.3813
WVFGRD96 20.0 10 80 30 3.43 0.3794
WVFGRD96 21.0 180 80 -45 3.47 0.3757
WVFGRD96 22.0 180 80 -45 3.48 0.3752
WVFGRD96 23.0 180 80 -45 3.49 0.3744
WVFGRD96 24.0 180 80 -45 3.49 0.3738
WVFGRD96 25.0 180 80 -45 3.50 0.3735
WVFGRD96 26.0 185 85 -40 3.50 0.3727
WVFGRD96 27.0 185 85 -45 3.51 0.3728
WVFGRD96 28.0 185 90 -40 3.51 0.3734
WVFGRD96 29.0 185 90 -45 3.52 0.3742
WVFGRD96 30.0 185 90 -40 3.52 0.3753
The best solution is
WVFGRD96 15.0 185 90 -35 3.41 0.3924
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 componnet is plotted to the same scale and peak amplitudes are indicated by the numbers to the left of each trace. The number in black at the rightr of each predicted traces 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 bandpass filter used in the processing and for the display was
hp c 0.02 3 lp c 0.10 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. |
The P-wave first motion data for focal mechanism studies are as follow:
Sta Az(deg) Dist(km) First motion INTR 50 21 iP_C RNI2 119 42 eP_- CII 110 53 eP_+ MIDA 121 53 iP_D AQU 334 58 eP_X CERT 276 61 iP_C FIAM 311 65 eP_X VAGA 140 68 eP_+ FRES 83 80 eP_+ TERO 354 82 eP_+ BSSO 117 83 eP_X SACR 123 99 eP_X PSB1 129 118 eP_X MRB1 129 135 eP_X TOLF 278 143 eP_X SNAL 130 165 eP_X CING 346 170 eP_X MURB 328 181 eP_X SACS 306 183 eP_X MRLC 130 195 eP_X
The follwoing stations were not used because of excessive low frequency noise in the deconvolved waveforms: AMUR, GIUL, RNI2, SNAL, TRIV