2006/05/20 07:05:56 37.65N 14.95E 12 4.1 Italy
USGS Felt map for this earthquake
USGS Felt reports page for Intermountain Western US
SLU Moment Tensor Solution
2006/05/20 07:05:56 37.65N 14.95E 12 4.1 Italy
Best Fitting Double Couple
Mo = 4.27e+21 dyne-cm
Mw = 3.72
Z = 23 km
Plane Strike Dip Rake
NP1 85 65 -60
NP2 211 38 -137
Principal Axes:
Axis Value Plunge Azimuth
T 4.27e+21 15 154
N 0.00e+00 27 251
P -4.27e+21 59 38
Moment Tensor: (dyne-cm)
Component Value
Mxx 2.47e+21
Mxy -2.15e+21
Mxz -2.44e+21
Myy 3.57e+20
Myz -6.91e+20
Mzz -2.83e+21
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#########------------- -------------
#########-------------- P --------------
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--#####----------------------------#######
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--################### T ####
################## #
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Harvard Convention
Moment Tensor:
R T F
-2.83e+21 -2.44e+21 6.91e+20
-2.44e+21 2.47e+21 2.15e+21
6.91e+20 2.15e+21 3.57e+20
Details of the solution is found at
http://www.eas.slu.edu/Earthquake_Center/NEW/20060520070556/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 = 85
DIP = 65
RAKE = -60
MW = 3.72
HS = 23
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 0.5 250 45 -80 3.35 0.0514
WVFGRD96 1.0 65 45 -90 3.38 0.0514
WVFGRD96 2.0 250 45 -80 3.45 0.0584
WVFGRD96 3.0 90 30 30 3.44 0.0633
WVFGRD96 4.0 85 35 20 3.45 0.0662
WVFGRD96 5.0 295 80 65 3.50 0.0756
WVFGRD96 6.0 290 80 60 3.51 0.0842
WVFGRD96 7.0 290 80 60 3.53 0.0940
WVFGRD96 8.0 290 80 60 3.56 0.1006
WVFGRD96 9.0 290 80 55 3.57 0.1061
WVFGRD96 10.0 290 80 55 3.58 0.1118
WVFGRD96 11.0 290 80 50 3.58 0.1150
WVFGRD96 12.0 105 90 -50 3.58 0.1186
WVFGRD96 13.0 100 85 -50 3.59 0.1207
WVFGRD96 14.0 95 75 -50 3.61 0.1229
WVFGRD96 15.0 90 70 -55 3.63 0.1277
WVFGRD96 16.0 90 70 -55 3.63 0.1294
WVFGRD96 17.0 90 70 -55 3.63 0.1312
WVFGRD96 18.0 90 65 -55 3.64 0.1339
WVFGRD96 19.0 90 65 -55 3.64 0.1346
WVFGRD96 20.0 90 65 -55 3.64 0.1357
WVFGRD96 21.0 85 65 -60 3.71 0.1410
WVFGRD96 22.0 90 65 -55 3.71 0.1413
WVFGRD96 23.0 85 65 -60 3.72 0.1416
WVFGRD96 24.0 90 65 -55 3.72 0.1410
WVFGRD96 25.0 90 65 -55 3.73 0.1403
WVFGRD96 26.0 85 60 -60 3.74 0.1393
WVFGRD96 27.0 90 65 -55 3.73 0.1368
WVFGRD96 28.0 90 65 -55 3.74 0.1359
WVFGRD96 29.0 90 65 -50 3.75 0.1342
WVFGRD96 30.0 90 65 -50 3.75 0.1321
The best solution is
WVFGRD96 23.0 85 65 -60 3.72 0.1416
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 50 107 iP_D CLTB 268 153 eP_X WDD 191 202 eP_- TIP 42 232 eP_+ CUC 16 271 iP_D MCRV 3 348 eP_X SNAL 3 364 eP_- CAFE 4 376 iP_C AMUR 21 389 eP_X NOCI 27 393 eP_+
The follwoing stations were not used because of excessive low frequency noise in the deconvolved waveforms: AMUR, GIUL, RNI2, SNAL, TRIV