2005/10/30 19:09:46 38.53 15.93E 24 3.6 Italy
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
SLU Moment Tensor Solution
2005/10/30 19:09:46 38.53 15.93E 24 3.6 Italy
Best Fitting Double Couple
Mo = 2.45e+21 dyne-cm
Mw = 3.56
Z = 14 km
Plane Strike Dip Rake
NP1 45 59 -106
NP2 255 35 -65
Principal Axes:
Axis Value Plunge Azimuth
T 2.45e+21 12 147
N 0.00e+00 14 54
P -2.45e+21 71 277
Moment Tensor: (dyne-cm)
Component Value
Mxx 1.65e+21
Mxy -1.04e+21
Mxz -5.15e+20
Myy 4.38e+20
Myz 1.02e+21
Mzz -2.09e+21
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Harvard Convention
Moment Tensor:
R T F
-2.09e+21 -5.15e+20 -1.02e+21
-5.15e+20 1.65e+21 1.04e+21
-1.02e+21 1.04e+21 4.38e+20
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/NEW/20051030190946/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 = 255
DIP = 35
RAKE = -65
MW = 3.56
HS = 14
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 0.05 3The results of this grid search from 0.5 to 19 km depth are as follow:
DEPTH STK DIP RAKE MW FIT
WVFGRD96 0.5 170 40 80 3.37 0.4325
WVFGRD96 1.0 305 85 10 3.11 0.3587
WVFGRD96 2.0 160 45 70 3.44 0.4571
WVFGRD96 3.0 160 45 75 3.44 0.4250
WVFGRD96 4.0 300 85 60 3.37 0.4419
WVFGRD96 5.0 300 85 55 3.38 0.4981
WVFGRD96 6.0 115 90 -55 3.39 0.5350
WVFGRD96 7.0 105 80 -55 3.39 0.5634
WVFGRD96 8.0 105 80 -55 3.42 0.5883
WVFGRD96 9.0 250 25 -70 3.53 0.6169
WVFGRD96 10.0 240 30 -85 3.52 0.6487
WVFGRD96 11.0 250 30 -70 3.55 0.6755
WVFGRD96 12.0 260 30 -55 3.57 0.6928
WVFGRD96 13.0 250 35 -70 3.56 0.7056
WVFGRD96 14.0 255 35 -65 3.56 0.7098
WVFGRD96 15.0 265 35 -50 3.59 0.7046
WVFGRD96 16.0 255 40 -65 3.56 0.6989
WVFGRD96 17.0 265 40 -50 3.59 0.6901
WVFGRD96 18.0 250 45 -70 3.56 0.6743
WVFGRD96 19.0 260 45 -55 3.58 0.6670
WVFGRD96 20.0 265 45 -50 3.60 0.6572
WVFGRD96 21.0 260 45 -55 3.63 0.6575
WVFGRD96 22.0 250 50 -70 3.61 0.6477
WVFGRD96 23.0 255 50 -65 3.62 0.6422
WVFGRD96 24.0 260 50 -55 3.64 0.6340
WVFGRD96 25.0 265 50 -50 3.65 0.6223
WVFGRD96 26.0 250 55 -70 3.62 0.6100
WVFGRD96 27.0 255 55 -65 3.63 0.5987
WVFGRD96 28.0 265 55 -50 3.65 0.5884
WVFGRD96 29.0 275 55 -35 3.69 0.5766
WVFGRD96 30.0 305 90 30 3.65 0.5666
The best solution is
WVFGRD96 14.0 255 35 -65 3.56 0.7098
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 0.05 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 CEL 186 30 iP_C TIP 45 102 eP_X CUC 357 163 eP_X MRLC 351 250 eP_X MCRV 346 259 eP_X NOCI 21 269 eP_X AMUR 12 270 eP_+ VULT 354 271 eP_X SNAL 347 273 eP_X CAFE 348 284 eP_X PSB1 343 314 eP_X WDD 203 321 eP_X
The follwoing stations were not used because of excessive low frequency noise in the deconvolved waveforms: AMUR, GIUL, RNI2, SNAL, TRIV